Building Investment Casting Slurries with Fumed Silica

摘要

This paper reports on a study that examined the feasibility of fumed silica as a binder in an investment casting shell. Ceramic test bars were made using zircon flour as the refractory in the prime and backup coats, with zircon sand as the stucco. The binders in these test bars were colloidal silica, fumed silica, and mixtures of both. Varying binder amounts were used to determine the optimum mixture and loading level that resulted in the ideal binder system. Shells made with fumed silica binders were found to behave similarly to those made with colloidal silica during the dipping and drying process. Strength measurements were performed using a 3 point bend test. It was found that in comparison to pure small particle colloidal silica, it was possible to achieve a 20% increase in strength in the dry state and a 10% increase in strength in the wet state by using an optimal combination of fumed and colloidal silica.