Dalian Xinmiao Casting Industry Co., Ltd. — Providing Casting Solutions for You
Causes of Shrinkage Cavities in Precision Casting and Preventive Measures
2021-09-22
Cause of formation: The fundamental cause of shrinkage cavities is that, during liquid contraction and solidification, a particular region of the casting—typically the last-to-solidify hot spot—fails to receive timely feeding from the molten metal, resulting in the formation of a shrinkage cavity at that location.
For eutectic alloys or alloys with a narrow solidification temperature range, castings are prone to the formation of concentrated shrinkage cavities. When the alloy composition is fixed, the primary causes of shrinkage cavity formation include non-uniform wall thickness, an excessive number and size of hot spots, improper design of the gating and riser system that hinders sequential solidification, resulting in insufficient replenishment of molten metal to the various hot spots in the casting, or excessively high pouring temperature.
Preventive measures:
1. Optimize the casting structure to achieve uniform wall thickness, minimize thermal sections, or design wall-thickness variations to promote sequential solidification.
2. Properly design the gating and riser system to achieve sequential solidification. For complex castings with multiple hot spots, the gating and riser system should be designed with even greater care.
3. Assemble the modules appropriately to maintain a certain distance between castings, thereby preventing localized heat dissipation difficulties.
4. The mold shell and molten metal pouring temperatures must be appropriate; the pouring temperature must not be too high.
5. During pouring, ensure that the downsprue and riser are completely filled with molten metal, or add a heat-keeping agent and an insulation agent to the pouring cup and riser.
6. Optimize the melting process to reduce gas and oxide inclusions in the molten metal, thereby enhancing its fluidity and feeding capability.
Previous article:
