The Investment Process
The wax is then coated with an “investment” - a liquid refractory ceramic material. It is a colloidal silica material that was developed in part by NASA and in part by the metal casting industry. Anywhere from 6 to 20 layers are applied creating a stable mold that can take from a few days to several weeks to make. Our investment material is in two distinctive liquids - a primary coat (yellow in color) that is designed to capture all the details from the wax pattern and a deluxe coat (either grey or orange in color) that builds up quickly and is primarily for structure and support. The tanks that hold the liquid slurry must be stirred regularly to keep the liquid from hardening. The two motors in each slurry tank have propellers on them that stir the tank for twenty minutes at a time, 24/7, 365.
Each liquid layer also has a layer of silica sand added to it before it dries for additional strength. (This type of silica is NOT the sharp edged silica that can cause silicosis, it is rather a smooth edged silica similar to sand you might find on a sea shore). Our sand is kept in large round vats which have air forced up through the bottom, thus creating a fluidized sand bed. This allows us to “dip” each piece into the sand as though we were dipping it into liquid.
Once the correct amount of material is built up around the wax pattern, we drill expansion holes into the ceramic shell material for the burn-out of wax and cut down to the opening of the sprue cup exposing the wax. The dried shell is then delivered to the burn-out for dewaxing and curing. The shell room is humidity and air controlled. We do not allow our visitors to walk through in an attempt to maintain the best possible atmosphere for our shells. You may view the room through both of the doorways.