Development and Performance Studies of Pyrotechnic Compositions for Pressure-generated and Delay Cartridges
By
Azizullah Khan
School of Chemical and Materials Engineering (SCME) National University of Sciences and Technology (NUST) 2018
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Development and Performance Studies of Pyrotechnic Compositions for Pressure- generated and Delay Cartridges
Name: Azizullah Khan Reg No: NUST201590309PSCME2515F
This thesis is submitted as a partial fulfillment of the requirements for the degree of PhD in Energetic Materials Engineering Supervisor: Dr. Abdul Qadeer Malik
School of Chemical and Material Engineering (SCME) National University of Sciences and Technology (NUST) H-12, Islamabad, Pakistan December, 2018
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DEDICATED TO MY
Dearest Family
My Mother, Wife and Children
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ACKNOWLEDGMENTS
All Praises are to Almighty Allah, the Most Beneficent, and the Most Merciful. I am thankful to the Almighty Allah who showered his blessings by helping me and provided me the ability and skills to accomplish this goal. Allah blessed me with understanding, determination and willpower to achieve this milestone. I should like to thank my supervisor Dr. Abdul Qadeer Malik. He guided me with patience, wisdom and professionalism throughout my research work. I can never forget his caring guidance, illustrative advice and keen interest. My thanks are also due to Dr. Zulfiqar H. Lodhi for his able guidance and technical support. During the entire PhD work he guided me in a professional way. My special thanks are due to all the members of GEC for their step by step guidance for the accomplishment of this work. Honorable members of the GEC include Dr. Arshad Hussain (Principal/Dean SCME) and Dr. Tayyaba Noor. I should like to express my thanks to Dr. Muhammad Ahsan for helping me during research publications. I shall also thankful to Mr. Amer Ahmad, Mr. Shahid Irfan, Mr. Muhammad Fayaz, Mr. Naseer-ud-din, Mr. Nasir Karim, Mr. Rafaqat, Mr. Zain-ul- Abdin, Mr. Azmant and Mr. Kashif for helping me in every possible manner for the conduct of experimental tests and Lab analysis. My special thanks for Mr. Mr. Khalid Naeem, Mr. Gul Badsha and Mr. Amaar Husain for their help during review of the research work. I pay my tribute and sweet feeling of love and respect to my family including my mother, my wife and my children who prayed for me all the time and helped me in every possible manner. It would not have been easy to complete this work without their support and prayers. (AZIZULLAH KHAN)
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Abstract
The work presented in this thesis is focused on the development and performance studies of different types of pyrotechnic compositions for pressure-generated and delay cartridges. A lot of work has been carried out in the field of pyrotechnic compositions; however, there is not much data available on the development and selection of the suitable igniter and booster pyrotechnic compositions for pressure-generated cartridges, coupled with lack of understanding of detailed parametric studies on pyrotechnic delay compositions to improve their burning performance. The published work in the field of pyrotechnic delay compositions presents individual studies of one or two parameters affecting burning performance. The present work is a concerted effort to provide an insight into the detailed studies of a number of parameters to investigate and improve the performance of particular delay compositions.
For this purpose B, Zr and Pb(SCN)2 were used as fuels and KNO3, KClO4, KClO3 as oxidizers for the development of igniter and booster pyrotechnic compositions, whereas B and Si were used as fuels while BaCrO4, PbO and Pb3O4 as oxidizers while FG, CMC, Dextrin as binders for the development of different types of pyrotechnic delay compositions. The first part of this research work pertains to develop different types of high energy igniter and booster pyrotechnic compositions: B/KNO3, Zr/KClO4 and Pb(SCN)2/KClO3 as igniter compositions while B/Mg/KClO4/Bi2O3 and B/Mg/KClO4 as booster pyrotechnic compositions. The study shows that the best combination for igniter and booster compositions in terms of safety, calorific values and cartridge functionality are Zr/KClO4
(40/60) and B/Mg/KClO4 (30/10/60), respectively. Further, the development and parametric studies of different types of pyrotechnic delay compositions comprising B/BaCrO4/Binder, Si/Pb3O4/Binder, Si/PbO/Binder and
Si/Pb3O4/PbO/Binder was conducted. Effect of fuel contents, binders, temperature variation, loading pressure, ingredients mixing and body material on the burring time and burning rate/mass consumption of these delay compositions were experimentally investigated and Calorific values were determined. These studies revealed that burning performance of a pyrotechnic delay composition could be modified by altering these parameters through an in- depth study of these parameters to enable the end-user to develop and optimize the burning performance of pyrotechnic compositions as done in this work.
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Variation in the burning time has been significantly reduced in these delay compositions through homogenous mixing as being a problem in delay mixtures. The burning rate and mass consumption of these compositions increased with increase in fuel contents until maximum value was achieved. These values then decreased on further increase in fuel contents until misfire condition was recorded. It was also revealed during this study that binders also play an important role in modifying the burning rate of delay compositions. Variation in loading pressure did not significantly affect the burning performance. Burning rate of these delay compositions increased with the decrease in ambient temperature and vice versa. By replacing the stainless steel body material with brass and controlling the laboratory operating conditions further reduced the variation in the burning time. In the last part of the thesis, studies were undertaken for the measurement of minimum pressure together with ejection velocity, required for the release of the external stores from military aircraft on powerful pressure generating cartridge. Pressure generating cartridge converts chemical energy into mechanical energy. Mission effectiveness and sustainability for military aircrafts are highly dependent on ability to separate the external stores with required velocity to minimize risk during mission flight. The prediction of ejection velocity for the separation of external stores from the military aircrafts is an important task in the aerodynamic design area. It not only requires to separate the stores safety from the aircraft but also requires a relatively smooth release for good delivery accuracy. The experimental data shows that minimum pressure required to separate the external store from Ejection Release Unit (ERU) must be more than 70 bars depending on the mass of store. The ejection velocity with single cartridge is between 3.59~4.5 m s-1 The upshot of this work is that it provides new insight in the function and performance of pyrotechnic delay compositions and pressure generated-cartridges to enable the end-user to optimize the performance of these compositions, as per requirement.
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List of Publications Journal Papers (Published)
1. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar Hameed. Lodhi, and Gul Badsha, Study of effect of binder and loading pressure on the performance of the time delay pyrotechnic compositions, “Published in Journal of Energetic Material”. DOI: 10.1080/07370652.2018.1441925. Vol. 36, 2018, Issue 4, P 386-397.
2. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar H. Lodhi, “Development and Study of high energy igniter/booster pyrotechnic compositions for impulse cartridges”, Published in Central European Journal of Energetic Materials (CEJEM)”. Cent. Eur. J. Energ. Mater. DOI: 10.22211/cejem/76881, 2017, 14(4): 933-951.
3. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar Hameed Lodhi, and Syed Ammar Hussain, “Development and Parametric Study of B/BaCrO4/FG Pyrotechnic Delay Composition” Published in Journal of Combustion Science and Technology; DOI:10.1080/00102202.2017.1410800, Vol. 190, 2018, Issue 5, P 823-833.
4. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar H. Lodhi, “Development and
Experimental Investigation on Delay Time Consistency of Modified Si/PbO/Pb3O4/FG Pyrotechnic Delay Composition” Published in Engineering, Technology & Applied Science Research Vol. 7, No. 6, 2017, 2167-2170.
5. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar H. Lodhi, Zain Ul Abdin “Effect of body material and ambient temperature on the performance of the time delay pyrotechnic compositions”, published in Journal of Defense Technology. DOI: 10.1016/j.dt.2018.03.006, Vol. 14, Issue 3, June, 2018, Page 261-265.
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6. Azizullah Khan, Abdul Qadeer Malik, Zulfiqar H. Lodhi “Effect of silicon contents on different oxidizers” Used in Delay Composition”, accepted for publication in Journal of Chemical Society of Pakistan.
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Table of Contents Chapter No.1: General Introduction ...... 1 1.1 Energetic Materials...... 1 1.1.1 Low Explosives: ...... 1 1.1.2 High explosives: ...... 1 1.1.3 Pyrotechnics ...... 2 1.1.4 Similarity in High Explosives, Low Explosive and Pyrotechnics ...... 3 1.1.5 Difference among High Explosive, Low explosive and Pyrotechnics ...... 3 1.1.6 Applications of Pyrotechnics ...... 3 1.1.6.1 Some common applications of the pyrotechnics are: ...... 4 1.1.6.2 Aircraft system: ...... 5 1.1.6.3 Spacecraft systems: ...... 5 1.1.6.4 Missile systems ...... 5 1.2 Pyrotechnic ingredients ...... 5 1.2.1 Fuel: ...... 5 1.2.1.1 Properties of fuel: ...... 6 1.2.2 Oxidizer: ...... 6 1.2.2.1 Properties of oxidizer: ...... 6 1.2.3 Binders: ...... 7 1.3 Pyrotechnic delay device ...... 7 1.3.1 Priming composition ...... 8 1.3.2 Igniter composition ...... 8 1.3.3 Delay pyrotechnic compositions: ...... 9 1.3.3.1 Gassy delay compositions: ...... 9 1.3.3.2 Gasless delay compositions: ...... 10 1.3.3.3 Properties of delay compositions: ...... 10 1.4 Pyrotechnic Impulse/ Pressure generated Cartridges ...... 11 1.4.1 Igniter pyrotechnic composition ...... 12 1.4.2 Booster pyrotechnic compositions ...... 12 1.4.3 Propellant charge ...... 13
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1.5 Propagation of combustion ...... 13 1.6 Safety precautions for pyrotechnics compositions ...... 14 1.7 Factors effecting burning rate of pyrotechnic delay Compositions ...... 14 1.7.1 Confinement effect: ...... 14 1.7.2 Obturation effect ...... 15 1.7.3 Vented effect ...... 15 1.7.4 Effect of particles sizes: ...... 16 1.7.5 Percentage of fuels: ...... 16 1.7.6 Delay column diameter: ...... 17 1.7.7 Effect of ingredients: ...... 17 1.7.8 Effect of ingredients ratio: ...... 17 1.7.9 Effect of ambient temperature:...... 18 1.7.10 Effect of ambient Pressure: ...... 18 1.7.11 Effect of consolidation/ loading pressure:...... 19 1.7.12 Effect of water: ...... 19 1.7.13 Effect of terminal charge:...... 19 1.7.14 Effect of ignition/first fire composition: ...... 20 1.7.15 Effect of delay body material: ...... 20 1.7.16 Effect of Storage on burning time: ...... 21 1.7.17 Charge increment: ...... 21 1.7.18 Effect of binders: ...... 22 1.7.19 Effect of mixing/ intimate contact of ingredients on burning rate: ...... 22 1.8 Measurement techniques: ...... 22 1.9 Literature Survey and Scope of the present research work: ...... 23 1.10 Outlines of this thesis:...... 24 1.11 Objective of present research work: ...... 25 1.12 Research work Plan ...... 26 References ...... 27 Chapter No. 2:Experimental Measurement Techniques and Materials used ...... 29 2.1 Experimental Measurement Techniques: ...... 29 2.2 Equipment used for Pyrotechnic compositions preparation ...... 31
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2.2.1 Pyrotechnic mixing machine ...... 31 2.2.2 Manual Pestle and Mortar ...... 32 2.2.3 Sieves and Sieves Shaker ...... 32 2.2.4 Vacuum drying Oven ...... 33 2.3 Equipment used for conditioning of explosive devices ...... 34 2.3.1 Environmental chamber ...... 34 2.3 Equipment used for delay time measurement: ...... 35 2.3.1 Chronometer with Detector ...... 35 2.3.2 Digital Oscilloscope ...... 35 2.3.3 Power supply ...... 36 2.4 Equipment used for thermal analysis ...... 37 2.4.1 Oxygen Bomb Calorimeter (OBC) ...... 37 2.5 Equipment used for the safety tests of igniter compositions ...... 38 2.5.1 Static discharge equipment ...... 38 2.5.2 Stray voltage tester ...... 38 2.5.3 Maximum No Fire current measurement equipment: ...... 39 2.6 Equipment used for the ballilstic parameters measurement of Impulse cartridges...... 40 2.6.1 Charge calibrator ...... 40 2.6.2 Pressure transducer...... 41 2.7 Material Used in the present research work ...... 41 2.7.1 Fuels and oxidizers ...... 41 2.7.2 Binders: ...... 42 2.7.3 Delay body Material ...... 43 2.8 Pyrotechnic composition preparation procedure ...... 43 2.9 Procedure for burning time measurement ...... 44 2.10 Procedure for the measurement of peak pressure and time to peak pressure ...... 45 References ...... 46 Chapter No. 3: ... Development and study of high energy igniter and booster pyrotechnic compositions 48 3.1 Introduction ...... 48 3.2 Experimental conditions...... 50 3.2.1 Characteristics of the used materials ...... 50
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3.2.2 Compositions preparation ...... 51 3.2.2.1 Igniter and booster pyrotechnic compositions (without binder) ...... 51 3.2.2.2 Booster pyrotechnic composition(with binder):...... 51 3.2.3 Calorimetric measurement ...... 52 3.2.4 Safety tests ...... 52 3.2.4.1 Maximum No fire current test ...... 52 3.2.4.2 Static Discharge test ...... 52 3.2.4.3 Stray Voltage test ...... 53 3.2.5 Manufacturing of igniter for Impulse Cartridge...... 53 3.2.6 Cartridge assembly and Functional Tests in closed chamber ...... 54 3.3 Results and discussion ...... 57 3.3.1 Calorimetric measurement of igniter compositions ...... 57
3.3.1.1 B/KNO3 igniter mixture-A ...... 57
3.3.1.2 Zr/KClO4 igniter mixture-B ...... 58
3.3.1.3 Pb(SCN)2/KClO3 igniter mixture-C ...... 60 3.3.2 Safety Tests Results ...... 61 3.3.2.1 Maximum No fire current test ...... 61 3.3.2.2 Static Discharge test ...... 61 3.3.2.3 Stray Voltage test ...... 62 3.3.3 Calorimetric measurement of booster compositions ...... 63 3.3.3.1 Existing Booster Composition ...... 63 3.3.3.2 Newly prepared high energy Booster Composition (New-1) ...... 63 3.3.3.3 Newly prepared high energy Booster Compositions(New-2) ...... 64 3.3.4 Selection of best igniter and booster compositions for impulse cartridge ...... 66 3.3.5 Functional tests results ...... 68 3.4 Conclusions ...... 70 References ...... 71
Chapter No. 4: ...... Development and parametric studies of B/BaCrO4 pyrotechnic delay composition 73 4.1 Introduction ...... 73 4.2 Experimental conditions...... 76 4.2.1 Preparation of Pyrotechnic Delay Composition ...... 77
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4.2.1.1 Mixing of ingredients of pyrotechnic delay compositions:...... 77 4.2.1.2 Grains formation of pyrotechnic delay compositions: ...... 77 4.2.2 Safety during mixing ...... 78 4.2.3 Loading procedure ...... 78 4.2.4 Configuration of delay device ...... 79 4.2.5 Assembly of the delay device ...... 79 4.2.6 Testing procedure ...... 80 4.3 Results and discussion ...... 81
4.3.1 Effect of Boron contents on burning rate/ charge consumption of B/BaCrO4 delay mixture 81
4.3.2 Effect of Binders on burning rate and charge consumption of B/BaCrO4 mixture ...... 84
4.3.3 Effect of temperature variation on burning rate of B/BaCrO4/FG delay mixture ...... 92
4.3.4 Effect of Boron contents on Calorific value of B/BaCrO4/ FG delay composition ...... 94
4.3.5 Effect of body material on burning time and burning rate of B/BaCrO4/ FG delay composition ...... 95
4.3.6 Effect of loading pressure on the burning time and burning rate of B/BaCrO4/ FG delay composition ...... 97
4.3.6 Effect of loading pressure on consolidation and %TMD B/BaCrO4/ FG delay composition 99 4.4 Conclusions ...... 100 References ...... 102
Chapter NO. 5 Development and parametric studies of Si/Pb3O4, Si/PbO and Si/PbO/Pb3O4 pyrotechnic delay compositions ...... 104 5.1 Introduction ...... 104 5.2 Experimental conditions ...... 107 5.2.1 Formulation of different types of Pyrotechnic Delay Compositions ...... 107 5.2.2 Pressing of the pyrotechnic delay compositions in the delay body ...... 108 5.2.3 Design of pyrotechnic delay device ...... 108 5.2.4 Assembly of delay device ...... 109 5.2.5 Functional Testing procedure ...... 109 5.3 Results and Discussion ...... 110
5.3.1 Effect of Si content on the delay time and mass consumption of Si/Pb3O4/FG delay mixtures 110
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5.3.2 Effect of Si content on the burning time and mass consumption of Si/PbO/FG delay mixtures...... 114 5.3.3 Effect of fast red lead mixture on the burning time and mass consumption of Si/PbO/ FG delay mixtures ...... 117
5.3.4 Effect of ingredients mixing on the burning time and burning rate of Si/PbO/Pb3O4/FG delay composition ...... 119 5.3.4.1 Mixing in(3-D) Automatic Tumbler Mixing Machine...... 119 5.3.4.2 Manual Mixing in Mortar and Pestle: ...... 119 5.3.4.3 Filling of delay body: ...... 120 5.3.4.4 Results and Discussion: ...... 120 5.3.4.4.1 Test results of composition mixed in (3-D) automatic Tumbler Mixing Machine ...... 121 5.3.4.4.2 Test results of composition Manually Mixed in Mortar and Pestle: ...... 124 5.3.4.4.3 Effect of loading pressure on delay composition (Manually Mixed in Mortar and Pestle) 126
5.3.5 Effect of temperature variation on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition ...... 127
5.3.6 Effect of loading pressure on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition ...... 129
5.3.7 Study of effect of body material on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition ...... 131
5.3.8 Effect of binders on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition 134 5.3.9 Effect of loading pressures on the consolidation density and %TMD ...... 136 5.4 Conclusions: ...... 137 References ...... 139 Chapter No. 6:Experimental validation for the Safe Separation of External Store from Military Aircraft 141 6.1 Introduction ...... 141 6.2 Experimental conditions: ...... 143 6.2.1 Materials used ...... 143 6.2.2 Formulation of igniter and booster pyrotechnic compositions ...... 143 6.2.3 Manufacturing of Impulse cartridge: ...... 144 6.2.4 Close chamber Tests ...... 144 6.2.4.1 Environmental Tests: ...... 144
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6.2.4.2 SafetyTests: ...... 146 6.2.5 Measurement of Ejection velocity and pressure ...... 146 6.2.5.1 Linear Voltage Displacement Transformer (LVDT) ...... 146 6.2.5.2 Pressure measurement in closed chamber: ...... 147 6.2.6 Power supply: ...... 147 6.3 Results and Discussion ...... 147 6.3.1 Closed chamber Test result ...... 147 6.3.2 Cartridge Evaluation on the Pylon of Military Aircraft (Static Test) for determining minimum pressure and ejection velocity ...... 149 6.4 Conclusion ...... 151 References ...... 152 Chapter No. 7:General Conclusion ...... 153
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List of Figures
Figure 1.1: Pyrotechnic train for delay devices……………………………………………………..8 Figure 1.2: Pyrotechnic train for Impulse/ Pressure cartridge……………………………………...12 Figure 1.3: Process flow chart for execution of this research work………………………………...26 Figure 2.1: (3-D) Pyrotechnic Automatic Tumbler Mixing Machine………………………………31 Figure 2.2: Agate Pestle and Mortar for mixing of the compositions……………………………...32 Figure 2.3: Haver test shaker EML 200-89 digital…………………………………………………33 Figure 2.4: Vacuum drying Oven Model VO500…………………………………………………..34 Figure 2.5: Environmental chamber for conditioning of samples………………………………….34 Figure 2.6: TDS 2024 Digital Storage Oscilloscope……………………………………………….36 Figure 2.7: TTZ CP*200 Power Supply……………………………………………………………36 Figure 2.8: Oxygen Bomb Calorimeter Parr 6200………………………………………………….37 Figure 2.9: Static Discharge tester ESD 300……………………………………………………….38 Figure 2.10: TG 550 Pulse generator……………………………………………………………….39 Figure 2.11: Type 6907B Charge Calibrator……………………………………………………….40 Figure 2.12: Type 7005 Pressure Sensor…………………………………………………………...41 Figure 2.13: Process flow for preparation of pyrotechnic compositions…………………………...44 Figure 3.1: Schematic diagram for igniter of impulse cartridge……………………………………54 Figure 3.2: Schematic diagram of impulse cartridge……………………………………………….55 Figure 3.3: Schematic diagram for experimental setup of pressure-generated cartridge…………...56
Figure 3.4: Plot of exothermicity against Boron content for a range of B-KNO3 igniter mixture…58
Figure 3.5: Plot of exothermicity against Zirconium content for a range of Zr-KClO4 igniter mixture………………………………………………………………………………….59
Figure 3.6: Plot of exothermicity against Pb(SCN)2 content for a range…………………………..61 Figure 3.7: Plot of peak pressure of three booster pyrotechnic compositions……………………...69 Figure 3.8: Plot of time to peak pressure of all three booster pyrotechnic compositions…………..69 Figure 4.1: Stain Less steel body Delay device……………………………………………………..79 Figure 4.2: Schematic diagram for burning time measurement pyrotechnic delay device…………80
Figure 4.3: Effect of Boron content on mass consumption and burning rate of B/BaCrO4/FG delay mixture……………………………………………………………………………84 Figure 4.4: Plot of burning rate in mm/sec at normally operating temperature ranges…...... 93
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Figure 4.5: Plot of delay time of B/BaCrO4/FG mixture in stainless steel and in Brass delay body…………………………………………………………………………………….96
Figure 4.6: Plot of burning rate of B/BaCrO4/FG mixture in stainless steel and in Brass delay body…………………………………………………………………….97
Figure 4.7: Plot of Loading pressure vs %TMD for B/BaCrO4/FG= 15/84/1 delay mixture…….100 Figure 5.1: Stain Less steel body Delay device…………………………………………………...109 Figure 5.2: Schematic diagram for burning time measurement of pyrotechnic Delay device…………………………………………………………………………..110
Figure 5.3: Effect of Silicon content on mass consumption of Si/Pb3O4/FG delay mixture……..113 Figure 5.4: Effect of Silicon content on mass consumption of Si/PbO/FG delay mixture………..116 Figure 5.5: Design of modified Delay device……………………………………………………..117
Figure 5.6: Effect of Si/Pb3O4/FG=20/79/1.0 mixture on mass consumption of Si/PbO/ FG delay Mixtures………………………………………………………………………………..118 Figure 5.7: Plot of Maximum percent variation of delay time from mean against applied loading Pressure………………………………………………………………………………..123 Figure 5.8: Plot of burning rate and delay time against applied loading pressure………………...123 Figure 5.9: Plot of percent variation of delay time from mean for each sample………………….125 Figure 5.10: Plot of burning rate and delay time for each sample………………………………...125
Figure 5.11: Plot of burning time vs temperature variation for Si/PbO/Pb3O4/FG mixture……....128
Figure 5.12: Plot of burning rate vs temperature variation for Si/PbO/Pb3O4/FG mixture…….....128
Figure 5.13: Plot of delay time of Si/PbO/Pb3O4/FG mixture in stainless steel and in Brass delay body……………………………………………………………..133
Figure 5.14: Plot of burning rate of Si/PbO/Pb3O4/FG mixture in Stainless Steel and in Brass delay body………………………………………………………...134
Figure 5.15: Plot of Loading pressure vs %TMD for Si/PbO/Pb3O4/FG= 18/21/60.3/0.3 delay Mixture……………………………………………………………………………….137 Figure 6.1: Plot of peak pressure of qualification Lot…………………………………………….148 Figure 6.2: Plot of propellant weight vs pressure of single cartridge in ERU…………………….150 Figure 6.3: Plot of Propellant Pressure vs ejection velocity of single cartridge in ERU………….151
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List of tables
Table 2.1: List of fuels used in present work……………………………………………………...42 Table 2.2: List of oxidizers used in present work………………………………………………….42 Table 3.1: Specification of igniter for Impulse Cartridge………………………………………….54
Table 3.2: Exothermicity measurements for range of B-KNO3 igniter mixture…………………...57
Table 3.3: Exothermicity measurements for range of Zr- KCLO4 igniter mixture………………..59
Table 3.4: Exothermicity measurements for range of Zr- KCLO4 igniter mixture………………..60 Table 3.5: Comparison of different results of ignition compositions……………………………...62 Table 3.6: Calorific value of original booster pyrotechnic composition…………………………..63 Table 3.7: Calorific value of newly prepared booster pyrotechnic composition (New-1)………...64
Table 3.8: B/Mg/KClO4 booster pyrotechnic composition (New-2)………………………………65 Table 3.9: Summary of calorific value of newly prepared booster composition (New-2)………...66 Table 3.10: Comparison among all three igniter compositions……………………………………67 Table 3.11: Final selected igniter and booster pyrotechnic compositions…………………………67
Table 3.12: Test results in closed chamber of volume 230 cm3 (Weight = 4.40g single base propellants)…………………………………………………………………………….68
Table 4.1: Test results of B/BaCrO4/FG delay mixtures with varying boron contents……………82
Table 4.2: Effect on burning rate and burn time with varying Fish Glue contents in B/BaCrO4 delay mixture……………………………………………………………………………87
Table 4.3: Effect on burning rate and burn time with varying CMC contents in B/BaCrO4 delay mixture………………………………………………………………………………….88
Table 4.4: Effect on burning rate and burn time with varying Dextrin contents in B/BaCrO4 delay mixture…………………………………………………………………………………..89
Table 4.5: Test results of mass consumption of B/BaCrO4/FG delay mixtures with varying FG contents…………………………………………………………………………………91
Table 4.6: Effect of binder on different results of B/BaCrO4/Binder delay mixture………………91
Table 4.7: Test results of B/BaCrO4/FG=15/84/1 delay mixture at different operating temperatures……………………………………………………………………………93
Table 4.8: Calorific values of B/BaCrO4 mixture at different Boron content……………………..94
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Table 4.9: Test results of delay B/BaCrO4/FG =14/85/1.0 in Stainless Steel and Brass delay body……………………………………………………………………...... 96
Table 4.10: Test results of loading pressure on B /BaCrO4 /FG =15/84/1 delay mixture………….98
Table 5.1: Test results of Si/Pb3O4/ FG delay mixtures at different Silicon contents……………112 Table 5.2: Test results of Si/PbO/ FG delay mixtures at different Silicon contents……………..115 Table 5.3: Test results of different Si/PbO/ FG delay mixtures by incorporating an increment of
Si/Pb3O4/FG=20/79/1.0 mixture……………………………………………………....118 Table 5.4: Ingredients and their percentages……………………………………………………..121 Table 5.5: Test results of delay mixture mixed in (3-D) automatic Tumbler Mixing Machine….122 Table 5.6: Test results of delay time at different loading pressure……………………………….126
Table 5.7: Temperature dependency of delay Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 in Brass delay body…………………………………………………………………………………...127
Table 5.8: Test results of effect of loading pressure on Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 delay mixture………………………………………………………………………………...130
Table 5.9: Test results of Si/PbO/Pb3O4/FG delay mixture in Stainless steel delay body……….131
Table 5.10: Test results of Si/PbO/Pb3O4/FG delay mixture in Brass delay body……………….133
Table 5.11: Effect on burning rate and burning time with varying Fish Glue contents in
Si/PbO/Pb3O4 delay mixture…………………………………………………………136 Table 6.1: Ingredients of Pyrotechnic compositions and propellant used in impulse cartridges...143 Table 6.2: Test Result of Impulse Cartridge at different environmental conditions……………..148 Table 6.3: Pressure, Function time and ejection velocity of impulse cartridges with various propellant weights…………………………………………………………………….150
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List of Abbreviations and Symbols
A Ampere (Current) Al Aluminum B Boron
BaCrO4 Barium Chromate cc Cubic centimeter CMC Carboxyl Methylene Cellulose DC Direct Current DEE Discharge of Electrostatic Energy
DTA Differential thermal analysis
EEDs Electro Explosive Devices EMP Electromagnetic Pulse ESD Electrostatic Discharge FAE Fuel Aix Explsive FG Fish Glue g gram HMX High Melting Explosive/ Her Majesty‟s Explosive (Cyclotetramethylenetetranitarmine) j/g joule per gram LCD Liquid Crystal Display MIL-STD Military Standard mm millimeter PbO Lead monoxide MPa Mega Pascal m/s Meter/second mm/s millimeter per second ms millisecond OBC Oxygen Bomb Calorimeter OEM Original Equipment Manufacturer
Pb3O4 Lead Tetroxide
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PBX Plastic Bonded Explosive PC Personal Computer Psi Pound square inch % percentage TGA Thermal Gravimetric Analyzer %TMD Percent Theoretical Maximum Density R&D Research and Development RDX Research Department Explosive (Cyclotrimethylenetrinitarmine) S Second Si Silicon TNT Trinitrotoluene µm micrometer VDC Volt Direct Current VOD Velocity of Detonation
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Chapter No.1: General Introduction
1.1 Energetic Materials
The term Energetic Materials is used to refer Pyrotechnics, Low Explosives and High Explosives. The energetic Materials possess a large amount of energy which is released at very high rate when suitably initiated. Energetic Materials are classified into:
Low Explosive(Propellants)
High Explosive
o Primary High Explosives
o Secondary High Explosive
Pyrotechnics
1.1.1 Low Explosives:
Low explosives are also called propellants. They produce hot gases but release their energy much slowly than do high explosives. They may be pure material such as Nitrocellulose etc. or mixture of Nitrocellulose and Nitroglycerine etc. The burning rate of low explosive is much less than 1800 m/s.
