Details of cooling operation in precision casting processing

The application range of precision machining is becoming wider and wider, and the production process is becoming more and more. The refrigeration process is an indispensable process. Some people need to experience the solid change of aluminum alloy, and the more morbidity of the change of metal materials. For example, the volume of carbon steel changes from the δ phase to the γ phase, and the volume increases when the γ phase changes due to eutectoid changes.

However, if the temperature of each part of the casting is mutually different, the disease may not occur when the solid changes, but there is only external economic geostress. When the change temperature is higher than the critical pressure of plastic-ductility change, the aluminum alloy is in plastic deformation during the change. Even if there is temperature in each part of the casting, the resulting change in ground stress is not large and will gradually Reduce or even subside.

If the change temperature of the casting is less than the critical pressure, and the temperature of each part of the casting is very different, the change time of each part is not the same, it will cause the external economy to change the ground stress, because the change time is different, the changed ground stress may become temporary ground stress Or remaining ground stress.

When the solid part of the thick wall of the casting changes, the part of the thin wall is still in plastic deformation. If the specific volume of the new phase exceeds the specific volume of the old phase during the change, part of the thick wall expands during the change, and part of the thin wall suffers plastic deformation. Deformation pulls out, the result is that there is only a small tensile stress inside the casting, and it gradually disappears with time. Under such conditions, if the casting is continuously cooled, a part of the thin wall will change and increase the volume. Since it is already in a ductile condition, the part of the thick wall will be stretched by the inner ductility to form tensile stress. However, a part of the thin wall is compressed by the ductility of the surface layer to form a compressive stress. Under this type of standard, the signs of the remaining change of the ground stress and the remaining thermal stress can be mutually offset.

When a part of the thick wall of a casting is converted to solids, part of the thin wall is already in ductility. If the new contrast exceeds the old phase, part of the thin wall is subjected to tensile stress due to ductility, and part of the thick wall is reduced by ductility. Tightly constitute temporary compressive stress. At this time, changing the sign of the stress is the same as the sign of the thermal stress, that is, the ground stress is accumulated. When the casting is continuously cooled to the extent that a part of the thin wall changes, the specific volume expands and expands, so that the changed ground stress formed by the previous section subsides. "