Production of High-Quality Cast Iron in a Gas Cupola with the Use of Induction Crucible Furnace

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 7, July 2018, pp. 990–996, Article ID: IJMET_09_07_105 Available online at http://iaeme.com/Home/issue/IJMET?Volume=9&Issue=7 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

PRODUCTION OF HIGH-QUALITY CAST IRON IN A GAS CUPOLA WITH THE USE OF INDUCTION CRUCIBLE FURNACE

Vladimir Grachev A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences, 31, Bldg 4, Leninsky prospect, 119071, Moscow, Russia

ABSTRACT The author has studied the process of cast iron smelting in cupola and induction furnaces and has proposed a design of gas cupola furnaces and a technology of smelting high quality cast iron. The cupola furnace properties have been studied. It has been demonstrated that the properties of cast iron made in a gas cupola furnace were better, its structure and composition were more suitable for critical casting that was achieved by the decrease in the detrimental content of sulfur and by the appropriate content of nitrogen and oxygen in the microstructure of solidified cast iron. It has been noted that a combination of gas cupolas and induction furnaces was particularly effective. The article represents the results of introduction of the both furnace types as progressive methods of cast iron smelting. Keywords: gas cupola furnace, induction furnace, cast iron smelting, production of high quality cast iron, duplex process “gas cupola – induction furnace”. Cite this Article: Vladimir Grachev, Production of High-Quality Cast Iron in a Gas Cupola with the Use of Induction Crucible Furnace, International Journal of Mechanical Engineering and Technology, 9(7), 2018, pp. 990–996. http://iaeme.com/Home/issue/IJMET?Volume=9&Issue=7

1. INTRODUCTION A cupola has remained a major unit in the foundry industry used for cast iron smelting all over the world for many years. The use of such cupolas has been associated with a distinctive gas and dust pollution of air in the shop and the adjacent areas [1, 2, 3]. Getting high-quality cast irons in cupolas is associated with certain difficulties, making it necessary to resort to electric smelting, which is much more expensive. For example, the Volga Car-Making Plant (VAZ) and many foreign plants have chosen electric smelting. However, Likhachev Car-Making Plant (ZIL) has chosen using gas cupolas [4]. Fig. 1 shows the world's first gas cupola. It has been operated at the Penza Compressor Plant since November, 2, 1963, i.e., already for 53 years.

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2. THE PROCESS

Figure 1 The world's first gas cupola with a step-shaped shaft and the productivity of 7 t/h. Authors: Grachev V.A., Chernyi A.A., et al. Certificates of authorship: CA No. 949295; 209656; 251776; 293487; 167613; 256930; 250368; 293489; 873739; 187251; 238105; 941823; 243151; 257700. Implemented at the Penza Compressor Plant and other plants in Russia The process where original melt is prepared in cupolas, and finishing the cast iron in order to bring it up to a required quality level is performed in an electric furnace, is considered to be the most promising one. Therefore, at the Penza Compressor Plant, where the world's first gas cupola with the productivity of 7-10 t/hour has been designed and is still being operated, there are induction electric furnaces installed next to it.

3. EXPERIMENTAL

Figure 2 Smelting department of the foundry shop of OJSC "Penzokompressormash" Four types of gas cupolas have been designed and put into operation over the long history of designing and implementing gas cupolas - and the author himself has been already engaged in this process for 55 years, i.e. since 1961 (Fig.3).

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Figure 3 Gas cupolas: step-shaped (a), with partitioning (b), with external chamber (c), with heterogeneous checker (d) Over a long period of time, smelting of cast iron has been conducted both in coke and in gas cupolas in the foundry shop at the plant. The same metal components of the charge have been used. This provided a unique opportunity of comparing the quality of cast iron, including its gas content. In order to determine gas-content of cast iron, cylindrical specimens having the diameter of 10 mm and the length of 12 mm were cut out from samples and castings. Gas-content of cast iron was determined using a vacuum extraction method with heating the above at a physico-technical research unit of the "Dynamo" plant in Moscow, Russia. Table 1 presents the results of the analysis relating to the gas-content of cast iron smelted in the coke cupola, while Table 2 presents the same results for gas cupolas.

