PLASTER MOLDING PROCESS AND ITS ADAVANTAGES

In this method, the mold is prepared in gypsum or plaster of Paris. In practice, The plaster of Paris is mixed with talc, asbestos, fibers, silica flour, and a controlled amount of water to form a slurry. This plaster slurry is poured over the metallic pattern confined in a flask. The mold is vibrated and the slurry allowed to set. The pattern is removed after about 30 minutes when the setting is complete and the mold is dried. and backed by slowly heating it to about 200*C in a conveyor oven. Inserts and cores are placed, cope and drag matched by guide pins. Molten metal is then poured into the mold. Finally, the casting is cooled in the mold, shaken out and the mold is destroyed. Castings are then trimmed of gates, sprues and flash.

Advantages of Plaster Molding are :

1. Warping and Distortion of thin sections can be avoided since plaster has no chilling tendency due to low rate of heat conductivity.

2. A high degree of dimensional accuracy and surface finish is obtained, and machining cost, is therefore , eliminated.

3. Highly suitable for reproduction of fine form and detail as are necessary for ornamental castings , statues, jewelry, etc. besides being used for engineering components.

Limitations of Process are :

1. Low Permeability of Plaster of Paris.

2. Suitable only for non-ferrous castings owing to the fact that plaster of Paris destroys at 1200*C

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