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PATTERN:
Pattern is the model of the required casting made in wood, metal, plastic, etc
It is used to produce the mould cavity in sand .
Types of Patterns :
Solid pattern
Split pattern
Loose piece pattern
Match plate pattern
Sweep pattern
Skeleton pattern
Segmental pattern
Shell pattern
PATTERN ALLOWANCES :
Patterns are not made to the correct sizes of the castings. Patterns are made slightly larger than the required castings. This extra sizes given on the pattern is called pattern allowance.
Pattern allowances are given for the purpose of compensating the metal shrinkage, to provide extra metal for machining, to avoid metal distortion, for easy withdrawal of pattern from mould and for rapping.
If allowances are not given on the pattern, the castings will become smaller (ie) undersize.
The various types of pattern allowances are:
Shrinkage allowance
Machining or finish allowance
Draft allowance
Distortion or camber allowance
Rapping allowance
This types of pattern allowances are explained in this video briefly.
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