How to cool investment castings?

The application scope of high-precision lost foam casting is getting wider and wider, and the production process is getting more and more numerous. The refrigeration process is an indispensable process. Some need to experience the solid phase transformation of aluminum alloy, and the metal changes more frequently during the phase transformation, such as carbon steel δ go in opposite directions γ The phase change volume becomes smaller, γ When the phase changes, the volume expands.

However, if the ambient temperature of all parts of the casting is the same, the external economic stress may not occur when the solid phase changes, but only the external economic stress. When the phase change ambient temperature is higher than the critical pressure of plastic elastic change, the aluminum alloy is in plastic deformation during phase change. Even if there is temperature in each part of the workpiece processed by the EPC manufacturer, the phase change stress is not large, and will gradually reduce or even disappear.

If the ambient temperature of casting phase transformation is lower than the critical pressure, and the temperature difference between parts of the casting is relatively large, and the parts of the casting phase transformation are different from time to time, the external economic phase transformation stress will be caused. Because the phase transformation is different from time to time, the phase transformation stress may become temporary stress or residual stress.

When a part of the thick wall processed by EPC is undergoing solid phase transformation, the thick wall is still in plastic deformation. If the vaporization heat of the new phase exceeds the vaporization heat of the old phase during the phase transformation, part of the thick wall will expand during the phase transformation, and part of the thick wall will suffer plastic deformation stretching. As a result, the internal structure of the casting will only experience a small tensile stress, and will be widened and gradually subsided at any time. In this case, if the casting keeps cooling, a part of the thick wall will undergo phase change and increase its volume. Because it is already in elastic condition, a part of the thick wall will be stretched elastically by the inner layer and form a tensile stress. While a part of the thick wall is elastically compressed by the surface layer to form a compressive stress, under these standards, the remaining phase change stress and residual thermal stress marks can offset each other in reverse.

When part of the thick wall of the casting is converted to solid phase transformation, part of the thick wall is already in elastic condition. If the new specific volume exceeds the old phase, part of the thick wall is elastically stretched to form a tensile stress, while part of the thick wall is elastically compressed to form a temporary compressive stress. At this time, the sign of phase transformation stress is the same as the sign of thermal stress, that is, stress accumulation. When the casting is continuously cooled until a part of the thick wall undergoes phase change, the expansion of the vaporization heat causes expansion, which makes the phase change stress formed in the previous section dissipate.