The ordinary silica sol type shell has low wet strength, long drying time and long shell making period. The quick drying silica sol shell not only has higher wet strength, high temperature strength, but also has low residual strength and is easy to shell out. Therefore, using a quick-drying silica sol as an adhesive can effectively improve the shelling performance of the shell. The use of quick-drying silica sol as an adhesive can effectively improve the shell shelling performance and shorten the shell-making cycle, and has been widely used abroad. Although China's current high cost of dry silica sol, it is difficult to be widely used. However, the use of fast-drying silica sol as a binder is the technical direction and development trend for improving the shelling performance of silica sol shells in the future.

Fused Silica as Refractory Material The silica sol type shell consists of a binder and a refractory material. The SiO2 content in the silica sol, the characteristics and combination of the refractory materials determine the high temperature strength and residual strength of the shell, and it is an effect on the shell expulsion. major factor. The shelling properties of various refractory materials are different and must be targeted for production. Most of the refractory materials have a positive proportional relationship between the high temperature strength and the residual strength, except for the exception of fused silica. The good shelling performance is an important factor in the sudden emergence of fused silica. The application of precision casting is the amorphous SiO2 melt produced by the rapid cooling of quartz sand after melting, and the residual strength of the shell is much lower than that of aluminum-silicon materials. Because fused silica will crystallize at about 1200°C, and transform into cristobalite, about 70% of fused silica can transform into cristobalite at the pouring temperature. When the shell temperature drops to about 300°C, the cristobalite transforms from the high temperature type to the low temperature type. At the same time, the volume changes abruptly. The shell generates many cracks and the intensity drops sharply. It is clear that the shelling property is greatly improved. In addition, if aluminum-silicon type shells are subjected to a chemical cleaning method such as caustic digestion, alkali explosion, or the like in the subsequent treatment process, the alkali can dissolve only SiO2 in the binder and cannot dissolve refractory aggregates. However, for the fused silica type shell, the alkaline solution can be eroded and dissolved by the binder and the refractory granules. Therefore, the choice of fused silica as a refractory material also facilitates the chemical process such as caustic digestion and alkali explosion of castings, and improves the production efficiency after precision casting.

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