1.1.2 High explosives:
High explosives undergo combustion by detonation phenomenon. Detonation is very fast and violent chemical reaction associated with extremely high pressures and temperatures. High explosives are designed to release their energy as rapidly as possible. The expansion resulting from creation of very hot gases produces the required destructive effect [1]. High explosives may be pure chemicals e.g., TNT, RDX, HMX,
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PETN or usually mixtures of pure explosives with or without other chemicals e.g. RDX/TNT, PBX, Torpex (TNT/Al), Composition-B(RDX/TNT/Wax) etc. High explosives are designed to detonate to produce the maximum rate of energy release as a shock wave. Velocity of detonation of high explosives normally ranges from 1800~ 10,000 m/s. Fuel Air explosive have the lowest VOD (1800 m/s). HMX has the highest VOD (9100 m/s) and CL-20 approximately 10,000 mm/s. High explosives are classified into:
. Primary high explosives
. Secondary high explosives
1.1.3 Pyrotechnics
The name pyrotechnics is derived from Greek word „pyro‟ which means fire and „technics‟ means art, so pyrotechnics means „art of fire‟. Pyrotechnics are an important class of energetic materials and are called the brains of weapon systems. Pyrotechnics are composed of fuels and oxidizers together with certain binders. A pyrotechnic composition when suitably initiated produces effects such as:
Heat, Light, Sound, Gas, Smoke, Burning time etc.
Pyrotechnic compositions are mixture of ingredients, which usually are not themselves explosive, and are designed to burn but not to detonate. Burning rate of pyrotechnic compositions can vary from below 0.001 m/sec to over 1.0 m/sec. Pyrotechnic compositions can be used as loose powders, incremental pressing in the delay column or as pressed pellets. The physical form of the pyrotechnics can greatly affect its burning
2 propagation. In an explosive device the pyrotechnic composition is used as igniter, booster or delay composition.
1.1.4 Similarity in High Explosives, Low Explosive and Pyrotechnics
Pyrotechnics, Low explosives (Propellants) and High explosives are all Energetic Materials. They have the common characteristic of ready chemical decomposition to produce much heat and often considerable quantities of gas. They all derive their energy from chemical reaction between fuels and oxidizer, both oxidizer and fuel present in energetic material itself. This reaction does not require oxygen from air except Fuel Air Explosive (FAE) which is dependent on atmospheric oxygen.
1.1.5 Difference among High Explosive, Low explosive and Pyrotechnics
High explosive, Low explosive and Pyrotechnics are differentiated on the basis of the type of their combustion or rate of reaction. The combustion of low explosive and pyrotechnics take place by deflagration phenomena. [2]. Deflagration means rapid and fast reaction due to layer by layer burning. Combustion takes place by the detonation phenomena in case of high explosive. Detonation takes place due to shock wave moving toward the unreacted explosive material at a supersonic speed. The detonation phenomenon is associated with very high pressure and temperature.
1.1.6 Applications of Pyrotechnics
Pyrotechnics are widely used for military and civilian applications to achieve required output results. Main difference between Civilian and Military Pyrotechnic is that, no systematic studies are available for civilian pyrotechnic. Similarly results of civilian pyrotechnics are also not reproducible i.e. same quality may not be reproduced. In addition to this less data is available on the Kinetic studies of civilian pyrotechnics.
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Military pyrotechnics are reliable and reproducible because extensive research has been carried out. These are used for safety purposes and to perform different operations during flight e.g. rockets and space shuttle. Pyrotechnics devices are used in very critical applications such as safety operation for opening of emergency exit; an improper operation could lead to serious accidents and mission failure. Numbers of pyrotechnic devices are used in rocket system e.g. pay load separation, 1st, 2nd and 3rd stage boosters separation etc. Pyrotechnic pressure generated cartridge are used for release of external stores from military aircrafts. Pyrotechnic pressure generated cartridges are also used for the seat ejection of Military aircrafts during emergency. One of the most important applications is that pyrotechnic delay compositions are used in delay devices in sophisticated missiles and space shuttles. These devices provide predetermined burning time before performing certain effects. Pyrotechnic compositions used for different applications are due to their:-
High energy density Long storage/shelf life Resistance to Electromagnetic Pulse (EMP) Low energy requirement for reliable initiation
1.1.6.1 Some common applications of the pyrotechnics are:
Incendiary rounds, welding and cutting, thermal batteries Illuminating and signal flares, tracers and flare, photo flash, missile decoys Signaling and screening smoke Rapid inflation(car air bags), oxygen candles Different pyro-mechanisms Igniter, booster and delay devices
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1.1.6.2 Aircraft system:
Seat ejection systems Release ejections for tanks, external stores and equipment Emergency and rescue system such as initiating the fire extinguisher system Drone systems
1.1.6.3 Spacecraft systems:
Launch and control systems Emergency systems Stage separation systems Recovery and landing systems
1.1.6.4 Missile systems
Safety and Arming systems Ignition systems Control systems Stage separation systems Destruct systems
1.2 Pyrotechnic ingredients
Pyrotechnic compositions are consists of fuels, oxidizing agents, binders and sometime solvents to give the special effect as required [3].
1.2.1 Fuel:
Fuel reacts with the liberated oxygen from oxidant to produce an oxide and heat. Heat liberated during chemical reaction of pyrotechnic composition, produces a numbers of
5 effects i.e. color motion, light, smoke and noise. Fuel is either a metal, non-metal, In- organic and Organic compounds. Commonly used fuels for military pyrotechnics delay compositions are Boron, Silicon, Zirconium, Magnesium, Zinc, Lead Thiocynate etc.
1.2.1.1 Properties of fuel:
Should possess a reasonable heat of combustion Should readily oxidized by oxygen Form products which give the required effects Should require minimum quantity of oxygen for combustion Fuel should chemically and physically stable in the normally operating temperature ranges -40 °C to +70 °C Should be non-hygroscopic Should be non-toxic Should be easily available and ignited with the available energy
1.2.2 Oxidizer:
In a pyrotechnic reaction the energy is released by oxidation of fuel. Atmospheric oxygen is not required for this process of chemical reaction of fuel and oxidizer. Required oxygen is delivered from chemical compound called oxidizer. The oxidizer is oxygen rich solid compound that decomposes, liberating oxygen gas. The oxygen gas then reacts with fuel. Commonly used oxidizers for military pyrotechnic compositions are Barium Chromate (BaCrO4), Bismuth (III) Oxide (Bi2O3), Lead monoxide (PbO),
Potassium per chlorate (KClO4), Potassium chlorate (KClO3), Red Lead(II,IV) oxide(Pb3O4), Lead dioxide (PbO2), Potassium Nitrate (KNO3) etc.
1.2.2.1 Properties of oxidizer:
Should contain maximum quantity of oxygen Should easily give up oxygen during burning process.
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Should be chemically and physically stable in the normally operating temperature ranges -40 °C to +70°C Should be-non hygroscopic Should be easily available Should by non-toxic to human beings. The oxidizer should have minimum sensitive to mechanical shocks otherwise these can impart explosive properties to the pyrotechnic compositions.
1.2.3 Binders:
Binders are compounds which increase cohesion between particles of fuel and oxidizer, aiding consolidation. Binders also vary the burning rate and thus the performance pyrotechnic compositions. Binder reduces the sensitivities to stimuli as friction. Binders protect the pyrotechnics compositions from environmental effects such as humidity. Some binders do not substantially affect the burning time and hence the burning rate [4, 5]. By adding material other than the stoichiometric amounts of the fuel and oxidizer cause to effect propagation of pyrotechnic delay compositions. Binder is added in small percentages in a pyrotechnic mixture to bind fuel and oxidizer together in the form of free flowing granules and to provide ease of loading in the delay body. Without a binder fuel and oxidizer segregate during composition preparation and in storage due to difference in their densities [6-8]. Binder also affects the burning rate of a delay composition. The burning rate of a mixture of 54.0% red lead and Barium sulphate with 1.0% surfactant (Solsperse 20000) reduces from 22 ms/ mm to 80 ms/ mm when the surfactant (Solsperse 20000) content is increased to 2.0% [9].
1.3 Pyrotechnic delay device
A pyrotechnic delay device contains pyrotechnic delay composition. A time delay is obtained by adding a pyrotechnic delay composition into an explosive train. The pyrotechnic composition burns at a selected and reproducible rate, providing a pre- determined time delay between activation and production of main effect. The delay
7 device consists of a delay body, pyrotechnic delay composition and igniter assembly. Pyrotechnic delay device is initiated both by electrically and mechanically means. These devices are classified as long, medium and short delay devices. Pyrotechnic train of a delay device consists of:
Priming composition Igniter composition Delay composition
Igniter Priming Delay Pyrotechnic Pyrotechnic composition composition composition
Figure 1.1 Pyrotechnic train for delay devices
1.3.1 Priming composition
Priming composition is painted or pressed onto the surface that is to be initiated so that it forms a physical part of it. The energy produced by the igniting charge some time is not sufficient to initiate the main pyrotechnic delay composition so an increment of relative sensitive charge is pressed or pasted on the surface.
1.3.2 Igniter composition
The igniter compositions contained at a stand off from the surface to be ignited. This may be in the form of a pellet or powder. Ignition results largely from hot gas or streams of hot reactive particles. Different compositions can be used as an igniter composition such as B/KNO3, Mg/KNO3/Phenolic resin-based, Zr/KClO4 mixture, Pb(SCN)2/ KClO3 etc. [10-12].
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In igniter and first fire composition, hot solid or liquid particles are desirable to ensure the transfer of sufficient heat to ignite the main delay composition. Fuels producing mainly gaseous products are not commonly used in igniter and first fire composition
1.3.3 Delay pyrotechnic compositions:
A pyrotechnic delay composition is a general term for a mixture that burns at a selected, reproducible rate. A pyrotechnics delay composition provides a predetermined time delay between ignition and the delivery of end result. Modern practice of requiring pyrotechnic delays is to function very precise. This has led to an intensive research into the mechanism and control of combustion both of gas producing and of gasless pyrotechnic mixtures. Pyrotechnic delay compositions have narrowed the field of investigation to the relatively few combustible materials. These can be considered suitable for this kind of precise applications. There are two types of pyrotechnic delay compositions, gassy delay mixture and gasless delay mixtures.
1.3.3.1 Gassy delay compositions:
Gassy compositions generate relatively greater than 20 cc/ g on combustion at Standard Temperature and Pressure. Burning rate is very dependent on the pressure of the system. The delay devise must usually be vented or, if sealed, have adequate free volume. The fuel is usually organic and the oxidizer an oxy salt. Properties of gassy delay composition are:
Are used in varied conditions and low attitudes e.g. black Powder. The burning rate of delay compositions can be very fast i.e. mm/ ms or quiet slow mm/s. Those pyrotechnic delay compositions which have a fast burning rate of more than 0.001 m/ ms are used in projectiles and bombs that detonate on impact. Pyrotechnics delay compositions which have a slow burn rate between 0.001 and 0.006 mm/s are used in ground chemical munitions such as tear gas and smoke grenades.
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Change in ambient pressure affect burning rate of gassy compositions. They must be freely vented to the surrounding atmosphere in order to get constant burning rate.
1.3.3.2 Gasless delay compositions:
Gasless delay mixture generate little < 5 cc/ gram of gas on combustion. Burning rate of gasless composition is relative insensitive to ambient pressure. Fuel is usually metallic or metalloid, and the oxidizer a metal oxide [1]. Gasless delay compositions are used in confined conditions or at high attitude, where it is important that variations from normal, ambient condition do not occur. Commonly used fuels and oxidizers in these mixtures are Boron, Silicon and potassium dichromate, Lead chromate, barium chromate and manganese etc. These compositions are used for producing a controlled amount of heat and for time delays in a number of military applications. Combustion is characterized by high reaction temperature and formation of mainly solids products. By controlling the properties & proportions of the ingredients of the mixture, both the burning rate and calorific value can be varied over fairly wide range. Gasless pyrotechnics delay compositions are particularly valuable for use in short delays detonators and delay cartridges. Gasless delay compositions are usually a combination of a metal oxide or chromate with an elemental fuel. Fuels are metals or high heat non-metal elements such as silicon or boron. When organic binder is used such as Nitro cellulose, the resulting mixture is low gassy rather than gasless due to the formation of CO, CO2, and N2. These gaseous products are resulted from combustion of the binder used for granulation purpose.
1.3.3.3 Properties of delay compositions:
Pyrotechnic delay compositions should not detonate but only burn. Some delay compositions when heavily confined incorrectly initiated by stimulus are capable of detonation. The pyrotechnics mixture must be stable during preparation and storage.
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Materials having low hygroscopic should be used. Pyrotechnics mixture should be easily ignited from ignition stimulus. There must be minimum variation in the burning rate of the composition with changes in external temperature and pressure. Pyrotechnics mixture should be readily ignited and easily burn at low temperature and pressure. There should be a minimum change in the burning rate of pyrotechnics composition with small percentage change in the various ingredients ratio. Burning rate of pyrotechnic composition must be reproducible, both within a batch and between different batches. Oxidizer used should be exothermic or slightly endothermic For slower delay composition, metals with less heat output per unit mass should be used. Oxidizer with high decomposition temperature and more endothermic heat of decomposition should be utilized. The ratio of oxidizer to fuel can be changed for a given binary pyrotechnic composition to get significant changes burning rate. Fastest burning rate should correspond to an oxidizer/fuel ratio near the stoichmetric ratio, with neither substance present in large excess. Ingredients should have highest purity and ingredients should be compatible with each other. When a fast burning rate is desired. A metallic fuel with high heat output per unit mass should be used together with an oxidizer of low decomposition temperature. The composition should be easily mixed, loaded in delay device with minimum risk.
1.4 Pyrotechnic Impulse/ Pressure generated Cartridges
Impulse cartridges are Electro Explosive Devices (EEDs) consisting of pyrotechnic igniter and booster compositions followed by propellant charge. These EEDs use
11 electrical energy as initial stimulus to initiate the igniter composition for subsequent initiation of the pyrotechnic train. An impulse cartridge generates pressure inside the chamber of pylon, which is used for the release of weapon from the Military Aircraft. The electrical igniter of Impulse cartridge consists of igniter composition, resistive wire, igniter body, pole piece and washer. The igniter composition is initiated through electrical or mechanical stimulus. When an electric energy passes through the bridge wire, it heats up and dissipates energy, and this energy loss ignites the igniter composition in pyrotechnic train.
Pyrotechnic train for impulse/ pressure generated cartridges consists of:
Igniter composition Booster pyrotechnic composition Propellant charge
Igniter Booster Propellant Pyrotechnic Pyrotechnic Charge composition composition
Figure 1.2 Pyrotechnic train for Impulse/ Pressure cartridge
1.4.1 Igniter pyrotechnic composition
Detail of igniter composition is given in Para 1.3.2
1.4.2 Booster pyrotechnic compositions
The energy of the igniter composition is generally not sufficient to reliably initiate the main propellant charge in pressure generated impulse cartridge, used to release store from the Military Aircraft. Therefore, a booster pyrotechnic composition is incorporated between the igniter and main propellant charge to boost the output pressure. Booster pyrotechnic composition should be sensitive enough to be easily initiated by igniter
12 composition. Booster pyrotechnic composition must have high heat output to easily initiate the main propellant charge in the impulse cartridge to produce the required pressure.
1.4.3 Propellant charge
Single and double based propellant charge is used in Impulse/ Pressure generated cartridges to provide the required impulse for the release of store from the Military Aircraft. In this research work single based propellant has been used to produce desired peak pressure.
1.5 Propagation of combustion
Basis of pyrotechnics is a combustion reaction. The reaction between fuel and oxidizer produces heat as the mixture of reactants is converted into a mixture of solid, liquid or gaseous reaction products.
Some of the heat is used for the reaction to propagate through the mixture
Some of the heat is lost through the delay body
Part of this heat is used to produce the pyrotechnics special effect.
In 2nd world war, a propagation index was proposed by Mclain. This method is used for evaluating the suitability of a delay composition which should sustain combustion in a long narrow delay tube:
Propagation Index = (Heat of Reaction)/ (Temperature of Ignition)
Once a portion of a pyrotechnic composition has been ignited, propagation (burning throughout) is normally not guaranteed. Heat is produced by the burning composition when the reactants react. Heat is transferred to the unreacted composition. If enough heat is transferred to the next layer of unreacted composition to raise that to the ignition temperature, burning will continue. If the heat loss to the surrounding is more than that
13 of the heat generated then combustion will not propagate and die out. Propagation can be assumed of as continuing self-ignition [13].
1.6 Safety precautions for pyrotechnics compositions
Respect Pyrotechnic compositions Don‟t be over confidant while working on pyrotechnic compositions Keep your work area clean and tidy Always handle small quantity of pyrotechnic composition Be sure you are familiar with the properties of the composition you work with Ground your work table, be aware of the static charge built-up Always wear earth strap while mixing and weighing pyrotechnic compositions Chemicals shall be ground, separately, never together Carefully wash and clean equipment before grinding chemicals Mixing should be done in the blast proof fuming hood designed for the purpose Dry chemicals should not be mixed in metal or glass containers to prevent a shrapnel hazard Safe guard pyrotechnic composition against friction, static charge, flame etc. Keep pyrotechnic composition away from heat source Always wear a face shield, or at least safety glasses Always wear a dust mask when handling powder chemicals Have a source of water and fire extinguisher readily available Always expect an accident and prepare accordingly, even if all these safety precautions are observed.
1.7 Factors effecting burning rate of pyrotechnic delay Compositions
1.7.1 Confinement effect:
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Burning performance of delay compositions is greatly affected by confining the delay device. If the confinement of gassy or low gassing mixtures provides only a small vent volume, burning time of pyrotechnic composition is considerably increased. A pyrotechnic delay composition is when burnt in a confined delay device, pressure inside delay column increased and thus helps in increasing burning rate and reduces burning time of the delay composition. Burning rate of identical compositions varies according to the extent to which the delay device is confined [14- 15, 19]. Pressure and temperature inside the delay column also increase when a burning composition is confined, because high temperature gases and radiant energy cannot escape. Both temperature and pressure inside column act to increase burning rate of delay compositions. Thus, confinement considerably increase burning rate of gassy delay compositions. The confined delay devices are normally used when the composition is not gassy. For gasless pyrotechnic delays, the confinement does not much effect the burning rate. Gasless pyrotechnic delay composition is generally used in small delay elements such as delay cartridges and delay detonators to produce consistence burning time.
1.7.2 Obturation effect
An obturated delay device is designed to provide an internal empty space between the igniter assembly and the delay composition. Delays devices in which gases produce are vented internally into closed delay device are called obturated delay devices. All the gasses produced during combustion of igniter and delay compositions are contained in the empty space. These devices are sealed and not affected by environmental conditions such as humidity, temperature and pressure. Short and intermediate delay devices are normally obturated [19].
1.7.3 Vented effect
An opening is provided in the delay devices through which the gases produced during combustion of the igniter and delay compositions escape. Vented delay devices are normally used for gasses producing pyrotechnic delay compositions. These are also used
15 for gasless delay compositions where long delay time is required, in order to eliminate the pressure buildup with in delay device. The vented delay devices are exposed to environmental effects such as temperature, pressure and humidity. Therefore these devices require sealing up to the time of functioning [19].
1.7.4 Effect of particles sizes:
Effect of particles sizes of ingredients of delay mixture on the burning performance is of great importance, especially metal fuels. The surface area and diameter of fuel used in the composition is very important. The finer is the material, the greater the surface area of material available for reaction, and the faster the compositions will burn [1]. The specific surface of the fuel usually has better effect on the burning rate of the composition than mean diameter. Combustion is a surface phenomenon, greater is the surface area greater will be combustion propagation. In order to get the required particles sizes the compound is passed through a particular sieve after grinding. The more the ingredient is irregular the faster will be burning rate. The grain size of an oxidizer such as potassium per chlorate has not great effect on the burning time, though it may influence ignitibility. Normally the burning rate is inversely proportional to the particles sizes of the ingredients of the mixtures.
1.7.5 Percentage of fuels:
Percentage of fuel in a composition has a greater influence on burning rate. By increasing the fuel content the burning rated increases until a maximum burning rate is achieved. The burning rate then starts to decrease on further increase of the fuel content until a misfire condition occurs. With excess of metal fuel, burning rate of pyrotechnic delay composition become faster and faster [16]. Excess fuel causes to increase heat conductivity of the composition rather than of the increased surface area of the active fuel. By increasing percentage of fuel in composition the reaction will be mainly solid/solid in nature and vice versa. The rate of reaction is maximum at 30 wt. % Si in
Si/ Pb3O4 delay mixture for course Silicon and rate of reaction is maximum at 15 wt. %
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Si in Si/ Pb3O4 delay mixture for fine silicon [17]. It means that both fuel content and geometry affects the burning rate of the pyrotechnic mixture.
1.7.6 Delay column diameter:
Effect of diameter of the delay column become critical when the composition burns slowly and the heat output is small, as is often the case. Radial losses of heat from delay composition can stop or extinguished the reaction in a delay column. Such losses become more serious as the column diameter, burning rate and ambient temperature are reduced. Pyrotechnic delay composition may perform adequately at normal and at higher temperature. When temperature is low, heat may soak away in the surrounding delay body. Glow front becomes narrower and literally tapers off so that burning may terminate before the terminal fire transfer point is reached. These effect combine to cause in a failure diameter associated with a given delay composition for a given ambient condition. For manganese delay mixture, the failure diameter for 0.118 sec/mm composition is less than 2.78 mm at –54 °C. Whereas the failure diameter for 0.394 sec/ mm manganese delays mixture is between 3.175 mm and 3.962 mm. [19].
1.7.7 Effect of ingredients:
Rate of reaction of pyrotechnic composition can be affected by changing the types of the fuel and oxidizer. The chemical nature of ingredients of pyrotechnic mixture has greater effect on the burning propagation of a chemical reaction for many reasons. For any chemicals reaction to occur between fuel and oxidizer it is also necessary there be an intimate contact between fuel and oxidizer. Intimate contact is produced by homogenous mixing and compaction of the reactants of mixture.
1.7.8 Effect of ingredients ratio:
Rate of reaction is related to the exothermicity of the pyrotechnic composition. It is generally observed that in a binary delay mixture the composition of maximum burning rate has more fuel than the mixture of maximum exothermicity. The thermal
17 conductivity of fuel is usually greater than that of oxidizer. For B/ KNO3 pyrotechnic mixture system, the composition has maximum burning rate occurs at 50.0 % B. whereas the exothermicity of this pyrotechnic composition is maximum near 17.0 % B.
1.7.9 Effect of ambient temperature:
At low initial temperature, pyrotechnics composition burns more slowly than at higher temperature. Burning rate of pyrotechnic composition at two different temperatures is normally expressed by;
bT/T R = r0 e °
Where R, r0 are burning rates at absolute temperature T andT0, and b is constant for the pyrotechnic composition. The higher the initial temperature of the reactants, the more easily will the delay composition achieves required activation energy. Ambient temperature of the surrounding and also the temperature of the unreacted delay composition effect burning rate. As ambient temperature is raised, activation energy is lowered because less energy is required to raise a composition to its ignition temperature. Thus the burning rate increases and less time is required to reach the ignition temperature. Burning rates of a delay composition increases when temperature is increased. For B/BaCrO4 =10/90 pyrotechnic composition, burning rate increases when temperature is increased. Burning rates of some commonly used tungsten and manganese based pyrotechnic delay compositions may change as much as 15.0 % with ambient change of 76 °C. Such large changes may be unacceptable, particularly in precise delay applications such as aircraft ejection systems [18].
1.7.10 Effect of ambient Pressure:
Energy in the combustion zone that radiates back from the hot combustion products of pyrotechnic reaction also increase burning rate of delay mixture. If the combustion products of pyrotechnic mixture are gases then the contribution is sensitive to the gas pressure. If the products are not gaseous, then the gas pressure will have small effects on
18 the burning rate of delay mixture. Reality lies between the two. The pressure dependence generally follows vielle‟s law as given below: α R = BP
Where, R is the burning rate at constant pressure P, α and β are constant for chemicals. This formula shows that, the more is the gassy composition the greater is the value of α and greater is the rate of reaction.
1.7.11 Effect of consolidation/ loading pressure:
Effects of consolidation pressures on the burning rate of pyrotechnic compositions are more complex. If combustion reaction is completely solid phase (i.e. no melting in the combustion zone), the increase in loading pressure allow better contacts between reactants. It means that reaction rate increase is solid phase. If the reaction is not solid phase then this effect is less predictable. Increase in loading pressure decrease the porosity, prevent hot gases permeating the reactants and thus reduce the burning rate. In most cases it is the linear burning (mm/s) of the composition, which is of interest to the designer, but the mass consumption rate (g/s) is also importance because that is a measure of the power output from the device.
1.7.12 Effect of water:
Effect of water is very significant on the performance of pyrotechnic delay compositions. Water can act as a volatile heat sink and make the pyrotechnic composition less sensitive. Water can increase the pressure in an unvented delay body. Sensitivity to moisture may cause ignition failure of delay device, effect burning propagation or chemically destroy the compositions. Humidity also affects the shelf life of most of the delay compositions. Most of the delays devices are now properly hermitically sealed to protect the device from environmental conditions.
1.7.13 Effect of terminal charge:
Burning characteristics of pressed pyrotechnic delay compositions are changed when a thermally sensitive bursting charge or primary high explosive is pressed at the end of
19 delay composition. The overall burning time and the reproducibility are both decreased under these conditions. The anticipatory effect has been observed with a variety of thermally sensitive end charges for both gasless and gaseous pyrotechnic delay compositions. Effect has also been observed for typical end item delay composition having a lead styphnate and Lead Azide as terminal charge. Reduction in burning time that occurs with delay elements having thermally sensitive terminal charges has been compared with similarly pressed delay columns without a terminal charge. Delay time approaches a constant value when the length of the delay column above the terminal charge increases. The reduction in burning rate is small for fast burning compositions. Obturation (empty volume between igniter and delay composition), substantially increases the magnitude of this effect. The anticipatory effect is normally reduced by barriers, between the delay charge and the thermally sensitive end explosive charge, which would reduce the flow of gases [19, 20].
1.7.14 Effect of ignition/first fire composition:
Some gasless pyrotechnic delay compositions are difficult to initiate. Normally a small charge of an ignition composition on top of the delay column is pressed. Silicon powder fuel form very sensitive ignitable mixture with oxides of lead e.g. Pb3O4 or PbO2.
Pyrotechnics compositions containing Silicon, red lead (Pb3O4) and titanium are commonly used igniter or first fire composition. The initiation of combustion of pyrotechnic mixture needs that a part of this composition be raised to its ignition temperature. Some pyrotechnic delay composition are not easily initiated, an explosive train similar that use in high explosive devices is used to produce the ignition stimuli is used to initiate the pyrotechnic train [21].
1.7.15 Effect of delay body material:
Body into which a delay composition is loaded act as a heat sink, generally metals is better conductors of heat than pyrotechnic delay compositions. More is the thermal conductivity of the body material, the more will be the heat loss to the surrounding, and the less will be the rate of reaction. Delay columns close to their low temperature failure
20 diameters tend to have larger temperature coefficient as the surrounding wall thickness is increased. For materials well above their failure diameters, this effect of wall thickness is of greater importance [19].
Main limitation associated with pyrotechnic delay is the accuracy that lies between ± 10.0 % to ± 20.0 % of mean value over a military operating temperature of – 40 °C to + 70 °C. Consistency of pyrotechnic delay composition has been improved from ±10.0 % to ±4.0 % at given temperature by improving the design in respect of the body of the delay material. Better accuracy is achieved when brass is used as delay body compared to stainless steel, aluminum and carbon steel [22].
1.7.16 Effect of Storage on burning time:
Reliability and effectiveness of a delay device depends of the accuracy of the burning time. Normally delay devices are stored for a long time, it is important to know the effect of storage conditions on burning times of pyrotechnic delay composition. When the compositions are stored in dry condition for relatively long periods of time results in little change in burning time e.g. B/BaCrO4 pyrotechnic delay compositions loaded and stored over a desiccant show little change in burning rate up to 2 years. For loose powders stored up to two years in unheated magazines and then tested in delay body, slight increase in burning time has been observed. Storage under dry conditions prevents increase in burring time and may reverse the trend. Manganese delay composition is when stored in dry environment; the burning time would not increase more than 5.0 % during eight weeks storage at +71 °C [19].
1.7.17 Charge increment:
To get burning time with high degree of accuracy, the charge composition is pressed in small increments. The increment height is always less or equal to the increment diameter to maintain uniform density of the increments, and thus uniform density of the composition is maintain throughout the delay column.
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1.7.18 Effect of binders:
Binders are added to delay compositions in small quantity; they may produce less energy than the principal fuel or oxidizer. The presence of these binders lowers the overall heat of reaction for the delay composition, and therefore, generally increase the burning time as well. Binder is used for the primary purpose of adjusting burning rate up or down. A burning rate modifier can act to reduce burn rate as described for typical binders. A burning rate modifier can act to increase burn rate. This will occurs when it increases the heat of reaction or if it increases the efficiency of thermal energy feedback.
1.7.19 Effect of mixing/ intimate contact of ingredients on burning rate:
Mixing or intimate contact has an important effect of the burning rate of the delay composition. More is the intimate contact the more is the reproducible burning time. Proper mixing of the fuel and oxidizer is ensure during the ingredient mixing and grains formation. Densities difference of the fuel and oxidizer effect the intimate contact of the ingredients especially during storage. Therefore during mixing a certain percentage of the binder is added to the mixture to prevent the fuel and oxidizer from being segregation in addition to its other advantages.
1.8 Measurement techniques:
This research work has been divided into the following three main sections:
1. Development and study of different types of igniter and booster pyrotechnic compositions for Impulse/ pressure-generated cartridges. Following equipment/ techniques were used for the measurement of different performance parameters.
