With the development of investment casting industry

the performance

especially the high performance of the silica sol shell was been highly required

so it was necessary to improve the quality of the shell. It was important to improve the quality of shells and castings by investigating the high temperature performance of the shell. Surface change and residual strength of the shell baked at 900

1

600 ℃ were analyzed comparatively. The results show that existence of impurities in the refractory materials is closely related to the change of surface morphology of the shell. Fe

Mg

Ca

Na

and K in the refractory material can react with Al2O3 and SiO2 during baking process at high temperature to generate the low point phase

leading to the change of shell surface morphology and possible soft behavior of shell at high temperature. To ensure high surface quality and desirable de-shell ability and to reduce the possibility of high temperature softness of shell during pouring process

impurities in the shell should be strictly controlled. Residual strength of the shell exhibits basically stable at 900

1

200 ℃

and residual strength of the shell is increased at 1 200

1

500 ℃ as a result of mullite secondary reaction and effects of impurities

existing in the possibility of high temperature softness. Residual strength is greatly increased due to recrystallization of shell at above 1 500 ℃

resulting in the deterioration of de-shell performance.