The casting changes greatly during cooling
Castings are produced by precision casting with many production processes and technical parameters. The process of investment casting is strong, and the production process is complex. Investment castings have many advantages. One of the characteristics of investment castings is near mold casting products, which can be used without machining or with less machining. Parts have high dimensional accuracy, good surface quality and high finish.
There are many casting processes, and the quality of each processing link will affect the overall product quality, so each link cannot be ignored. The details of cooling operation of castings during processing are one of the focuses we should pay attention to.
With the continuous improvement of production technology, the use scope of castings is becoming wider and wider, and the processing technology is also constantly innovating, but the cooling process is an essential process. Because some of the cooling process will go through the solid phase transformation of the alloy, the characteristics of the metal will change during the phase transformation. For example, the carbon steel is composed of δ Opposites γ Phase change and volume reduction, γ When the phase changes eutectoid, the volume increases and so on.
If the temperature of all parts of the casting is the same, the micro stress may not occur when the solid phase transformation occurs, but only the micro stress. When the phase transformation temperature is higher than the critical temperature of plastic elastic change, the alloy is in a plastic state during phase transformation. Even if there is temperature in each part of the casting, the phase transformation stress is small, and will gradually reduce or even disappear. If the phase transformation temperature of the casting is lower than the critical temperature, and the temperature difference of each part of the casting is large, and the phase transformation time of each part is different, the micro phase transformation stress will be caused. Because the phase transformation time is different, the phase transformation stress may become a temporary stress or residual stress.
The cooling process of investment casting has the same meaning as that of traditional casting production, both of which are aimed at obtaining corresponding structures and properties, so this link is very important.