Evaluation of Surface Roughness of Castings Made from Silica-Bentonite-Bottom Ash Mix Refractory Coatings

The effect of silica-based refractory coatings on the surface roughness of evaporative pattern castings (EPC) was evaluated in this study. Two major processes were carried out, namely, the development of refractory coatings and the production of EPC. The refractory coatings contained three major components which were silica flour, bentonite, and bottom ash. Methyl alcohol served as the liquid carrier. The silica flour was obtained from silica sand procured from the Isasa River, Gbongan in Osun State Nigeria. Bentonite was obtained from the River Osun in Oshogbo, Osun State Nigeria, while the bottom ash was obtained from the coal procured from Lafia in Nasarawa State, Nigeria. The three coating constituents were blended using Taguchi’s L9 experimental design approach. Nine coatings were developed and used in the production of EPC. The surface roughness of each casting was determined by using Image J software. The values of the surface roughness were between 14.92µm and 24.91µm. The analysis of variance singled out silica flour with 66.63% contribution as the major factor that contributed to the surface roughness of the castings. Conclusively, the coating sample produced from silica flour, bentonite and bottom ash with respective mixing ratio 90:15:10 by mass had the best quality.