ARCHIVES of FOUNDRY ENGINEERING

ARCHIVES ISSN (1897-3310) Volume 11 of Issue 3/2011

149 – 154 FOUNDRY ENGINEERING

Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences 25/3

Effect of pouring temperature on the Lost Foam Process

T. Pacyniak*, R. Kaczorowski Department of Materials Engineering and Production Systems, Technical University of Łódź, 1/15 Stefanowskiego Str., 90-924 Łódź, Poland *Corresponding author. E-mail address: [email protected]

Received 10-05-2011; accepted in revised form 13-05-2011

Abstract

In this study, the analysis of the influence of the pouring temperature on manufacture process of castings by the Lost Foam method was introduced. In particular, numerical simulation results of effect of silumin and grey cast iron pouring temperature on pouring rate and gas gap pressure were analyzed. For simulating investigations of the Lost Foam process introduced mathematical model of the process was used. For calculations, the author's own algorithm was applied. The investigations have proved that with increasing pouring temperature the pouring rate increases, while pressure in the gas gap are decreasing. The author’s own investigations showed a more significant effect of the silumin pouring temperature than grey cast iron pouring temperature on the lost foam process.

Keywords: Foundry Engineering, Lost Foam, Foamed Polystyrene Patterns

. the use of pure sand instead of moulding mixture 1. Introduction eliminates the effect of moisture causing casting

defects, with an extra advantage of cheaper sand The growth of the interest in the process of making castings reclamation, by Lost Foam technology became at the close of the eighties of . less of foundry tooling and equipment is needed (no past century when this technology started being used for mass moulding machines, mixers for moulding sand, etc.), production of castings characterized by high accuracy and . lower labour input in final fettling operations due to the repeatability of dimensions, made of light metal alloys and ferrous absence of flashes, burn-on defects, etc. alloys both. The great interest in the Lost Foam technology was mainly due to a definitely lower cost of castings manufacture and Many factors have an influence on the quality of casts made financial outlays very encouraging when compared with the by this technology among other things: traditional process [1]. Respective of the traditional casting . density of foamed polystyrene from which its the process using standard moulding sands, this novel technology strength depends of the pattern and the quality of its offers a number of undeniable advantages, including also the surface, following ones: . the kind of sand, and in the peculiarity its permeability, . it is possible to reproduce holes in castings without the . refractory coating applied on the pattern which makes necessity of using cores, the working surface of the mould. This coating allows . significantly lower costs of the production, to obtain a necessary quality of cast surface and . the lack of parting planes and cores reduces the number prevents metal penetration inside the sand grains, of operations necessary for casting fettling and . and pouring rate. finishing,

ARCHIVES of FOUNDRY ENGINEERING Volume 11, Issue 3/2011, 149- 1 5 4 149 The kind of alloy and pouring temperature are one’s of factors turns out that the process of thermal decomposition of polystyrene have influence on pouring rate. depends on the temperature at which decomposition occurs. Mould pouring should be as short as possible, without breaks, Decomposition in the temperature about 500 C causes that to avoid the formation of defects. It is believed that the smaller volatilized products consist primarily of styrene monomer C8H8 the distance (gap) between the model and the metal front, the [2]. As the temperature is increased further, the monomer lower the risk cracking refractory coating and collapse mold molecule undergoes additional fragmentation to yield light cavity. Pouring temperature is generally higher than traditional hydrocarbons such as C7H8, C6H6, C2H4 and C2H2. At sand casting, this follows from the fact that the alloy loses some temperatures greater than 1000 C, thermal degradation of heat, which is passed to the evaporation of polystyrene pattern. polymer may produce significant quantities of graphitic carbon and even hydrogen. However, studies have failed to identify over 50% of the compounds [2]. Volume of gas produced per unit mass 2. Technological aspects of the pouring of polystyrene, depending on the pouring temperature 750 and 1300 C respectively amount to 250 cm3/g and 800 cm3/g [3]. temperature and kind of alloy Thermal degradation of the expanded pattern also depends on the type of polymer. Table 1 presented physical parameters for Pouring temperature is determined by the type of casting the expanded polystyrene (EPS) and expanded polymethyl alloy. In the present study analyzed the effect of temperature of methacrylate (PMMA) patterns. grey cast iron and silumin AlSi11 on evaporation process of foamed polystyrene pattern and mould cavity filling process. It

Table 1. Physical parameters primary polymers used in the lost foam process [4] EPS PMMA Glass transition temperature (°C) 80 do 100 105 Collapse temperature (°C) 110 do 120 140 do 200 Melting temperature (°C) 160 260 Temperature for start of volatilization (°C) 275 do 300 250 do 260 Peak volatilization temperature (°C) 400 do 420 370 End temperature for volatilization (°C) 460 do 500 420 do 430 Heat of polymerization (J/g) 648 578 Heat of degradation (J/g) 912 842 Gas field at. 750°C (cm3/g) 230 273 Gas field at. 1300°C (cm3/g) 760 804 % non-volatile residue at 1400°C 15 3

