The defects of shrinkage cavity and porosity are briefly introduced. Combined with the theories of filling capacity of liquid metal, solidification mode of steel castings and shrinkage of steel castings, the process design of traditional steel castings is carried out by taking the accessory bracket of a construction machinery as an example.
The volume reduction of steel castings in the cooling process of liquid, solidified and solid is called shrinkage. The physical essence of contraction is that the distance between atoms decreases with the decrease of temperature, and the number of holes between atoms decreases. Therefore, shrinkage is the physical property of cast alloy itself. Shrinkage is the basic cause of stress and defects such as shrinkage cavity, shrinkage porosity, hot crack, deformation and cold crack in steel castings.
When steel castings shrink, cavities often appear at the last solidified part of the castings, which is called shrinkage defects. Large and concentrated holes are called concentrated shrinkage defects, or shrinkage defects for short. Small and scattered holes are called dispersed shrinkage defects, or shrinkage porosity defects for short.