Patterns are the replicas of the casting required. These are similar in shape and size to the final product to be prepared, but not exactly. Which is prepared with suitable materials and these patterns are used for making mould cavity. Usually, the mould is prepared in wet sand, to which some binder is added to hold sand particles together. The pattern is then withdrawn from inside the sand mould in such a manner that the impression/cavity made in the mould is not damaged or broken in anyway. Finally molten metal is poured into this cavity and allowed to solidify and cool down to room temperature, it forms reproduction of the pattern which is known as 'Casting'.
The requirements of a good pattern are :
1) Secure the desired shape and size of the casting.
2) Pattern should be cheap and readily available.
3) Patterns should be simple in design for ease of manufacturing.
4) They should be light in mass and convenient to handle.
5) Have high strength and long life in order to make as many moulds as required.
6) Retain it's dimensions and rigidity during the definite service life.
7) It's surface should be smooth and wear resistant.
8) Able to with stand rough handling.
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