3. Investigation of an effect of pouring g c T1 T2. par c rp c2.c T2. par T2.top Fpar dy y2 y1 h temperature and kind of alloys on 2 d rt c2.m T2.top T2.0 F2 2 the mould cavity filling (1)

3.1. System of equations describing the 1 L L P F 2 2 wg wd g L y P process of mould filling with molten alloy atm 2 H 1 1 1 d F 2 d F 2 1 wg 1 g d 1 stwg wg stwd wd d Lwg Lwd y1 The remarks reported [5] concerning kinetics of the F1 1 F F F evaporation process of foamed polystyrene pattern, on the wg wd 1 dynamics of the mould cavity filling process and changes of gas (2) pressure in the gap enabled the process of pattern evaporation and mould filling to be written as a system of differential equations dy1 (3) 1 presented below: d

150 ARCHIVES of FOUNDRY ENGINEERING Volume 11, Issue 3/2011, 149- 1 5 4 dP c F R T 1,57 P 2 P 2 K d s R T cast iron). Moreover, in simulation tests the following parameters g par p k 3 2 3 (4) were adopted: density of pattern ρ2=20 kg/m , permeability of d y2 y1 F1 F1 l Patm -9 2 refractory coating Kp=7,7·10 m /Pa·s, pressure in mould Pk=100 Pg d y2 y1 2 kPa, ingate section Fwd=0,5 cm . The simulation tests of an effect y y d 2 1 of pouring temperature on the process of mould cavity filling 3 were carried out for AlSi11 silumin (ρ1=2700 kg/m ) and for grey For simulation testing of the lost foam process, and specially 3 cast iron EN-GJL 200 (ρ1=7200 kg/m ). of the effect of pouring temperature on mould cavity filling with casting alloy, the presented mathematical model of the process 3.2.2. Analysis of the results of simulation tests was used along with the author’s own algorithm for calculation of the effect of pattern thickness on, among others, raising of metal Simulation tests were carried out on a model mould shown in column surface in the mould, gas pressure in the gas gap. Tests Figure 1, and parameters comprised in the range of investigations. was conducted for the gray cast iron and silumin. On the basis of the obtained results of calculations, a dependence

was plotted for time-related changes of the main parameters, characteristic of the process of mould filling with molten metal. 3.2. Simulation tests of the Lost Foam Process

3.2.1. The scope of simulation tests

Tests enclosed analysis of the pouring temperature in the range of T1=973÷1123 K (for silumin) and T1=1523÷1723 K (for Y Fwg

wg L

q q

1 y

y Lwd l X

S Fwd

Fig. 1. Schematic representation of the process of mould cavity filling and pressure distribution inside mould

ARCHIVES of FOUNDRY ENGINEERING Volume 11, Issue 3/2011, 149- 1 5 4 151

The effect of silumin pouring temperature on pouring rate is Comparison of average pouring rate for silumin and cast iron shown in Figure 2. Hence it follows that with increasing pouring depending on the pouring temperature is presented in Figure 4. temperature υ1, pouring rate increases, which seems obvious. For For the simulation studies concerning silumin, the increase in pouring temperatures in the range from 973 K to 1123 K was temperature of 150 degrees has increased the pouring rate from obtained the maximum pouring rate from 5 cm/s to about 6.5 cm/s υ1=3,8 cm/s to 5,6 cm/s and is almost proportional. However, in respectively. the case of cast iron for a higher range of pouring temperatures (200 C) were slightly lower an of the pouring rate υ1=9,4 cm/s to 9 do 10,8 cm/s. The temperature of pouring can be a parameter, Pouring 8 which in a quite simple way to control the pouring rate of mould temperature, K depending on the specific casting, on its thickness, shape and 973 7 complexity, and even weight. 998

s / 6 1023

m 12 c

1073 ,

e 5 11 Cast iron t 1123

a Silumin

4 s 10

, 9 o

3 e

a r

2 g

n i

r 7 u

1 o

n 6 a

0 e

M 5 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 4 Pouring time, s Fig. 2. Changes in pouring rate υ1=f(τ) for different silumin 3 pouring temperature T1 950 1050 1150 1550 1650 1750 1000 1100 1500 1600 1700 Pouring temperature, K

The change of the cast iron pouring rate for different pouring temperatures is shown in Figure 3. From the presented results Fig. 4. Mean pouring rate vs. pouring temperature T1 follows that pouring rate is about two times higher in comparison with silumin. Furthermore, character of pouring rate changes in Effect of pouring temperature on the gas pressure in the gas gap is the initial phase of pouring is more dynamic, which is associated shown in Figure 5 (silumin) and Figure 6 (cast iron). This figures with a significantly higher density of cast iron. it follows that with increasing the pouring temperature the gas

