The strength of coating in the lost foam casting process

Abstract

The functions of the coating in the lost foam casting (LFC) process include developing the strength to support unbonded sand and providing permeable channels to permeate the decomposed expandable polystyrene pattern in-mould. The strengths of coatings developed at room temperature differ from those at a high temperature owing to the heat effect introduced by the filling metal. In this study, we examine the effect of shape and size of refractory particle, and type and added weight per cent of binder in the coating on the strength of the coating.Experimental results indicate that for either a given particle size or a given wt% of a binder, the coating using flaky alumina and acrylic resin (binder B) develops the greatest strength at room temperature and the greatest hot strength. If a polyvinyl acetate (binder A) is used, the coating generally develops an inferior strength to that of acrylic resin (binder B). For a given resin used in the coating, angular silica used as the refractory particle decreases the strength of the coating at room temperature and its hot strength. In addition, pouring trials demonstrate that if alumina particles (74 μm, mesh No. 200) are added to the coating, the optimum wt% of acrylic resin is 0.25% to 1%. Those coatings produce sound and smooth grey iron plate castings, (5 mm in thickness). Moreover, the optimum wt% of acrylic resin is 0.25% for those producing sound and smooth thick plate castings, (20 mm in thickness).