Plaster Moulding:

It is a specialized casting procedure utilized to cast non-ferrous materials. Castings produced by this procedure have smoother surfaces and larger dimensional accuracy than attained in permanent moulding or sand moulding. In this procedure, a plaster, typically calcium sulphate or gypsum is mixed with talc, asbestos, sand and sodium silicate and water to make slurry. This slurry is sprayed on the polished surfaces of the pattern halves (typically brass). The slurry sets in less than 15 minutes to make the mould. The mould halves are extracted from the pattern carefully, and then dried in an oven.

The mould halves are assembled carefully, along with the cores. The molten metal is poured in the moulds. Later than the metal cools down, the plaster is broken and the cores washed out. Usually Parts cast are small to medium size, ranging in weight from 30 g to 7 kg. The section thickness might be as short as 0.6 mm and tolerances are 0.2 % linear. The draft allowance is 0.5-1.0 degree. The surface terminate of 1.25 µm to 3 µm can be attained.