Development and application of shell casting in China

Although the application of shell casting in China is more than ten years later than that in foreign countries, it has been nearly 40 years since the beginning of experimental research. As early as the mid-1950s, the experimental research work of shell mold casting was jointly carried out by the former Technology Institute of the first machinery department and Tsinghua University, and achieved good results. At that time, the resin for shell casting was unable to guarantee the supply and expensive, and the process and equipment were just starting, so it was stopped in the early 1960s. By the mid-1960s, the first automobile factory and other units began to carry out targeted experimental research on shell mold casting on the basis of the original in China, trying to apply this new process to mass casting production as soon as possible. In the late 1960s, the 2000 shell molding sand (coated sand) mixing device of American fordath company was imported. Based on a large number of experimental studies, a set of sand mixing process and shell mold (core) production process of thermal coated sand are formulated. Thus, the problems of material, technology and equipment of shell casting are basically solved, which lays a good foundation for the application and development of shell casting.

The application scope of shell mold casting in China is roughly the same, which is mainly used in mass casting production of automobiles, engineering machinery, tractors and engines. There are also many factories that use shell casting to produce single piece and small batch castings. The application of shell core (mold) method to representative castings includes:

Ⅰ. Engine casting: the manufacturing quality and service life of the engine are directly related to the quality of the casting. Castings such as engine cylinder block, cylinder head and exhaust pipe require good surface finish and dimensional accuracy of the inner cavity. The shell core method can be used to make hollow thin-walled sand cores with high strength, which can not only ensure the smoothness and dimensional accuracy of castings, but also reduce the functional quality of castings and save metal materials and modeling materials. Since 1987, Tianjin internal combustion engine factory introduced aps-h4 static pressure molding line of Japan Xindong company and shell core machine of langsu company to produce Dafa and Xiali Automobile Engine Castings, the first and second automobile factories, Beijing internal combustion engine general factory, Shanghai Diesel Engine Factory and Changzhou Diesel Engine factory have also used shell mold (core) method to produce engine casting sand cores.

Ⅱ. Auto parts castings: with the development of auto parts castings to “precision and cleanliness” with high strength, high dimensional accuracy and high-definition cleanliness, the castings of supercharger compressor housing, turbine housing, crankshaft, camshaft and other auto key parts have also been produced by shell mold method, which plays a key role in improving the dimensional accuracy and surface finish of castings.

Ⅱ. Hydraulic torque converter castings: core making is the key to obtain high-quality hydraulic torque converter castings. The casting shall not only ensure the geometric dimension and position accuracy of the three-dimensional distorted shape of the blade space, but also ensure the surface finish of the blade. Using hot core box and grease sand core, it is often difficult to ensure the technical requirements of castings. Shandong Bulldozer General Factory has introduced the casting technology of metal mold solid shell core assembly of Komatsu company in Japan to produce two types of hydraulic torque converters with domestic materials, processes and equipment. Through the test of Tianjin Construction Machinery Research Institute, all six main performance and technical parameters meet Komatsu kes acceptance standard. The three wheel casting accuracy of hydraulic torque converter in this factory is in the leading position in China.

Ⅲ. Hydraulic parts casting: hydraulic parts are important basic components with many varieties and specifications, requiring precision pressure resistance and high cleanliness of inner cavity. High quality sand core is the key to obtain high-quality castings, especially valve castings with sprue. Yuci Hydraulic parts factory and Beijing hydraulic parts foundry have introduced the hydraulic parts casting technology of Vickers and Rexroth respectively, and the hydraulic castings produced have met the technical requirements. The former adopts air impact line modeling and shell (core) production line to make mold (core); The latter uses high-voltage molding line, imported automatic shell core machine and domestic semi-automatic shell core machine.

Ⅳ. Oil seal ring casting: the oil seal ring casting requires smooth surface, accurate size, small deformation, less casting defects on the working face, high hardness and good wear resistance on the working face. In the past, investment casting, pressure casting and powder metallurgy hot die forging were widely used to produce oil seal ring castings in China, which can basically meet the requirements; However, there are many shortcomings, such as many processes, high scrap rate, high cost and difficult to produce large-diameter rings. The shell mold and core sand block produced by shell mold method have high strength, are not easy to deform, can be poured in series, and the internal quality of castings is good. Shanghai Pengpu machinery factory and the first Design Institute of the Ministry of mechanical and electrical engineering have absorbed and digested the casting technology of oil seal ring shell and core stack introduced with the manufacturing technology of Japanese bulldozers, and produced high-quality castings of five specifications with domestic materials and equipment.

The castings produced by shell mold method also include crankshaft, camshaft, radiator, belt covering plate and high-power diesel engine. In recent years, the application of phenolic resin in the formation of mold and casting shell has been studied intensively.

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