The effect of reduced molecular weight of the pattern on the properties of Al alloy castings made by the lost foam casting process

In the Lost Foam casting of Al alloys, heat from the cast liquid metal causes the foam pattern to degrade and results in the evolution of gas and formation of liquid polymer byproducts. These can cause a reduction in the casting quality if they become entrapped in the liquid metal. However, the liquid polymer byproducts can be absorbed by the permeable pattern coating, once their molecular weight (Mw) is sufficiently reduced by the action of heat. Therefore using a lower molecular weight (Mw) pattern may lead to higher quality castings because less reduction in Mw will be required before absorption of the liquid polymer byproduct into the pattern coating. In this work the Mw of expanded copolymer foam patterns has been be reduced by exposure to γ-radiation. The properties of castings made with these irradiated foam patterns, such as porosity content and fatigue properties, were compared with the properties of castings made from unirradiated foam, to show the advantages of using the former.