Stainless Steel Precision Casting Technology is Maturing, But It Needs to Be Improved Urgently

At present, there are many mature technologies and processes in stainless steel precision parts casting.

Silica sol shell technology. Silica sol shell-making process is widely used in the more sophisticated internal combustion engine parts foundry industry. The coating used in this method has good stability, does not need chemical hardening process, and has high temperature resistance and better deformation resistance. However, the disadvantage of this technology is that the temperature and wettability of wax pattern is poor. Although it can be improved by adding surfactants, it will increase investment to a certain extent.

Water glass shell technology. The technology of sodium silicate shell was invented very early, and it was introduced from the Soviet Union in 1950s and 1960s in China. The technology has low cost, relatively simple operation, and low requirements for raw materials. It is widely used in stainless steel precision parts casting. However, compared with the silica sol shell-making process, the biggest problem of this technology is that the surface quality of the castings obtained is general and the dimensional accuracy is low. However, due to its cost advantages, this technology is still used in some civil or low-precision internal combustion engines in China. Since the introduction of this technology, Chinese researchers have made considerable improvements on it, mainly in improving shell coatings, optimizing hardeners and adopting composite shell.

The main improvement of the improved shell coating is to add a certain amount of refractory clay to the back coating of the shell, which greatly improves the strength of the shell and realizes single shell roasting and injection. In the aspect of optimizing hardener, ammonium chloride is commonly used as traditional hardener, but this material will release a large amount of ammonia and nitrogen oxide gas in the casting process, which will pollute the atmosphere. Therefore, the hardener is changed to aluminium chloride solution, and then to aluminium chloride crystallization. The effect of this hardener is similar to that of ammonium chloride.

In the use of composite shell, there are some defects in the surface quality of water glass coating shell. Therefore, many castings are cast in the form of multi-layer mold composite, on the one hand, it saves costs, on the other hand, it also improves the surface quality of castings.

In addition, in the development of new technology, there are self-priming casting process, foam plastic mold and investment mold shell casting process. However, these processes have obvious advantages and disadvantages in some respects, and they still need continuous improvement by scientists and technicians in the future.

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