MECHANICAL THEORY

What are the different Types of allowances in Casting process?

Casting is a process in which the molten metal is poured into the casting cavity and it is allowed for solidification.After solidification take the casting out by breaking the mould called as casting process.The different types of allowances observed during and after casting process and are as follows.

Types of allowances in Casting process
What are the different Types of allowances in Casting process?

Types of allowances:

  1. Shrinkage Allowance
  2. Machining Allowance
  3. Draft Allowance
  4. Shake Allowance
  5. Distortion Allowance

The explanation of above types of allowances are as follows..

1.Shrinkage Allowance:

During cooling of the material in Casting process,in all the Three stages,the material is getting shrinking(reducing its dimensions or volume).But ,shrinkage allowance taking place in 1st two stages is called as Liquid Shrinkage.

  • Shrinkage in 3rd -stage is called as Solid shrinkage.
  • Liquid shrinkages are always compensated by providing a riser in casting process.
  • Liquid shrinkages are always specified as “% by Volume”.
  • Out of different metals casted in the industry, “Aluminum(Al) ” is having highest liquid shrinkage which is about 6%.
  • Solid shrinkage is specified as (Percentage/Dimensions).
  • Solid shrinkage is influenced by four factors.

2.Machining Allowance:

The extra dimension provided on the casting and it will be removed by machining after the casting has been completed is called as Machining Allowance.

Detailed explanation of Machining allowance is as follows.

3.Draft Allowance:

Making the vertical surfaces of the pattern into inclined surfaces is called as Draft Allowance.

4.Shake Allowance:

To maintain the required size of the casting,the original size of the pattern has to be reduced by an amount called as Shake Allowance.

5.Distortion Allowance:

To get the vertical legs of U shaped[Distortion Allowance complete].the original pattern has to be bend inverse so that during solidification,the legs are bending outwards and becoming vertical legs.The amount by which the legs are bending Inverse is called as Distortion or Bending allowance.

This is the complete explanation of all types of allowances in a detailed manner.

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