Causes of shrinkage in precision casting and preventive measures

Cause of formation: The basic reason for the formation of shrinkage cavities is that when the alloy shrinks and solidifies in the liquid state, a certain part of the investment casting (usually the hot spot where the final solidification) cannot be fed by the liquid metal in time, shrinkage cavities are generated there.

For eutectic alloys or alloys with a narrow solidification temperature range, the castings are prone to concentrated shrinkage. When the alloy composition is fixed, the shrinkage cavity is mainly caused by uneven wall thickness of the investment casting, too many hot joints, too large, improper design of the pouring riser system, which is not conducive to sequential solidification, and the hot joints of the casting cannot be supplemented by molten metal. Or the pouring temperature is too high.

  • Preventive measures: 1: Improve the structure of the castings, strive for uniform wall thickness, reduce hot spots, or change the wall thickness to cause sequential solidification.
  •      2: Reasonably set up the pouring and riser system to cause sequential solidification. The pouring and riser system for complex parts with multiple hot spots should be considered.
  •      3: Assemble the modules reasonably so that there is a certain distance between the investment casting to prevent local heat dissipation difficulties.
  •      4: The pouring temperature of the mold shell and molten metal should be appropriate, and the pouring temperature should not be too high
  •      5: When pouring, make sure that the sprue and riser are filled with molten metal, or add heating agent and heat preservation agent on the sprue cup and riser
  •      6: Improve the smelting process, reduce the gas and oxides in the molten metal, and improve its fluidity and feeding capacity