Oxygen Bomb Calorimeter Closed bomb chamber Power supply Pressure calibrator Pressure transducer
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2. Development and experimental investigation of different types of pyrotechnic delay compositions. For measurement of performance parameters of these pyrotechnic compositions, following equipment /techniques have been used.
Digital Oscilloscope Customized Chronometer Detector Electromechanical switch Firing chamber Oxygen Bomb Calorimeter
3. Study of an impulse cartridge for the release of external store from Military Aircraft. For data measurement and analysis, following equipment/ techniques were used:- Digital Oscilloscope Power supply Pressure calibrator Pressure transducer Closed bomb chamber Ejection Velocity Measurement System
1.9 Literature Survey and Scope of the present research work:
A comprehensive literature survey has been carried out to identify different research areas, include: Igniter and booster pyrotechnic compositions for impulse cartridges Parametric studies of pyrotechnic delay compositions Delay time consistency in delay compositions Study of different binders in delay compositions Effect of temperature, pressure variation and body materials on burning rate Safe release of external store from Military aircraft at static condition
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To the best of our knowledge not much data is available in the reported literature on the effect of multiple parameters on burning performance of pyrotechnic delay compositions. Similarly very limited data was found on igniter and booster pyrotechnic compositions for impulse cartridges and finding the best igniter and booster composition is still an unresolved problem.
Earlier reported works present study of one or two parameters affecting burning performance of a particular pyrotechnic composition. Reported literature also lacked in detail study of binders affecting burning rate of delay compositions. Consistency in burning time is also a problem in pyrotechnic delay compositions
Details of the literature survey and work done in each specific area will be discussed chapter wise in the next part of this thesis; however, a brief and general introduction to these work areas has been discussed in the following paragraphs.
Aim of this research work was to develop different types of pyrotechnic igniter, booster and delay compositions for Military use, together with the development and parametric studies of pyrotechnic delay compositions. Development and detail parametric studies on the performance of pyrotechnic delay compositions would help the end user to optimize the burning rate of pyrotechnic compositions for intended application.
1.10 Outlines of this thesis:
Chapter 2 of the thesis provides details of different materials used in formulation of different types of pyrotechnic compositions. Methods for the preparation of these pyrotechnic compositions and different testing techniques have also been discussed in this chapter.
Chapter 3 of the research work focus on the development and study of different types of igniter and booster pyrotechnic compositions for pressure-generated cartridges. Different formulations of these compositions were studied to select the best igniter and booster pyrotechnic compositions. Some studies on igniter and booster compositions and
24 pressure cartridges have been published in the literature [23-25]. How to select the best igniter and booster composition for pressure generated cartridges, the earlier reported literature is lacked in this area.
Chapter 4 of this thesis focus on the development and study of B/BaCrO4 delay composition along with the study of effect of different parameters on the burning performance of this pyrotechnic delay composition.
Chapter 5 of this research work emphasis on the development and study of Si/Pb3O4/FG,
Si/PbO/FG and Si/PbO/Pb3O4 pyrotechnic delay compositions along with the study of effect of different parameters on the burning time and the burning rate of these pyrotechnic delay compositions. Published work mainly focuses on Silicon/Boron and red lead based pyrotechnic delay composition [17, 26-30]. Reported work is lacked in the study of more than one oxidizers in a delay composition. Published literature is also lacked in experimentally investigation of effect of multiple parameters on the performance of the time delay pyrotechnic compositions.
Chapter 6 of this research work address the study pertains to the measurement of minimum pressure together with time and ejection velocity required for the release of the external stores from military aircraft. Survivability and the mission effectiveness of the military aircraft are highly dependent upon the ability to deliver air- launched weapons with minimum risk. Impulse cartridges are pressure generated cartridge use to release the stores from the Military aircraft.
1.11 Objective of present research work:
A detailed literature survey of the published work was carried and more than two hundreds Journal/Conference papers, different books, Military Standards and patents related to energetic materials were consulted to outline the objectives of the present research work.
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Following goals were set while undertaking this work:
1. Development and Study of high energy igniter/booster pyrotechnic compositions for Impulse cartridges (Chapter 3)
2. Development and parametric studies of B/BaCrO4 pyrotechnic delay composition (Chapter 4).
3. Development and experimental investigation of different parameters affecting burning performance of Silicon and lead based pyrotechnic compositions (Chapter 5).
4. Experimental validation for the Safe Separation of External Store from Military Aircraft (Chapter 6).
1.12 Research work Plan
Development and Development and Development different studies of high energy studies of high energy pyrotechnic delay igniter pyrotechnic booster pyrotechnic compositions compositions compositions
Study of impulse Parametric studies of Parametric studies of
cartridge for store silicon and lead based B/BaCrO4 delay release mechanism delay compositions composition
Figure 1.3 Process flow chart for execution of this research work
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References
[1] N. Davies, Pyrotechnics Hand Book, the Ammunitions Systems and Explosives Department, Cranfield University (2002).
[2] B. Zaheer, Thermal, kinetic and morphological studies of available and synthesized pyrotechnic/ propellant compositions and their ingredients, PhD thesis (2015). [3] A. Bailey, S.G. Murray, Royal Military College of Science, Shrivenhan, UK, Explosives, Propellant and Pyrotechnics (1988). [4] M.W. Beck, M. E. Brown, Combust. Flame 66(1986)67. [5] M.W. Beck, Delay Composition and Device, US Patent No. 5,147,476(1992). [6] R.Aube, Delay composition and Detonation Delay Device Utilization, US Patent 0223242 A1 (2008). [7] E.F. Garner, C. Saugus, Pyrotechnic Composition with Combined Binder- Coolant, US Patent 3901747 (1975). [8] C.H. Martinez, C. Park, C. R. Finger hood, pyrotechnic composition comprising solid oxidizer, boron and aluminum additive and binder, US Patent 3257801(1966). [9] G.M.Clifford, P. Kempton, R.Craig , Edenvale, Production of pyrotechnic delay composition, US 2009/0314397 A1. [10] A.S. Redkar, V.A. Mujumdar. S.N, Singh, Defence Sci J, 41(1996)41
[11] J.S. Lee, L.K. Lina, C.H. LIN, P.J. Chen, C.W. Huang, S.S. Chang, Thermochim. Acta, 173 (1990) 211. [12] J.A. Conkling, Chemistry of Pyrotechnics Basic Principles and Theory, Department of Chemistry Washington College Chestertown, Maryland (1985). [13] K.L. B.J. Kosanke, L.J.white, Lecture Notes Pyrotechnic chemistry, Reference series No.2 J. Pyrotech, inc (2004). [14] A.Khan, A.Q. Malik, Z.H.Lodhi, Theory Pract. Energ. Mater., Proc. Int. Autumn Semin. Propellants, Explos. Pyrotech (2011) 491. [15] M.W. Beck, M.E. Brown, Combust. Flame 65(1986)263
27
[16] H. Ellern, Military and Civilian Pyrotechnics, Chemical publishing company inc (1968). [17] S.S. Al-Kazraji, G.J.Ress, Fuel 58(1979)139.
[18] W.C. Eller, F.J. Valenta, Temperature compensated pyrotechnic delays, United states Patent 3,851,586(1974). [19] AMC. Pamphlet, US Army Material Command Engineering Design Hand Book, Military Pyrotechnic Series Part-A, Theory and Application Washington D.C (1967). [20] M. Gilford, B. Werbel, G. Weingarten, D.Key, The anticipatory effect, a study of the burning mechanism of delay -relay columns(1964).
[21] AMC. Pamphlet, 706-210 Engineering Design Hand Book, Ammunition Series Fuzez, Headquarter, U.S. Army Material Common (1969).
[22] S.M. Danali, R.S. Paliaiah, K.C. Raha, Defence Sci J 60(2010)152.
[23] J.S. Lee, L.K.Lin, C.H. Lin, P..J Chen, C.W.Huang, S.S.Chang, Thermochim. Acta, 173 (1990)211. [24] L.C. Yang, L. Flintridge, AIAA/ASME/SAE/ASEE Joint Propulsion Conference Proc. Conf., 49th, San Jose, CA (2013). [25] S.L.Hobin, L.Flintridge, AIAA/ASME/SAE/ASEE Joint Propulsion Conference Proc. Conf., 40th, Fort Lauderdale, Florida (2004). [26] J. Jakubko, Z.V. Indet, J. Energ. Mater 15(1997)151. [27] Y.Li, Y.Cheng, Y.L. Hui, S .Yan, J. Energ. Mater 28(2010)77. [28] J. Jakubko, Combust. Sci. and Tech 146(1999)37. [29] H. Ren , Q. Jiao, S.Chen, J. Phys. Chem. Solids 71 (2010)145. [30] S.S. AL-Kazraji, G. J. Rees, Combust. Flame 31(1978)105.
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Chapter No. 2: Experimental Measurement Techniques and Materials used
2.1 Experimental Measurement Techniques:
A pyrotechnic time delay device plays a very critical role in modern missile and weapon systems. A pyrotechnic delay is used to achieve the required function within pre- determined delay time. Reproducible and consistent burning time of pyrotechnic delay devices is one of the most important factors. Different measurement equipment are used to measures the burning time of a pyrotechnic delay device. Resolution of measurement instruments ranged from nanosecond up to second. The burning time of a pyrotechnic delay device starts on the electronic timer/chronometer or Oscilloscope when the ignition of the igniter in the pyrotechnic train is initiated. Burning time stops when the light from the composition is detected by the detector. Different techniques and methods have been reported in the literature for the measurement of burning time of pyrotechnic delay devices [1-5]. The accuracy of the measurement instruments is very important especially in short pyrotechnic delay devices. These delay devices are used where accurate burning time is required to produce an end result with in the predetermined delay time. Short pyrotechnic delay devices are normally in milliseconds ranges, therefore, the resolution of these measurement instruments must be in micro or Nano second ranges to avoid motion blur.
Calorific value or heat of reaction is also an important parameter of pyrotechnic compositions and propellant charges. It is an amount of energy produced per unit charge (J/g). Calorific value is determined experimentally by a calorimeter. Calorific values for different types of pyrotechnic compositions have been reported in literature [6-9].
Safety of any electrically initiated explosive device, especially impulse cartridge is also very important. Different types of safety tests are performed to qualify the explosive device as per applicable Military Standards. Maximum No fire current, stray voltage and 29 static discharge tests are the most important safety tests of electrically-initiated explosive devices. These tests are performed to ensure the safety of explosive devices during handling and transportation [10-16]. After successful qualification of safety tests, the delay and impulse cartridges are then subjected to the functional test to determine the intended ballistic parameters.
Pyrotechnics delay time measurement, Ballistic parameters measurement; safety tests and calorific value measurement techniques have been used in the research work. These techniques were used to accurately measure the burning time of pyrotechnic delay device, ballistic parameters including peak pressure and time to peak pressure of impulse cartridge, and safety requirement of pyrotechnic compositions. Analytical apparatus and measurement instruments/ techniques that have been used to carry out the present research work are given below:
1. Pyrotechnic mixing machine 2. Manual Mortar and Pestle 3. Sieves and Sieves Shaker 4. Heating Oven 5. Chronometer 6. Oscilloscope 7. Detector 8. Power supply 9. Delay measurement chamber/ fixture 10. Oxygen Bomb Calorimeter(OBC) 11. Static discharge equipment 12. Stray voltage tester 13. Safe current measurement 14. Environmental and humidity chambers 15. Vacuum drying Oven 16. Closed volume chamber 17. Pressure calibrator 18. Pressure transducer
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19. Linear Variable Differential Transformer (LVDT) 20. Pico Log software
2.2 Equipment used for Pyrotechnic compositions preparation
2.2.1 Pyrotechnic mixing machine
Three dimensions (3-D) Inversina shaker mixer has been used for Mixing of different types of igniter, booster and delay pyrotechnic compositions during this research work. This is an automatic mixing machine for mixing of different types of pyrotechnic compositions. The mixing machine was placed on a stable surface. The fuels and oxidizers were first ground separately in the mortar pestle before mixing in the machine. The ground fuels and oxidizers were carefully poured in the bottle; the knob was set as per requirement. The protection hood was kept down and the machine was then switched ON. The mixing was continued until the composition is properly mixed, after mixing waited for five minutes for the composition to settle down. Machine was then switched off by lifting up the protection hood. All the safety precautions were observed while operating the machine. Schematic diagram of 3-D Inversina shaker mixing machine which has been used in present research work is shown in Figure 2.1.
Figure 2.1 (3-D) Pyrotechnic Automatic Tumbler Mixing Machine
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2.2.2 Manual Pestle and Mortar
After mixing of the compositions in the 3-D Inversina shaker mixer, Manual Mortar and Pestle was then used for homogenous mixing of small quantity of the pyrotechnic compositions. The quantity for manual mixing was limited to 5~10 g in order to minimize risk during handling and preparation of pyrotechnic compositions. Manual mixing in the Mortar and Pestle ensure homogenous mixing of the ingredients. Manual mixing ensure intimate contact of the ingredients and increases time consistency in the pyrotechnic delay compositions. Mortar and Pestle are shown in Figure 2.2.
Figure 2.2 Agate Pestle and Mortar for mixing of the compositions
2.2.3 Sieves and Sieves Shaker
The compositions already mixed in agate pestle and mortar was transferred into granules for ease of loading in delay body. Fish Glue, Carboxyl Methylene Cellulose (CMC) and Dextrin were used as binders in the required quantities. Binder solutions were prepared in ethyl acetate and water as solvent for the formulation of granules. As it was a small scale experiment, the granulation was done by wetting the composition in solvent. For
32 larger scale process, special granulation machines are normally used. The compositions were converted into grains of required sizes by passing the composition through sieves in order to prevent separation of oxidizers and fuels due to different in their densities. Grains prepared in binders also protect the composition from environmental effects. Haver test shaker EML 200-89 digital as shown in Figure 2.3 was used for preparation of grains of required particle size. Filled the pyrotechnic composition in the upper test sieve and then fixed sieve cover with knurled nuts. Set the vibration intensity and preset the sieving time as per requirement [17].
Figure 2.3 Haver test shaker EML 200-89 digital
2.2.4 Vacuum drying Oven
A calibrated Vacuum Oven VO500 as shown in Figure 2.4 was used for drying of the individual fuels/ oxidizers and the pyrotechnic compositions. The oven has temperature range of 20 °C ~200 °C. Temperature for drying the individual chemicals and mixed compositions was set between 70 ºC to 80 ºC. The drying time was varied as per the requirement of each chemical and composition.
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Figure 2.4 Vacuum drying Oven Model VO500
2.3 Equipment used for conditioning of explosive devices
2.3.1 Environmental chamber
Figure 2.5 Environmental chamber for conditioning of samples Environmental chamber Model# BTRC as shown in Figure 2.5 was used for the conditioning of the pyrotechnic delay cartridges, Igniters and Impulse cartridges. The chamber has the temperature ranges of -60 °C ~200 °C. This chamber was used for
34 conditioning of these explosives devices at different temperatures ranged from -54 °C to °
100 C.
2.3 Equipment used for delay time measurement:
2.3.1 Chronometer with Detector
This equipment was used for the measurement of time elapsed between initiation of igniter and detection of flame by the detector. The measuring range of the chronometer was ranged from nano sec to sec. Chronograph consisted of two channels that give digital display. The Chronograph was connected to detector and firing mechanism/ electromechanical switch. Pyrotechnic delay device was mechanically initiated; the delay time was measured from the striking of the percussion of the primer with a striking pin to the appearance of flame detected by the photodiode detector. The delay time started on the chronometer when pin stroked the percussion and stopped when the heat/ flame of the composition detected by detector of chronometer. The chronometer displayed the burning time in ms on the screen.
2.3.2 Digital Oscilloscope
Four channels Digital Storage Oscilloscope Model Tektronix TDS 2024 with following specification was used for measurement of burning time of delay device as shown in Figure 2.6.
Time scale of the Oscilloscope range from nanosecond to second Maximum frequency = 200MHz.
The primary function was to provide a graph of signal voltage against time. This is useful for measuring propagation delay of signal rise and fall time. This method has proven to be very reliable, simple and accurate one [18]. The delay time of delay device based on the ability of oscilloscope to respond to initial signal supplied from power
35 supply and its response to flash detected by the detector. Two channels of the Oscilloscope were used for the measurement of the burning time.
Figure 2.6 TDS 2024 Digital Storage Oscilloscope
2.3.3 Power supply
Figure 2.7 TTZ CP*200 Power Supply
Calibrated Power supply Model TTZ CP*200, as shown in Figure 2.7 was used to provide required energy to operate the chronometer, electromechanical switch and Oscilloscope. Power supply was also used to provide the required energy for the
36 initiation/firing of impulse cartridges. Power supply was set on 5 VDC and 100 mA to operate the chronometer, Oscilloscope and electromechanical switch. Impulse cartridge was fired at 28V DC and 3A.
2.4 Equipment used for thermal analysis
2.4.1 Oxygen Bomb Calorimeter (OBC)
Oxygen Bomb Calorimeter measure the heat of reaction or calorific value of different combustible materials including energetic material.
Figure 2.8 Oxygen Bomb Calorimeter Parr 6200
Oxygen Bomb Calorimeter Parr 6200 with oxygen bomb 1108 as shown in figure 2.8 was used in this research work for the measurement of calorific value of different pyrotechnic compositions [19]. The system consists of 2000 ml temperature controlled, tank with built in circulating pump. This is a closed circuit system in which water is re- used continuously.
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No oxygen is required from the environment for combustion of these compositions, because pyrotechnic compositions contain its own oxygen. Sample size was kept between 0.5~1.0 gram. The measured calorific values of every pyrotechnic composition have been discussed in the relevant sections.
2.5 Equipment used for the safety tests of igniter compositions
2.5.1 Static discharge equipment
This is a laboratory safety and reliability test, simulating handling and transportation conditions.
Figure 2.9 Static Discharge tester ESD 300
These igniters were subjected to the 25000 volt simulated human electrostatic discharge to qualify the requirement of applicable MIL-Standard [20]. The purpose of this test was to qualify the igniters to provide protection against mission degradation due to the Discharge of Electrostatic Energy (DEE) and following initiation of explosive devices. The igniter should not fire during this test. Static Discharge tester ESD 300 System of EMC PARTNER as shown in figure 2.9 was used for the purpose.
2.5.2 Stray voltage tester
Stray Voltage tester/ pulse generator of Thurlby Thunder Instrument Part No TG 550 as shown in figure 2.10 was used for stray voltage tests. A Digital Oscilloscope was used to
38 displays the pulses generated by pulses generator. This is a safety test in which the initiator shall be capable of withstanding the effects of a stray voltage environment without pre-igniting.
Igniters were subjected to 2000 pulse of direct current. Each pulse was of 300 milliseconds duration and pulse rate was 2 pulses per second. Each pulse had minimum amplitude of 100 ± 5 milli amperes to qualify the requirement of applicable MIL- Standard [20].
Figure 2.10 TG 550 Pulse generator
2.5.3 Maximum No Fire current measurement equipment:
This is a safety test for functional reliability, handling and tactical safety. The igniters of impulse cartridges were subjected to not less than 1watt/ 1A current for five minute to qualify the requirement of applicable MIL-Standard [20]. The igniters should not fire during this test. A Calibrated Power supply was used for measurement of Maximum No fire current test.
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2.6 Equipment used for the ballilstic parameters measurement of Impulse cartridges
2.6.1 Charge calibrator
Pressure/charge calibrator is used to measure the pressure produced by different types of energetic material when fired in a closed bomb chamber. Pressure calibrator Type 6907 of Kstler Company as shown in Figure 2.11 was used for the measurement of pressure of Impulse cartridge both in closed chamber and during release of store from pylon. The input of this calibrator of Kistler Company was connected with pressure transducer (installed in closed chamber) with low-noise cable. Output peak pressure of the impulse cartridge was displayed on the front screen of the pressure calibrator.
Figure 2.11 Type 6907B Charge Calibrator
Pressure was recorded in bar and displayed on the LCD. The output was sent to the Pico software through a Digital to Analog converter. Pico Software of Kistler Company was used to measure and displayed the peak pressure and time to peak pressure on the screen. The sensitivity and other parameters were set on the front panel of the pressure calibrator.
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2.6.2 Pressure transducer
Pressure transducer is a pressure sensor, ideal for measuring pressure such as pressure pulses in hydraulic and pneumatic system. In present research work, pressure sensor type 7005 of Kistler Company as shown in the Figure 2.12 was used for sensing the pressure produced by pressure generating cartridge in closed bomb chamber. The sensor was mounted directly on the closed bomb chamber by means of nut and connecting nipple. Pressure generated cartridge was installed in the closed bomb chamber from the other side. The sensor sensed the pressure produced by the impulse cartridge.
Figure 2.12 Type 7005 Pressure Sensor
2.7 Material Used in the present research work
2.7.1 Fuels and oxidizers
High purity analytical (AR) grade fuels and oxidizers of renowned companies like Sigma Aldrich/Fluka, Fisher and Dura Thight as shown in tables 2.1 and 2.2 were purchased and used for manufacturing of ignition, booster and delay pyrotechnic compositions in present research work. These fuels were used in different ratios as per requirement of a specific composition and have been discussed in detailed in the relevant sections of this research work.
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Table 2.1 List of fuels used in present work
S# Description OEM Purity Particle size Part No 1 Boron powder Fluka 95~97 % Fine Powder 13112 2 Magnesium Powder Aldrich ≥99 % Fine Powder 215619 3 Silicon Powder Aldrich 99 % 44 µm 96570 4 Zirconium Powder Fluka ≥97 % Fine Powder 1.04944 5 Lead Thiocynate Dura Thight ≥99.9 % Fine Powder 11282 6 Zinc Aldrich ≥98 % < 10 µm 209988
Table 2.2 List of oxidizers used in present work
S# Description OEM Purity Particle size Part No 1 Barium Chromate Aldrich ≥98 % Fine Powder 401056 2 Bismuth(III) Oxide Aldrich 99.9 % 10 µm 223891 3 Potassium Per Chlorate Fluka ≥99.9 % Fine Powder 60440 4 Lead(II) Oxide(PbO) Aldrich 99 % 1~2 µm 242547
5 Lead Oxide Pb3O4 Aldrich ≥99.9 % <10 µm 211907 6 Potassium Chlorate Fluka ≥99 % Fine Powder 15580 7 Potassium Nitrate Fisher ≥95 % Powder P/6040/60
All steps including mixing, manufacturing and testing process of these compositions have been carried out in controlled humidity and temperature environment. The individual fuel and oxidizer were ground in the manual pestle and mortar and passed through the sieves to bring them into the required particle sizes. Fuels and oxidizers were of very high purity so no further purification was required. Fuels and oxidizers used for formulation of different types of pyrotechnics compositions are shown in Table 2.1 and Table 2.2.
2.7.2 Binders:
Carboxyl Methyl Cellulose (CMC) of CalBiochem, Dextrin of Merk and commercial grade Fish Glue were used as binders in different pyrotechnic compositions. The purity
42 of these binders was more than 95 %. These binders were used to increase cohesion between particles of fuel and oxidizer aiding consolidation. These binders also modified the burning rate and thus the performance, and also protected the pyrotechnics compositions from environmental effects. These binders were used in different percentages to check their effects on burning rate and burning time of different pyrotechnic compositions developed during this research work. Binders also affected Heat of reaction of igniter, booster and delay pyrotechnics compositions.
2.7.3 Delay body Material
Stainless steel and Brass material were used for the manufacturing of the delay tubes. The internal diameter of the delay tube was 4.0 mm while the column length was kept 9.0 mm, 11.0 mm, 14mm and 20.0 mm in different experiments.
2.8 Pyrotechnic composition preparation procedure
Pyrotechnic compositions were prepared by mixing the fuels, oxidizers and binders in the required ratios. Before mixing, the individual ingredients were dried in a heating oven to remove the moisture contents and to ensure accurate masses. Following three types of pyrotechnic compositions with different ingredients ratios were prepared during this research work:
Igniter pyrotechnic compositions Booster pyrotechnic compositions Delay pyrotechnic compositions
General process flow for the preparation of these compositions is given in Figure 2.13. Detail description of preparation of each type of pyrotechnic composition is given in the relevant chapters.
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Booster/ Delay Igniter pyrotechnic pyrotechnic composition composition
Drying of the ingredients Drying of the ingredients
Weighing of fuel/ oxidizer Weighing of fuel/ oxidizer/ binder
Mixing of ingredients in Mixing of ingredients in 3-D Mixer 3-D Mixer
Mixing of ingredients in Mixing of ingredients in Mortar and pestle Mortar and pestle
Filling/pasting of igniter Granulation process composition in igniter body
Sieving and assy in Assy of igniter in delay/Cartridge body delay/Cartridge body
Testing
Figure 2.13 Process flow for preparation of pyrotechnic compositions
2.9 Procedure for burning time measurement
Burning time of all pyrotechnic delay compositions were measured by using Digital Oscilloscope and Chronometer. Burning time was measured between striking the igniter
44 and detection of flash by the detector. Pyrotechnic delay device was initiated through mechanically mean by hitting the igniter assembly with a striking pin. Firing mechanism consists of electromechanical system which is a combination of mechanical striking pin and electrically operated switch. Burning time started when the pin hit the percussion primer which then operated the switch. The operation of the percussion primer, which ignites the pyrotechnic delay composition in the delay tube, simultaneously started the oscilloscope. The termination of the burning was recorded when the light from the end of the delay composition fell on the photodiode detector, which sent a signal to the measuring instruments. Channel 1 of digital oscilloscope was connected with the firing switch and Channel 2 of the oscilloscope was connected to the detector.
2.10 Procedure for the measurement of peak pressure and time to peak pressure
Peak pressure and time to peak pressure of the pressure generated cartridges were measured in a closed pressure chamber by using charge calibrator, pressure sensor, Analog to Digital converter and PICO log software of Kistler Company. Following steps were followed for measuring these ballistic parameters.
Before testing the pressure chamber was properly cleaned. Firing mechanism and pressure sensor were installed in the chamber and it was ensured that there is no leakage from the chamber. Cartridge was then installed in the chamber by observing required safety precautions. Pressure sensor was connected with pressure calibrator with low resistance wire. The output of the pressure calibrator was connected to PC through Analog to Digital Converter to display pressure-time curve. Firing lead was then connected with electric firing unit and DC power supply. Required energy for the initiation of the pressure cartridge was provided though power supply.
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References
[1] Sabeh S. Al-Kazraji and Gwilym J. Rees, Fuel. 58(1979)139 [2] T. Boddington and P.G. Laye, Thermochimica Acta. 120(1987)203. [3] Michael W. Beck and Michael, Combust. Flame. 66(1986) 67. [4] Yanchun Li, Yi Cheng,Yun-Long Hui, and Shi Yan, J. Energ. Mater. 28(2010)77. [5] Jan Jakubko, Journal of Energetic Materials.15(1997)151. [6] Jinn-Shin Lee, Chung King Hsu, Li-Kuo Lin and Chin- Wang Huang, Journal Thermal Analysis and Calorimetry. 56(1999)223. [7] S. H. Fischer and N1.C. Grubelich, 24th International Pyrotechnics Seminar Monterey, CA. July(1998). [8] Lachute, R.A. Delay composition and Detonation Delay Device Utilizing same. Patent US 8066832B2,2011. [9] AI-Kazraji, S.S. ; Rees,G.J. Fuel. 58(1979)139. [10] Takehiro Kohno and Chia Hsiang Wang, Pyrolant. Propellants Explos. Pyrotech. 29 (2004)56. [11] Jinn-Shing Lee and Chung-King Hsu, Thermochimica Acta 367~368 (2001) 375. [12] Jinn-Shing Lee, Thermochimica Acta. 392-393(2002) 147.
[13] Electro Explosive Subsystems, Electrically Initiated, Design Requirements and Test Methods. MIL-HDBK-1512 (USAF), Department of Defense Hand Book, 1997. [14] Fred, L. M. A Compilation of Hazard and Test Data for Pyrotechnic Compositions. US Armament Research and Development Command, 1980. [15] Brown, M. H.; Crossley, J. F.; Hamilton, Ch. R.; Hoelzen, W. R. Electric Initiators for Explosives, Pyrotechnics and Propellants. Patent US 3117519, 1964. [15] Electro Explosive Subsystems, Electrically Initiated, Design Requirements and Test Methods. MIL-HDBK-1512 (USAF), Department of Defense Hand Book, 1997. [17] Operating instructions, for Haver Test Shaker EML 200-89 Digital, Feb, 1993. [18] Zahid Mehmood SCME (NUST), Thesis: Influence of primary charge load pressure on function time and sensitivity of a hot wire detonator.
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[19] Operating Instruction Manual No.442M for Oxygen Bomb Calorimeter Parr 6200. [20] Detail Specification, Initiators Electric, General Design Specification, MIL- DTL-23659E, 2007.
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Chapter No. 3: Development and study of high energy igniter and booster pyrotechnic compositions
3.1 Introduction
Work presented in this chapter reports the development of different types of igniter (Primary) and booster (Secondary) pyrotechnic compositions for impulse/pressure cartridges. In order to initiate suitably an impulse cartridge and to get the desired peak pressure, high energy igniter and booster pyrotechnic compositions may be required.
