Heat-transfer conditions in hot-top mould and cold-shut formation mechanism on DC continuously cast non-ferrous alloy rods

AbstractThe existence and severity ql swlace defects such as cold shuts on direct-chill continuously cast products depend to a large extent on the heat-transfer conditions in the mould. An examination of the heat-transfer conditions at the mould/insert junction of a hot-top continuous-casting mould was performed as part of a study of the cold-shut formation mechanism on horizontal continuously cast 20 mm diameter lead, tin, and zinc alloy rods. It was found that there are two stages in the formation of a cold shut: intellace-controlled solidification, followed by diffusion-controlled solidification. The effective heat-transfer coefficient at the mould/insert junction lras found to be comparable to the very large values found during splat cooling. Using a steady-state numerical model of the solidification process, the concept of a critical casting speed for cold-shut formation was developed. If the actual casting speed is greater than this critical speed, cold shuts will not be produced. Alternatively, the...