Shrinkage defect of investment casting

Shrinkage porosity is a common casting defect in investment casting, which is often distributed in the axis area of the wall thickness of investment casting, the thick part, and the vicinity of the gate, and the shrinkage porosity defect is often hidden in the investment casting, which is not easy to find on the appearance. Due to the complex shape of precision castings, large wall thickness difference, many hot spots, hot shell casting, etc., there are great limitations in the formulation of casting process, and due to poor heat dissipation conditions, many investment castings can not be filled at the hot spots, resulting in shrinkage defects. The main reasons are that the low hydrostatic head of molten steel leads to the insufficient shrinkage of molten steel, the isolated hot spot of investment casting, the unsmooth shrinkage channel, and the poor heat dissipation conditions. The causes and solutions are introduced.

The best way to solve the shrinkage defect is to design the investment casting structure reasonably. From the perspective of casting structure, small castings, thin-walled castings and investment castings with complex structure and difficult to fill should be poured at high temperature; For thick and large parts, the principle of “high temperature tapping and low temperature pouring” shall be adopted. Rapid casting is applicable to investment castings requiring simultaneous solidification; Slow pouring is applicable to investment castings requiring sequential solidification.

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