These comprise B/KNO3, Zr/KClO4 and Pb(SCN)2/KClO3 as igniter compositions, and
B/Mg/KClO4/Bi2O3 and B/Mg/KClO4 as booster compositions. Three different types of igniter with varying fuel contents and 18 different types of booster compositions were developed and studied. The investigated oxidizers for the igniter compositions were
KClO3, KClO4 and KNO3, whereas the fuels were B, Zr and Pb(SCN)2. Similarly for the booster pyrotechnic composition the oxidizers were BaCrO4, KClO4 and Bi2O3 whereas the fuels were B and Mg. Different ratios of the fuels and oxidizers were studied based on heat of combustion and best igniter and booster pyrotechnic compositions were selected. Heat of combustion was determined using Oxygen Bomb calorimeter. Static discharge tester, stray voltage tester, Power supply were used for safety tests. Pressure transducer and Pressure calibrator were used for measurement of peak pressure. Different ballistic parameters such as burning time and peak pressure were studies to select the best igniter and booster compositions for Impulse Cartridge firing in the closed chamber. Different safety and functional tests of these compositions are also reported in this chapter. Pyrotechnics are types of energetic materials which produce special effects when suitably initiated. The pyrotechnic compositions are used for military as well as for civilian applications and the reactions produce special effects such as heat, light, sound and coloration [1-3]. These pyrotechnic compositions consist of fuel, oxidants and binders. The nature of these ingredients has an effect on the ignitibility of the
48 igniter, booster and delay pyrotechnic compositions. The most important applications of pyrotechnic compositions for military use are in impulse cartridges. Impulse cartridges are Electro Explosive Devices (EEDs) consisting of a pyrotechnic igniter and booster compositions followed by a propellant charge. These EEDs use electrical energy as the initial stimulus to initiate the igniter composition for subsequent initiation of the pyrotechnic train. Impulse cartridges are used for the release of external store from Military Aircraft. Pyrotechnic train for an impulse cartridge is:
Igniter Pyrotechnic Booster Pyrotechnic Propellant
composition composition Charge
Electrical igniter of an impulse cartridge consists of an igniter composition, resistive wire, igniter body, pole piece and washer. Igniter composition is initiated through electrical or mechanical stimulus. The resistive wire ignites the igniter composition by the joule effect when an electric current is passed. The performance of a high energy pyrotechnic composition depends upon:
the ability to ignite the material using an external ignition source,
the ability of the composition, once ignited, to sustain propagation in the remaining composition.
Igniter composition of an impulse cartridge should not be very insensitive otherwise it would be very difficult to initiate by the required stimulus. On the other hand, the igniter composition should also not be too sensitive to accidental initiation when subjected to electrical energy below a pre-determined level. Therefore, the igniter composition must qualify the required safety tests including maximum no fire current, static discharge and stray voltage, to ensure safe handling, transportation and storage, along with a reduction of hazard during its life cycle [4- 8]. The energy of the igniter composition is generally not enough to initiate reliably the main propellant charge, therefore, a booster pyrotechnic composition is incorporated between the igniter and the main propellant 49 charge to enhance the output energy [9, 10].The booster pyrotechnic composition should be sensitive enough to be initiated by the igniter composition and must have a high heat output to easily initiate the main propellant charge in the impulse cartridge to produce the required pressure. The calorific value or heat of reaction is an important parameter of igniter/booster pyrotechnic compositions and propellant charges. It is the amount of energy produced per unit charge (J/g). The calorific value is determined experimentally by using a bomb calorimeter. Calorific values for different types of pyrotechnic compositions have been reported in the literature [11-14]. Different type of igniter compositions such as B/KNO3, Zr/KClO4, Zr/BaCrO4, Al/ Fe2O3 are commonly used in igniters [15-22].
A thorough literature survey was conducted but not much data was found on igniter and booster pyrotechnic compositions for impulse cartridges and finding the best igniter and booster composition is still an unresolved problem. The present study was aimed to develop best igniter and booster pyrotechnic compositions to be employed in impulse cartridges to enhance its performance in term of peak pressure for Military use. These compositions were required to have high heat output to increase the pressure of impulse cartridge inside the closed firing chamber. Additionally, the igniter composition was also required to pass the required safety tests including Max No fire current (1watt/ 1A current for five min), Stray voltage and Static discharge as applicable in Military Standard [24]. To the best of our knowledge, the present study has been undertaken for the first time.
3.2 Experimental conditions
3.2.1 Characteristics of the used materials
High purity Analytical grade fuels and oxidizers (Fluka/Sigma Aldrich) and commercial grade Fish Glue and Nitrocellulose Lacquer as additives/binders were used during this research work. Purity of these chemicals was 97-99 %. The used fuels and oxidizers were fine powders. All of these fuels and oxidizers were passed through a 325 mesh sieve to obtain a final particle size of ≤ 44 μm.
50
3.2.2 Compositions preparation
3.2.2.1 Igniter and booster pyrotechnic compositions (without binder)
Moisture content was removed from both fuels and oxidizers by drying these ingredients in an oven at 80 °C for 2 hours. The chemicals were weighed according to the required percentages and then the ingredients were mixed in a three dimensional (3-D) automatic Tumbler Mixing Machine. From the already mixed composition small batches of 5 g each were further processed by mixing the chemicals in a mortar and pestle in a specially designed fuming hood for 30 min in order to further homogenize the compositions. Three different types of igniter mixtures, A = B/KNO3, B = Zr/KClO4, and C = Pb(SCN)2/KClO3, with the fuel content being varied from 10 % to 90 %, were prepared. These igniter compositions were slurried in a nitrocellulose dipping grade lacquer in a 2:1 ratio. The slurry was then pasted onto the bridge wire of the igniters. Igniter assemblies pasted with igniter compositions were dried in the heating oven at about 70 °C for four hours.
3.2.2.2 Booster pyrotechnic composition(with binder):
In order to remove the moisture, both fuels and oxidizers were dried in a heating oven at 80 °C for 2 hours. The chemicals were weighed according to the required percentages and then the ingredients were mixed in a three dimensional (3-D), automatic Tumbler Mixing Machine. From the already mixed composition small batches of 5 g each were further processed by mixing the chemicals in a mortar and pestle in a specially designed fuming hood for 30 min in order to further homogenize the compositions. A binder solution of 4.0 % fish glue was prepared in distilled water and this solution was mixed with the composition. A homogenous paste was prepared by using a spatula in an agate container. The paste composition was semi-dried in a drying oven at 80 °C. To avoid the formation of lumps, the semi-dried composition was carefully broken up with a spatula in an agate container. The composition was sieved gently through a 50 mesh sieve and retained on a 150 mesh sieve to obtain grain sizes of 106-297 μm. A Haver test shaker EML 200-89 digital was used for the preparation of grains of the required particle sizes
51
[23]. The grains were dried for 4 hours at 80 °C to remove moisture content. The finished composition was stored in a special container and placed in a desiccator for 24 hours to stabilize the composition.
3.2.3 Calorimetric measurement
An oxygen bomb calorimeter Parr 6200 with oxygen bomb 1108 was used in this work for the measurement of the calorific value of different igniter and booster pyrotechnic compositions. No oxygen was required for combustion because a pyrotechnic composition contains its own oxygen. The sample size was kept to ~0.5 g for each test.
3.2.4 Safety tests
Safety and reliability are the two most important parameters of any explosive device. The igniter of the impulse cartridge must be safe and reliable to produce the required results. The safety of an impulse cartridge is ensured by the design of the igniter and by preparing the igniter composition to qualify all the required safety tests in order to ensure safe operation, handling, transportation and storage as per the requirements of the applicable Military Standard [24].
3.2.4.1 Maximum No fire current test
This is a laboratory test for functional reliability, handling and tactical safety. Fifteen igniters were manufactured for this test. Out of which five igniters were pasted with each igniter compositions A=B/KNO3, B=Zr/KClO4 and C=Pb (SCN)2/KClO3 respectively. These igniters were then subjected to not less than 1watt/ 1A current for five minute to qualify the requirement of applicable MIL-Standard [24]. The igniter should not fire during this test. A Calibrated Power supply was used for measurement of Maximum No fire current test.
3.2.4.2 Static Discharge test
This is a laboratory safety and reliability test simulating handling and transportation conditions. Fifteen igniters were manufactured for this test. Out of which five igniters
52 were pasted with each igniter compositions A=B/KNO3, B=Zr/KClO4 and C=Pb
(SCN)2/KClO3 respectively. These igniters were subjected to the 25000 volt simulated human electrostatic discharge to qualify the requirement of applicable MIL-Standard [24]. The igniter should not fire during this test. Static Discharge tester ESD 300 System of EMC PARTNER was used for the purpose.
3.2.4.3 Stray Voltage test
This is a safety test in which the initiator shall be capable of withstanding the effects of a stray voltage environment without pre-igniting. Similarly for this test a total of fifteen igniters were manufactured as well. Out of these five igniters were pasted with each igniter compositions A=B/KNO3, B=Zr/KClO4 and C=Pb (SCN)2/KClO3 respectively.
These igniters were subjected to 2000 pulse of direct current. Each pulse was of 300 milliseconds duration and pulse rate was 2 pulses per second. Each pulse had minimum amplitude of 100 ± 5 milli amperes to qualify the requirement of applicable MIL- Standard [24]. Stray Voltage tester of Thurlby Thunder Instrument Part No TG 550 was used for stray voltage tests.
3.2.5 Manufacturing of igniter for Impulse Cartridge
Igniter is the main part of an impulse cartridge. Igniter consisted of a hot bridge wire, an igniter mixture pasted onto the bridge wire and mechanical components including an igniter body pole piece, washer and insulating cup.
Igniter was manufactured by assembling the mechanical parts followed by spot welding/soldering of the hot bridge wire onto the pole piece of the igniter. The prepared paste of the igniter composition was slurried in nitrocellulose dipping grade, in a 2:1 weight ratio. Paste of the igniter composition was then applied to the bridge wire of the igniter. It was then dried at 80 °C for 2 h. The specifications and Schematic diagram of igniter is shown in Table 3.1 and Figure 3.1 respectively.
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Table 3.1 Specification of igniter for Impulse Cartridge
Description Specification Bridge wire material (Nickel/ Chromium) 80/20 Wire diameter 0.046 mm Wire length 4.0 mm Resistance of wire per mm 0.097 Ω Length to diameter ratio of bridge wire 87 Distance between pots 4.0 mm Igniter mixture blended in NC Lacquer 2:1
B/KNO3 30% Boron
Zr/KCLO4 60% Zirconium
Pb(SCN)2/KCLO3 40% Pb(SCN)2 Mechanical components 01set
Figure 3.1 Schematic diagram for igniter of impulse cartridge
3.2.6 Cartridge assembly and Functional Tests in closed chamber
Impulse or pressure generated cartridge consists of the following: Cartridge body/casing
54
Igniter assembly Booster composition Propellant charge Closing cup Sealant
Following steps were followed for the manufacture of the impulse cartridges:
Assembly of the igniter in the main cartridge body Filling of the booster composition in the cartridge body Filling of the main propellant charge in the cartridge body Assembly of front disc in the cartridge Sealing and crimping of the impulse cartridge.
Design of Impulse/pressure generated cartridge is shown in Figure 3.2
Figure 3.2 Schematic diagram of impulse cartridge
55
In this research work a closed chamber of volume 230 cm3 was used during functionality tests. A pressure transducer of 0 ~ 250 bar, pressure calibrator and PICO software of the Kistler Company were used for the measurement of peak pressure and time to peak pressure. Schematic diagram for the measurement of peak pressure and time to peak pressure is shown in Figure 3.3.
ADC Card
Result Display
Impulse Cart
Pressure calibrator
Transducer Closed firing chamber Power supply
Figure 3.3 Schematic diagram of the experimental setup of pressure-generated cartridge
56
Peak pressure and time to peak pressure of the impulse cartridges was recorded in a closed bomb chamber [25]. The selection of the volume of the closed chamber for peak pressure and time to peak pressure measurements depends on the specific application.
3.3 Results and discussion
3.3.1 Calorimetric measurement of igniter compositions
3.3.1.1 B/KNO3 igniter mixture-A
Calorific values of B/KNO3 igniter mixture are shown in Table 3.2 and Figure 3.4. These results show that the calorific values of this igniter mixture increased with increasing boron content until the maximum calorific value of 7549 J/g was recorded at 30 % boron − almost all of the fuel reacted with the oxidant.
Table 3.2 Exothermicity measurements for range of B-KNO3 igniter mixture
Test # Boron [%] KNO3 [%] Mean Cal Value [J/g]
1 10 90 3144 2 17 83 6062 3 20 80 6389 4 25 75 7377 5 30 70 7549 6 40 60 7231 7 50 50 7080 8 60 40 6879 9 70 30 5711 10 80 20 4024 11 90 10 NR*
*NR means Not Recorded and ignition not observed
57
Calorific value then decreased on further increase in boron content, until a misfire occurred in the calorimeter at 90 % boron. Sensitivity of this composition was reduced at 90 % boron and the energy produced by the hot resistive wire was insufficient to ignite this mixture. A minimum calorific value of 3144 J/g was recorded at 10 % boron.
Figure 3.4 Plot of exothermicity against Boron content for a range of
B-KNO3 igniter mixture
3.3.1.2 Zr/KClO4 igniter mixture-B
Potassium perchlorate is one of the important oxidizers in pyrotechnic formulations. It decomposes exothermically, as compared to other oxidizers. Zirconium fuel is a powerful reducing agent and reacts with an oxidizer at high temperature to release enough heat to ignite booster pyrotechnic mixtures. The reaction of zirconium and potassium perchlorate is a very fast reaction. The reaction of this fuel and oxidizer is given below.
2Zr+KCLO4 = 2ZrO2 + KCL
Experimental results for the calorific values of Zr/KClO4 mixtures are presented in Table 3.3 and Figure 3.5.
58
Table 3.3 Exothermicity measurements for range of Zr- KCLO4 igniter mixture:
Test# Zirconium [%] KCLO4 [%] Mean Cal Value [J/g]
1 10 90 NR* 2 20 80 2654 3 30 70 2868 4 40 60 4392 5 50 50 4919 6 60 40 6125 7 70 30 5782 8 80 20 4513 9 90 10 2922 *NR means Not Recorded and ignition not observed
Figure 3.5 Plot of exothermicity against Zirconium content for a range of Zr-
KClO4 igniter mixture
These results revealed that the calorific value of this igniter composition increases with increasing zirconium content and a maximum value of 6125 J/g was observed at 60 % zirconium − almost all of the fuel reacted with the oxidant. Further increase in zirconium
59 content decreased the calorific value. At 10 % zirconium content the igniter mixture failed to ignite because the energy produced by the resistive wire was not enough to ignite this mixture. A minimum value of 2654 J/g was recorded at 20 % zirconium. An almost identical result (6061 J/g) was reported by Jinn-Shing Lee at 60 % zirconium [26]. Safety tests reported in the literature were conducted using a Pt/Ir 80/20 alloy hot bridge wire. In the present work, the same tests for the Zr/KClO4 igniter composition were conducted using an 80/20 % nickel/chromium alloy hot bridge wire, in order to qualify the safety tests of the applicable Military Standard. Both results are in fair agreement.
3.3.1.3 Pb(SCN)2/KClO3 igniter mixture-C
Different ratios (10~90 % fuel) for these igniter compositions were tested to determine their calorific values. The value increased with increases in lead thiocyanate content. The maximum calorific value of 4333 J/g was recorded at 40 % lead thiocyanate. The calorific value then decreased with further increases in lead thiocyanate content. A minimum calorific value of 1030 J/g was recorded at 30 % fuel.
Table 3.4 Exothermicity measurements for range of Pb(SCN)2-KClO3 igniter mixture
Test# Pb (SCN) 2 [%] KClO3 [%] Mean Cal Value [J/g] 1. 10 90 NR* 2. 20 80 NR* 3. 30 70 1030 4. 40 60 4333 5. 50 50 2935 6. 60 40 2579 7. 70 30 2206 8. 80 20 2039 9. 90 10 NR* *NR means Not Recorded and ignition not observed
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Composition misfired at 10 %, 20 % and 90 % lead thiocyanate because the sensitivity of these compositions was reduced at these ratios and the energy produced by the resistive wire was insufficient to ignite this mixture.
Results of the calorific values of the Pb(SCN)2/KClO3 igniter mixtures are presented in Table 3.4 and Figure 3.6.
Figure 3.6 Plot of exothermicity against Pb(SCN)2 content for a range of Pb(SCN)2/ KClO3 igniter mixture
3.3.2 Safety Tests Results
3.3.2.1 Maximum No fire current test
None of the igniters fired during safety tests, and all of the igniters passed this test when subjected to 1 watt/1 A, a direct current of not less than one ampere supplying a minimum of one watt applied to the bridge circuit for a period of at least five minutes. Results are shown in Table 3.5.
3.3.2.2 Static Discharge test
None of the igniters fired and all of the igniters passed this test when subjected to the requirements of a 500 ±5 % pF capacitor charged to 25000 ±500 V and 500 ±5 % Ω
61
resistors connected in a 5 μH total inductance series circuit between pairs of pins. The results are shown in Table 3.5.
3.3.2.3 Stray Voltage test
None of the igniters fired and all of the igniters passed this test when subjected to 2000 pulses of direct current. Each pulse was of 300 ms duration and the pulse rate was 2 pulses per second. Each pulse had minimum amplitude of 100 ±5 mA. Results of these tests are shown in Table 3.5.
Tests results in Table 3.5 show that the 40 % Pb(SCN)2/KClO3 mixture is the most
sensitive whereas 30 % B/KNO3 is the least sensitive to electrical stimuli of the three compositions. All of the igniter compositions are suggested as reliable igniter compositions for qualifying the above tests, 1 W/1 A direct current for not less than 5 minutes, static discharge and stray voltage, for impulse cartridges. These compositions were investigated by using (nickel/chromium) = 80/20 %, with diameter 0.046 mm and length 4.0 mm, as a hot wire bridge. If the type or diameter of the bridge wire were changed, then re-qualification would be required, because the sensitivity of the igniter composition changes with a change in type and diameter of the hot bridge wire.
Table 3.5 Comparison of different results of ignition compositions
S#S Mixture Description Calorific Safe Stray Static Firing Value Current Voltage Discharge current[A] [J/g] [A] at 1VDC Mixture 30/70 = 7549 1 W/ 1 A Passed Passed 1.7~1.8
-A B/KNO3 Mixture 60/30= 6125 1 W/ 1 A Passed Passed 1.4~1.5
-B Zr/ KClO4 Mixture 40/60= 4333 1 W/ 1 A Passed Passed 1.2~1.3
-C Pb(SCN)2
/KClO3
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When the diameter of a bridge wire is decreased, the resistances of the bridge wire increases because the resistance is inversely proportional to the diameter of the wire. When the resistance of the bridge wire is increased, the composition becomes more sensitive to electric currant and vice versa. The larger the resistance of the hot bridge wire, the greater is the heat dissipated from the bridge wire and hence the composition becomes more sensitive. Further investigation would be required for the qualification of the safety tests of these igniter compositions if the type or diameter of the bridge wire were changed.
3.3.3 Calorimetric measurement of booster compositions
3.3.3.1 Existing Booster Composition
A booster pyrotechnic composition with weight percentages of B/Mg/KClO4/
Bi2O3/BaCrO4 = 5:17:31:7:40 was taken as the reference booster composition for the comparison of newly developed booster compositions. Three samples of this composition were tested for their calorific value. The calorific value of this original/reference booster composition was 6100 J/g, as shown in Table 3.6.
Table 3.6 Calorific value of original booster pyrotechnic composition
Ingredients and %age of Binder and Grain Size Mean Cal Booster composition Its % age Value[J/g]
B/Mg/KClO4/Bi2O3/BaCrO4 Fish Glue 4% 6100 106~297 µm = 5:17:31:7:40 additional
3.3.3.2 Newly prepared high energy Booster Composition (New-1)
Two fuels and two oxidizers were used during preparation of this mixture. Different ratios of these ingredients, B, Mg, KClO4, Bi2O3 and fish glue were tested, and the best result was obtained with B/Mg/KClO4/Bi2O3 = 5:17:71:7 and 4 % additional fish glue as binder. Results are shown in Table 3.7. The purpose of adding fish glue as a binder was
63 to protect the composition from environmental effects, especially humidity, because most of the pyrotechnic compositions are affected by the humidity. Additionally, the binder also reduces the sensitivity of the composition to avoid accidental initiation during the manufacturing process, especially during grain preparation when the composition is passed through sieves. The maximum mean calorific value recorded for a series of booster compositions was 6770 J/g.
Table 3.7 Calorific value of newly prepared booster pyrotechnic composition (New-1)
Ingredients and Binder and Particle Size Mean. Cal their %age its % age Value[J/g]
B/Mg/KClO4/Bi2O3 Fish Glue (106~297) µm 6770 = 5:17:71:7 4 % additional
These results reveal that the calorific value of the newly prepared booster pyrotechnic composition (New-1) is almost 11 % higher than the original/reference booster pyrotechnic composition
3.3.3.3 Newly prepared high energy Booster Compositions(New-2)
A total of 16 different types of booster compositions were investigated as shown in Table 3.8. Mostly, these compositions consisted of two fuels and one oxidizer. Different ratios of the ingredients, B, Mg, KClO4 and fish glue were tested. The results presented in Table 3.8 show that the initial five mixtures were not ignited by the hot bridge wire of the bomb calorimeter, because the compositions with these ratios were not sufficiently sensitive to be initiated.
In other words, the compositions containing magnesium, potassium perchlorate and less than 5 % boron were not initiated by the heat liberated by the hot bridge wire of the calorimeter. At ≥ 5 % boron, the mixture was initiated by the hot bridge wire of the
64 bomb calorimeter. Results in Table 3.8 also show that the calorific value significantly increased when the potassium perchlorate content was reduced to 60 %. At this percentage of the oxidizer, the calorific value varied from 9902 J/g to 10362 J/g on changing the ratios of the two fuels boron and magnesium.
Table 3.8 B/Mg/KClO4 booster pyrotechnic composition (New-2)
Test B[%] Mg[%] KClO4[%] Mean Cal Binder/Grain No Value[J/g] size 1 0 15 85 Misfired Without Binder 2 1 14 85 Misfired Without Binder 3 2 14 84 Misfired Without Binder 4 3 15 82 Misfired Without Binder 5 4 15 81 Misfired Without Binder 6 5 15 80 4279 Without Binder 7 5 15 80 6360 106~297 µm 8 0 40 60 Misfired Without Binder 9 5 35 60 9952 Without Binder 10 10 30 60 9998 Without Binder 12 20 20 60 9902 Without Binder 13 30 10 60 10161 Without Binder 14 30 10 60 10190 106~297 µm 15 40 0 60 10362 Without Binder 16 40 0 60 10048 106~297 µm
Results in Table 3.9 give a summary of the booster compositions (New-2). There is no significant difference in the calorific values of the booster mixtures at these ratios. However, the maximum calorific value recorded for the newly prepared booster composition B/KClO4 = 40/60 was 10362 J/g, without binder and for B/Mg/KClO4 = 30:10:60 was 10190 J/g with 4 % binder.
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This means that the calorific value of the newly prepared booster pyrotechnic composition (New-2) is almost 70 % and 67 % higher than the original/reference booster pyrotechnic composition, without and with 4 % binder, respectively.
Table 3.9 Summary of calorific value of newly prepared booster composition (New-2)
S# Ingredients and %age Mean. Calorific Binder/Grain size of Booster composition value [J/g]
1 B/Mg/KClO4 = 9952 Without Binder 5:35:60
2 B/Mg/KClO4 = 9998 Without Binder 10:30:60
3 B/Mg/KClO4 = 9902 Without Binder 20:20:60
4 B/Mg/KClO4 = 10101 Without Binder 30:10:60
5 B/Mg/KClO4 = 10190 106~297 µm 30:10:60
6 B/KClO4 = 40:60 10362 Without Binder
7 B/KClO4 = 40:60 10048 106~297 µm
3.3.4 Selection of best igniter and booster compositions for impulse cartridge
Zr/KClO4 = 60:40 was selected as the final igniter composition. Although this composition has a calorific value less than that of the B/KNO3 mixture, this composition has a bulk density greater than that of the B/KNO3 mixture. The average weight of the
Zr/KClO4 mixture accumulated in the total available volume of the igniter body was 113 mg, whereas the average weights of igniter compositions A = B/KNO3 and C =
Pb(SCN)2/KClO3 accumulated in the total available volume of the igniter body were 123 mg and 84 mg, respectively. Therefore the total resultant heat output of the Zr/KClO4 =
66
60:40 igniter composition was 8.4 % and 23 % higher than the total heat output of the B/
KNO3 = 30:60 and Pb(SCN)2/KClO3 = 40:60 igniter compositions, respectively. The charge weights, calorific values and calculated total heat outputs of these igniter compositions are listed in Table 3.10.
Table 3.10 Comparison among all three igniter compositions
Igniter composition Mass(mg) in Calorific Total heat primer body value [J/g] output[J]
30% B/KNO3 84 7549 634
60% Zr/ KClO4 113 6125 692
40% Pb(SCN)2/KClO3 123 4333 533
Quantity of booster pyrotechnic composition in the impulse cartridge was kept fixed during each of the tests for the measurement of peak pressure and time to peak pressure.
Of the seven different types of booster pyrotechnic compositions tested, B/Mg/KClO4 = 30:10:60 wt. % was selected as the final booster composition. The grains sizes and calorific value of this composition were 106~297 μm and 10190 J/g, respectively, as shown in Table 3.11. However the calorific value of this composition is slightly smaller than 10362 J/g (B/KClO4 = 40:60).
Table 3.11 Final selected igniter and booster pyrotechnic compositions
Type of Ingredients and %age Mean. Calorific Binder/ composition of composition value [J/g] Grain size
Igniter Zr/ KClO4= 60:40 6125 Without grain
Booster B/Mg/KClO4 = 30:10:60 10190 106~297 µm
Reason for the selection of this composition as the final one was because it contains a binder and the binder protects the fuel and oxidizer from environment effects such as humidity. Additionally the binder also increased the cohesion between particles of fuels
67 and oxidizers to protect them from being segregated due to their difference in density. Grains also provided ease of loading of the composition in the cartridge body.
3.3.5 Functional tests results
Functional test results (peak pressure and time to peak pressure) are shown in Table 3.12 and in Figures 3.7 and 3.8.
Table 3.12 Test results in closed chamber of volume 230 cm3 (Weight = 4.40g single base propellants)
Existing Booster Newly prepared New-1 Booster Newly prepared New-2 Composition composition Booster composition Peak pressure Time to peak Peak pressure Time to peak Peak pressure Time to peak [bar] pressure [bar] pressure[ms] [bar] pressure[ms] [ms] 131.6 39.89 143.1 49.10 139.0 30.68 134.5 42.96 137.5 36.82 143.4 42.96 129.4 36.82 142.3 24.55 143.8 30.68 131.3 36.82 138.9 36.82 143.4 36.82 130.5 42.96 138.0 42.96 143.1 30.68 130.1 36.82 136.5 42.96 139.9 30.68 Mean values 131.23 39.37 139.38 38.87 142.1 33.75 increase in decrease in increase in decrease in time peak time to peak peak to peak pressure pressure pressure pressure 6.2 % 1.3 % 8.3 % 14.3 %
These results show that the newly prepared igniter composition Zr/KClO4 = 60:40 and booster composition B/Mg/KClO4/Bi2O3 = 5:17:71:7 increased the peak pressure of the impulse cartridge by 6.2 % in a closed chamber of volume 230 cm3.
Similarly, the same igniter composition and the booster composition B/Mg/KClO4 = 30:10:60 increased the peak pressure of the impulse cartridge by 8.3 % in the closed
68 chamber due to the high heat output by these compositions. Test results of the peak pressure measurements are shown in Figure 3.7.
Figure 3.7 Plot of peak pressure of three booster pyrotechnic compositions
Generally, when the pressure in the closed chamber increases, the rate of reaction also increases and the time to peak pressure decreases; similar results were recorded for these mixtures as shown in Figure 3.8.
Figure 3.8 Plot of time to peak pressure of all three booster pyrotechnic compositions
69
Time to peak pressure decreased by 14.3 % for the finally selected igniter and booster compositions. The volume of the close chamber is inversely proportional to the pressure developed inside the chamber. During the design stage, the volume of the chamber is generally finalized for pressure measurements and it remains fixed throughout the life cycle of the product.
3.4 Conclusions
From the analysis of all of the investigated igniter and booster pyrotechnic compositions, it was concluded that all of the newly-developed igniter and booster pyrotechnic compositions have shown promising results. Among these, the best igniter and booster compositions in terms of impulse cartridge functionality based on the peak pressure
(bar) and time to peak pressure (ms) were the mixtures 60 % Zr, 40 % KClO4 and 30 %
B, 10 % Mg, 60 % KClO4, 4.0 % additional binder, respectively. These compositions also passed all of the requisite safety tests and are considered the best compositions for impulse cartridges for the safe release of weapons from Military Aircraft.
70
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Chapter No. 4: Development and
parametric studies of B/BaCrO4 pyrotechnic delay composition
4.1 Introduction
The work presented in this chapter reports the development and parametric studies of newly developed B/BaCrO4/Binder pyrotechnic delay composition. Boron (B) is a fuel;
BaCrO4 is oxidizers, whereas Fish Glue, CMC and Dextrin were used as binders. Delay pyrotechnic composition consists of fuels, oxidizing agents and sometime binders. Pyrotechnics are special class of energetic material, when suitably initiated give special effect as required, reported by Bailey and Murray [1]. Pyrotechnic is general term for a mixture that burns at a selected, reproducible rate, providing a time delay between activation and production of main effect. Like other applications one of the most important applications of pyrotechnic delay compositions is their use in delay devices for Military applications. The delay device provides pre-determined delay time before performing certain functions.
Delay pyrotechnic compositions are material that rapidly burn when ignited and thus creating time delay. A pyrotechnic delay composition must produce enough heat to compensate the heat loss through the rigid delay body especially in low temperature environment in order to sustain reliable burning propagation in the delay body [2]. There are two types of pyrotechnic delay compositions, a gassy delay composition which generate gases relatively greater than 20 cc/ g on combustion at Standard Temperature and Pressure, and a gasless delay composition which generate little less than 5 cc/ g on combustion [3]. A pyrotechnic delay composition is developed to perform some function after a predetermined time delay. Therefore reproducibility in burning rate, burning time and charge consumption are critical outcomes of any pyrotechnic delay composition for some special applications. Factors which may effect consistency in burning time,
73 burning rate and charge consumption of pyrotechnics delay composition include, confinement, particles size, percentage of fuel, diameter of the tube, thickness of delay body, conductivity of delay body, geometry of the delay body, ingredients, ingredients ratios, initial temperature, ambient temperature, ambient pressure, consolidation pressure, moisture, terminal charge, ignition composition, delay body material, storage condition , charge increment, binders, intimate contacts of ingredients etc. [4-11].
