COMPOUND PROCESS INVESTMENT CASTING Compound process investment casting is between silica sol investment casting and water glass process investment casting.During the sand shell preparation,compound process uses finer sand particles derived from silica sol process for the first 2 innerlayers,and then use coarse sand particles derived from water glass process for the other outer layers. It has better casting tolerance and surface roughness than water glass process but with lower price than silica sol process. Usually water glass process pours carbon steel and low alloy steel,and silica sol process pours stainless steel and high alloy steel. Compound process can pour pour stainless steel and other high value low alloy steelat more affordable prices.