Metal/mould interfacial heat transfer during solidification of cast iron in sand moulds

Abstract

Heat transfer at the metal-sand interface was investigated for the case of solidification of cast iron in (1) cylindrical sand moulds and (2) ceramic cylindrical moulds with sand blocks at the bottom. An inverse method of solving the one-dimensional heat conduction equation was used to determine the metal-sand interfacial heat flux transients and heat transfer coefficients with the heat conduction equation modified to take into account the packed bed nature of the sand mould, the effect of convection of the mould gases and the evolution and absorption of heat due to mould reactions. However, temperature measurements in the moulds during the experiments revealed that the heat transfer in the cylindrical sand moulds was not truly radial and could therefore not be used to obtain accurate interfacial heat transfer results. In the case of solidification of cast iron against sand blocks, mean values of the heat flux of about 50 kWm-2 were measured for green and dry clay-bonded silica sands, with and without additions of seacoal. The corresponding heat transfer coefficients were about 625 Wm-2K-1. Within the scatter of results obtained there was no discernible difference in the heat flux or the heat transfer coefficients with the different sand formulations. The heat transfer mechanisms through the sand-casting interface were interpreted from an examination of the nature of the sand and casting surfaces. Heat transfer through the interface is proposed to occur by conduction through the gas forming the atmosphere of the interface and by radiation, in approximately equal amounts.