Causes of Shrinkage in Precision Casting And Preventive Measures

Causes of shrinkage

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 casting (usually the hot spot where the last solidification) cannot be fed by the liquid metal in time, will produce shrinkage cavities there.

For eutectic alloys or alloys with a narrow solidification temperature range, the castings are prone to concentrated shrinkage. When the alloy composition has been set, the shrinkage cavity is mainly caused by the uneven wall thickness of the casting and excessive hot spots. Improper design of the pouring and riser system is not conducive to solidification so that the hot joints of the casting cannot be supplemented by molten metal, or the pouring temperature is too high.

Preventive measures

• Improve the structure of castings, strive for uniform wall thickness, reduce hot spots, or make wall thickness changes conducive to sequential solidification.

• Reasonably set up the pouring and riser system, resulting in sequential solidification. The pouring and riser system for complex parts with multiple hot spots should be considered.

• Assemble the modules reasonably so that there is a certain distance between the castings to prevent local heat dissipation difficulties.

• The pouring temperature of the mold shell and molten metal should be appropriate, and the pouring temperature should not be too high.

• 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.

• Improve the smelting process, reduce the gas and oxides in the molten metal, and improve its fluidity and feeding capacity.

The above are the issues about causes of shrinkage in precision casting and preventive measures. Do you understand? Hurry up and contact us to customize the sand casting design that suits your wishes! Yifei is a professional manufacturer and supplier for custom die casting, precision investment casting, sand mold casting and custom forging in China.