Causes of casting shrinkage and preventive measures

Cause of formation: The basic reason for the formation of shrinkage cavity is that when the alloy shrinks and solidifies in the liquid state, a certain part of the casting (usually the hot joint of solidification) cannot be fed by the liquid metal in time, and the shrinkage cavity occurs 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 casting, excessive 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 castings, strive for uniform wall thickness, reduce hot spots, or make wall thickness changes conducive to sequential solidification.

2: Reasonably set 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 castings to prevent local heat dissipation difficulties.

4: The pouring temperature of the shell and molten metal should be appropriate, and the pouring temperature should not be too high

5: When pouring, ensure 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.