Skin Dried Moulding:
Skin-dried or air-dried molds are sometimes preferred to green sand molds where assurance is desired that the surface moisture and other gas-forming materials are lowered. By skin drying the face of the mold after special bonding materials have been added to the sand molding mixture, a firm mold face is produced similar to that obtained in dry sand practice. Shakeout of the mold is almost as good as that obtained with green sand molding. Skin-dried molds are commonly employed in making medium-heavy and heavy castings.
Generally, the surface of the mold is washed or sprayed with a refractory mold coating. The most common method of drying the refractory mold coating uses hot air, gas or oil flame. Skin drying of the mold can be accomplished with the aid of torches, a bank of radiant heating lamps or electrical heating elements directed at the mold surface.
- This process reduces surface moisture and other gas-forming materials from mold. It can commonly be used in the production of medium-heavy to heavy castings.
- These molds are more expensive to produce. Mold sections must be completely dry and cool prior to assembly.