CASTABILITY OF MODIFIED AND UNMODIFIED PINDIGA BENTONITE CLAY AS A BINDER FOR MOULD MATERIALS IN CASTING APPLICATIONS

Abstract

This study investigated the castability of both unmodified and modified Pindiga bentonite clay as synthetic moulding materials for sand casting applications. The investigation involved the design of the pouring gate, pattern, core box, cope and drag, as well as casting evaluation. The pouring gate design demonstrated an area of 4581.04 mm², which supports good practice by ensuring controlled metal flow and minimising turbulence. A high gating ratio of 20 mm was adopted to regulate metal velocity, thereby reducing defects such as oxidation and turbulence. The pattern design was assessed based on shape, surface texture, handle design, precision, and material selection (polymer). The cope and drag dimensions were recorded as 180 mm in base, 230 mm in length, and 80 mm in height, while the core diameter measured 46 mm to ensure a proper fit during mould preparation. Casting evaluations revealed that both brass and aluminium castings produced using the modified sample exhibited excellent inner and outer surface finishes, in contrast to those made from the unmodified sample, which displayed defects such as turbulence, misruns, air entrapment, and oxide inclusions. However, surface veining defects were observed in castings (mugs) from both modified and unmodified samples. While these defects did not render the castings unserviceable, they necessitate additional fettling, offsetting the benefit of an otherwise high-quality surface finish. Castings with close dimensional tolerance were achieved using the modified sample. Grain structure analysis indicated that casting with modified sand promotes grain refinement. The study concludes that modified bentonite enhances microstructural quality, and it is therefore recommended that modified Pindiga bentonite be utilised as a binder for sand casting.