RESIN COATED SAND GRAIN FOR SHELL MOLD

PROBLEM TO BE SOLVED: To lessen the generation of formaldehyde at the time of molding by consisting indispensably of a binder of sand grains of at least one kind selected from a novolak type phenolic resin, urea compd. and triazole compd. SOLUTION: This resin coated sand grain is formed by adding 0.5 to 5 pts.wt. novolak type phenolic resin to 100 pts.wt. refractory particles and adding 5 to 30 pts.wt. hardener per 100 pts.wt. binder thereto. The urea/triazole compds. of the binder are intended to capture the formaldehyde generated at the time of the reaction with the novolak type phenolic resin and the hardener, more particularly hexamethylene tetramine and are exemplified by various kinds of the compds. One or more kinds among biurea, biuret and 1, 2, 4 triazoles are preferably used as a mixture composed of urea for the blocking resistance and hardenability of the resin coated sand. The amt. of the addition is specified 1 to 5 pts.wt. per 100 pts.wt. novolak type phenolic resin.