Pattern Practices - Manufacturing processes:
Pattern Practices : A pattern may be defined as a replica or fascimile model of the desired casting which, when packed or embedded in a suitable moulding material, produces a cavity called mould.
1.Types of patterns : These depends upon many factors like the bulk of casting, type of moulding processes, number of castings required and the anticipated difficulty of moulding, on account of the typical shape or design of casting.
The following types of patterns are commonly used :
1. Solid or single piece pattern 2. Two-piece or split pattern
3. Multi-piece pattern 4. Match plate pattern
5. Gated pattern 6. Skeleton pattern
7. Sweep pattern 8. Pattern with loose piece
9. Cope and drag pattern 10. Follow board pattern
11. Segmental pattern
2.Allowances for pattern : A pattern is always made larger than the required size of the casting in order to allow for various factor, such as shrinkage, machining, distortion and rapping etc. The following allowances are provide in a pattern :
1. Shrinkage allowance 2. Machining allowance
3. Draft allowance 4. Rapping or shake allowance
5. Distortion allowance
6. Mould wall movement allowance