An understanding of the solidification or freezing of metals is important to the foundry-man who wants to know how to make good castings.
Solidification of a casting starts by the formation of micro sized, solid grains next to the surface of the mould.
These grains grow inwardly from the surface until they meet other grains growing from other surfaces. When these growing surfaces meet, the casting is solid.
Improper foundry practice will cause many defects which can be explained and avoided if proper attention is given to the way in which the metal solidifies.
Casting defects which can occur if the freezing characteristics of metals are not taken into account are as follows:
- Microshrinkage,
- Centerline shrinkage,
- Shrink or blow holes,
- Certain types of gas holes, including piping,
- Hot tears.
These casting defects can be minimized if proper attention is given to the practices described in later course modules, one of the most important books you will read in our course material will be the “Design Of Gates and Risers”.