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Casting
Casting involves melting metal and
pouring it into a mould of the desired shape. In schools this is normally limited to
aluminium.
Stages in Casting
1 A wooden pattern is made which is the same shape as the metal article you require.
2 The pattern is placed inside a box called a drag (which is open at both top and
bottom).
3 A powder called parting powder is sprinkled onto the pattern.
4 A special type of sand is rammed round the pattern making sure there are no gaps. (the
sand which is called green sand is damp and is capable of forming very delicate shapes
without collapsing).
5 After the sand covers the mould it is rammed to fill the drag completely and the uneven
top surface is removed with a metal bar called a levelling bar.
6 The drag is then turned over to reveal the bottom of the pattern.
7 More parting powder is placed on the sand and exposed part of the pattern then another
box (called a cope) is placed over the drag.
8 This box is then filled with sand, but before doing so two tapered wooden 'bars' called
sprues are placed into the cope so that after filling two holes (one either side of the
pattern) are present all the way through the thickness of the sand.
9 The cope is then lifted from the drag. The pattern and sprues are lightly tapped to
loosen them from the sand and then they are lifted out.
10 After the sprues and pattern have been removed channels are cut in the drag sand to
form a way for the molten metal to run into the mould.
11 Metal which has been melted in a crucible is then poured into one of the sprue holes.
When molten metal starts coming out of the second sprue hole the mould is full and pouring
can cease.
12 After cooling the sand is broken away from the now solid metal and you are left with
the shape which the wooden pattern made in the sand, but this time it is made of metal.
Stages in Casting
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