It played evident role for production of investment castings since middle-temperature wax

shell mold made of sol silicate-ZrO2 slurry-ZrO2 face layer and dewaxing by vaporization were used by the end of 1980’s. However

ZrO2 sand （powder） possesses expensive price and limited resource

resulting in the high production cost. The shell-making method of special sand （powder） substituted for ZrO2 sand （powder） was described. The surface roughness and size precision of the investment castings are very desirable

obviously reducing the production cost.