Wicking of liquid polystyrene degradation products into the pattern coating in the lost foam casting process

Entrapment of liquid polystyrene degradation products during filling is detrimental to the quality of aluminium lost foam castings. In this study, the degradation of expanded polystyrene under different heating conditions, and the ability of two pattern coatings of different permeability to absorb the partially degraded liquid polymer, was determined using gel permeation chromatography and scanning electron microscopy. It is suggested that, with the degradation of the polystyrene to a sufficiently low molecular weight liquid, significant absorption of the liquid polystyrene can occur with each coating. A number of simple plate patterns were cast in a real-time x-ray facility to determine the effect of each coating type on filling behaviour and casting quality. Similar tensile properties were found in each case, although the high permeability coating was associated with a filling velocity about twice that associated with the low permeability coating.