What are the common shell making processes for precision castings

At present, there are four widely used shell making processes in domestic precision casting production:

A. Water glass shell; B. Composite shell; C. Silicone sol shell (low-temperature wax); D. Silicone sol shell (medium temperature wax). The first three options all use low-temperature wax (mold).

1. The process of water glass shell has a production history of nearly 50 years in China, and its factory number still accounts for over 75% of China's precision casting manufacturers. After half a century of unremitting efforts from colleagues in the precision casting industry, the application and research of water glass shell technology have reached a high level. Over the years, due to the improvement of back layer shell refractory materials and the promotion and application of new hardening agents, the strength of water glass shell has increased exponentially. The surface quality, dimensional accuracy, and yield of castings have greatly improved, and they still occupy a large market share and replace foreign sand castings for mass export. The advantages of low cost, short production cycle, excellent shelling performance, and high breathability are still unparalleled by any other shelling process to this day.

2. In order to overcome the shortcomings of the aforementioned water glass shell, many factories currently The second layer is converted to zircon and mullite silica sol shell. The back layer still adopts the original water glass shell process. It is an improvement plan that combines the excellent surface quality of silicone shell with the advantages of low cost and short cycle of water glass. Compared with water glass shell, its casting surface quality has been greatly improved, with reduced surface roughness, reduced surface defects, and reduced repair rate.

3. The process of silica sol (low-temperature wax) shell molding is in line with national conditions, and has greater adaptability and advantages (compared to medium temperature wax) when casting medium and large castings weighing over 1kg, especially 5kg. Generally speaking, the quality requirements for medium to large castings, especially the requirements for surface roughness, dimensional accuracy, and geometric tolerances, are not too high, and it is not necessary to use high melting point medium temperature wax. Medium temperature wax requires high pressure (greater than 6-7MPa) or liquid wax pressure injection into wax molds, resulting in high equipment investment.

4. Silicone sol (medium temperature wax) shell is a commonly used precision casting production process, which has The quality of castings The repair rate is particularly suitable for small and medium-sized parts (2-1000g) with high surface roughness requirements (Ra0.8-3.2) and high dimensional accuracy (CT3-CT5 level). However, due to equipment and cost limitations, it is less commonly used for medium to large items (5-100kg).