Consistency and accuracy of delay time is very important in a delay device especially in short pyrotechnic delay cartridges and detonators used to function after a pre-determined delay time. Modern pyrotechnic devices require to be consistent and precise in delay time [10, 12-15]. Delay device is normally vented, obturated or confined. In case of confined delay device pyrotechnic composition is required to be gasless in order to avoid development of pressure inside the devices. Boron-Barium chromate is a gasless delay composition. The propagative burning of pressed delay column of this gasless delay composition is a combustion reaction in which B and BaCrO4 react to give solid products. DTA and TGA studies of the fuel and oxidizer in B/BaCrO4 delay mixture do not indicate the formation of a gaseous phase [16]. Reported reaction between B and
BaCrO4 is given below.
4B+ BaCrO4 4BO+Ba+Cr [17-18]
The above reaction scheme implies that stoichiometry corresponds to a boron content of approximately 15 % by weight. Like other parameters which effect burning rate of a pyrotechnic delay composition, the variation in fuel content, binder contents along with ambient temperature, loading pressure, body material and exothermicity are very critical parameters and required due consideration while developing a new pyrotechnic delay composition for some specific applications.
By increasing the fuel content the burning time and the burring rate is effected. Similarly Exothermicity of the delay composition is also affected by varying the fuel contents. Binders are compounds which increase cohesion between particles of fuel and oxidizer aiding consolidation. Binders affect the sensitivities to stimuli and also protect the
74 pyrotechnics compositions from environmental effects. Binder material when added to a delay mixture modifies the burning rate and thus the performance of the delay composition. [9, 19]. Binder also protects the metal fuel from reacting with atmospheric oxygen. By adding any material other than the stoichiometric amounts of the fuel and oxidizer cause to effect propagation of the delay pyrotechnic compositions [1, 20]. Some binders do not substantially affect the delay time and hence the burning rate [21]. Binder is added in small percentages in a mixture to bind fuel and oxidizer together in the form of free flowing granules and to provide ease of loading in the delay tube. Without a binder fuel and oxidizer segregate during composition preparation and in storage due to difference in their densities. Loading pressure also affects the burning rate of a pyrotechnic delay composition and hence the burn time [22-24]. The effect of loading pressure on burning rate is some time very complex. Loading pressure consolidates the composition inside the delay column and effect the burning propagation. Different loading pressures are applied to consolidate the delay composition inside the delay column depends upon the required applications [25-26]. Standard practice of loading a pyrotechnic delay composition is ranged between 207 MPa and 276 MPa [16]. Pyrotechnic based delay devices used in delay fuzes are sometime subjected to high acceleration in order to detonate the warhead after penetration in the thick hard target after certain delay time [27].
The overall aim of this study was:
To develop B/BaCrO4 pyrotechnic delay composition that is safe to process into delay element and easily ignitable by primer and feature a high consistent delay time. Additionally this composition must also be reliably initiated when compacted at high loading pressure.
To investigate experimentally the effects of the following parameters on the performance of B/BaCrO4 pyrotechnic delay composition:
1. Effect of Boron content on Burning time and Burning rate/ mass consumption
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2. Study of different binders and their effect on Burning time and Burning rate 3. Effect of temperature variation on Burning performance 4. Exothermicity/ Calorific value 5. Effect of Loading pressures on Burning time and Burning rate 6. Effect of body material on Burning time and Burning rate 7. Effect of loading pressures on the consolidation density and Percent Theoretical Maximum Density (%TMD)
Like other parameters, these selected parameters also affect the burning propagation of any pyrotechnic delay composition. Therefore before developing a pyrotechnic delay composition due consideration should be given to these important parameters. Thorough literature survey was carried out to find out detail on the different parameters affecting the burning time and burning rate/ mass consumption of B/BaCrO4 delay mixture but very limited data is available. Effect of boron content on delay time and mass consumption of B/BaCrO4 delay mixture along with determination of the calorific value had been reported by AMC Pamphlet and J.A Conkling [16, 18]. But the published literature related to this delay composition lacked in study of Binder, temperature variation, loading pressures, body material and %TMD on the burning performance. All these parameters have been studied in detailed in this research work. Binder Fish Glue,
CMC and Dextrin have also been studies for the first time in B/BaCrO4 delay mixture. Fish Glue is a natural product which is obtained by cooking fish skin, followed by evaporation reported in literature [28]. Binder and loading pressure also effect the consolidation and Percent Maximum Theoretical Density (%TMD) of different delay compositions when loaded in a delay tube [26, 29].
4.2 Experimental conditions
High purity analytical grade Boron Powder and Barium Chromate were purchased from Sigma Aldrich Company. Boron powder was more than 95 % pure and had a particle size less than 5µm.The purity of the Barium Chromate was ≥ 98 %.
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Binders Carboxyl Methyl Cellulose (CMC) and Dextrin were purchased from CalBiochem and Merk respectively, whereas commercial grade Fish Glue was used in this pyrotechnic delay mixture. This binder is very economical and easily available in market. Purity of these binders was ≥95 %.
4.2.1 Preparation of Pyrotechnic Delay Composition
4.2.1.1 Mixing of ingredients of pyrotechnic delay compositions:
Individual chemicals (fuels, oxidizer and binders) were dried in a heating oven at 80 °C for 1 hour to remove the moisture. Chemicals were weighed according to the required percentages and first mixed the ingredients in the three dimensional (3-D) automatic tumbler mixing machine for 3 hours. These materials were dried in order to ensure accurate masses in delay mixture because different ingredients have different absorptivity. Relative Humidity of the composition preparation room was maintained between 40 % and 60 %. From the already mixed composition small batches of about five gram each were further processed by mixing the chemicals in Mortar and Pestle in a specially designed fuming hood for 30 min in order to further homogenize the compositions. Purpose of homogenous mixing was to increase time consistency in these pyrotechnic delay compositions.
4.2.1.2 Grains formation of pyrotechnic delay compositions:
Binders solutions of CMC, Dextrin and Fish Glue were prepared in distilled water followed by mixing the binder solutions in the already mixed composition (Para 4.2.1.1).
Three binders CMC, Dextrin and Fish Glue were used in B/BaCrO4 delay composition. A homogenous paste was prepared by using the spatula in agate container. Semi dried the composition (paste) in the Drying Oven at 80 °C. To avoid the formation of lumps, the semi dried composition was broken by spatula in a special container carefully. Composition was sieved gently through 212 mesh sieves to get grains sizes of ≤65 µm.
An automatically operated Haver test shaker EML 200-89 digital was used for
77 preparation of grains of required particle sizes. Grains were dried for 4 hr at 80 °C to remove the water/moisture. Stored the finished composition in a special container and placed it in desiccator for 24 hr to stabilize the compositions.
4.2.2 Safety during mixing
Since these compositions are very sensitive to friction, especially the processes of dry mixing and grains formation, therefore the following safety precautions were implemented in order to avoid any accidental initiation of the compositions.
Ensure the exposure of minimum number of operators during processing steps.
Quantity of pyrotechnic composition for each batch was kept to 5 gram.
A specially designed Mortar and Pestle was used.
A bullet proof screen was used while dry mixing the composition.
Fire proof goggles/ faces protective cover and gloves were used while handling and preparing the compositions.
4.2.3 Loading procedure
Finished composition was then loaded into a stainless steel and brass delay tubes with an internal bore diameter of 4.0 mm and a column length of 15 mm in four equal increments of 100 mg.
A hydraulic press machine installed with a calibrated gauge was used to consolidate the delay composition in the delay body. Each increment was pressed at a loading pressure of 276 MPa in the delay tube. No starter composition was loaded between the igniter assembly and delay composition. B/BaCrO4/FG delay composition was directly initiated through the energy produced by the igniter assembly.
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4.2.4 Configuration of delay device
Configuration of the delay device used in this research work is shown in Figure 4.1. This delay device consists of stainless steel delay body, pyrotechnic composition, igniter assembly and O-ring. Igniter assembly is further divided into igniter body with anvil and percussion primer. A free volume of about 3.5 cm3 was provided to provide an obturation effect to accumulate the gasses produced during the burning of the delay composition. An O-ring was used to hermetically seal the delay composition from environmental effects and to allow the excess high pressure gasses to escape from the delay devices. Front of the delay devices was sealed with aluminum foil.
4.2.5 Assembly of the delay device
After loading the delay composition in the delay body a mechanical percussion primer was then assembled in the igniter holder, and the igniter assembly was then assembled in the delay tube. Furthermore an O-ring was installed in the delay tube from the igniter side followed by the assembly and crimping of aluminum disc.
Figure 4.1 Stain Less steel body Delay device
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4.2.6 Testing procedure
Delay device was initiated through mechanically mean by hitting the igniter assembly with a striking pin. Firing mechanism consisted of electromechanical system which is a combination of mechanical striking pin and electrically operated switch. Delay time started when the pin hit the percussion which then operated the switch and the delay time stopped when the photodiode detector detects the flame of the delay composition. Delay time was measured with Digital Storage Oscilloscope TDS2024 of Tektronix Company.
Detector Oscilloscope
Delay cart
Firing chamber Power supply
Figure 4.2 Schematic diagram for burning time measurement pyrotechnic delay device
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The burning rate was calculated by dividing the length of B/BaCrO4/Binder filled delay column with recorded burning time, while the charge consumption was measured by dividing the charge consumed in mg with recorded burning time. Burning time measuring principle is illustrated in Figure 4.2.
Oxygen Bomb Calorimeter Parr 6200 with oxygen bomb 1108 was used in this research work for the measurement of calorific value of Boron- Barium Chromate pyrotechnic compositions by varying Boron contents.
4.3 Results and discussion
4.3.1 Effect of Boron contents on burning rate/ charge consumption of B/BaCrO4 delay mixture
Recipe for different B/BaCrO4/FG delay compositions with varying boron contents is shown in Table 4.1. In these experiments Boron contents were varied from 5 % to 45 % and Barium chromate contents were varied from 54 % to 94 %. By increasing the fuel content, the oxidizer content was decreased accordingly with the same ratio, while the binder content was kept at 1.0 %. Test results of burning time, burning rate, charge consumption, and standard deviation of these compositions with varying Boron contents are shown in Table 4.1 and Figure 4.3. Study was started with B/BaCrO4/FG = 5/94/1 delay composition for the determination of burning time and charge consumption. Further studies were carried out by increasing the Boron content, and the oxidizer content reduces with a similar ratio. Five samples with each boron content were tested and the burning rate and charge consumption were calculated. Mean values of burning time, burning rate, and charge consumption of B/ BaCrO4/FG delay pyrotechnic delay mixture at different Boron contents were measured. Mean standard deviations of burning time, burning rate and charge consumption were also calculated. Heat produced during the chemical reaction of the fuel and oxidizer transferred to the unreacted mixture through conduction, which sustained burning propagation. The reaction products are solid so the burning rate of this mixture is relatively insensitive to ambient pressure.
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Data presented in Table 4.1 reveals that, when the Boron content in the delay mixture was increased, the bulk density of the delay composition decreased and, hence, the mean charge weight of the delay mixture decreased accordingly. Results in Table 4.1 and Figure 4.3 show that both the charge consumption and burning rate of the delay mixture increased with an increase in Boron content until the maximum charge consumption of 1135 mg/s and burning rate 55 mm/s was recorded at 18 % Boron. On further increase in Boron content beyond 18 %, both charge consumption and burning rate showed a downward trend and a minimum value of 213 mg/s for charge consumption and 12 mm/s for burning rate were recorded at 40 % Boron. Due to further increase in Boron content up to 45 %, the delay time was not recorded by the detector. Five samples were tested at 45 % Boron content. In two samples out of these five samples, the delay composition was not initiated by the igniter, while in the remaining three samples partial burning was observed; hence, burning propagation of this delay composition did not
sustain in the delay column. Thus, B/BaCrO4/FG pyrotechnic delay composition at above 40 % Boron failed to produce reliable combustion.
Table 4.1 Test results of B/BaCrO4/FG delay mixtures with varying boron contents.
Pyrotechnic mixture MCW MDT MBR MCC MSDDT MSDBR MSDCC
5% B, 94% BaCrO4, 349 0.571 26 611 0.008 0.27 11.63 1.0% FG 10% B, 89% BaCrO4, 340 0.394 38 863 0.010 0.73 19.82 1.0% FG 15% B, 84% BaCrO4, 325 0.290 52 1121 0.008 0.95 19.82 1.0% FG 18% B, 81% BaCrO4, 312 0.275 55 1135 0.006 0.77 13.73 1.0% FG 20% B, 79% BaCrO4, 300 0.308 49 974 0.007 0.73 11.56 1.0% FG 25% B, 74% BaCrO4, 285 0.383 39 744 0.006 0.48 19.33 1.0% FG 35% B, 64% BaCrO4, 270 0.820 18 329 0.009 0.14 10.58 1.0% FG 40% B, 59% BaCrO4, 259 1.214 12 213 0.050 0.50 15.57 1.0% FG ≠ ≠ ≠ 45% B, 54% BaCrO4, 247 NR* NR* NR* NA NA NA 1.0% FG
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*NR = Not Recorded, ≠NA= Not Applicable, MCW= Mean Charge Weight (mg), MDT=Mean Delay Time (s), MBR=Mean Burning Rate (mm/s), MCC= Mean Charge Consumed (mg/s), MSDDT=Mean Std. Dev. in Delay Time, MSDBR=Mean Std. Dev. in Burning Rate, MSDCC= Mean Std. Dev. in Charge Consumed.
Generally any variation from stoichiometry reduced both the charge consumption and burning rate, because the heat production reduced at both fuel rich and fuel lean mixture, which subsequently reduced both charge consumption and burning rate.
At 40 % Boron content, the pressing pressure was reduced from 276 Mpa to 138 Mpa in order to increase the sensitivity of the composition to igniter, but the propagation burning of the composition did not sustain and partial burning was observed. It means that the heat produced by the delay composition containing Boron content above 40 % was not enough to sustain propagation. In other words, the heat lost through the rigid delay body was more than the heat produced by the delay composition at above 40 % Boron, and thus burning propagation of the delay composition stopped due low heat production. It means that this delay mixture produced reliable burning propagation from 5 % to 40 % without containing a starter composition. The burning rate could be varied between 12 mm/s and 55 mm/s as shown in Table 4.1. Mean Standard Deviation in Burning Rate also reveals that this delay composition is consistent in burning rate and the same was ensured by controlling the manufacturing/Laboratory operating conditions and testing procedures.
Almost similar results of burning time and hence burning rate were reported in [16]. In the reported study the minimum burning time and maximum burning rate was recorded at about 15 % Boron content without using binder in the composition. Similarly the delay composition failed to sustain burning propagation at 45 % and above boron content.
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Figure 4.3 Effect of Boron content on mass consumption and burning rate of
B/BaCrO4/FG delay mixture
4.3.2 Effect of Binders on burning rate and charge consumption of B/BaCrO4 mixture
In addition to fuel and oxidizer, binder is the third important ingredient of pyrotechnic mixtures. Binder fastens together particles of both fuel and oxidizer in the form of free flowing grains. Binder protects the fuel and oxidizer from environment effect such as humidity. Additionally binder also increases cohesion between particles of fuels and oxidizers to protect them from being segregation due to their density difference especially during composition preparation, storage or use over a long period of time and therefore increase homogeneity [2, 18, 30-31]. Grains also provided ease of loading of the composition in the cartridge body. Free flowing grains of the mixture have also the ability to flow freely when poured from one container to another. Binder is normally used in the range of 0.2 % to 0.6 % by weight of the total composition [2]. The granulation process becomes difficult with increasing the binder content in the composition. Three binders Fish Glue, Carboxyl Methyl Cellulose and Dextrin were studied in B/BaCrO4 pyrotechnic delay mixture. Binders were added to collect the particles to bind together in the form of free flowing grains. Binders protected the fuel
84 and oxidizer from environment effect such as humidity. The grains also provided ease of loading of the composition in the cartridge body.
The experiments were started by using Fish Glue in B/ BaCrO4 pyrotechnic delay mixture and its content was varied from 0 % to 3.0 %. Five different types of delay compositions were prepared with different wt % of Fish Glue. The recipes for these pyrotechnic compositions are shown in Table 4.1. By increasing the Fish Glue content, the oxidizer content was decreased accordingly in the same ratio, while the fuel content was kept constant as 15 %.
Five delay devices were prepared and tested for each composition, and the results were averaged. These tests were conducted in stainless steel tube of 4 mm internal diameter with effective column length of 11 mm. These compositions were loaded in the delay tube at 207 MPa. The mean values of burning time and burning rates along with mean standard deviations in burning time and burning rates were measured. The burning rate dependency of B/BaCrO4 delay mixture on Fish Glue is shown in Table 4.1. From these results it can be seen that a linear relationship exists between the binder and the burning rate. Results reveal that B/BaCrO4 delay mixture burnt slower as the Fish Glue content increased. This relationship between binder and burning rate gives sufficient information to the designer to optimize a delay composition of the required burning rate for some specific application.
B/ BaCrO4 delay mixture burnt rapidly and the burning time of 0.155 s and burning rate of 71.0 mm/s was recorded with 0 % binder. When the binder content was increased to 0.5 %, burning time increased to 0.176 s and burning rate decreased to 62.5 mm/s. On further increase in Fish Glue content to 1.0, the burning time increased to 0.215 s and the burning rate decreased to 51.2 mm/s. Similarly when the binder content was further increased to 2.0 %, the burning time further increased 0.239 s and the burning rate decreased to 46 mm/ sec. By increasing the content of the Fish Glue to 3.0 % the same trend of increasing the burning time and decreasing the burning rate was recorded. At 3.0 % Fish Glue content, the burning time was 0.289 s, whereas the burning rate was
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38.1 mm/s. These results show an overall increase of 86.5 % in burning time and overall reduction of 46.3 % in burning rate of this delay mixture.
At 0 % binder, the loading of the delay composition in the delay tube was not easy because grains could not be prepared without binder; therefore addition of binder in the delay mixture was essential for grains formation and subsequent ease of loading in the delay body. Results showed that the burning rate was inversely proportional to the binder content, the burning rate decreased with the increase in the binder content.
The decrease in burning rate of B/BaCrO4 pyrotechnic delay compositions was 12 %, 18.1 %, 10.2 % and 17.2 % by adding 0.5 %, 1.0 %, 2.0 % and 3.0 % Fish Glue respectively, while the calculated mean standard deviation in burning rate was 1.60, 1.21, 1.25, 1.10, 1.42 at these weight percentages of Fish Glue.
It means that not only the binder gave protection to the delay composition from environmental effects and provided ease of loading into the delay column, but it also reduced the burning rate of this delay mixture. Therefore, before designing a pyrotechnic delay composition, due consideration should be given to the binder because this parameter affects the burning propagation of the pyrotechnic delay mixture.
Granulation process becomes difficult and sensitivity of composition decreases if the binder content is increased beyond this range. In the present work, Fish Glue created no problem during grain formation as well as during loading of the composition in the delay tube up to 2.0 %, However when the content was increased to 3.0 %, both grains formation and loading of the composition in delay tube became problematic.
Therefore, the recommended range of the Fish Glue in the delay composition is 0.1% to 2.0 %. These results also show that for a fixed length of the delay column, the burning rate can be modified by varying the binder content in the delay mixture.
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Table 4.2 The effect on burning rate and burn time with varying Fish Glue contents
in B/BaCrO4 delay mixture
Boron BaCrO4 Fish Glue Mean Burning Mean Burning Std. Dev in [%] [%] [%] Time [s] rate[mm/s] burning rate 15 85.0 0 0.155 71.0 1.60 15 84.5 0.5 0.176 62.5 1.21 15 84.0 1.0 0.215 51.2 1.25 15 83.0 2.0 0.239 46.0 1.10 15 82.0 3.0 0.289 38.1 1.42
B/BaCrO4/FG = 15/84/1 delay composition was also burnt in the vented delay tube. Burning propagation only slightly decreased. Mean burning time increased by 3.26 %, while the burning rate decreased by 3.22 %. This change in burning time and burning rate was less significant, which indicates that this composition produced minimal gaseous products. No composition ejected from the tube when burnt in vented delay body. A solid slag was recovered from the tube after complete burning of the pyrotechnic delay composition.
Result also reveals that B/BaCrO4 is a fast burning pyrotechnic delay composition as compared to Si/PbO/Pb3O4 delay mixture. The burning rate of Si/PbO/Pb3O4 delay mixture at 1.0 % Fish Glue was 16.4 mm/s, whereas the burning rate of B/BaCrO4 was 51.2 mm/s, at the same binder content which is almost 212 % higher than the burning rate of Si/PbO/Pb3O4 delay mixture as shown in Table 4.2 and Table 5.11(Chapter 5).
Experiments were repeated by incorporating the Carboxyl Methyl Cellulose (CMC) binder in B/BaCrO4 delay composition. Weight percent of CMC was varied from 0 % to 1.0 %. Ingredients of the different delay mixtures are presented in Table 4.3. By increasing the CMC content, the oxidizer content was decreased accordingly in the same ratio, while the fuel content was kept constant as 15 %.
Compositions were loaded one by one in the delay tubes at loading Pressure of 207 MPa. The burning time and burning rate were measured. Each data point listed in Table
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4.3 represents an average of five measurements for every mixture. Results show that the burning time increased and burning rate decreased with increase in Carboxyl Methyl Cellulose content in the delay mixture.
Study was conducted by using the B/BaCrO4 delay mixture without adding CMC. The increments of powders were equally weighted and loaded in the delay body. Delay time and burning rate recorded at 0 % binder was 0.155 s and 71 mm/s respectively. Experiments were repeated by adding 0.5 % Carboxyl Methyl Cellulose to the delay mixture which increased the delay time to 0.165 s and decreased the burning rate to 66.7 mm/s. On further increase in CMC content to 1.0 %, the delay time further increased to 0.178 s and the burning rate decreased to 61.8 mm/s. The overall increase and decrease in delay time and burning rate were 14.8 % and 13.0 % respectively by varying the CMC content from 0 % to 1.0 %. Grains formation were easy for CMC content up to 0.5 %, between 0.5 % to 1.0 % CMC content, the granulation process became difficult, and when the CMC content was increased beyond 1.0 %, the grains formation as well as the loading of the composition in the delay tube became more problematic. High content of the binder caused the delay composition to become sticky. Therefore, it is recommended that CMC from 0.1 % to 0.5 % is considered the best in the delay compositions.
Table 4.3 The effect on burning rate and burn time with varying CMC contents in B/BaCrO4 delay mixture
Boron BaCrO4 CMC Mean Delay Mean Burning Std. Dev in [%] [%] [%] Time [s] rate[mm/s] burning rate 15 85.0 0 0.155 71.0 1.67 15 84.5 0.5 0.165 66.7 1.14 15 84.0 1.0 0.178 61.8 1.32
Dextrin was studied as a third binder in B/BaCrO4 delay mixture and its content was varied from 0 % to 3.0 %. Percentages of the ingredients in the composition are shown
88 in Table 4.4. By increasing the Dextrin content, the oxidizer content was decreased accordingly in the same ratio, while the fuel content was kept constant.
Composition was loaded in the delay tube at pressing pressure of 207 MPa. Burning time and burning rate dependency of the B/BaCrO4 delay mixture on Dextrin is shown in Table 4.4. Burning time and burning rate of the composition recorded at 0 % Dextrin was 0.155 s and 71 mm/s respectively. Experiments were repeated by adding 0.5 % Dextrin to the delay mixture which increased the delay time to 0.167 s and decreased the burning rate to 65.9 mm/s. On further increase in Dextrin content to 1.0 %, the delay time further increased to 0.180 s and the burning rate decreased to 61.1 mm/s. When the binder content was increased to 2.0 %, the delay time increased to 0.223 s and the burning rate further decreased to 49.3 mm/s. A further increase in binder content up to 3.0 %, the delay time increased to 0.288 s, while the burning rate decreased to 38.2 mm/s. The overall increase in burning time and decrease in burning rate was 85.8 % and
46.2 % respectively, by varying the Dextrin content from 0 % to 3.0 % in B/BaCrO4 mixture. Calculated standard deviation in burning rate was 1.67, 1.11, 0.94, 1.71 and 0.51 at 0 %, 0.5 %, 1.0 %, 2.0 % and 3.0 % Dextrin respectively. There was also no problem in grains formation and loading of the delay composition in the delay tube by adding up to 3.0 % Dextrin.
Table 4.4 The effect on burning rate and burn time with varying Dextrin
contents in B/BaCrO4 delay mixture
Boron BaCrO4 Dextrin Mean Delay Mean Std. Dev in [%] [%] [%] Time[s] Burning burning rate[mm/s] rate 15 85.0 0 0.155 71.0 1.67 15 84.5 0.5 0.167 65.9 1.11 15 84.0 1.0 0.180 61.1 0.94 15 83.0 2.0 0.223 49.3 1.71 15 82.0 3.0 0.288 38.2 0.51
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Mass consumption of B/BaCrO4 pyrotechnic delay mixture was also studied by varying the Fish Glue content in the delay mixture. Fish Glue content was varied from 0 % to 3.0 %. Five different types of delay compositions were prepared with different wt % of Fish Glue. Contents for these pyrotechnic compositions are shown in Table 4.5. As the binder content increases, the ratio of oxidizer decreases accordingly, while the fuel content remains 15 %.
Delay charge consumption dependency of B/BaCrO4/FG delay mixture on binder ranged from 0 % to 3.0 % is shown in Table 4.5. Five tests were conducted for every mixture in a stainless steel tube with an internal diameter of 4 mm. Mean values of the burning time and charge consumption was measured.
Mean standard deviations of delay time, mass consumption, were also measured as shown in Table 4.5. Results show that delay charge consumption decreased with an increase in binder contents. Maximum charge consumption of 1507 mg/s were recorded when no binder was used (grains were prepared in distilled water for ease of loading in the delay column).
Similarly, the minimum charge consumption of 898 mg/s was recorded at 3.0 % binder. The charge consumption reduced 1507 mg/s to 898 mg/s when 3.0% binder was used. The addition of 3.0 % binder showed a 40 % reduction in charge consumption.
The increase in delay time by the addition of the Fish Glue means that the burning rate of the delay composition decreases as the % age of fish glue increases. It means that the addition of Fish Glue did not contribute to the production of gases but rather decreases the production of gases. Using Fish Glue as a binder not only gives protection to the delay composition from environmental effects and provides ease of loading into the delay column, but also reduced both the burning rate and charge consumption of this delay mixture. Therefore, before designing pyrotechnic delay composition, due consideration should be given to binder because, like other parameters, binder also effects the charge consumption of the delay mixture.
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Table 4.5 Test results of mass consumption of B/BaCrO4/FG delay mixtures with varying FG contents
Pyrotechnic mixture MBT MBR MCC MSDBT MSDBR MSDCC
15% B, 85% BaCrO4, FG 0 % 0.210 71 1507 0.006 1.67 18.70
15% B, 84% BaCrO4, FG 1.0 % 0.290 52 1121 0.008 0.95 19.82
15% B, 83% BaCrO4, FG 2.0 % 0.317 47 935 0.008 0.91 21.20
15% B, 82% BaCrO4, FG 3.0 % 0.382 39 898 0.003 1.12 17.80
MBT=Mean Delay Burning Time (s), MCC= Mean Charge Consumed (mg/s), MSDBT=Mean Std. Dev. in Burning Time, MSDBR=Mean Std. Dev. in Burning Rate, MSDCC= Mean Std. Dev. in Charge Consumed.
Influence of binder on the consolidation density and percent Theoretical Maximum
Density (%TMD) was also studied. Delay composition B/BaCrO4/Binder = 15/84.5/0.5 was used for this study. Fish glue, dextrin, and CMC were used as binders. The weight of all the three binders was kept 0.5 %. Composition was pressed in the delay tube at 207 MPa. All three binders helped consolidation and reduced void space. This is indicated by consolidated and %TMD values in Table 4.6. Both consolidation density and %TMD increased with addition of binders. These results also show that addition of binders decreased the burning rate of these compositions.
Table 4.6 Effect of binder on different results of B/BaCrO4/Binder delay mixture
Binder Consolidated %TMD Burning Density[g/cm3] Rate [mm/s] Without binder 2.65 63.0 71.0
Fish Glue 2.91 69.1 62.5
Dextrin 2.96 70.2 65.9
CMC 3.00 71.4 66.7
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4.3.3 Effect of temperature variation on burning rate of B/BaCrO4/FG delay mixture
During burning of pyrotechnic delay composition in the delay body, heat is continuously being transferred to the rigid delay body from the delay column and thus to the surroundings. Reaction of the pyrotechnic composition is exothermic and the delay column at very low temperature acts as a heat sink. In most situations, the heat, when transferred to the body of the delay element, thus slows down the burning rate of the delay composition and therefore affects the reliability of the burning time. Heat sink effect becomes more pronounced at very low ambient temperature. At high ambient temperature most of the pyrotechnic delay compositions are less temperature dependent; in other words, high ambient temperature produces a smaller change in delay time then a temperature change occurs at low ambient temperature.
Delay cartridges filled with this newly developed delay composition were subjected to the normally operating Military temperature ranges of –40 °C, +21 °C, and +70 °C in order to determine the effect of these environmental conditions on the burning rate of this delay mixture. Explosive devices are normally subjected to such temperature ranges during mission.
