AbstractA finite difference model has been developed to study the effects of polymer degradation on the temperature of the liquid metal during the formation 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 conducted for pure aluminium and a commercial aluminium alloy. The results indicate that the temperature of the metal front decreases continuously during the formation of the casting. The degradation of the polymer establishes thermal gradients in the bulk of the casting of the order of 2–2·5 K cm−1. Thermal gradients as high as 50 K cm−1may be achieved in a zone near the metal front. The heat transfer coefficient at the metal/mould interface has been estimated to be 420 Wm−2K−1. The model suggests that the thickness of the gas layer at the metal front is negligibly small. The model confirms the experimental observation that a large fraction of the polymer is converted to a viscous residue during the thermal degradation of the polymer. The data from the model are in good agreement with experimental resultsfor a variety of conditions.MST/1922