Every metal alloy has an acceptable range of cooling time after it is poured before proceeding with the casting. In order to ensure that no defects occur, manufacturers and casting operations must determine the optimal cooling rate for each alloy, furnace, and casting process. In general, a much faster cooling rate is associated with higher quality castings, which often result in better mechanical properties and longer service lives.
The connection between the second cooling rate and casting quality has long been debated. In particular, many experts suggest that the second cooling rate should be as fast as possible in order to produce higher quality castings. This assertion has been backed up by research, which has shown that a critical temperature plateau is often reached at the end of the second cooling rate, which is defined as the time between the castings release from the poured and the end of the initial cooling period. At this point, further cooling of the casting is considerably less effective in improving the mechanical properties of the casting.
However, research has also suggested that while a slow second cooling rate may not necessarily improve the mechanical properties of the casting, it can improve the quality of the cast ingot. The slower cooling rate allows more time for the structure of the grain boundaries to align, which can produce castings with fewer defects. As a result, lower temperatures are often achieved, which can help reduce any residual stresses or deformation, producing a higher quality casting.
While the connection between the second cooling rate and casting quality may not be a perfect correlation, it is clear that cooling times need to be judiciously applied in order for manufacturers and casting operations to produce high quality castings. The effectiveness of any particular cooling rate will depend on the alloy, furnace, and process being used, and the optimal solution must be adjusted accordingly. Nevertheless, evidence suggests that faster cooling rates often achieve higher quality results, and that manufacturers should strive to maximize the critical temperature plateau at the end of the second cooling period.