Results in Table 4.7 and Figure 4.4 show the effect of low, normal, and high temperatures on the burning rate of the B/BaCrO4/FG delay mixture. These samples were placed in a calibrated environmental chamber. Temperature was brought to required limits of –40 °C, +21 °C, and +70 °C and the samples were then kept for 2 hours in the chamber. After 2 hrs, we immediately removed the sample from the environmental chamber and fired the delay devices within 3 min for measurement of delay time and calculation of burning rate.
Mean burning times for this delay mixture recorded were 0.310 s, 0.295 s and 0.273 s at –40 °C, +21 °C and +70 °C, respectively. Similarly, the calculated mean burning rates of this mixture were 48.0 mm/s, 51.0 mm/s, and 55.0 mm/s at –40 °C, +21 °C and +70 °C.
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These results show that the mean burning time of this delay mixture decreased by 5.0 % and increased by 7.5 % when studied at –40 °C and +70 °C, respectively, with respect to ambient temperature, which is quite an acceptable variation in burning time.
Table 4.7 Test results of B/BaCrO4/FG=15/84/1 delay mixture at different operating temperatures
Operating MDT MBR MSDDT MSDBR temperature[°C] -40 0.310 48 0.008 1.14 +21 0.295 51 0.005 1.00 +70 0.273 55 0.003 0.71
MDT=Mean Delay Time (s), MBR=Mean Burning Rate (mm/s), MSDDT=Mean Std. Dev. in Delay Time, MSDBR=Mean Std. Dev. in Burning Rate
Figure 4.4 Plot of burning rate in mm/s at normally operating temperature ranges
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Mean standard deviations in delay time and burning rate were also calculated for this delay mixture at these operating temperatures and are shown in Table 4.8. These results verified that the delay time and burning rate of this newly developed delay pyrotechnic composition would barely be affected by the normally operating temperature during mission and is considered to be a reliable delay composition for use in short delay devices.
4.3.4 Effect of Boron contents on Calorific value of B/BaCrO4/ FG delay composition
Calorific values of B/BaCrO4/FG delay composition are shown in Table 4.8. Results show that the calorific values of this delay mixture increase with increase of the Boron contents and a maximum value 4594 J/g was recorded at 15 % Boron, almost all fuel reacted with the oxidant. Calorific value then decreased on further increasing the Boron contents until a misfire condition was recorded at 45 % Boron in calorimeter.
Table 4.8 Calorific values of B/BaCrO4 mixture at different Boron content
Boron content Calorific value [%] [J/g
5.0 2720
10.0 3096
15.0 4594
20.0 4058
25.0 3473
35.0 2561
40.0 2050
45.0 NR*
*NR = Not Recorded
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The reason could be the low oxygen contents in the composition which reduced the sensitivity of the composition at this ratio. It means that the energy produced by the hot resistive wire was not enough to ignite this mixture at Boron content of more than 40 %. Minimum value of 2050 J/g was recorded at 40 % Boron.
4.3.5 Effect of body material on burning time and burning rate of B/BaCrO4/ FG delay composition
The delay composition B/BaCrO4/FG was studied in the stainless steel and brass body to determine the effect of body material on the burning time and burning rate of this delay mixture. This delay mixture was filled in 4 mm internal diameter with 11mm column length. Composition was loaded at loading pressure of 207 MPa. Table 4.9 represents the burning time and burning rate of this delay composition in the Stainless steel tube.
The mean charge weight of the delay composition was 283 mg. The average burning time and burning rate of the delay B/BaCrO4/FG were 0.208 s and 52.95 mm/s respectively. Maximum percent variation in delay time and burning rate from the mean was 16.83 % and 17 % respectively. Standard deviation in the delay time and burning rate were 0.013 and 3.38 respectively.
Results also show that B/BaCrO4/FG=14/85/1.0 is a fast pyrotechnic delay composition and its average burning rate is 81.3% faster than Si/PbO/Pb3O4/FG=18/21/60.7/0.3 delay mixture in stainless steel delay body, while average burning rate of
B/BaCrO4/FG=14/85/1.0 is 80.2 % faster than Si/PbO/Pb3O4/FG=18/21/60.7/0.3 delay mixture in Brass delay body.
Similarly pyrotechnic delay mixture B/BaCrO4/FG was also filled and tested in brass delay body. Results are shown in Table 4.9. Mean charge weight of the delay composition was 280 mg. Average burning time and burning rate of this delay mixture was 0.213 s and 51.61 mm/s respectively. Maximum variation in burning time and burning rate was 9.39 % and 9.69 % respectively. Standard deviation in the burning time and burning rate was 0.0085 and 2.124 respectively. Variation in burning time and burning rate reduced from 16.83 % to 9.69 %.
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Table 4.9 Test results of delay B/BaCrO4/FG =14/85/1.0 in Stainless Steel and Brass delay body
Sample No Stainless steel delay body Brass delay body Burning time Burning rate Burning Burning rate [s] [mm/s] time [mm/s] [s] 1 0.225 48.89 0.220 50.00 2 0.216 50.93 0.200 55.00 3 0.190 57.89 0.220 50.00 4 0.206 53.40 0.210 52.34 5 0.205 53.66 0.217 50.69 Mean Value 0.208 52.95 0.213 51.61 Max Variation 16.83 17.0 9.39 9.69 (Expressed in %) Standard deviation 0.013 3.38 0.0085 2.124
Results also show that the mean burning rate decreased from 52.95 mm/s to 51.61mm/s when tested in brass delay body, which shows 2.53 % decrease in burning rate. This slight reduction in burning rate may be due to the more heat loss through brass delay body than through the stainless steel delay body. The more is the heat lost from a delay composition, the slower the burning rate and vice versa. Figure 4.5 and Figure 4.6 show the comparison of the delay time and burning rete of B/BaCrO4/FG delay mixture in stainless steel and Brass delay body.
Figure 4.5 Plot of delay time of B/BaCrO4/FG mixture in stainless steel and in Brass delay body
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Figure 4.6 Plot of burning rate of B/BaCrO4/FG mixture in stainless steel and in Brass delay body
4.3.6 Effect of loading pressure on the burning time and burning rate of
B/BaCrO4/ FG delay composition
Delay composition B/BaCrO4 /FG =15/84/1 was subjected to different loading pressures. Loading pressure was varied from 103 MPa to 414 MPa. Effect of loading pressure is a design parameter for the pyrotechnic delay devices. Loading pressure is more complex than the other parameters, especially on a new composition. A small change in ingredient ratios or change in particle size can change the burning behavior markedly.
Effect of loading pressure on burning rate is normally considered to be of the secondary importance. For every pyrotechnic delay composition, a certain loading pressure is finalized to get the required compaction and optimum burning rate. The burning rate of
B/BaCrO4/FG = 15/84/1 delay mixture increased with increase in loading pressure. The maximum burning rate was recorded at 414 MPa.
B/BaCrO4 pyrotechnic composition is a gasless pyrotechnic delay mixture. Generally the burning rate of the gasless delay mixture increases with increase in loading pressure due to increase in compaction. The thermal conductivity also increases with increase in compaction. In the present work, the burning rate of B/BaCrO4 mixture slightly
97 decreased with increase in loading pressure. The reason could be the presence of impurities in the fuel and oxidizer or due to the addition of fish glue.
A small and systematic change in the burning rate was observed by varying the loading pressure. Results are shown in Table 4.10. Some gasless pyrotechnic delay compositions are difficult to ignite at high compaction because the surface becomes smoother and less porous. Therefore, a small amount of the igniter composition is pressed above the delay composition. B/BaCrO4 mixture does not require an increment of igniter composition and easily initiate even pressing in the delay tube at such a high loading pressure.
Pyrotechnic delay composition is sometimes subjected to high impact g-shocks before initiation of the payload of the munitions. The payload functions after penetrating in the hard target with in a predetermined delay time.
Therefore this composition was pressed up to a very high loading pressure of 414 MPa. Results show that even at high loading pressure of 414 MPa, the composition was still sensitive, and ignited by the standard percussion primer. The composition also functioned successfully and produced reliable combustion propagation. No misfire of the delay mixtures was recorded in any experiment.
Table 4.10 Test results of loading pressure on B /BaCrO4 /FG =15/84/1 delay mixture
S# Loading Delay Burning Std. Dev in pressure[MPa] time[s] rate[mm/s] burning rate 1 103 0.185 59.5 1.40 2 138 0.197 55.0 1.20 3 207 0.215 51.2 0.95 4 276 0.217 50.7 1.30 5 345 0.222 49.5 0.70 6 414 0.224 49.1 1.10
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The purpose of pressing this composition at high loading pressure was to increase the compaction in order to sustain high impact g-shocks. If the composition is not compacted at high loading pressure, the composition can detach from the delay body. Cracks may also develop in the delay column during high g-shock impact, which may affect the reliability and functionality of the delay device. This pyrotechnic delay composition was reliably initiated at these ranges of loading pressures.
During loading, it was found that if the strength of pressing pin is not high enough then it does not sustain high loading pressure. It may result in bending of the pin. The hardness of the pin must be sustainable to high loading pressures.
4.3.6 Effect of loading pressure on consolidation and %TMD B/BaCrO4/ FG delay composition
Consolidation density is measured as the mass of the delay mixture to the volume of the delay tube filled with composition
Consolidation density = Mass of the delay composition/ Volume of the delay tube
ρ = M delay composition/ V delay column
After mixing process, the pyrotechnic delay composition was pressed in the delay tube using hydraulic press machine installed with calibrated pressure gauge.
Percent Theoretical Maximum Density (%TMD) was calculated as weighted average of the pure solid densities of different ingredients of the pyrotechnic delay mixtures. The TMD was expressed in g/cm3. Following formula is used for the calculation of Theoretical Maximum Density (TMD) of the delay mixture.
TMD = mass friction of ingredient (A) * density of ingredient (A) + mass friction of ingredient (B)* density of ingredient (B) +...... (1)
% TMD = Consolidation density/ TMD*100
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Consolidation and percent Theoretical Maximum Density (%TMD) of B/BaCrO4/FG= 15/84/1 delay mixture was measured by varying the loading pressure from 138 MPa to 483 MPa. Increase in loading pressure increased the consolidation of the delay composition in the delay column. Increase in loading pressure resulted in greater packing efficiency and correspondingly less void space.
Figure 4.7 shows effect of varying loading pressure on the %TMD of B/BaCrO4/FG = 15/84/1 delay composition.
Figure 4.7 Plot of Loading pressure vs %TMD for B/BaCrO4/FG= 15/84/1 delay mixture
Increase in loading pressure also increases the consolidation of the delay composition in the delay column. %TMD varied linearly over a range of 138 MPa to 483 MPa
4.4 Conclusions
B/BaCrO4 delay composition provided reliable burning propagation between 5 % ~ 40 % Boron contents. However, above 40 % Boron, this delay mixture failed to produce sustainable burning propagation. Maximum charge consumption and burning rate of this delay mixture was recorded at 18 % Boron, while the maximum calorific value was at
100 about 15 % Boron. From this study it revealed that the burning rate of B/BaCrO4 delay composition decreased with increase in binder contents. Fish Glue binder effected both the charge consumption and burning rate and both these parameters decreased as the binder content was increased. Carboxyl Methyl Cellulose (CMC) and Dextrin decreased the burning rate of B/BaCrO4 delay mixture relatively less than Fish Glue. Variation in loading pressures showed marginal effect on the burning time as well as the burning rate of this delay composition. Both consolidation density and percent Theoretical Maximum Density (%TMD) of this composition increased by adding binders and increase in loading pressure. Burning rate of this delay mixture was also not much affected by temperatures variation, and decreased in burring rate was observed as temperature was decreased. From the analysis of B/BaCrO4/FG delay compositions in the stainless steel and brass delay body, it is concluded that using brass delay body the variation in both burning time and the burning rate reduced. Delay time slightly increased in brass delay body due to the high thermal conductivity This pyrotechnic delay composition also produced reproducible burning time and burning rate. It has been concluded from this study that this delay composition can be reliably used in both short time delay cartridges and delay detonators without having to use the customary starter charge as is used in most cases.
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References
[1] A. Bailey, S.G. Murray, Explosives, Propellant and Pyrotechnics, Royal Military College of Science, Shrivenhan, UK (1989), Vol.2, Chap.7.pp. 115-127. [2] R. Aube, Delay compositions and Detonation delay devices utilizing same US Patent No. 0223242A1 (2008). [3] N. Davies, (Pyrotechnics Hand Book, the Ammunitions Systems and Explosives Technology Department, UK: Cranfield University (2002), Chap.4 pp. 5. [4] W.C. Eller, F.J. Valenta, Temperature Compensated Pyrotechnic delays US Patent No. 3851586 (1974). [5] M.W.Beck, M.E. Brown, Combust.Flame 65(1986)263. [6] M. Fathollahi, S.M. Pourmortazavi. S.G Hosseini, Combust.Flame 138(2004)304. [7] S.M. Danali, R.S. Palaiah, K.C Raha, Def. Sci. J 60( 2010)152. [8] A.Khan, A.Q. Malik, Z.H. Lodhi, A study of effect of confinement, Obturation and Vending on burning rate of modified pyrotechnics delay composition in delay detonator. Theory Pract. Energ. Mater., Proc. Int. Autumn Semin. Propellants, Explos. Pyrotech (2011) 491. [9] C.G.Morgan, K.Park. C. Rimmington, Production of pyrotechnic delay composition, US Patent 0314397A1 (2009). [10] Li.Y. Cheng, Y.L. Hui , S. Yan, J. Energ. Mater 28(2010)77. [11] H. Ren, Q. Jiao, S. Chen, J. Phys. Chem. Solids 71(2010)145. [12] J. Jakubko, Z.V. Indet, J. Energ. Mater 15( 1997)151. [13] I.M.M. Ricco, W.W. Focke, C. Conraide, Combust. Sci. Technol 176(9) (2004)1565. [14] X.D.Wei, D.H. Hai, C.Z.Gang, Explos. Mater 3(2005)11 [15] W.Youcheng, J. Song, Explos. Mater 29(2)(2000)23. [16] AMC. Pamplet, Design Hand Book, Military Pyrotechnic Series Part-A, Theory and Application Washington D.C (1967), Chap.5pp. 33-38. [17] J.H. McLain, Pyrotechnics from the Viewpoint of Solid State Chemistry, Franklin Institute Press, Philadelphia (1980)
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[18] J.A. Conkling, Chemistry of Pyrotechnics Basic Principles and Theory, Department of Chemistry, Washington College Chestertown, Maryland, USA (1985), Chap.6. pp.125-140. [19] M.W. Beck, M. E. Brown, Combust. Flame 66(1986) 67. [20] Z. Babar, Ph.D. Thesis,Thermal, kinetic and morphological studies of available and synthesized pyrotechnic/ propellant compositions and their ingredients(2015). [21] M.W. Beck, Delay Composition and Device, US Patent No. 5147476(1992). [22] A.Z. Moghaddam, Thermochim. Acta 223(1993)193. [23] K.L. and B.J.Kosanke, Lecture Notes for Pyrotechnic Chemistry, J. Pyrotech (2004) [ISBN 1-889526-16-9].
[24] Manganese Delay Composition, MIL-M-21383A (1995). [25] Standard: NPFC – NAVY, Delay Composition, Z-1, MIL-D-85866 (1990).
[26] J. C. Poret, A. P. Shaw, M.C. Christopher, K.D. Oyler, J. A. Vanatta, G. Chen,
ACS Sustainable Chem. Eng 1(2013)1333.
[27] M.D. Ghislain, R. Lavertu, Pyrotechnic Delay for Hgh g‟s, US Patent
4760792(1988).
[28] T. Petukhova, A History of Fish Glue as an Artist's Material: Applications in Paper and Parchment Artifacts, Vol 19, The American Institute for Conservation (2000) [29] A. P. Shaw, J. C. Poret, R. A. Gilbert, J. A. Domanico, E. L. Black, Propellants Explos. Pyrotech 35(2013) 1. [30] E.F. Garner, Saugus and Calif, Pyrotechnic Composition with Combined Binder- Coolant, US Patent 3901747(1975). [31] C.H.Martinez, C.Park, C. R. Finger hood, pyrotechnic composition comprising solid oxidizer, boron and aluminum additive and binder, US Patent 3257801(1966).
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Chapter NO. 5 Development and
parametric studies of Si/Pb3O4, Si/PbO
and Si/PbO/Pb3O4 pyrotechnic delay compositions
5.1 Introduction
Work presented in this chapter reports the development and parametric studies of a newly developed Si/Pb3O4/FG, Si/PbO/FG and Si/PbO/Pb3O4/FG pyrotechnic delay compositions. Different ratios of fuel, oxidizers and binder were mixed to prepare different types of mixtures. Pyrotechnics delay composition comprises a fuel, oxidizer usually in combination with a binder. A pyrotechnic reaction is an exothermic. Pyrotechnic is a general term for a mixture that burns at a selected, reproducible rate, providing a pre-determined time delay between ignition and the delivery of main effects
[1, 2]. Different types of fuels such as Si, B, Sb, W, and Oxidants such as PbO, Pb3O4,
BaCrO4, KMnO4, KClO4, K2Cr2O7, and Bi2O3 are normally used in pyrotechnic delay compositions [2-5]. Fuel is selected as an energetic material which liberate sufficient amount of heat when oxidized. Fuels can be categorized as metal, nonmetal or organic compound. Binder is added for granulation and it also reduces sensitivity and improves stability of pyrotechnic delay composition.
A pyrotechnic delay mixture is one of the most important components pressed in between the percussion primer and the detonating charge in the delay device to control the burning time of the delay device. The mechanism of the delay device starts from initiating the delay composition by the percussion primer. Burning time and the column length of the delay composition are used to measure the burning rate. Burning rate is calculated by dividing the column length with recorded burning time. Although a pyrotechnic delay composition is not accurate than an electronic and mechanical delay
104 device, but the pyrotechnic delay composition is still used in delay devices due to its simple design and low cost [6].
Pyrotechnic Delay compositions are classified as fast, medium and slow burning according to their burning rate. Delay compositions are either gassy which produce large volume of gas on combustion, greater than 20 cc/g, and gasless delay composition which generate little gas on combustion, less than 5 cc/g [7-8].Quality Control of the ingredients of mixture and mixing of the compositions is very important together with stoichiometry, which effect burning rate. Burning rate of pyrotechnic delay composition depends on number of parameters such as particle size, confinement, impurities, material of delay tube, environmental conditions including temperature, ambient pressure, humidity, pressing load, binder, ingredients and their ratios etc. [9-14].
Delay time consistency is the most importance parameter while designing any pyrotechnic delay composition. Main problem in pyrotechnic delay compositions is the accuracy that ranges between ±10 % to ± 20 % of the average value over the normally military operating temperature of -40 °C to + 70 °C [15]. In some pyrotechnic, the time delay increases up to 25 % from mean at low temperature of -54 °C [16-18]. There is a risk of combustion failure especially when the delay device is operating in low temperature environment. Pyrotechnic composition must produce more heat than the heat loss to the environment due to thermal conductivity to sustain combustion propagation [19, 20]. Pyrotechnic delay compositions due to controlled chemical reactions are also strongly effected by the ambient temperature. Variation in the ambient temperature changes the burning rate of a pyrotechnic composition. High ambient temperature normally produces smaller change in burning time than when a temperature change occurs at lower ambient temperature [21]. Material of the delay body affects the burning rate of the delay composition because the rigid delay body acts as a heat sink during burning of the delay composition. Metals are generally better conductors of heat than the delay compositions. Silicon fuel based pyrotechnic compositions attracted interest for delay devices and detonators applications due to their excellent end results
105 for a certain application [22-25. Modern pyrotechnic delay device requires to reliably initiate and produce accurate and consistence delay or burning time [26].
Si-Pb3O4 delay composition is a fast burning delay mixture. According to published literature, Lead oxide reacts with Silicon to give solid products SiO2 and Pb[27,28]. The reactions are given below.
Pb3O4 3PbO + 1/2O2
Pb3O4 + 2 Si 3Pb + 2SiO2
Si+O2 SiO2
2PbO+ Si SiO2 +2Pb
Si-PbO-FG is also a delay composition but not much data is available in published literature on this delay composition. Fish Glue has also been used for the first time as binder in these delay compositions. The purpose of this research work was to carry out detailed experimental study of the effect of Si varying from 5 % to 55 % on mass consumption and burning time of Si-Pb3O4-FG and Si- PbO-FG delay compositions. Due to variation of Si content the density of the delay composition changes. So for the same column length the charge weight cannot be kept constant.
The overall aim of this study was:
1. To develop different types of Si, PbO and Pb3O4 based pyrotechnic delay compositions that are safe to process into delay element and easily ignitable by primer and feature a high consistence delay time. Additionally these compositions must also be reliably initiated when compacted at high loading pressure.
2. To investigate experimentally the effects of the following parameters on the burning performance of Si and lead based pyrotechnic delay composition.
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(a) Effect of Silicon contents on different Oxidizers in delay compositions (b) Effect of ingredients mixing on the burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition (c) Effect of temperature variation on burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition
(d) Effect of loading pressure on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition
(e) Effect of body material on burning performance of Si/PbO/Pb3O4/FG time delay pyrotechnic composition
(f) Effect of binder on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition (g) Effect of loading pressure on the consolidation density and Percent Theoretical
Maximum Density (%TMD) of Si/PbO/Pb3O4/FG delay composition
5.2 Experimental conditions
5.2.1 Formulation of different types of Pyrotechnic Delay Compositions
Different ratios of fuel, oxidizers and binder were used to formulate different pyrotechnic delay compositions to study their burning performance. Silicon was used as fuel, whereas Lead monoxide (PbO) and Read lead (Pb3O4) were used as oxidizers. Commercial Fish Glue was used as a Binder. Silicon powder with purity of more than 99 % and particles sizes of less than 44 µm was purchased from Sigma Aldrich Company.
Powder Lead (II) Oxide (PbO) and Red Lead Oxide (Pb3O4) with purity of more than 99 % were purchased from Sigma Aldrich.
These individual fuel and oxidizers were dried in heating oven at 80 °C for one hour to remove the moisture content in order to ensure the accurate masses. Weight the chemicals according to the required percentages and firstly mixed the ingredients in the three dimensional automatic Tumbler Mixing Machine for 3 hours. From the already
107 mixed composition small batches each were further processed. Chemicals were mixed in a specially designed mechanized Mortar and Pestle in specially designed fuming hood for 30 minutes to further homogenize the compositions. Homogenous mixing increase burning time consistency in pyrotechnic delay compositions. Binder solutions of 0.3 %, 0.5 %, 1.0 %, 2.0 % and 3.0 % Fish Glue were prepared in distilled water followed by mixing the binder solutions in the compositions. A homogenous paste was prepared by using the spatula in agate container. Semi dried the composition (paste) in the Drying oven at 80 °C. To avoid the formation of lumps, the semi dried composition was broken by spatula in an agate container carefully. The composition was sieved gently through - 212 mesh-granulator sieves to get grain size of ≤ 65 µm. Different types of delay compositions were prepared by varying Silicon content by using same procedure. Haver test shaker EML 200-89 digital was used for preparation of grains of required particle sizes [29]. Grains were dried for four hours at 80 °C to remove the moisture content. Stored the finished composition in special containers and the containers were placed in desiccators for 24 hours to stabilize the compositions.
5.2.2 Pressing of the pyrotechnic delay compositions in the delay body
Finished composition was then loaded into stainless steel and brass delay tubes of internal bore diameter of 4.0 mm. Weight of each increment was 100 mg. A hydraulic press machine installed with a calibrated pressure gauge was used to consolidate the delay compositions in the delay bodies. Each increment was pressed at different loading pressures in the delay tubes. No starter or first fire composition was loaded between the igniter assembly and delay compositions. The delay composition was directly initiated through the output energy produced by the percussion primer assembly.
5.2.3 Design of pyrotechnic delay device
Configuration of the delay device used in this research work is shown in Figure 5.1. This delay device consisted of stainless steel delay body, pyrotechnic composition, igniter assembly and O-ring. Igniter assembly further comprised igniter body with anvil and percussion primer. A free volume of about 3.5 cm3 was provided to provide an obturation effect to accumulate the gasses produced during the burning of the delay
108 composition. The O-ring was used to hermetically seal the delay composition from environmental effects and to allow the high pressure gasses to escape from the delay devices. The front of the delay devices was sealed with aluminum foil.
5.2.4 Assembly of delay device
After loading the delay composition in the delay body a mechanical percussion primer was then assembled in the igniter holder and the igniter assembly was then assembled in the delay tube. Furthermore an O-ring was installed in the delay tube from the igniter side followed by the assembly and crimping of aluminum foil from the other side.
Delay increment
Igniter assembly
Figure 5.1 Stain Less steel body Delay device
5.2.5 Functional Testing procedure
Delay device was assembled in the firing fixture and then installed in the firing chamber. A flash detector was inserted in the firing chamber from the other side. Flash detector was connected to channel 2 of Oscilloscope. Channel 1 of the Oscilloscope was connected with firing unit.
Delay device was initiated through mechanically mean by hitting the igniter assembly with a striking pin. Firing mechanism consisted of an electromechanical system which is a combination of mechanical striking pin and electrically operated switch. Delay time started when the pin stroke the percussion, which then operated the switch, and the delay time stopped when the photodiode detector detects the flame of the delay composition.
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Delay time was measured with Digital Storage Oscilloscope TDS2024 of Tektronix Company. Burning rate was calculated by dividing the length of delay column with recorded burning time, while the charge consumption was measured by dividing the charge consumed in mg with recorded burning time. Delay time measuring principle is illustrated in Figure 5.2.
Igniter Pyrotechnic delay device Detector
Firing mechanism Oscilloscope
Figure 5.2 Schematic diagram for burning time measurement of pyrotechnic Delay device
5.3 Results and Discussion
5.3.1 Effect of Si content on the delay time and mass consumption of Si/Pb3O4/FG delay mixtures
Mass consumption and burning time of Si/Pb3O4/FG delay mixture with different Silicon contents is shown in Table 5.1 and Figure 5.3. Silicon content was varied from 5.0 wt. % to 55 wt. % in these delay mixtures. Ingredients of the different delay mixtures are 110 shown in Table 5.1. A total of nine delay mixtures with different Silicon contents were prepared. Five tests were conducted for each mixture and the results were averaged. Delay composition was loaded in the delay tube at pressing loading of 276 MPa. The mean values of mass consumption and delay time were measured. Mean standard deviation of charge weight; delay time and mass consumption were also calculated.
Results show that at 5.0 wt. % Silicon contents, the delay composition did not completely burn, partial burning was observed and the flame did not detect by the detector due to its low intensity. Si/Pb3O4/FG pyrotechnic delay composition at 5.0 wt. % Silicon contents failed to produce reliable combustion propagation. In order to increase the sensitivity of these delay mixtures at 5.0 wt. % Silicon, the loading pressure was reduced from 276 MPa to 138 MPa. As sensitivity of the delay composition increases with reducing the loading pressure, but the sensitivity of this delay mixture did not increased with decreasing in loading pressure and similar result was observed and burning propagation failed even at low pressure of 138 MPa. This failure of the burning propagation shows that the heat produced by the delay composition at 5.0 wt. % Silicon was not enough to sustain burning rate. It means that the heat loss to the surrounding was more than the heat produced by the burning of the delay mixture and thus burning of the delay mixture stopped.
When the Silicon content was increased from 5.0 wt % to 10 wt %, the delay mixture started reliable burning and complete burning propagation was observed. Mass consumption of 0.536 mg/ms was recorded at 10 wt % Silicon, whereas the burning time recorded at 10 wt % was 663 ms. As the mass consumption increases, the burning time decreases because these are inversely proportion to each other. When the Silicon content was further increased to 15 wt %, the mass consumption increased to 0.829 mg/ms and burning time decreased to 456 ms, it means that the mass consumption of Si/Pb3O4/FG delay mixture increased by 55 % and burning time decreased by 31 %. On further increasing the Silicon content to 20 %, the mass consumption further increased to 0.880 mg/ms, which shows a further 6.0 % increase in mass consumption, whereas the burning time decreased from 456 ms to 441 ms, which shows 3.3 % decrease in burning time.
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Table 5.1 Test results of Si/Pb3O4/ FG delay mixtures at different Silicon contents Pyrotechnic MCW MDT MCC MSDCW MSDDT MSDCC mixture
5% Si, 94% Pb3O4, 476 NR NA NA NA NA 1.0% FG 10% Si, 89 % 355 663 0.536 10.51 6.52 0.022
Pb3O4, 1.0% FG 15% Si, 84 % 378 456 0.829 3.97 4.83 0.009
Pb3O4, 1.0% FG 20% Si, 79 % 380 441 0.880 5.45 5.12 0.012
Pb3O4, 1.0% FG 25% Si, 74 % 392 390 1.005 8.26 6.88 0.021
Pb3O4, 1.0% FG 35% Si, 64 % 323 300 1.080 6.77 6.35 0.034
Pb3O4, 1.0% FG 45% Si, 54 % 349 343 1.017 5.22 10.08 0.036
Pb3O4, 1.0% FG 50% Si, 49 % 340 NR NA NA NA NA
Pb3O4, 1.0% FG
55 Si, 44 % Pb3O4, 340 NR NA NA NA NA 1.0% FG
MWC = Mean Charge Weight in mg, MDT= Mean Delay Time in ms. MCC = Mean Charge Consumed in mg/ms, MSDCW = Mean standard deviation in charge weight, MSDDT = Mean standard deviation in delay time, MSDCC = Mean standard deviation in charge consumed, N/R = Not Recorded, N/A Not Applicable
When the fuel content was increased to 25 %, mass consumption also increased from 0.880 mg/ms to 1.005 mg/ms and thus a further 14 % increase in mass consumption was recorded. Similarly the burning time further decreased from 441 ms to 390 ms, which shows 11.6 % decrease in burning time. The trend of increasing the mass consumption
112 and decreasing the burning time of this delay mixture continued and the maximum mass consumption of 1.08 mg/ms and minimum burning time of 300 ms for Si/Pb3O4/FG pyrotechnic delay composition was recorded at 35 % Silicon content. A similar result had also been earlier reported by A. Kazraji [27], but in that reported work Corboxymethyle Cellulose (CMC) was used as binder, where as in this research work Fish Glue has been used as a binder.
