Name the important factors in selecting sand for molds Descr

Name the important factors in selecting sand for molds. Describe the stages involved in the contraction of metal during casting. Describe the differences between expendable and permanent molds; give two examples of each category. With use of diagram Explain the phenomena of shrinkage in casting process. Describe also the method to eliminate the effect of shrinkage in sand casting. Explain two types of die casting and describe the advantages and disadvantages of die casting

Solution

Imporatant factors for selecting sand

Expendable and Permanent molds

1. Expendable molds

2. Permanent molds, made of metals that maintain their strength at high temperatures.

Two types of Die casting:

Advantages of Die Casting:

Disdvantages of Die Casting:

Shrinkage in Casting occurs in three phases.

The effect of shrinkage can be eliminated by providing allowance on the pattern. Note, for some metals like grey cast iron, pattern is given negative shrinkage allowance, i.e., they expand when cooled.

Stages involved in contraction of metal(same as shrinkage)