Shrinkage Allowance in Casting | RTO | GATE | Study Material | Manufacturing Engineering

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👉 The dimensions of the pattern are different from the final dimensions of the casting required. This is known as pattern allowances. There are five types of allowances. 
  1.  Shrinkage Allowance
  2.  Draft Allowance
  3.  Machining Allowance
  4.  Distortion Allowance
  5.  Shaking or rapping allowance
    In this page, I will share with you Shrinkage Allowance. so, let's start....

Shrinkage Allowance


  • All material expands during heating and contrast during cooling.
  • Degree of superheat is provided to maintain the fluidity of molten metal upto fulfillment of the cavity.
  • The shrinkage allowance is provided to cater for the contraction of the casting.
  • The overall contraction of the casting takes place in three stages.

  1. Liquid shrinkage: Contraction of liquid when its temperature changes from pouring temperature to freezing temperature.
  2. Contraction due to phase change from liquid to solid at freezing temperature.
  3. Solid shrinkage: Contraction of solid from freezing temperature to room temperature. 

✓   It is noted that for first two stages of shrinkage, riser provided to molten metal. hence for third stage only shrinkage allowance is provided to size of pattern is higher then casting.

✓   Shrinkage allowance is provided in linear direction but not in volume. 


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