Heat transfer at the casting metal-mold interface during solidification

This investigation focused primarily on the effect of surface roughness on heat transfer coefficient values whilst exploring the dynamics and mechanisms of heat transfer at the casting metal-mold interface during solidification of liquid metal. Several experimental, computational and analytical techniques were developed and utilized. A cylindrical and horizontally oriented casting configuration with fixed metallostatic head was used. To evaluate quantitatively the effects of Surface Roughness, Thermal Conductivity and Contact Temperature on the heat transfer coefficient at the metal mold interface during the solidification of liquid metal is the object of this study.; To effect this investigation a novel apparatus was developed. This apparatus was instrumented with thermocouples, displacement sensors-LVDT (Linear Variable Differential Transformer) and electrical contact detection circuit. It not only provided the base for obtaining accurate temperature profiles in casting and chill; it also recorded data that helped in characterizing mold expansion and the detection, formation and development of an air gap in the latter stage of metal solidification.; Data collected from experiments (using commercial purity aluminum and aluminum alloys (A319 and A356) against different chill materials including steel, cast iron and copper) was used as input into an Inverse Heat Transfer Code developed in the course of this work. Different surface roughness was applied to each chill material used. Consequently, surface roughness was observed to have varying degrees of effect depending on superheat, chill and alloy materials. Heat transfer coefficient values during the development of air gap initially suffer from a drastic reduction followed by a recovery to almost constant values. Generally, an increase in surface roughness results in the decrease of heat transfer coefficient at the metal-mold interface. Further, analysis of the heat transfer data revealed that two dominant heat transfer modes occur during air gap development: 'conduction' followed by 'convection' in the same order.