Mould shell damage and falling off may lead to casting surface slag and internal inclusion defects

which directly affect the product quality. The use of water washing process in production can ensure the cleanliness of mould shell

effectively avoiding the defects. One of shell materials widely used in investment casting of titanium alloy is surface layer of rare earth powder+zirconium glue+zirconium sand with the back layer of zirconium powder+silica sol+Mullite（1#glue）

and the other is surface layer of rare earth powder+neutral glue+zirconium sand with the back layer of mullite powder+silica sol +Mullite（2# glue）. The water washing testing was conducted on both materials

and the results indicate that the shell of 1# glue is not suitable for washing due to the remelting phenomenon

while the shell of 2# glue can be washed. By comparing the drying effect at different holding temperature and holding time

the amounts of surface and internal defects are decreased by above 20% after optimizing the shell washing process.