Application of chills to the production of sound castings

With the increasing demand for high quality castings in aircraft and automobile industries foundrymen have to go for improved technological aspects with proper scientific understanding. Chills are widely used by foundrymen in the production of sound castings. A rational approach and understanding is very essential in their use. The authors, in this paper make an attempt to give a broad outlook of the influence of external chills on solidification and soundness of nonferrous and ferrous alloy castings. Castings solidifying with steeper temperature gradient and shorter solidification times result in high soundness. This signifies the importance of freezing index (defined as the ratio of the solidification time to average temperature gradient) in studying the soundness of castings. The mechanism by which the chills contribute high soundness and mechanical properties in these castings is discussed. However the best effect of the chills can be achieved only by proper application technique on the shop floor.