A chill is an object used to promote solidification in a specific portion of a metal casting mold.
When the geometry of the molding cavity prevents directional solidification from occurring naturally, a chill can be strategically placed to help promote it.
[1] Internal chills are pieces of metal that are placed inside the molding cavity.
[1] External chills are masses of material that have a high heat capacity and thermal conductivity.
[1] Chills can be made of many materials, including iron, copper, bronze, aluminium, graphite, and silicon carbide.