Pattern: It is the replica of the casting to be produced.Replica means, the shape of the pattern remains same as that of the shape of the casting to be produced.
- The main modifications in the pattern 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.
- Runner, Ingate, and Riser are the part of the sand casting process used to feed the molten metal into the casting cavity.
- The quality of the casting produced is dependent upon the type of material, its construction, and Design.
- Patterns with high surface finish can reduce the defects in the casting process.
Properties Possessed by the Pattern:
- No moisture absorption by the pattern material would take place.
- Surface finish produced on the pattern material must be good or excellent.
- The material should be of low density.
- Easiness in fabrication.
- It should be cheaper(Pattern Cost).
Types of Patterns:
The different types of patterns are as follows.
- Solid pattern
- Split pattern
- Match plate pattern
- Cope and drag pattern
Types of Pattern Materials:
The different types of pattern materials used in casting process are as follows.
Except for moisture absorption, the wood is possessing all other properties which are required as a pattern material and out of all the different woods, the wood which is absorbing less moisture will be used as a pattern material.
Example: Teak wood, Mohagaoni etc.
In the case of metal patterns, the density is high and it is difficult to manufacture the metal patterns.
Ex: Aluminium, white metal, Titanium has low density, but they are of very costly.
Aluminium = 2.7 gm/cc
White metal = 3.2 gm/cc
Titanium = 4.3 gm/cc
When wooden parts are used for producing metal patterns, the double shrinkage allowance must be provided on the wooden pattern.
They are processing all the properties which are required for pattern material.hence in today’s manufacturing industry, plastics are the most commonly used pattern materials.
Ex: Epoxy resin, PVC, Nylon, Cellulose, Polystyrene etc.
Polystyrene: It is used for producing very large castings where the removal of the pattern is not possible.
Ex: Producing bed of Machine.
It will be selected as a pattern material for producing the complex shape of the pattern, to produce the Complex shape of the casting i.e. because of the highest softness of the wax material, it is possible to produce the Complex shape of the pattern easily.
- With wax patterns, removal of the pattern will be easier in the form of a liquid and this liquid wax will be reused.
- When compared to other patterns, the surface finish produced with the wax material will be better.
Disadvantages of using wax pattern:
- Wax patterns are not effective with green sand moulding because the ramming force will be disturbing the pattern shape. So only low ramming force can be applied i.e. only loose sand moulds can be produced with Green Sand.
- If a wax pattern is used with Green Sand mould, chances of formation of rat tail defects are high.
- Because of very hair softness, during handling of the pattern due to self-weight, the pattern may get distorted. Hence, to avoid the distortion of the pattern, the maximum size of the wax material is up to 5 kg only.
Applications of using Wax Pattern:
Component Produced are
- Gold and Silver Ornaments
- turbine blades
- a waveguide for a radar system
- surgical instruments etc.
- It has many disadvantages like high-density, high poisonous and high cost. Still,l the mercury is used as a pattern material for producing excellent surface finish on the casting even with Green Sand mould also.
- The Mercury will be used as a pattern material for the space applications where a small size castings are to be produced with excellent surface finish without any machining.
This is the explanation of Pattern-Properties, Types of Pattern Materials, Disadvantages and Applications in a detailed way. If you have any doubt, you can ask from the comments section.
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