PURPOSE: To produce the collapsible sand core having an excellent coating property by subjecting the front surface of a sand core prototype consisting of the system sand compounded with a hardener having a specific compsn. to uniform coating.
CONSTITUTION: The process for production of the sand core is constituted of a stage for molding the sand core prototype by the system sulfate, a furan resin and the hardener for curing the furan resin into aggregate for molding the sand core prototype and kneading the compound, a stage for coating the surface of this sand core prototype with a slurry-like coating liquid consisting of a neutral aq. dispersion essentially consisting of powdery refractories and a stage for drying the sand core obtd. by the coating. As a result, gelatinization is induced in the part where the colloidal silica in the coating liquid comes into contact with the surface of the sand core prototype and the coating liquid is thereby thickened, therefor, the penetration of the coating liquid into the sand core prototype is suppressed and the coating layer having a uniform thickness is formed.
KAWASHIMA GENZO
KAWAMURA NOBUYUKI
OKAMOTO HIDEMASA
