HEAT TRANSFER FROM THE CASTING TO THE DIE DURING THE SOLIDIFICATION OF ALUMINIUM ALLOY DIE CASTINGS

摘要

Interfacial heat transfer coefficients have been determined during the solidification of Al alloys against die steel chills coated with commercial insulating die coatings. The casting and coating surface roughness parameters were used to characterise the interface and develop equations to predict the heat transfer coefficient. Predicted values were in good agreement with measured values. These equations covered three types of interfacial contact; (i) light contact between the casting and the coated die steel surfaces, (ii) the formation of an air-gap and, (iii) where the casting surface was forced against the coated die steel. The equations demonstrated the important role played by the layer of air trapped between the rough casting and coating surfaces that reduced the heat transfer coefficient to values below what would be expected if interfacial heat transfer was controlled by the coating alone.