Mold material composition and method for preparing mold

A method for preparing a self-hardening mold for producing further molds useful for producing metal castings, which method comprises mixing a mold material composition comprising:

• 100 parts by weight of molding sand, about 0.1 to 6 parts by weight of a component (a), about 0.1 to 4 parts by weight of a component (b), about 0.05 to 2.0 parts by weight of a component (c) as SiO.sub.2, and about 0.01 to 0.5 parts by weight of a component (d) on the basis of 100 parts by weight of component (b),
• wherein the component (a) comprises a crude diphenyl-methanediisocyanate or derivatives thereof;
• the component (b) comprises an aliphatic polyetherpolyol mixture having a hydroxyl value of about 350 to 1600, comprising an aliphatic aminopolyetherpolyol having a hydroxyl value of about 400 to 1600 and 2 to 6 functional groups, obtained by an addition reaction of aliphatic amine with alkylene oxide, and an aliphatic non-aminopolyetherpolyol having a hydroxyl number of about 100 to 800 and from 2 to 8 functional groups, the aliphatic polyetherpolyol mixture comprising from 5 to 80% by weight of the aliphatic aminopolyetherpolyol, from 95 to 20% by weight of the aliphatic non-aminopolyetherpolyol and from 5 to 85% by weight of primary hydroxyl-containing polyetherpolyol, wherein the content of the primary hydroxyl-containing non-aminopolyetherpolyol in the component (b) is at least 5% by weight;
• the component (c) is selected from the group consisting of silicate ester, its hydrolysis products, a water dispersion-type silica sol, an alcohol dispersion-type silica sol and mixtures thereof;
• and the component (d) is a catalyst for urethanization, and preparing a mold from the resulting mixture.