Cooling of a casting is a very complicated process. The most important part is the rate at which a casting cools down. Many properties of the casting are affected by this rate, which eventually determines the quality of the finished product. The cooling rate affects: -
- Microstructure of the casting.
- Quality of the casting.
- Properties of the casting.
Much depends on the type of casting and the underlying processes. Let’s understand this with an example. Sand-casting and slurry-mold processes lead to slower cooling because of large and thick walls. As a result the grain size of the metal increases and hence its strength decreases (because of a coarse microstructure). Sand casting and slurry-mold processes lead to: -
- Slower cooling.
- Increased grain size of the metal.
- Weak casting.
- Faster cooling.
- Small grain size of the metal.
- Strong casting.
- Escape of alloy elements, thus decreased strength.
- Escape of gases and waste metal, thus increased strength.
- Holds the alloy elements, hence increased strength.
- Holds gases and waste elements, hence decreased strength.