Table 1 Total content of gases in cast No. of Oxygen, Oxygen, Hydrogen Hydrogen Nitrogen Nitrogen, iron from 3 3 3 analysis cm /100 g wght. % cm /100g wght. % cm /100 g wght. % coke cupola, V, cm3/100 g 1 18.35 1.31 0.00187 5.50 0.000492 11.54 0.014444 2 15.03 1.00 0.00143 5.21 0.000464 8.82 0.011000 3 23.37 2.06 0.00294 10.05 0.000899 11.26 0.01406 4 14.29 1.65 0.00236 4.54 0.000405 8.10 0.01010 5 9.95 0.82 0.00117 2.28 0.000204 6.85 0.00858 6 24.56 2.05 0.00293 6.91 0.000618 14.6 0.01822 7 19.67 1.49 0.00213 3.98 0.000355 14.20 0.17778 8 24.83 1.34 0.00192 3.49 0.000313 20.00 0.02500 9 39.47 3.85 0.00291 9.62 0.000860 26.00 0.03250 10 16.32 1.26 0.000180 4.26 0.000380 10.80 0.01350 Avg. value 20.584 1.683 0.002146 5.584 0.000499 13.217 0.016518 When comparing the above data with the data from Table 2, it is possible to arrive at the conclusion that the content of gases in the cast iron smelted in gas cupolas does not exceed the content of gases in the cast iron from coke cupolas, and in an overwhelming majority of cases, it is significantly lower. This may be explained by a number of reasons associated with the peculiarities of design of the Penza Compressor Plant gas cupola, and those of the cast iron smelting process [15, 20]. The gas cupola has a shallow basin for liquid cast iron at the hearth bottom of the overheating chamber.

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Table 2

. t . t t h

g g g n , g

n e

Quantity of wg 0 n w e 0 0

e 0

, g 0 0 n , o g extracted 1 o 1 1 n e / r n / / % % % y r No. of analysis e g 3 e d t 3 3 x gases, gm3/100 g o g y o m r m m O y Ni r c H c c g d x t y O Ni H 102 9.67 2.00 0.00286 4.00 3.76 0.00471 103 10.99 1.16 0.00166 7.28 2.55 0.00319 104 9.65 0.90 0.00128 6.32 2.43 0.00303 0.000357 105 16.65 1.23 0.00176 10.98 4.44 0.00554 0.000650 106 8.64 1.17 0.00168 4.54 2.93 0.00366 0.000566 107 13.01 1.51 0.00216 5.69 5.81 0.00728 0.000980 108 16.11 1.36 0.00194 6.32 8.43 0.01055 0.000405 109 13.66 1.41 0.00202 5.76, 6.49 0.00811 0.00050 110 9.54 0.62 0.00089 5.95 2.97 0.00373 111 14.28 0.95 0.00136 10.28 3.05 0.00382 Avg. Value 12.229 1.231 0.001761 6.712 4.286 0.00536 Based on the data available, it is possible to conclude that the gas cupolas of the Penza Compressor Plant make it possible to smelt cast iron with a reduced gas content, which improves the properties of the above. The quality of castings significantly increases upon transition from coke smelting of cast iron to gas smelting the above. This is primarily due to the fact that in metal, smelted in the gas cupolas, the content of sulfur is 3 – 4 times lower compared to the metal smelted in the coke cupolas. The production smelting analysis has shown that, when using the same charge materials as in coke cupolas, cast iron produced in gas cupolas possesses higher strength and density. As can be seen from the plot presented in figure a, in case of smelting cast iron Sch 21 – 40 in gas cupolas, the tensile strength limit is more than 21 kg/mm2. The produced metal is dense and has a fine-grained structure. Hardness of cast iron is closer to the upper limit for Sch 21 – 40 grade (figure b), which insures higher wear-resistance properties of cast iron. The hydro test of the castings using cast iron from gas cupolas has shown a high degree of tightness of the cast iron. The cast iron produced in gas cupolas is used for making such castings as cylinders, frames and other basic parts of compressors, as well as small thin-walled castings (Fig. 4).

Figure 4 Assembly view of the smelting department of OJSC "Penzokompressormash" Thus, the operation of gas cupolas in the production environment shows that they make it possible to smelt quality cast iron with high mechanical properties, suitable for casting critical machine components. The implementation of gas cupolas culminated in their introduction at ZIL (Fig. 5).

