Development of patterns is the first step in the casting process. Patterns can be re-used to make more moulds and, if looked after, can last for many years making thousands of moulds.
For producing a mould or impression of desired shape in moulding sand, one needs to have a wooden or metallic pattern similar to the shape of the mould. The art and science of designing the pattern is called pattern making.

Common Metals that are used for creating patterns are –

· Wood
· Metal
· Plaster
· Plastic

Types of Pattern
The type of patterns selected for a particular casting depends upon many factors such as type of moulding process, number and size of casting difficulty of moulding on account of design or typical shape of casting. The most common types of pattern are listed and described below:
(a) Solid or Single Piece Pattern
(b) Split Pattern
(c) Gated Pattern
(d) Sweep/Skeleton Pattern
(e) Match Plate Pattern

(a) Solid or Single Piece Pattern

The one piece or single pattern is the most inexpensive of all types of patterns. This type of pattern is used only in cases where the job is very simple and does not create any withdrawal problems. It is also used for application in very small-scale production or in prototype development. This type of pattern is expected to be entirely in the drag and one of the surface is is expected to be flat which is used as the parting plane. A gating system is made in the mold by cutting sand with the help of sand tools.

(b) Split Pattern
Split or two piece pattern is most widely used type of pattern for intricate castings. It is split along the parting surface, the position of which is determined by the shape of the casting. One half of the pattern is molded in drag and the other half in cope. The two halves of the pattern must be aligned properly by making use of the dowel pins, which are fitted, to the cope half of the pattern. These dowel pins match with the precisely made holes in the drag half of the pattern.

Categories: Foundry

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