Figure 5.3 Effect of Silicon content on mass consumption of Si/Pb3O4/FG delay mixture
An overall increase of 101 % in the mass consumption was recorded by increasing the Silicon content from 10 wt % to 35 wt %. On further increase in fuel content, the mass consumption started to decrease and 1.017 mg/ms was reported at 45 % Silicon content. At 50 % Silicon partial burning was observed and on further increasing the silicon content to 55 %, the composition did not initiate/ ignite by the percussion. Si/Pb3O4/FG pyrotechnic delay composition at 55 % Silicon content failed to be ignited by the standard percussion. At these ratios of the fuel and oxidizers the sensitivity reduced and the energy produced by the percussion was not enough to initiate the delay composition
113 and even partial burning was also not observed. Pressing load was then reduced from 276 MPa to 138 MPa but similar result was observed.
After analyzing these results, it was observed that Si/Pb3O4/FG delay mixture produced reliable burning propagation from 10 wt % to 45 wt % and can be reliably used in pyrotechnic delay devices at these ranges of silicon contents.
5.3.2 Effect of Si content on the burning time and mass consumption of Si/PbO/FG delay mixtures
Mass consumption and delay time of Si/PbO/FG delay mixtures at different Silicon contents are shown in Table 5.2 and Figure 5.4. Silicon content was varied from 5.0 wt. % to 40 wt. % in different delay mixtures. A total of eight delay mixtures with different Silicon contents were prepared. Five tests were conducted for every mixture in stainless steel tube of 4 mm internal diameter and the results were averaged. Loading pressure was kept 276 MPa for pressing the delay compositions in the delay tubes. Mean values of mass consumption were calculated along with mean standard deviations of charge weight, delay time and mass consumption.
Results in Table 5.2 show that at 5.0 wt % Silicon, the Si/PbO/FG pyrotechnic delay composition did not initiate by the standard percussion primer. At this fuel oxidizer ratio the energy produced by the percussion was not enough to initiate the delay composition. In order to increase the sensitivity of this delay mixture at 5.0 wt. %, the loading pressure was reduced from 276 MPa to 138 MPa. But this reduced pressure also did not initiate the delay composition and similar result was observed.
When the Silicon content was increased to 10%, the percussion igniter initiated the mixture and complete propagation was observed. Mean mass consumption of 0.306 mg/ms was recorded. On further increasing the Silicon content to 15 %, the mass consumption increased to 0.458 mg/ms, which shows an increase of 50 % in mass consumption of this delay mixture.
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Table 5.2 Test results of Si/PbO/ FG delay mixtures at different Silicon contents
Pyrotechnic MCW MDT MCC MSDCW MSDDT MSDCC mixture 5 % Si, 94% PbO, 365 NR NA NA NA NA 1.0 % FG 10 % Si, 89 % 370 1209 0.306 7.12 10.9 0.006 PbO, 1.0 % FG 15 % Si, 84 % 375 819 0.458 3.49 5.45 0.003 PbO, 1.0 % FG 20 % Si, 79 % 363 913 0.398 3.50 20.2 0.096 PbO, 1.0 % FG 25 % Si, 74 % 363 751 0.484 2.8 19.2 0.104 PbO, 1.0 % FG 30 % Si, 69 % 348 574 0.609 3.5 25.4 0.923 PbO, 1.0 % FG 35 % Si, 64 % 355 NR NA NA NA NA PbO, 1.0% FG 40 % Si, 59 % 360 NR NA NA NA NA PbO, 1.0 % FG
MWC = Mean Charge Weight in mg, MDT= Mean Delay Time in ms. MCC = Mean Charge Consumed in mg/ms, MSDCW = Mean standard deviation in charge weight, MSDDT = Mean standard deviation in delay time, MSDCC = Mean standard deviation in charge consumed, N/R = Not Recorded, N/A Not Applicable
On further increasing the silicon contents beyond 15 %, the delay composition did fire but did not produce consistence results. At 20 %, 25 % and 30 % Silicon, the mean mass consumptions were, 0.398 mg/ms, 0.484 mg/ms and 0.607 mg/ms respectively. Standard deviations of the delay mixtures were 20.2, 19.2 and 25.4 respectively which were very high and not acceptable in any pyrotechnic delay composition. Moreover at 30 % Silicon
115 content, 1.0 sample out of 5.0 partially fired and the flam did not detect by the detector and thus the delay time was not recorded.
Similarly at 35 % Silicon contents, the composition did not completely burn, partial burning observed and the flame did not detect by the detector due to its low intensity, so the Si/PbO/FG pyrotechnic delay composition at 35 % silicon failed to produce reliable combustion. Pressing pressure was reduced to 138 MPa to increase the sensitivity of the delay mixture to percussion output energy, but similar result was observed and the propagation failed. It means that the heat produced by the delay composition was not enough to sustain burning propagation at this ratio of the fuel and oxidizer. In other words the heat loss was more than the heat produced and thus burning propagation stopped. At 40 % and above 40 % Silicon content the composition did not initiate by the standard percussion.
These results reveal that the reliable burning of the Si/PbO/FG delay mixture was observed from 10 % to 15 % Silicon content. These results show that this mixture is not suitable to be used in the delay devices beyond the ranges of 10 % to 15 % Silicon content.
Figure 5.4 Effect of Silicon content on mass consumption of Si/PbO/FG delay mixture
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5.3.3 Effect of fast red lead mixture on the burning time and mass consumption of Si/PbO/ FG delay mixtures
In order to increase the sensitivity of Si/PbO/ FG delay mixtures, an increment of fast burning delay mixture Si/Pb3O4/FG=20/79/1.0 was incorporated between primer and Si/PbO/FG delay mixture as a first fire mixture as shown in Figure 5.5. By adding an increment of fast red lead, the mass consumption of Si/PbO/FG delay mixture considerably increased. Test results in Table 5.3 and Figure 5.6 show that the mass consumption of Si/PbO/FG = 10/89/1.0 delay mixture increased by 39 % when an increment of 100 mg fast read lead was added as first fire between primer and the
Si/PbO/ FG delay mixture . Similarly Si/Pb3O4/FG=20/79/1.0 was also added to Si/PbO/ FG = 15/84/1.0, Si/PbO/ FG = 20/79/1.0 and Si/PbO/ FG = 25/74/1.0 delay mixtures and their mass consumption increased by 34 %, 75 % and 46 % respectively.
Percussion
Increment of Si/Pb3O4/ FG Increments of Si/PbO/FG Delay body
Figure 5.5 Design of modified Delay device
Results also reveal that the mass consumption of Si/PbO/ FG = 30/69/1.0 delay composition was not much affected by incorporated an increment of fast red lead mixture and almost similar mass consumption (without fast red lead) was recorded.
An increment of fast red lead when added to Si/PbO/ FG = 35/64/1.0 delay mixture, the composition completely burnt and flame detected by the detector, the mean mass consumption recorded for this delay mixture was 0. 616 mg/ms. Above 35 % Silicon
117 content, the delay mixture did not initiate even with addition of an increment of fast red lead delay composition.
Table 5.3 Test results of different Si/PbO/ FG delay mixtures by
incorporating an increment of Si/Pb3O4/FG=20/79/1.0 mixture
Pyrotechnic MCW MDT MCC mixture 10 % Si, 89 % PbO, 385 906 0.426 1.0 % FG 15 % Si, 84 % PbO, 376 614 0.612 1.0 % FG 20 % Si, 79 % PbO, 358 515 0.695 1.0 % FG 25 % Si, 74 % PbO, 377 534 0.706 1.0 % FG 30 % Si, 69 % PbO, 384 625 0.614 1.0 % FG 35 % Si, 64 % PbO, 385 625 0.616 1.0 % FG 40 % Si, 59 % PbO, 380 NR NA 1.0 % FG MWC = Mean Charge Weight in mg, MDT= Mean Delay Time in ms. MCC = Mean Charge Consumed in mg/ms, N/R = Not Recorded, N/A Not Applicable
Figure 5.6 Effect of Si/Pb3O4/FG=20/79/1.0 mixture on mass consumption of Si/PbO/ FG delay mixtures
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5.3.4 Effect of ingredients mixing on the burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition
5.3.4.1 Mixing in(3-D) Automatic Tumbler Mixing Machine
Every ingredient of the delay mixture has different moisture absorptivity. To ensure accurate masses, the ingredients of the delay mixtures (fuels and oxidizer) were individually dried out in a heating oven at 80 °C for about 2 hr to remove the moisture. Quantities of the different ingredients were weighted according to the required percentages and blended thoroughly. Ingredients were then mixed in the three dimensional (3-D) automatic tumbler mixing machine for 3 hr. A binder solution of 0.3 wt. % fish glue was prepared in distilled water. Binder solution was mixed in the already mixed composition to form a homogenous paste by using the spatula in agate container. Composition was then semi dried in a drying oven at 80 °C. Semi dried composition was broken in to lumps by spatula in an agate container carefully. Composition was passed carefully through -212 mesh sieves to get grain size of ≤ 65 μm. Grains were dried out for 4 hr at 80 °C to remove the moisture. Finished composition was stored in container and placed it in desiccator.
5.3.4.2 Manual Mixing in Mortar and Pestle:
Similarly, the individual chemicals (fuels and oxidizers) were dried in a heating oven at 80°C for two hours to remove the moisture. The chemicals were weighted according to the required percentages. Small batches of 5~10 gram were prepared and the chemicals were mixed in mortar and pestle for 30 min to get homogenous mixture. A binder solution of 0.3 wt. % Fish Glue was then prepared in distilled water. Binder solution was mixed in the already mixed composition to form the homogenous paste by using spatula in agate container.
Composition (paste) was then semi dried in the drying oven at 80 °C. Semi dried composition was broken into lumps by spatula in an agate container carefully. Composition was passed carefully through -212 mesh sieves by using Haver test shaker
119
EML 200 to get grain size of ≤ 65 μm. [29]. Grains were then dried for eight hours at 80 °C to remove the moisture content. Finished composition was stored in desiccator for 24 hours to become stable.
5.3.4.3 Filling of delay body:
Stainless steel delay elements were made by drilling 4.0 mm diameter holes through stainless steel rods. Tube length was kept at 20 mm. Finished composition was then loaded into stainless steel delay tube in five equal increments. Each increment was accurately weighted separately and pressed in a delay tube one by one. Surface of the delay column was kept flushed with the end of the delay tube. Excess delay composition was removed by sliding the end of the delay tube.
A hydraulic press machine installed with a calibrated gauge was used to consolidate the delay composition in the delay tubes at compaction loads ranged from 69 MPa to 448 MPa. Consequently, for most of the tubes prepared in this way, the pressure was set at 207 MPa. A dwell time of about 2 sec was used before relieving the stress. A mechanically initiate percussion assembled in the holder was then installed in the delay tube. A rubber O-ring was used to prevent the composition from environmental effects such as humidity. The other end of the delay body was crimped.
5.3.4.4 Results and Discussion:
PbO/Pb3O4/Si/FG is a gasless delay mixture. Propagative burning of pressed column of this gasless delay composition is a combustion reaction in which PbO, Pb3O4 and Si react to give solid products.
Some of the heat produced during the chemical reactions is lost through the delay body to the surrounding and the remaining heat is transferred to the unreacted mixture through conduction that sustains propagation. Variation in the inner diameter and length of the
120 delay tube was kept at minimum. Ingredients and the percentages used during preparation of this modified delay composition are shown in Table 5.4.
Table 5.4 Ingredients and their percentages
S# Ingredients [Wt %]
1 Silicon 18.0
2 PbO 21.0
3 Pb3O4 60.7
4 Fish Glue 0.30
5.3.4.4.1 Test results of composition mixed in (3-D) automatic Tumbler Mixing Machine
Delay composition prepared in three dimensional (3-D) Automatic Tumbler Mixing Machine was loaded in a delay tube of 4.0 mm internal diameter. Length of the column was kept 20 mm. Burning rate and burning time were recorded. Maximum variation in burning rate and burning time was also calculated. These results are shown in Table 5.5. All functional tests were conducted at temperature range between 18 °C ~24 °C. As shown, the mean burning time and burning rate are 0.569 s and 35.1 mm/s. Maximum variation in burning time and burning rate are 23 % and 24.3 % respectively. These variations in burning time and burning rate are very high and are not acceptable in precise pyrotechnic delay devices.
It means that the pyrotechnic delay composition prepared in the 3-D automatic tumbler mixing machine did not produce consistent burning time and burning rate. Reason could be the non-uniform mixing of the ingredients of the composition. Automatic mixing machine did not produce intimate contact of the ingredients of the delay mixture.
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Table 5.5 Test results of delay mixture mixed in (3-D) automatic Tumbler Mixing Machine
Sample No Burning time Burning rate
[s] [mm/s] 1. 0.588 34.01
2. 0.626 31.95 3. 0.536 37.31 4. 0.493 40.57
5. 0.600 33.33 Mean 0.569 35.15 Max variation 23.0 % 24.3 %
Delay composition Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 was then subjected to different loading pressures in the delay column in order to determine the effect of loading pressures on the delay composition in the delay tubes. For this reason different loading pressures of 69 MPa, 83 MPa, 97 Mpa, 138 MPa, 165 MPa and 276 MPa were applied to consolidate the composition in the delay columns. Pressing the delay composition in the column increases compaction and hence increases density. Results in Figure 5.7 show that the burning rate and hence the burning time was not much effected by changing the applied loading pressure. Maximum variation in burning time at different loading pressures ranged from 15 % to 25 % as shown in Figure 5.7.
This variation in burning time though not very large is still very high considering our goal. The conclusion being that the time consistency of this delay mixture could not be achieved by varying the loading pressure. The mean burning time and burning rate at different applied loading pressures was calculated and are shown in Figure 5.8. Burning time and burning rate varied from 0.569 sec to 0.715 sec and 25.7 mm/sec to 35.2 mm/s respectively.
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Figure 5.7 Plot of Maximum percent variation of delay time from mean against applied loading pressure
Burning time and burning rate are inversely proportional to each other, when the delay time reduced the burning rate increased and vice versa. These results reveal that mixing of pyrotechnic delay composition through tumbler mixing machine is useful where large amounts of delay mixtures are required to be prepared and where burning time consistency is not required.
Figure 5.8 Plot of burning rate and delay time against applied loading Pressures
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5.3.4.4.2 Test results of composition Manually Mixed in Mortar and Pestle:
Ingredients of the pyrotechnic composition were mixed in manual Mortar and Pestle, the mixing procedure has been discussed in section 5.3.4.2. Composition was then loaded in the delay body with internal diameter and length of 4.0 mm and 20 mm respectively. Composition was consolidated at 207 MPa by using oil operated hydraulic press machine installed with calibrated pressure gauge. Dwell time of 2 sec was applied for each increment.
Results in Figures 5.9 and 5.10 show that, the variation in burning time of each sample ranged from 0.16 % to 4.38 %. Results also show that burning rate of the delay mixture varies from 31.0 mm/s to 34.0 mm/s. Mean burning time and burning rate are 0.617 sec and 32.4 mm/sec respectively. Standard deviation in burning time and burning rate are 0.0123 and 0.651 respectively. Maximum variation in burning time reduced from 25 % to 8.75 %. These results show that intimate contact of the fuel and oxidizers resulted in the reduction in delay time variation. Intimate contact was ensured through manual dry mixing in mortar and pestle followed by wet mixing. Additionally, the laboratory operating conditions i.e. controlling dry and wet mixing time, drying time, stabilizing the composition for a specific time, controlling the weighing of the individual ingredients, controlling the weighing of delay composition, using of calibrated measurement equipment were also ensured to be the same each time. Homogeneity and intimate contacts of ingredients play a key role in time reproducibility of this pyrotechnic delay composition. Dry mixing of the ingredients is not a very safe method as compared to automatic mixing, therefore proper safety precautions were observed during this critical operation. Composition was made slurry, which was then stirred thoroughly to ensure even distribution of the fuel and oxidizers. Fuels and oxidizers have different densities, and if binder is not used then the fuel and oxidizer separate due to their density difference. Main reason of adding fish glue as binder is to protect the fuel and oxidizer from environment effects such as humidity.
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Figure 5.9 Plot of percent variation of delay time from mean for each sample
Binder also increases cohesion between particles of fuels and oxidizers to protect them from being segregated due to their density difference. Grains also provided ease of loading of the composition in the cartridge body.
Figure 5.10 Plot of burning rate and delay time for each sample
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5.3.4.4.3 Effect of loading pressure on delay composition (Manually Mixed in Mortar and Pestle)
Manually mixed pyrotechnic delay composition Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 in Mortar and Pestle was then subjected to different loading pressures in a delay tubes with column length of 20 mm. Effect of different consolidation pressures on the burning performance of this delay composition was determined. Loading pressure was ranged from 138 MPa to 448 MPa. Test results of mean burning time, mean burning rate and variation in burning time is shown in Table 5.6. Data reveals that maximum variation in burning time ranged from 7.42 % to 9.38 % by varying the loading pressure from 138 MPa to 448 MPa. This variation in burning time is not significant, which means that burning performance of this pyrotechnic delay composition is not much effect by the varying loading pressure. Burning rate is relatively insensitive to loading pressure. Varying loading pressure from 138 MPa to 448 MPa, about 2.0 ~3.0 % variations in burning time was recorded. Results in Table 5.6 also show that even at 448 MPa, the composition did not become insensitive; easily ignited by the standard percussion primer and functioned successfully.
Table 5.6 Test results of delay time at different loading pressure
S# Mean burning %Variation in Mean burring Loading time[s] burning time rate[mm/s] pressure[MPa] 1 0.635 8.66 31.5 138
2 0.629 9.38 31.8 165
3 0.617 8.75 32.4 207
4 0.634 7.42 31.5 414
5 0.618 7.93 32.4 448
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5.3.5 Effect of temperature variation on burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition
Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 pyrotechnic delay mixture was loaded in a brass delay tubes of 11 mm column length , and conditioned in calibrated environmental chamber at -54 °C, -40 °C, -20 °C , 25 °C , 70 °C and 100 °C for 4 hrs each. After conditioning at these temperatures, the samples were shifted and tested for burning time measurement within three minutes after removal from the chamber to meet requirement of applicable Military Standard [30]. Average measured burning time and burning rate are shown in Table 5.7.
Each data point listed in Table 5.7 represents an average of five measurements. Mean charge weight of delay composition ranged from 535 mg to 548 mg. Results in Figure 5.11 and Figure 5.12 reveal that the burning time decreased and the burning rate increased with increase in the temperature. Minimum and maximum burning rates were recorded at -54 °C and 100 °C respectively. Temperature dependence of the burning rate of Si/PbO/Pb3O4/FG delay mixture is approximately linear.
Table 5.7 Temperature dependency of delay Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 in Brass delay body
Conditioning Mean Weight of Mean burning Mean burning
Temperature delay mixture time rate ° [ C] [mg] [s] [mm/s] -54 538 0.393 28.01 -40 535 0.359 30.65 -20 538 0.348 31.65 25 548 0.340 32.35 70 543 0.328 33.54 100 537 0.320 34.38
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Figure 5.11 Plot of burning time vs temperature variation for
Si/PbO/Pb3O4/FG mixture
Temperature of the surrounding and also the temperature of the unreacted delay composition affected burning rate. As ambient temperature is raised, activation energy is lowered because less energy is required to raise a composition to its ignition temperature. Thus the burning rate increased and less time was required to reach the ignition temperature.
Figure 5.12 Plot of burning time vs temperature variation for
Si/PbO/Pb3O4/FG mixture
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Burning rate increased from 28.01 mm/sec at -54 °C to 34.38 mm/sec at 100 °C, which shows an overall increase of 23.0 % in the burning rate. Burning time decreased from 0.393 sec to 0.320 sec when the temperature was increased from -54 °C to 100 °C, which shows an overall decrease of 18.58 %.
5.3.6 Effect of loading pressure on burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition
Delay composition Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 was subjected to different loading pressures in a delay tubes with column length of 10 mm. Loading pressure was varied from 138 MPa to 448 MPa to press this pyrotechnic delay mixture in the delay tubes. Loading pressure is more complex than the other parameters, especially on a new composition.
A small change in ingredient ratios or change in particle size can change the burning behavior markedly. Effect of loading pressure on burning rate is normally considered to be of the secondary importance. Loading pressure is a design parameter for the pyrotechnic delay devices. For every pyrotechnic delay composition a certain loading pressure is finalized to get the required compaction and optimum burning rate.
By increasing the loading pressure, the burning rate of Si/PbO/Pb3O4/FG =18/21/60.7/0.3 delay mixture produced a nonlinear trend. Variation in loading pressure affected the burning rate of this pyrotechnic delay composition less significantly. Variation in burning rate by varying the loading pressure ranged from 30.1 mm/s to 31.7 mm/s. Test results are shown in Table 5.8. Results reveal that the minimum standard deviation in burning rate was recorded at loading pressure of 448 MPa. Some gasless pyrotechnic delay compositions are difficult to ignite at high compaction because the surface becomes smoother and less porous. Therefore a small amount of the igniter composition is pressed above the delay composition.
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Table 5.8 Test results of effect of loading pressure on Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 delay mixture
Loading pressure Delay time Burning rate Std. Dev in [MPa] burning rate [s] [mm/s]
138 0.322 31.0 2.9
207 0.332 30.1 1.4
276 0.315 31.7 1.1
345 0.330 30.3 1.3
414 0.329 30.4 1.9
448 0.329 30.4 0.7
This newly developed Si/PbO/Pb3O4/FG delay composition was easily ignited with standard percussion primer. No misfire was recorded in any test; the compositions were sensitive to standard mechanical percussion at such a high loading pressures. Pyrotechnic delay composition is sometimes subjected to high impact g-shocks before initiation of the payload of the munitions. Payload functions after penetrating in the hard target with in a pre-determined delay time. Purpose of pressing these compositions at high loading pressure was to increase the compaction in order to sustain high impact g-shocks. If the composition is not compacted at high loading pressure then the composition can detach from the delay body. Cracks may also develop in the delay column during high g-shock impact, which may affect the reliability and functionality of the delay device. These pyrotechnic delay compositions were reliably initiated at these ranges of loading pressures. During loading it was found that if the strength of pressing pin is not high enough then it does not sustain such a high pressure and may result in bending of the pin. Hardness of the pin must be sustainable to high loading pressures.
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5.3.7 Study of effect of body material on burning time and burning rate of
Si/PbO/Pb3O4/FG delay composition
Pyrotechnic delay mixture Si/PbO/Pb3O4/FG was first studied in Stainless steel tube. Internal diameter of the delay tube was 4 mm while the column length was 11 mm. The mean charge weight of the delay composition was 544 mg. Each increment was accurately weighted with a calibrated weighing balance. Maximum variation in the weight of the delay composition was 3.86 %. Applied loading pressure to press the delay composition in the column was 207 MPa. Measured results of burning time and burning rate of this delay mixture is shown in Table 5.9. Results illustrate that the average burning time and burning rate of this mixture was 0.377 sec and 29.21 mm/sec respectively. Maximum variation in burning time and burning rate was 7.43 % and 7.57 % respectively. Standard deviation in the charge weight, burning time and burning rate was 0.008, 0.010 and 0.81 respectively.
Table 5.9 Test results of Si/PbO/Pb3O4/FG delay mixture in Stainless steel delay body
Sample No Weight of delay Burning time Burning rate mixture[g] [s] [ mm/s]
1 0.549 0.360 30.56 2 0.542 0.379 29.02 3 0.544 0.378 29.10 4 0.532 0.388 28.35 5 0.553 0.379 29.02 Mean 0.544 0.377 29.21 % Max 3.86 7.43 7.57 variation Standard 0.008 0.010 0.81 deviation
Results show the burning time and burning rate is inversely proportional to each other. No igniter composition was used as first fire between percussion and delay composition
131 for initiation of Si/PbO/Pb3O4/FG pyrotechnic delay composition. This delay mixture is sensitive to percussion primer and was easily initiated by output energy of the standard percussion primer.
Pyrotechnic delay composition Si/PbO/Pb3O4/FG = 18/21/60.7/0.3 was then loaded in the brass tube at same loading pressure of 207 MPa, and subjected to functional tests for the measurement of burning time and burning rate. Results of these parameters are shown in Table 5.10. Variation in the internal bore of the delay body significantly changes the burning time, therefore variation in the internal diameter of the tube was reduced from 7.7 % to 2.6 % during manufacturing process. Results as shown in Table
5.10 reveal that, the mean burning time and burning rate of the Si/PbO/Pb3O4/FG delay mixture recorded was 0.384 s and 28.64 mm/s respectively. Percent variation in the burning time and burning rate was 4.17 % and 4.12 % respectively. By comparing, burning time and burning rate of Si/PbO/Pb3O4/FG delay mixture in both body materials, results show that using brass as body material along with controlling variation in the column diameter, variation in the burning time decreased from 7.43 % to 4.17 %, whereas variation in burning rate reduced from 7.57 % to 4.12 %. An overall reduction of 43.88 % in burning time, and 45.57 % in burning rate was recorded. Standard deviation in charge weight, burning time and burning rate measured was 0.0128, 0.0062 and 0.456 respectively. Results also show that when the composition was tested in the brass delay body, the average burning time increased from 0.377 sec to 0.384 sec and average burning rate decreased from 29.21 mm/sec to 28.64 mm/sec. This slight increase in burning time and decrease in burning rate in brass delay tube could be due to the more heat lost from the delay composition in brass tube than in the stainless steel tube. Thermal conductivity of the brass (109 W/mk) is higher than Stainless steel (16 W/mk). Increasing thermal conductivity of the brass material caused more heat loss from the delay composition to the surrounding and thus slightly decreased the burning rate and increase the burning time.
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Table 5.10 Test results of Si/PbO/Pb3O4/FG delay mixture in Brass delay
body Sample No Weight of delay Delay time Burning rate mixture[g] [s] [mm/s] 1. 0.531 0.384 28.65 2. 0.556 0.394 27.92 3. 0.550 0.385 28.57 4. 0.566 0.378 29.10 5. 0.548 0.380 28.95 Mean 0.550 0.384 28.64 % Max variation 6.36 4.17 4.12 Standard 0.013 0.006 0.456 deviation
Figure 5.13 and Figure 5.14 show the comparison of the delay time and burning of
Si/PbO/Pb3O4/FG delay mixture in stainless steel and Brass delay body. These results show that burning rate slightly decreased and burning time increased when the compositions were tested in brass delay bodies.
Figure 5.13 Plot of delay time of Si/PbO/Pb3O4/FG mixture in stainless steel and in Brass delay body
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Figure 5.14 Plot of burning rate of Si/PbO/Pb3O4/FG mixture in Stainless Steel and in Brass delay body
5.3.8 Effect of binders on burning time and burning rate of Si/PbO/Pb3O4/FG delay composition
Only one binder fish glue was studied in Si/PbO/Pb3O4 delay mixture to determine the burning time and burning rate dependency of this mixture on the fish glue content. Fish glue content was varied from 0 % to 1.0 %. Percentages of the ingredients are shown in
Table 5.11. By increasing the fish glue content, the Pb3O4 content was decreased accordingly with the same ratio. Si and PbO contents were kept constant to maintain 100 wt % of the ingredients. This delay mixture was loaded in the delay tube at loading pressure of 207 MPa. These tests were conducted in stainless steel tube of 4 mm internal diameter with an effective column length of 9 mm. Test results are summarized in Table
5.11. Burning time and burning rate of Si/PbO/Pb3O4 composition recorded at 0 % fish glue were 0.233 sec and 38.6 mm/sec, respectively. Experiments were repeated by adding 0.3 % fish glue to the delay mixture. Burning time increased to 0.318 sec and the burning rate decreased to 28.3 mm/sec. A further increase in the binder content to 0.5 %, the burning time increased to 0.395 sec and the burning rate decreased to 28.2 mm/sec. When the binder content was increased to 1.0 %, burning time further increased to 0.548 sec and burning rate decreased to 16.4 mm/sec. The decrease in burning rates were 26.7 %, 19.4 %, and 28.1 % with the addition of 0.3 %, 0.5 %, and 1.0 % fish glue,
134 respectively. Similarly increases in the burning times were 36.5 %, 24.2 %, and 38.7 % with the addition of same wt. % of fish glue. Standard deviation measured in burning rate at 0 %, 0.3 %, 0.5 % and 1.0 % Fish Glue 1.31, 1.42, 1.60 and 1.51 respectively.
Binder was added to the ingredients of the mixture for binding them together in the form of free flowing grains. Binders protected the fuel and oxidizer from environmental effects such as humidity. Binders also increased cohesion between particles of fuels and oxidizers by protecting them from being segregated and consequently increased homogeneity. Grains of the delay coposition, prepared in the binder provided ease of loading of the pyrotechnic delay composition in the delay device. Grains of the delay mixtures prepared in the binders flow freely when poured from one container to another.
On one side, binders protected the delay composition from environmental effects and provided ease of loading into the delay column. On the other side binders reduced the burning rate of this delay mixture.
Therefore, before designing pyrotechnic delay composition, due consideration should be given to the binder and its contents. Binder is normally used in the range of 0.2 % to 0.6 % by weight of the total composition. The granulation process becomes difficult, and sensitivity of composition decreases if the binder content is increased beyond this range. In the present work, Fish Glue content up to 2.0 % created no problem in grains formation as well as during loading of the composition in the delay tube. When Fish Glue content was increased to 3.0 %, both grains formation and loading of the composition in delay tube became problematic.
