29-05-2012, 12:57 PM
SPECIAL CASTING TECHNIQUE
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CASTING
Casting is the process of producing metal component parts of desired shape by pouring molten metal into the prepared mould cavity and then allowing the metal to cool and solidify. The solidified part of the metal is called CASTING.
SPECIAL CASTING TECHNIQUE
NEED:-
Sand moulds which are widely used are single purpose moulds as they are completely destroyed after casting has been removed from the mold box and also there are certain limitations possessed by conventional sand casting techniques which necessitates development of special casting technique.
INVESTMENT MOLD CASTING
In investment casting, a wax pattern is placed inside a metal
cylinder called a flask. Wet plaster is poured into the cylinder around the
Wax shape. After the plaster has been hardened the cylinder containing
pattern and is placed in a kiln and heated until the wax is vapourised.
After the wax is fully burnt out the flask is removed from the oven and
molten metal is poured in to the cavity left by wax. When the metal is
cooled plaster is chpped away and casting is revealed.
This casting process is appropriate to cast sculptural objects or
engineering shapes with complex geometry. Some shapes which is difficult to
machine are more easily cast by this process.
One big advantage of investment casting is that it can allow for undercuts
in the pattern, while sand casting does not .
Make a mold.
A mold is the negative shape of your pattern
The mold is created from a mixture consisting of casting plaster, sand, and water.
The dry mixture of 1 part 30-minute casting plaster and 2 parts 30-grit sand is known as 30-30 mix
When it is mixed with water, it forms viscous slurry.
After about 30 minutes, the mixture “Sets up” or becomes solid.