Global Casting News

How to solve shell expansion of stainless steel investment castings?


When making stainless steel investment castings,we often meet shell expansion defect.Shell expansion defect is caused by volume solidification mode of modular cast iron ally and graphitization expansion in the process of eutectic transformation.Below Tongda will talk about how we will solve this problem.

1)Strictly control process at early stage(wax material ingredients, molding, welding position of sprue, coating hardening and module dry):Wax proportion according to the new and old material 50% each.Molding equipment is pneumatic pressure wax,electric heating wax injection gun and control wax material temperature between 42-50℃Welding location of sprue should be choosed in favor of biggest hot spots of stainless steel investment castings,in order to realize the solidification sequence.Coating with high strength shell,surface material with silica powder, silica sand, reinforcement layer with high aluminum, high alumina sand, powder coating liquid ratio is 1: 1,in order to increase the smearing and shell strength,adding 0.05% surfactant coating.

2)To minimize the effects for dewaxing expansion shell, we adopt the improved process is as follows:Remove wax rod before dewaxing;Using joint fusion method, namely the pouring system with water vapour first wax material melt loss or take candle stick, and then in the hot water loss of molten mould, the aim is to realize the wax material of the melt at the same time, to ensure that the wax material overflow channels unblocked.

3)Strictly control pouring temperature,casting speed and pouring liquid level height of stainless steel investment castings to effectively reduce the destruction of the shell during pouring process.