Identification of Microorganisms Present in Ceramic Slurry Used for Investment Castings in Automobile Industries

Ceramic shell making in the investment casting process starts with dipping the wax pattern assembly (generally by hand) into a slurry, referred to as the primary coating, which governs the surface finish of the final casting. This is usually carried out in controlled environmental conditions, with temperature maintained at 18–25 °C, and relative humidity at 70–90%. The slurry is usually prepared from a mixture of 300 to 400 mesh sized zircon flour (typically 75%) and hydrolyzed ethyl silicate or colloidal silica (typically 25%) as a binder. The shell making process is one of the most critical sub-processes of the investment casting process, and has very high rejection level (nearly 35%). It is a known fact that nearly one third of the total energy required to produce investment castings is consumed in the shell making process. The rejection in shell making is mostly driven by the quality of mixing the sand with the binder and additives. Also, the prepared slurry needs to be prepared by maintaining predefined levels of viscosity, pH as well as specific gravity. It was observed that deviation of these values results in increasing formation of microorganisms in ceramic slurry. This formation further affects the process of slurry making, quality of slurry, and in turn reducing life of slurry as well as cold strength of the mold.