18 pressure in the gas gap decreasing. The higher is the pouring 17 temperature, the higher is the gas temperature in the gas gap, and Pouring 16 temperature, K hence the viscosity of gases is lower, making them easy filtration 15 by refractory coating (higher permeability). Thus, the filtration of 14 1523

13 1573 gases through the refractory coating and sand with a higher s

/ 12 1623 permeability, may be to filter the same amount of gas at lower m

c 11 1673

, pressure. Gas pressure in the gas gap is significantly higher by

e 10

t 1723

a cast iron pouring, because at higher temperatures is formed

r 9

g 8 considerably higher amount of gaseous decomposition products of

n i

r 7 polystyrene. u

o 6

P 5 4 3 2 1 0 0.1 0.2 0.3 0.5 0.6 0.7 0.9 1 1.1 1.3 1.4 1.5 1.7 1.8 1.9 0 0.4 0.8 1.2 1.6 2 Pouring time, s

Fig. 3. Changes in pouring rate υ1=f(τ) for different grey cast iron pouring temperature T1

152 ARCHIVES of FOUNDRY ENGINEERING Volume 11, Issue 3/2011, 149- 1 5 4 110 122 Pouring 109 121.5 Grey cast iron

temperature, K a

Silumin P

108 973 k

, 121 P

998 p

, 107

1023 g

p 120.5

s a

1073 a g

106

s 1123

n a

i 120

g 105

e 106

e 104 r

s 105.5

s p

s 103

e n

r 105

a P 102 e M 104.5 101

100 104 950 1050 1150 1550 1650 1750 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 1000 1100 1500 1600 1700 Pouring temperature, K Pouring time, s

Fig. 5. Changes of pressure in the gas gap Pg=f(τ) for different Fig. 7. Mean pressure in gas gap vs. pouring temperature T1 silumin pouring temperature T1

4. Summary 130

127.5 Presented simulation studies in this article enable to analyse

125 of an effect that the pouring temperature to mould filling rate and a

P 122.5 pressure in gas gap. The investigations have proved that with

p 120 decreasing pouring temperature the pouring rate decreases, while

a g

117.5 pressure in the gas gap are increasing. Effect of pouring s

a temperature on the lost foam process is not as significant as other g

115 n

i parameters: density of polystyrene pattern [6], thickness and

112.5 Pouring e

r temperature, K permeability of refractory coating [7], pressure in mould [8]. u

s 110 1523 However, increasing pouring temperature of metal at 150-

s e r 107.5 1573 200 C can be simple way increase the speed of flooding of about P 1623 105 2 cm/s. An increase of the pouring rate ensures correct making of 1673 castings even of very intricate shapes and small wall thicknesses. 102.5 1723 100

0.1 0.2 0.3 0.5 0.6 0.7 0.9 1 1.1 1.3 1.4 1.5 1.7 1.8 1.9 0 0.4 0.8 1.2 1.6 2 Pouring time, s Acknowledgements

Fig. 6. Changes of pressure in the gas gap Pg=f(τ) for different The work was made as a part of the research project No. N N508 grey cast iron pouring temperature T1 443536 financed by funds for science in the years 2009-2011 by the Polish Ministry of Science and Higher Education. This nature of the effect of temperature on the quantity the gas pressure in the gas gap was confirmed in Figure 7 showing the change of mean pressure in the gas gap depending on the pouring temperature. For gray cast iron, the increase pouring temperature References about 2000 causes only slightly (0.2 kPa) decrease the average gas pressure in the gas gap. [1] Clegg A.J.: Expanded-polystyrene Moulding – a Status Report, Foundry Trade Journal International, June 1986, 51- 69. [2] Rossi M., Camino G., Luda M.P.: „Characterisation of smoke in expanded polystyrene combustion”, Polymer Degradation and Stability 74 (2001) 507–512.

ARCHIVES of FOUNDRY ENGINEERING Volume 11, Issue 3/2011, 149- 1 5 4 153 [3] Shivkumar S., Gallois B.: Physico-chemical aspects of the [6] Pacyniak T.: Effect of foamed pattern density on the Lost full mold casting of aluminum alloys, part II: metal flow in Foam process. Archives of Foundry Engineering. 2007 Vol. simple patterns”, AFS Trans. 95 (1987) 801–812. 7 Issue 3/2007, 231-236. [4] Moll and D. Johnson D.R.: Proceedings of the international [7] Pacyniak T.: Effect of refractory coating in the Lost Foam conference on advanced casting technology, 175-187; 1987, Process. Archives of Foundry Engineering, 2009, Vol. 9 nr Metals Park, OH, ASM International. 3/2009, 255-260. [5] Pacyniak T.: Teoretyczne i technologiczne podstawy [8] Pacyniak T., Kaczorowski R.: Effect of pressure in mould procesu wytwarzania odlewów metodą pełnej formy, cavity during underpressure casting. Archives of Foundry Zeszyty Naukowe Nr 985 Politechnika Łódzka 2006. Engineering. 2010 Vol. 10, Issue 4, 157-162.

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