MODELING OF TEMPERATURE LOSSES IN LIQUID-METAL DURING CASTING FORMATION IN EXPENDABLE PATTERN CASTING PROCESS

A finite difference model has been developed to study the effects of p olymer degradation on the temperature of the liquid metal during the f ormation of the casting in the expendable pattern casting process. The model has been used to estimate the endothermic losses in the liquid metal during the mould filling process. The calculations have been con ducted for pure aluminium and a commercial aluminium alloy. The result s indicate that the temperature of the metal front decreases continuou sly during the formation of the casting. The degradation of the polyme r establishes thermal gradients in the bulk of the casting of the orde r of 2-2.5 K cm(-1). Thermal gradients as high as 50 K cm(-1) may be a chieved in a zone near the metal front. The heat transfer coefficient at the metal/mould interface has been estimated to be 420 W m(-1) K-1. The model suggests that the thickness of the gas layer at the metal f ront is negligibly small. The model confirms the experimental observat ion that a large fraction of the polymer is converted to a viscous res idue during the thermal degradation of the polymer. The data from the model are in good agreement with experimental results for a variety of conditions.