Casting Defects of Metal Materials, part 6

The main defects of casting products are segregation, pores, shrinkage and shrinkage, inclusions, cracks, cold shut and other defects.

Cold shut

Wrinkles or layered defects on the surface of the ingot, or metal discontinuity inside are collectively referred to as cold shut.

The outer surface of the cold shut ingot is uneven, the layers are discontinuous, the cross section is layered, and there is often an oxide film in the middle with defects such as pores.

Cold shut can be divided into two types according to its shape: wrinkle type and layered type. When the casting temperature is low, the thin film shell produced on the metal liquid surface fails to fuse with the metal poured in later, resulting in a wrinkle type cold shut. Layered cold shut is more common.

This is because the static pressure of the metal liquid is greater than the surface tension of the metal and the strength of the oxide film. The metal liquid breaks through the oxide film and enters the wall of the crystallizer, but the strong cooling quickly reduces the fluidity of the metal, resulting in failure to fuse with the oxide film shell to form a layered cold shut.

Cold shut is divided into surface cold shut, subcutaneous cold shut and center cold shut according to the location of the cold shut.

Causes of cold shut: low casting temperature, high cooling water pressure, unstable casting speed, large liquid level fluctuation, intermediate interruption, and poor shrinkage compensation are important factors for cold shut; severe surface cold shut extends into the ingot and also causes subcutaneous cold shut; unreasonable design of the inner wall structure of the crystallizer and improper material selection can also lead to the occurrence of cold shut.

Cold shut is one of the common defects of ingot casting, which affects the integrity of the metal surface and interior, and affects processing and use. In severe cases, it causes processing cracks and other surface defects.