Investigation of shell mold casting technique in Ghana using indigenous materials

Abstract

Shell mold casting processes are more cost-intensive in terms of equipment, raw materials, and skills than the sand-casting technique. Sand casting is practiced in Ghana to cast mainly corn mill plates and occasionally vehicle and machine parts that lack good surface finish, better dimensional accuracy, and require a lot of effort/energy to bring the cast to the actual specification. As a result of the limitations of the sand-casting technique, the shell mold casting technique was adapted in this work. Indigenous clay chemically composed of 69.8% silica; 15.7% alumina was used. Washed and unwashed Silica from the Yakor River were investigated. The combination of clay, silica, and water was used to form a mold for the casting of a machine component. Of all the mixtures that were fired, the best mixture ratio was the sample which has the composition of 70% Mfensi clay, 10% silica sand, and 20% water selected from sixty-six samples. The mixture was tested based on its compressive strength and other parameters such as Acid Demand Value, pH Value, and Grain Fineness Number. Chemically, the final mold had a thickness of 16 mm which was able to withstand the high temperature (1450 °C) of the molten cast iron without the shell mold collapsing. A shell core made exhibited better core properties such as collapsibility, thermal stability, and permeability when the molten cast iron was poured into the mold for solidification.