Pattern
The pattern is a mirror image of casting. The mold is created by the pattern in the form of a cavity. When this cavity filled by casting and after solidification get desire product or job that is called casting. Some allowances are provided during pattern making.
- Allowance for shrinkage
- Allowance for machining
- Draft allowance for easy removal from sand
- Core prints in the form of extra projections to produce a sheet for cores.
Tools used for making Pattern
- Planer
- Saw
- Measuring
- Marking
- Miscellaneous tools
Pattern Materials
1. Wood
The most common materials for the pattern is wood has the following material.
1. Economically and easily available
2. Easy to convert in required shape and size
3. Light in weight and a good finish is obtained only by planning.
4. Can be preserved for a long time
2. Plaster
Plaster of pair can be cast easily to any shape due to high compressive strength make a small size of pattern with closer dimension. It has the property that can expand on solidification.
3. Metal
When the large quantity of pattern is fabricated and with more accuracy, the metal piece is used. There are some limitations.
- It is costlier than wood
- In the case of machining is required it can increase the cost of the pattern.
- It is heavier than wood
- It is affected by corrosion due to treatment.
4. Plastic
Plastic can be used due to light in weight and more strength with lesser wear. It gives a better finish and low shrinkage during melting and not much, not costlier.
5. Wax
In this case, the mold is made of two halves and wax is poured in this. The cooling of the die takes place by circulating of water.
Factor Affecting the Selection of Pattern Material
These are the point that must be considered while selecting material for the pattern
- The rate of production of casting
- Molding is done manually or by machine.
- What are the casting methods?
- Accuracy and surface finishing required in finishing.
