Lost-wax Casting - Casting Jewellery and Small Parts

Casting Jewellery and Small Parts

The methods used for small parts and jewellery vary a bit from those used for sculpture. A wax is obtained, either from injection into a rubber mold, or it is custom-made in wax. Occasionally, a custom-made wax might be molded in rubber first as insurance against the loss of the unique wax and related labor costs incurred in carving it. The wax or waxes are sprued and fused onto a rubber base, called a "sprue base". Then a metal flask, which resembles a short length of steel pipe that ranges roughly from 1.5 to six inches tall and wide, is put over the sprue base and the waxes. Most sprue bases have a circular rim which grips the standard-sized flask, holding it in place. Investment (refractory plaster) is mixed and poured into the flask, filling it. It hardens, then is burned out as outlined above. Casting is usually done straight from the kiln either by centrifugal casting or vacuum casting.

The lost-wax process can be used with any material that can burn, melt, or evaporate to leave a mold cavity. Some automobile manufacturers use a lost-foam technique to make engine blocks. The model is made of polystyrene foam, which is placed into a casting flask, consisting of a cope and drag, which is then filled with casting sand. The foam supports the sand, allowing shapes that would be impossible if the process had to rely on the sand alone. The metal is poured in, vaporizing the foam with its heat.