Effect of Bulk Density on the Shear Strength of Clay-Sodium Silicate Bonded Moulding Sand

This investigation is conducted to establish how changes in bulk density affect the shear strength of moulding sand bonded by clay and sodium silicate. Five sand mixes containing silica sand, sodium silicate gel (1 wt. % to 5 wt. %), potters' clay (2 wt. %), and about 3 wt. % water were produced. Each mix was divided into three portions to which 2 wt. % wood flour, 2 wt. % charcoal and a mixture containing 1 wt % charcoal and 1% wood flour was added to first, second and third portion respectively. In accordance with AFS procedure, each portion was thoroughly mixed and standard cylindrical specimens prepared. Thereafter, bulk densities and shear strength of the prepared standard specimens were measured. It was observed that using any of the three additives, with increasing bulk density the characteristic changes in shear strength assume parabolic form. The sand mix with 8 wt % sodium silicate and 2 wt % charcoal exhibited highest optimum shear strength and castings produced from such sand mix are likely to be less prone to pinhole and scab defect.