Geometric features of chill-cast surfaces

Abstract

Geometric features such as grooves, wrinkles, and laps are commonly observed on chill-cast surfaces. With lead used as a representative material, the occurrence of these features over a range of casting speeds from 0.025 to 17 cm/s (0.6 to 400 in./min) has been examined. On the basis of their assumed origin, three types of surface features have been recognized. The first two are associated with the mechanical behavior of the thermally stressed solidifying shell. Fine Type I grooves are the remnants of periodic shell corrugations formed near the meniscus during the earliest stages of solidification, and their spacing decreases with increasing casting speeds. More widely spaced Type II wrinkles are concavities that develop as solidification progresses, and are associated with the temperature perturbations that cause uneven thickening of the shell. Type III surface features occur at slow casting speeds when freezing of the meniscus gives rise to periodic surface lapping.