Influence of Slurry Composition on Mould Properties and Shrinkage of Investment Casting

Abstract

Ceramic shell mould plays a key role in achieving dimensional accuracy and quality of casting. This work investigates the effect of mould parameters such as silica concentration, filler to binder ratio and the number of secondary coats on mould properties, namely modulus of rupture, adjusted fracture load, and permeability. Experimental results report that enrichment in silica results in drastic growth in adjusted fracture load with a small increase in modulus of rupture and no change in permeability. Improvement in filler to binder ratio causes a significant increase in the adjusted fracture load and modulus of rupture with moderate decrease in permeability. An increase in number of ceramic coats increases the adjusted fracture load significantly and reduces permeability moderately. Impact of the adjusted fracture load on casting shrinkage has been studied by conducting various casting trials. Adjusted fracture load above 315 N is preferred which corresponds to 25–30% silica, filler to binder ratio of 1.25 and number of secondary coats as six to eight for reduced shrinkage variation.