| 摘要 |
PURPOSE:To obtain a sand core which withstands the pressure and speed of charging of molten metal and has a good collapsing property by forming coating layers of a mixture of refractories and colloidal silica and mica successively on the surface of the sand core using org. binders. CONSTITUTION:A sand core is molded by using aggregate such as silica sand and org. binders such as phenolic resins. Aq. slurry of a mixture of powder refractories such as silica flowers and colloidal silica is coated on the surface thereof and is dried, whereby the 1st coating layer is formed. Then the surface of the sand core has smoothness, but still fine cracks and holes exist therein. Thereupon, an aq. synthetic mica soln. is coated on the 1st coating layer and is dried, whereby the 2nd coating layer is formed. Then, the above-described cracks and holes are covered thoroughly and the penetration of molten metal into the core is prevented, whereby the sufficient pressure resistance is provided to the core. Since the synthetic mica has high cleavage characteristic and exhibits fluidity in contact with water, the 2nd coating layer stuck on castings after collapsing of the core and sand stripping after casting is reasily removed. |
