How does one deal with shell expansion in stainless steel investment castings?

We frequently encounter shell expansion defects when producing stainless steel investment castings. The defect of shell expansion is caused by the volume solidification mode of modular cast iron alloys and graphitization expansion during the eutectic transformation process. Tongda will discuss how we will solve this problem further below.

1. Control the process strictly at the beginning (wax material ingredients, molding, welding position of the sprue, coating hardening, and module drying): The proportion of wax is based on new and old material at 50% each. Molding equipment includes pneumatic pressure wax, an electric heating wax injection gun, and the ability to control the temperature of the wax material between 42 and 50 °C. In order to realize the solidification sequence, the sprue welding location should be chosen in favor of the largest hot spots of stainless steel investment castings. Coating with a high-strength shell,surface material with silica powder and silica sand, reinforcement layer with high aluminum and high alumina sand, powder coating liquid ratio of 1:1, adding 0.05% surfactant coating to increase smearing and shell strength.

2. To reduce the effects of dewaxing the expansion shell, we use the following improved process: Before dewaxing, remove the wax rod. The goal of using the joint fusion method, namely the pouring system with water vapour first to melt the wax material (or take a candle stick), and then in the hot water loss of a molten mould, is to realize the wax material of the melt at the same time, ensuring that the wax material overflow channels remain unblocked.