PRODUCTION OF SAND CORE FOR HIGH PRESSURE CASTING

PURPOSE:To obtain a core which withstands the high pressure of a molten metal and has a good collapsing property by forming a coating layer consisting of a synthetic mica-contg. slurry on the surface of a sand core molded by using an org. binder and forming a synthetic mica layer thereon. CONSTITUTION:A slurry prepd. by mixing powder refractories, synthetic mica and water soluble salt and adding NaOH to the mixture to make the same neutral and alkaline is coated on the surface of a sand core molded by using an org binder and is dried to form the 1st layer. An aq. synthetic mica soln. is coated on the layer and is dried to form the 2nd layer. The synthetic mica in said slurry is convenient to a decrease in the viscosity of the slurry and closes the fine pores on the surface of the core, thereby providing high pressure resistance to the formed layer. The 2nd layer prevents penetration of a molten metal into the fine cracks and holes of the 1st layer, the consequent difficulty in removing the coating layer from the product and the deterioration in the dimensional accuracy.