PATTERNS

PATTERNS:

             From the design, provided by an engineer or designer, a skilled pattern maker builds a pattern of the object to be produced, using wood, metal, or plastic; other materials to be used can be polystyrene or even sand strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Pattern-makers are able to produce suitable patterns using ‘contraction rules’. Different scaled rules are used for different metals because different metals/alloys contract at different rates. Patterns also have core prints; these create registers within the moulds, into which are placed sand cores. Sand cores are used to create undercut profiles and holes which cannot be moulded.

                 Paths for the entrance of metal during the pouring (casting) process into the mould cavity constitute the runner system and include the sprue, various feeders which ,maintain a good metal ‘feed’ and ‘runners’, and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via the riser, are added either in the pattern itself, or as separate pieces.

 TYPES OF PATTERNS:

            The common types of patterns are

1. Single piece pattern

2. Split piece pattern

3. Loose piece pattern

4. Gated pattern

5. Match pattern

6. Sweep pattern

7. Cope and drag pattern

8. Skeleton pattern

9. Shell pattern

10. Follow board pattern