Characteristics and remedy of segregation defects in sand casting

Defect characteristics and detection methods

In the center and upper part of the thick part of the casting, there are irregular spots from gray to black. It is often accompanied by porosity or shrinkage. It can be found by visual inspection after oxidation treatment.

Causes of formation
  1. The composition of alloy liquid is not even before pouring
  2. Pouring temperature is too high
  3. Cooling is too slow for heavy parts of castings
  4. Mixed with low melting point alloy elements
Prevention methods and remedial measures
  1. Strictly control the batching and smelting process of the alloy to prevent the impurities with low melting point and high melting point from mixing into the alloy liquid
  2. Stir the alloy liquid sufficiently before pouring to make its components uniform
  3. Place iron chill or air vent in the thick part with slow cooling of the casting, so as to make it cool quickly and prevent the large air cushion back pressure from hindering the alloy liquid from feeding
  4. Reduce pouring temperature and solidification time of castings