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Figure 5 Gas cupola, productivity of 20 t/h, implemented at AMO-ZIL. Specifications: natural gas consumption 1,800 – 2,100 m2/h consumption of air in the process of gas combustion, at А = 1.0 – 18,000-21,000 m2/h, temperature of liquid cast iron – 1,480-1,530°С, composition of refractory checker: chamotte refractory scrap (size of the sides: no less than 65 mm) – 33%, high-alumina refractory scrap (size of the sides no less than 120 mm) – 33%, graphite electrodes scrap (pieces of 100-300 mm) – 34%. Height of the refractory checker – 1200 mm, weight of the refractory checker – 5.6 t, number of combustion units – GVK 150-type gas burner – 12 pcs.

4. RESULTS AND DISCUSSIONS Induction crucible furnaces have been used for smelting cast iron since the second half of the 20th century, however, such type of smelting did not come into a widespread acceptance. A gas cupola remained a basic melting unit. An electric induction furnace is a pretty complex unit, and it works only in a periodic mode. Technical progress in the machine-building industry associated with the increase in reliability and durability of machines, and the reduction of their weight, places ever- increasing demands on the quality of cast iron castings resulting in improvement of the cupolas design. Cupolas are equipped with recuperators for air preheating, powerful fans, etc. However, despite significant changes in the cupolas’ design and the advantages of hot blast, in many cases cupola iron still does not meet the requirements as to the limits of variation of chemical composition, the content of harmful impurities, and the quality of metal. For smelting cast iron, the use of commercial-frequency induction furnaces is increasingly gaining acceptance. Starting from the late 1950s, the smelting of cast iron in electric furnaces, particularly induction furnaces, in the industrially developed countries, began to replace cupola smelting. From 1963 through 1968, the number of operating electric furnaces in the USA for cast iron smelting amounted to 4,000 units. 70 % of them were represented by commercial-frequency induction furnaces. Over the past 6 to 7 years, the number of cupolas in USA reduced almost by half, and the number of electric furnaces increased 2.5 times. The replacement of cupolas by electric furnaces may also be observed in Western Europe. In the USSR, the first shop equipped with induction furnaces instead of cupolas was put into operation at Kaunas cast iron foundry in 1963, i.e. almost simultaneously with gas cupolas. At OJSC "Penzokompressormash", both gas cupolas and electric induction furnaces have been used. The principal advantage of induction cast iron smelting as compared to cupola smelting lies in the possibility of controlling the overheating process relating to cast iron within a wide range of temperature and time, as well as performing deeper metallurgical treatment of the melt, accurately maintaining the chemical composition, and producing a high quality cast iron. The advantages of such furnaces also include the possibility of remelting non-briquetted cast iron turnings to 40% of metal charge, sheet-iron scraps, which reduces the consumption

http://iaeme.com/Home/journal/IJMET 994 [email protected] Production of High-Quality Cast Iron in a Gas Cupola with the Use of Induction Crucible Furnace of pig iron and scrap. At smelting, the losses of Si and Mn, and the costs of charge material decrease considerably, while the total loss does not exceed 2%. However, service charge increases (Table 3).

Table 3 Costs, % Cost items Coke cupola Gas cupola Induction furnace Charge materials 60.71 56.08 46.62 Fuel (process energy) 10.50 2.09 14.01 Materials (excl. the charge) 0.56 0.74 0.78 Electric furnace operation 0.31 0.12 0.76 Total 100% 100% 100% Nevertheless, cupolas are being increasingly [4 – 6] replaced by induction furnaces (Fig. 6).

Figure 6 Growth in the production of cast iron smelted in induction furnaces.

5. CONCLUSION When smelting cast iron in induction furnaces, the content of S in the melt decreases drastically that facilitates the production of nodular cast iron. The sanitary-hygienic conditions are improved. Release of harmful gases and dust is reduced, particularly if compared to the coke cupolas, which is especially important for urban and residential areas, as induction furnaces pollute the air manifold less as compared to the cupola process that requires bulky and expensive means of purification. Specific consumption of refractories is also reduced: in case of induction furnace, it amounts to 3 kg/t; in case of an acid-lined arc furnace, it amounts to 17.6 kg/t; and in case of a cupola, it amounts to 27 kg/t. It is lower for a gas cupola, as it may be operated without need for repairing during 2 to 3 weeks and it amounts to 13.6 kg/t. Atmospheric emission of dust from a gas cupola is 20 times lower when compared to a coke cupola, CO content is 50 times less, whereas SO2 content is 11 times less. A smelting department equipped with gas cupolas requires less capital expenditures during the reconstruction of foundry shops, and the costs of reconstruction of the existing coke cupolas are low. The use of induction electric furnaces for smelting cast iron is progressively increasing in the foundry industry. Conflicts of interests: none. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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