Characteristics of four kinds of shell making processes for precision casting
At present, the four shell-making processes widely used […]
At present, the four shell-making processes widely used in the domestic precision casting industry are water glass shell, composite shell, silica sol shell, and silica sol shell. Next I will introduce the difference between them.
1 water glass shell
This process has been in production for nearly 50 years in China. After years of unremitting efforts by colleagues in the fine casting industry, the application and research of the water glass shell process has reached a high level. Over the years, due to the improvement of back-shell shell refractories and the popularization and application of new hardeners, the strength of water-glass shells has doubled. Low cost, shortest production cycle, excellent shelling performance and high gas permeability are still beyond the reach of any other shell process.
2 composite shell
Compared with the water glass shell, the surface quality of the casting has been greatly improved, the surface roughness is reduced, the surface defects are reduced, and the repair rate is decreased. It can be applied to high alloy steels such as stainless steel and heat resistant steel. The production cycle is much shorter than the low temperature wax-silica sol shell and is similar to the water glass shell.
3 silica sol (low temperature wax) shell
This process conforms to the national conditions and has greater adaptability and superiority when casting more than 1kg, especially for large and medium-sized castings of more than 5kg. It is more stable than the composite shell, especially the dimensional accuracy of the casting. Because it has no water glass, the shell has high temperature performance. After firing at 1000-1200 °C, the shell has high gas permeability and strong creep resistance, which can be applied to Thin-walled parts, small and medium-sized parts with complex structure, can also produce extra-large parts weighing 50-100kg, such as water pump, impeller, diversion shell, pump body, ball valve body, valve plate and so on. For thin-walled small and medium-sized parts or large pieces, it can be directly poured in front of the furnace by using a fork shell or a lifting shell, and a high yield can be obtained.
4 silica sol (medium temperature wax) shell
This is the internationally popular production process of precision castings. It has the highest casting quality and the lowest repair rate. It is especially suitable for small and medium-sized parts and extra small parts (2-1000g) with high surface roughness and high dimensional accuracy. However, due to equipment and cost constraints, it is less used in medium and large parts (5-100kg).