Therefore, the recommended range of the Fish Glue in the delay compositions is 0.1% to 2.0 %. These results also show that for a fixed length of the delay column, burning rate can be modified by varying the binder content in the delay mixture.
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Table 5.11 Effect on burning rate and burning time with varying Fish Glue contents
in Si/PbO/Pb3O4 delay mixture
Silicon Pb3O4 PbO Fish Glue Mean Mean Std. Dev in [%] [%] [%] [%] Delay Burning burning rate Time[s] rate[mm/s] 18 61.0 21 0 0.233 38.6 1.31
18 60.7 21 0.3 0.318 28.3 1.42
18 60.5 21 0.5 0.395 22.8 1.60
18 60.0 21 1.0 0.548 16.4 1.51
Results reveal that B/BaCrO4 is a fast burning pyrotechnic delay composition as compared to Si/PbO/Pb3O4 delay mixture. Consequence of Fish Glue on the burning rate of Si/PbO/Pb3O4 mixture is more significant than on the burning rate of B/BaCrO4 delay mixture (discussed in chapter 4). Burning rate of Si/PbO/Pb3O4 delay mixture with 1.0 wt. % Fish Glue was 16.4 mm/sec.
Burning rate of B/BaCrO4 delay mixture was 51.2 mm/s with the same wt. % of Fish
Glue. Burning rate of B/BaCrO4 mixture is 212 % higher than the burning rate of
Si/PbO/Pb3O4 delay mixture with 1.0 wt. % of Fish Glue. These results are shown in
Tables 4.2 (Chapter-4) and 5.11. Similarly the bulk density of Si/PbO/Pb3O4 delay mixture is higher than B/BaCrO4.
5.3.9 Effect of loading pressures on the consolidation density and %TMD
Percent Theoretical Maximum Density (%TMD) of Si/PbO/Pb3O4/FG pyrotechnic delay compositions was measured by varying the loading pressures. Loading pressures were varied from 138 MPa to 483 MPa. Increase in loading pressure increased the consolidation delay composition in the delay column. Increase in loading pressure resulted in greater packing efficiency and correspondingly less void space. Figure 5.15
136 show the effect of varying loading pressure on the %TMD of Si/PbO/Pb3O4/FG= 18/21/60.7/0.3 delay composition. Theoretical Maximum Density (%TMD) varied linearly from 68 % to 93 % for Si/PbO/Pb3O4/FG= 18/21/60.7/0.3 delay composition.
Figure 5.15 Plot of Loading pressure vs %TMD for Si/PbO/Pb3O4/FG= 18/21/60.3/0.3 delay mixture
5.4 Conclusions:
Results of these analysis show that Si/Pb3O4/FG delay composition produced consistent and reproducible results between 10 % to 35 % silicon contents. This delay mixture can be reliably used in short and medium delay producing cartridges and detonators. Results also reveal that Si/PbO/FG is a slow delay composition, and can be reliably used with Silicon contents between 10 % to 15 %. Mass consumption and hence performance of Si/PbO/FG delay composition was improved by incorporating an increment of fast red lead delay mixture (Si/Pb3O4/FG=20/79/1.0) between primer and Si/PbO/FG delay composition in the delay tube.
Next effect of mixing on the burning time consistency of Si/PbO/Pb3O4 /FG delay composition was investigated. Result analysis showed that ingredients mixing along with controlling laboratory operating conditions are critical parameters for controlling
137 the burning time and burning rate of pyrotechnic delay composition in a delay device. Manual mixing is much better than mixing in automatic tumbler mixer, because tumbler mixer does not produce intimate contact of the ingredients. Burning time and burning rate of this pyrotechnic delay composition was not much effected by varying the loading pressure. Only about 2~ 3 % variations in burning time was recorded when the loading pressure varied from 207 MPa to 448 MPa. Temperature variation also affected the burning time and burning rate of Si/PbO/Pb3O4/FG delay mixture. Burning time increases and burning rate decreases as the temperature is raised. Effect of binders and loading pressure on Si/PbO/Pb3O4 pyrotechnic composition was also experimentally studied. Results show that burning rate of this composition decreased with increase in Fish Glue contents and vice versa. It means that the burning rate of this delay composition may be modified by changing the Fish Glue contents. Loading pressure did not show much effect on the burning performance of Si/PbO/Pb3O4/FG delay composition. Delay composition provided promising result and may be reliably used in short pyrotechnic delay devices. Si/PbO/Pb3O4/FG delay composition was also studied in stainless steel and brass delay bodies to determine the effect of body material on burning propagation. From the results, it is concluded that using brass delay body the variation in the burning time and the burning rate of this delay mixture reduced. Burning time slightly increased in brass delay body due to high thermal conductivity.
Consolidation density and percent Theoretical Maximum Density (%TMD) of
Si/PbO/Pb3O4/FG delay composition increased by adding binders and increase in loading pressure.
138
References
[1] J. C. Poret, A. P. Shaw, C. M. Csernica, K. D. Oyler, J. A. Vanatta, G. Chen, J. ACS Sustainable Chem. Eng 1(2013)1313. [2] H. Ren , Q. Jiao and S. Chen, J. Physics and Chemistry of Solids 71(2010)145. [3] M. W. Beck, M.E Brown, Combust. Flame 65(1986) 263. [4] T. Boddington, P.G. Laye, Thermochimica Acta, 120 (1987)203. [5] L. Kalombo, O. D. Fabbro, C. Conradie, W. W. Focke, Propellants Explos. Pyrotech 32(6) (2007)454. [6] U.S. Army Material Command, Engineering Design Handbook, Explosive Series, Explosive Trains,AMCP706-179,Washington, p. G2–3 (1974). [7] K.T. Lu, C.C. Yang, Propellants Explos. Pyrotech 33(3) (2008)403. [8] N. Davies, Pyrotechnics Hand Book, the Ammunitions Systems and Explosives Technology Department, Cranfield University, p. 2 (2002). [9] A. Bailey and S.G. Murray, Explosives, Propellant and Pyrotechnics, Royal Military College of Science, Shrivenhan, UK, p. 120 (1989) [10] C. Gordon Morgan, Production of pyrotechnic delay composition, Patent- US0314397 A1 (2009). [11] J A. Conkling, Chemistry of Pyrotechnics Basic Principles and Theory, Department of Chemistry Washington College Chestertown, Maryland, p. 111(1985). [12] S.M Danali, R.S. Palaiah, K.C. Raha, Defense Science Journal, 60(2010)152. [13] R. Aube and Lachute (CA), Delay composition and Detonation Delay Device Utilization, Patent-US 0223242 A1 (2008). [14] B. J. and K. L. Kosanke, Control of Pyrotechnic Burn Rat, Second International Symposium on Fireworks, 275 (1994). [15] S.M Danali, R.S. Palaiah, K.C. Raha, J. Defense Science 60(2010)152. [16] Military Specification, Manganese Delay Composition, MIL-M-21383A (1976). [17] Military Specification, Delay Composition T-10, MIL-D-85306A (AS) (1991) [18] Military Specification, Delay Composition, Tungsten-Fluorocarbon Copolymer, MIL-D-82710(OS), (1984).
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[19] Rejean Aube, Lachute (CA), Delay compositions and detonation delay device utilizing same, US Patent, 0223242A1(2008).
[20] L. Kalombo ,evaluation of Bi2O3 and Sb6O13 oxidants for silicon fuel in time delay detonator (2005) [21] Warren C. Eller and Frank J. Valenta, US Patent, 3851586, Temperature Compensated Pyrotechnic delays (1974). [22] S. S. AL-Kazraji and G. J. Rees, J. Therm. Anal, 16 35(1979)39. [23] J. Jakubko, Combust. Sci. and Tech 146(1999) 37. [24] J. Jakubko, E. Cernoskova, J. Therm. Anal Anal 50 (1997)511. [25] E. L. Charsley, C.H. Chen, Themochimica Acta. 35(1980)141. [26] Y. Li, Y. Ceng, Y. Hui, S. Yan, J. Energ. Mater 28(2010)77. [27] S.S. A. Kazraji, G.J. Rees, Combust. Flame, 58(1978)139. [28] S.S. Al-Kazraji, G.J. Rees, Combust. Flame 31(1978)105. [29] Operating instructions, Haver Test Shaker EML 200-89 Digital, (1993). [30] Military Specification, Design and Evaluation of cartridge for store suspension equipment, MiL-D-81303(AS).
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Chapter No. 6: Experimental validation for the Safe Separation of External Store from Military Aircraft
6.1 Introduction
Survivability and mission effectiveness of the military aircraft are highly dependent upon the ability to deliver air- launched weapons with minimum risk. Impulse launchers for weapon ejection are employed for the release of free fall or self- propelled weapons. The main purpose of these ejectors is to clear the delivery aircraft. Ejection is usually achieved by the expansion of gases due to ignition of the propellant charge. These impulse carriages are used for ejection purpose only. Nearly all free fall or glide weapons carried by aircraft are ejection-launched. At the time of launch, high pressure gases acts on the piston, forcing the hooks holding the weapons to open and simultaneously forcing the ejection foot against the weapons. This action physically ejects the weapons away from the aircraft, ensuring that it is clear of the aerodynamic flow around the aircraft [1-3].
Store jettison problem is very complex. There are many parameters which effect store separation. Two major parameters are aerodynamic parameters and physical parameters. Aerodynamic parameters are the store shape, stability, velocity, altitude, load factor and configuration of aircraft. Physical parameters include store mass, store moment of inertia, center of gravity, Ejector location and external store rack.
Generally, serious problems in external store jettison can occur if the impulse cartridge does not generate the required pressure. These problems can occur in these distinct areas: store to pylon collision, store to wing or body collisions and store to store collisions. Stores are installed close to the aircraft as possible due to aerodynamic reasons and stores are also required to be ejected away from aircraft when released to
141 ensure safety of aircraft. Pyrotechnic pressure generated cartridges are used to provide pressure to release stores.[4]. Energy and required pressure is generated by burning of propellant or pyrotechnic material, and is used to push a piston to release the external store. These are used to do mechanical work. These cartridges are physically small light weight sources of energy. Cartridge requires no maintenance once installed. These explosive devices are inexpensive and most importantly exhibit a high degree of reliability. Two cartridges are used to release the external store from military aircraft. Both the cartridges are fired simultaneously, the pressure of both the cartridges should not be much high otherwise it can damage the pylon and also danger for aircraft. One cartridge is normally used as a standby; it means that the pressure of the single cartridge should be sufficient to release the store.
Impulse cartridge utilizes electrical energy for initiation purpose for its function to release bombs from military aircraft. Propellant along with pyrotechnic igniter and booster composition generate peak pressure within pylon necessary for ejection. Specific volume of gases for desired peak pressure was measured in specially designed chamber. An Impulse cartridge consists of igniter, booster pyrotechnic compositions and main propellant charge.
Igniter charge of Impulse cartridge is initiated through electrical or mechanical stimulus. Electrical primer consists of resistive wire on which the igniter composition is pressed or coated. When an electrical pulse in provided to the cartridge, the energy passes through the resistive wire, heat is produced and the energy loss from the wire is used to initiate the igniter charge. Failure of fire transfer from igniter to main composition occurs when required energy is not transferred. An easily initiated composition is pasted/ pressed in small quantity on the top of main composition [5-7].
Main purpose of this study was to measure the minimum pressure and ejection velocity required for the ejection of external store from the military aircraft. Tests were performed in static condition on the actual pylon without considering the aerodynamic and other physical parameters.
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Cartridge was initially developed at maximum pressure and was being used for release of stores from military aircraft. But it was not known that how much pressure is actually required for the release of store from military aircraft, Moreover the ejection velocity was also not known. The objective of this research work was to determine the minimum pressure for the release of store along with the ejection velocity from the Military aircraft at static condition.
6.2 Experimental conditions:
6.2.1 Materials used
High purity Analytical grade fuels and oxidizers of Fluka/ Sigma Aldrich as shown in table 6.1 were used for igniter and booster pyrotechnic compositions and single based propellant was use as main propellant charge to generate required pressure. Purity of these chemicals is between 97~ 99 %. Fuels and oxidizers used were fine powders. All these fuels and oxidizers were passed through 325 meshes to get particle sizes of ≤ 44 µm.
Table 6.1 Ingredients of Pyrotechnic compositions and propellant used in impulse cartridges S# Description Ingredients Weight [g] 1 Primary High explosive Lead Styphnate 0.02 2 Igniter pyrotechnic Zirconium/Potassium 0.10 composition perchlorate = 60/40 3 Booster pyrotechnic Zinc/Potassium 0.80 composition perchlorate/CMC = 40/59.5/0.5 4 Single base propellant Nitro Cellulose/Binder =98/2 4.5
6.2.2 Formulation of igniter and booster pyrotechnic compositions
Ingredient of both the igniter and booster compositions were accurately weighted and mixed in in a special mechanized remotely operated mixing machine installed with agate
143 mortar and pestle. Mixing of the composition was completed in about 30 min. Homogenize mixing of the compositions were ensured. Weight of each batch of the composition was kept 5~10 gram.
For booster pyrotechnic composition a binder solution of 0.5 % CMC was prepared in distilled water and this solution was mixed with the composition. A homogenous paste was prepared by using a spatula in an agate container. Paste composition was semi-dried in a drying oven at 80 °C. To avoid the formation of lumps, the semi-dried composition was carefully broken up with a spatula in an agate container. Composition was sieved gently through a 50 mesh sieve and retained on a 150 mesh sieve to obtain grain sizes of ≤ 297 μm. A Haver test shaker EML 200-89 digital was used for the preparation of grains of the required particle size. Grains were dried for 4 hours at 80 °C to remove water/moisture. Finished composition was stored in a special container and placed in a desiccator for 24 hours to stabilize the composition.
6.2.3 Manufacturing of Impulse cartridge:
A detailed manufacturing process of the Impulse cartridge and testing method of the cartridge in closed chamber for the measurement of peak pressure and time to peak pressure have been discussed in Chapter 4.
Before using in actual system (Pylon) for release of weapons in static conditions, the cartridges were successfully tested as per applicable Military Standards in closed chamber [8, 9]. Different environmental, safety and electrical tests conducted are given below:
6.2.4 Close chamber Tests
6.2.4.1` Environmental Tests:
Leak Test
The cartridges were placed in the test chamber. A vacuum of 500 mg was created in a test apparatus by using vacuum pump. Vacuum was then filled with Helium gas of ≥
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99.9 % purity. The apparatus was kept for one hour. After one hour the cartridges were subjected to helium leak test one by one. All the cartridges passed leak test of 10-5 cc/see.
6-Feet drop test
Each cartridge was subjected to the 6-foot drop test. The cartridge should not fire during this drop test. After 6-foot drop test the cartridge was subjected to functional test in closed chamber.
15 ‘g’ Shock test
Cartridges were mounted on a text fixture and subjected to 10 shocks of 15 “g” maximum acceleration. The maximum acceleration of 15 “g” was reached in 8 ms and the acceleration exceeded 8 g in minimum of 11 ms. Cartridges were then subjected to functional test
Vibration test
Cartridges were mounted in a vibration testing fixture and then fixed on the vibration table. Cartridges were subjected in each of the following orientations.
Parallel to the longitudinal axis of the cartridge Perpendicular to the longitudinal of the cartridges
Low temperature test
Cartridges were conditioned at temperature of -54 °C for one hour in a calibrated environmental chamber. After conditioning, the cartridges were subjected to functional test within 3 min after removal from the chamber.
High Temperature test
Cartridges were conditioned at temperature of +93 °C for one hour in a calibrated environmental chamber. After conditioning, the cartridges were subjected to functional test within 3 min after removal from the chamber.
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6.2.4.2 SafetyTests:
Static Discharge Test
This is a laboratory safety and reliability test simulating handling and transportation conditions. The cartridges were subjected to the 25000 volt simulated human electrostatic discharge to qualify the requirement of applicable MIL-Standard [9]. The cartridges should not fire during this test. Static Discharge tester ESD 300 System of EMC PARTNER was used for the purpose.
Stray Voltage Test
This is a safety test in which the initiator shall be capable of withstanding the effects of a stray voltage environment without pre-igniting. The cartridges were subjected to 2000 pulse of direct current. Each pulse was of 300 ms duration and pulse rate was 2 pulses per sec. Each pulse had minimum amplitude of 100 ± 5 milli amperes to qualify the requirement of applicable MIL-Standard [9]. Stray Voltage tester of Thurlby Thunder Instrument Part No TG 550 was used for stray voltage tests
Maximum No-Fire Current Test
This is a laboratory test for functional reliability, handling and tactical safety. These cartridges were subjected to not less than 1watt/ 1A current for five minute to qualify the requirement of applicable MIL-Standard [9]. The cartridge should not fire during this test. A Calibrated Power supply was used for measurement of Maximum No fire current test.
6.2.5 Measurement of Ejection velocity and pressure
6.2.5.1 Linear Voltage Displacement Transformer (LVDT)
Linear Voltage Displacement Transformer (LVDT) was used along with data acquisition system and customized lab view software to measure ejection velocity. Velocity was measured by dividing the distance travel by piston to the time recorded.
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6.2.5.2 Pressure measurement in closed chamber:
Pressure was measured using transducer and pressure calibrator in peak pressure mode. Two different types of transducers (250 bar and 600 bars) were used for the recording the peak pressure.
Analog to Digital Converter (ADC) was used to convert from Analog to Digital form. Pressure was sensed by the transducers and display on the pressure calibrator in digital form. Pico software of Kastler Company was used to produce pressure vs burning time graph. This graph was used to measure peak pressure and time to peak pressure.
6.2.6 Power supply:
Power supply was used to provide required energy for initiation of cartridge. Channel 1 of power supply was set on 28 V and 03 A, this channel provides the power to control module. Channel 2 of power supply was set on +5V and 100 m A.
6.3 Results and Discussion
6.3.1 Closed chamber Test result
Before subjecting to the release performance test, the cartridge was qualified to meet requirement of the qualification as per applicable Military Standard. Configuration of propellant, igniter and Booster pyrotechnic compositions gave the desired pressure. Test results of the ballistic parameters such as the peak pressure, resistance and time to peak pressure are shown in Table 6.2 and Figure 6.1 of the qualification lot.
These are the actual pressure and time to peak pressure at which the cartridge was initially qualified. Weight of igniter and booster pyrotechnic compositions, and propellant was adjusted in such a manner to produce a peak pressure and time to peak pressure within the specified limits.
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Table 6.2 Test Result of Impulse Cartridge at different environmental conditions
Sample# Resistance Peak pr essure Time to peak pressure Test condition [Ohms] [bar] [ms] 1 0.409 150.4 43.43 6 Foot drop test 2 0.347 154.1 49.50 3 0.395 167.9 44.10 15 „g‟ Shock test 4 0.424 155.4 46.65 5 0.426 170.0 41.95 Vibration test 6 0.433 164.1 46.95 7 0.368 163.5 42.00 Low temperature 8 0.377 166.6 44.56 test( - 54 ºC) 9 0.391 164.0 44.93 High Temperature 10 0.418 159.3 38.11 test(+93 ºC)
Figure 6.1 Plot of peak pressure of qualification Lot
These data show that pressure of the qualification lot varies from 150.4 to 170 bar while resistance and time to peak pressure varies from 0.347~0.433 Ohm and 24.10~49.50 ms respectively.
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6.3.2 Cartridge Evaluation on the Pylon of Military Aircraft (Static Test) for determining minimum pressure and ejection velocity
Impulse cartridges initially qualified as per applicable Military Standard were used for the release of external store form the military aircraft. Pressure, function time and ejection velocity were recorded by the actual firing of these cartridges in the Pylon. Cartridges were fired electrically with standard 27±2 VDC, minimum firing current 1.5A and normal firing current 3.0 A. All the release tests were carried out at ambient temperature and pressure. Ejection velocity was calculated by dividing the distance over time.
Test results in Table 6.3 show peak pressure, time to peak pressure, ejection velocity and the equipment used for the recording of these data. Date in Figure 6.2 and Figure 6.3 represent a plot of peak pressure vs propellant weight and peak pressure vs ejection velocity respectively. Propellant weight in these cartridges was varied from 1.25 gram to 5.0 gram to ascertain the minimum pressure required for the release of external store.
Test# 01 as shown in Table 6.3 was performed by two pyrotechnic cartridges as used in actual pylon in military aircraft. In this case the pressure was not measure because there was no provision for installation of transducer in the system; however ejection velocity of 5 m s-1 was recorded. In Tests #2, Tests #3, Tests #4 and Tests #5, the time to peak pressure was not recorded because the pressure was very small as shown in the table 6.3 and did not release the weapon from the pylon and therefore the ejection velocity could not be recorded.
Results in Table 6.3 also show that, Test# 2 and Test# 3 were performed with propellant weight of 1.25 gram, which generated pressure of 5.25 bars and 6.0 bars respectively. Whereas Test# 4 and Test# 5 were conducted with propellant weight of 2.50 and 2.75 g, producing pressure of 18.7 and 30.4 bar respectively.
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Table 6.3 Pressure, Function time and ejection velocity of impulse cartridges with various propellant weights
Test# Prop. Wt No of Cart Pressure Time Ejection velocity Transducer used [grm] fitted [bar] [ms] [ms-1] 1 5.0 02 ** 360 5 0~ 250 bar range 2 1.25 01 5.25 NR* NR* -do- 3 1.25 01 6.00 NR* NR* -do- 4 2.50 01 18.7 NR* NR* -do- 5 2.75 01 30.4 NR* NR* -do- 6 3.75 01 61.8 502 3.59 -do- 7 3.90 01 69.9 500 3.60 8 4.40 01 181.8 460 3.90 -do- 9 5.00 01 243.0 410 4.4 -do- 10 5.00 01 256.0 400 4.5 0~ 600 bar range *NR means Not Recorded **No provision of transducer adjustment
Figure 6.2 Plot of propellant weight vs pressure of single cartridge in ERU
In Test # 6, Test #7, Test #8, Test #9 and Test #10, the weapon released and the ejection velocity of 3.59, 3.60 5 m s-1, 3.90 5 m s-1, 4.45 m s-1 and 4.5 m s-1 was recorded.
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Ejection velocity normally varies from 3.0 m/s to 7.0 m/s depending upon the types of the store to be released in case of 500 pound store, the ejection velocity is 6 m s-1[10].
Figure 6.34 Plot of Propellant Pressure vs ejection velocity of single cartridge in ERU 6.4 Conclusion
It has been concluded from above tests and trials that minimum pressure required to release stores from the pylon of the military aircraft must be more than 70.0 bars in static condition. This pressure can be achieved if the propellant weight of 3.90 g is used in the impulse cartridges. In this study, it is further concluded that impulse cartridges which generate pressure between 243.0 and 250.0 bars are considered to be safe for the separation of external store by considering aerodynamic and physical parameters during operational conditions. Ejection or separation velocity of store is varies 3.59~4.5 m s-1 bars due to different propellant grain weight. This separation velocity is very close to the Military Standard, which is 4~6 m s-1.
151
References
[1] A. Zyluk, J. Theor. Appl. Mech., 43(2005)855. [2] E. Covert, J. Aircr 18(1981) 624. [3] Y.H. Yoon, H.K. Cho, H.S. Chung, S.H. Lee, C.H. Han, J. Fluids Eng 13(2008) 80. [4] P. Anthony G. Middleton, Cartridge for store ejection from aircraft, US Patent 8353237B2 (2013). [5] J A. Conkling, Chemistry of Pyrotechnics Basic Principles and Theory, Department of Chemistry Washington College Chestertown, Maryland, 126-127(1985). [6] AMC Pamplet, US Army Material Command Engineering Design Hand Book, Military Pyrotechnic Series Part-A, Theory and Application Washington D.C, 5- 46(1967). [7] H. Ellern, Military and Civilian Pyrotechnics, Chemical publishing company inc New York, 189(1968). [8] Military Specification Design and Evaluation of Cartridge Stores Suspension Equipment, MIL-STD 81303A (AS) [9] Detail Specification, Initiators, Electric, General Design Specification for, MIL- DTL-23659E, 27 (2007). [10] Military Standard, Bomb Rack Unit (BRU) Aircraft, General Design Criteria, Mil STD, 2088A, (1994).
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Chapter No. 7: General Conclusion
Pyrotechnic is an important class of energetic materials and plays an important role in modern rockets, weapons and missiles systems. Therefore pyrotechnic compositions must be reproducible, reliable and safe. Besides other application, pyrotechnic compositions are also widely used to produce special effects such as heat, pressure and delay time. These effects of pyrotechnic compositions are also used for Military purposes. For Military applications these compositions are used as igniter, booster and delay charges. Igniter and boosters compositions are used to enhance the output pressure of pressure generating cartridges for the release of weapons from the Military Aircraft. Pyrotechnic delay compositions are used to produce reliable and consistent burning time before producing an end effect, especially in sophisticated missile systems, where warhead is required to function after penetration through hard target with in a pre- determined delay time.
During the first phase of the present study, different types of igniter and booster pyrotechnic compositions were developed and investigated. From the detailed analysis of all of these considered igniter and booster pyrotechnic compositions, it was concluded that all of the newly-developed compositions have shown promising results. Among these, the best igniter and booster compositions in terms of impulse cartridge functionality based on the peak pressure (bar) and time to peak pressure (ms) were the mixtures 60 % Zr, 40 % KClO4 and 30 % B, 10 % Mg, 60 % KClO4, 4 % additional binder. These newly developed compositions also passed the requisite safety tests and are considered the best compositions for impulse cartridges for the safe release of weapons from Military Aircraft.
nd In the 2 phase, series of B/BaCrO4 and Si/PbO/Pb3O4 delay compositions were developed and different parameters affecting burning performance were experimentally investigated. Results show that B/BaCrO4 mixture provided reliable combustion
153 propagation data from 5.0 %~40 % Boron contents. However, above 40 % Boron, this mixture failed to produce sustainable burning propagation. Maximum charge consumption and burning rate of this delay mixture is at 18 % Boron, while the maximum measured calorific value of this mixture is at about 15 % Boron. Burning rate of this delay mixture was affected by temperatures variation, and decreased in burning rate was observed as temperature was decreased.
Burning rates of both delay compositions B/BaCrO4 and Si/PbO/Pb3O4 decreased with increase in binder content. Decreased in burning rate was significantly higher for
Si/PbO/Pb3O4 delay mixture as compared to B/BaCrO4 composition, when Fish Glue was incorporated. Other two binders Carboxyl Methyl Cellulose (CMC) and Dextrin decreased the burning rate of B/BaCrO4 delay mixture less significantly than Fish Glue. By adding binders and increase in loading pressure, both consolidation and percent Theoretical Maximum Density (%TMD) of these compositions increased. After analysis of results it was concluded that B/BaCrO4 is a fast burning delay composition in comparison to Si/PbO/Pb3O4 delay mixture.
Delay time consistency of Si/PbO/Pb3O4 delay mixture was also studied. Result analysis of Si/PbO/Pb3O4 mixture showed that ingredient mixing along with controlling of the laboratory operating conditions are critical parameters for controlling variation and burning rate of pyrotechnic delay compositions. Manual mixing is much better than mixing in automatic tumbler mixer because the tumbler mixer did not produce intimate contact of the ingredients.
Si/PbO/Pb3O4/FG and B/BaCrO4/FG delay compositions were then studied in stainless steel and brass delay body. From the study, it is further concluded that using brass delay body along with controlling laboratory operating conditions, the variation in burning time and burning rate of both delay mixtures further reduced, provided that the variation in internal bore size and length of the delay tube is controlled. Burning time slightly increased in brass delay body due to the high thermal conductivity of this material. Temperature variation also affected the delay time hence the burning rate of
154
Si/PbO/Pb3O4/FG delay mixture. Burning time increased and the burning rate decreased as the ambient temperature was raised. Both delay compositions provided promising results and can be reliably used in short pyrotechnic delay devices including delay detonators without having to use the customary starter charge as is used in most cases.
Burning performance of Si/PbO/Pb3O4/FG delay mixture was also not much affected by varying the loading pressure. Only about 2 ~3 % variations in burning time was recorded when the loading pressure varied from 207 MPa to 448 MPa. These experimental results can be applied as design guidelines for the developing of any pyrotechnic delay composition.
Lead based Si/Pb3O4/FG and Si/PbO/FG delay compositions were also investigated.
Results of these delay compositions show that Si/Pb3O4/FG delay composition produced consistence and reproducible results between 10 % to 35 % silicon contents. Si/PbO/FG delay composition is a slow delay composition and can be used with Silicon contents between 10 % to 15 %. Mass consumption and thus performance of the Si/PbO/FG delay composition was improved by incorporating an increment of fast red lead delay mixture
(Si/Pb3O4/FG=20/79/1.0) between primer and Si/PbO/FG delay composition in the delay tube.
Static drop tests were conducted to validate the Safe Separation of External Store from Military Aircraft. Form this study, it has been concluded that minimum pressure required to release stores from the pylon of the military aircraft must be more than 70.0 bars in static condition. Pressure can be recorded if the propellant weight of 3.90 grams is used in the impulse cartridges. In this study, it is further concluded that impulse cartridges which generate pressure 243.0 bars ~ 250.0 bars are considered to be safe for the separation of external store by considering aerodynamic and physical parameters during operational conditions. Ejection or separation velocity of store is varies 3.59 m s-1 ~4.5 m s-1 due to different propellant grain weight. This separation velocity is very close to the Military Standard, which is 4 m s-1~ 6 m s-1. In a nutshell, the present studies provide a new insight in the understanding of the function and performance of pyrotechnic compositions and pressure generated
155 cartridges. This study would enable the end-user to optimize the performance of the compositions for the intended purpose.
Future Recommendation
Similar studies may be undertaken on other pyrotechnic compositions for their performance evaluation
156