What Is Pattern ?
- The pattern is the principal tool during the casting process. It is the replica of the object to be made by the casting process, with some modifications. The main modifications are the addition of pattern allowances, and the provision of core prints. If the casting is to be hollow, additional patterns called cores are used to create these cavities in the finished product.
- The quality of the casting produced depends upon the material of the pattern, its design, and construction.
- The costs of the pattern and the related equipment are reflected in the cost of the casting.
- The use of an expensive pattern is justified when the quantity of castings required is substantial.
|A typical pattern attached with gating and risering system|
Material used for making Pattern:
Typically, materials used for pattern making are wood, metal or plastics. Wax and Plaster of Paris are also used, but only for specialized applications. Mahogany is the most commonly used material for patterns, primarily because it is soft, light, and easy to work, but also once properly cured it is about as stable as any wood available, not subject to warping or curling. Once the pattern is built the foundry does not want it changing shape.
Types of Patterns:
The common types of patterns are as follows:
1. Solid or Single piece patterns
This is the simplest type of pattern, exactly like the desired casting. For making a mould, the pattern is accommodated either in cope or drag.
Used for producing a few large castings, for example, stuffing box of steam engine.
2. Split or two/multiple piece patterns
These patterns are split along the parting plane (which may be flat or irregular surface) to facilitate the extraction of the patternout of the mould before the pouring operation. For a more complex casting, the pattern may be split in more than two parts.
|types of patterns|
3. match plate pattern
4. cope and drag pattern
5. loose piece pattern
6. gated patterns
7. sweep pattern
8. skeleton pattern
9. shell pattern
10. segmental pattern
11. follow board pattern
12. lagged up pattern
13. left and right hand pattern