Core composition for casting, and method for preparing core for casting using the same

A core composition for casting, consisting essentially of:

• mold sand;
• a binder in amount of about 4 to 6 parts by weight with respect to 100 parts by weight of the molding sand, the binder consisting essentially of an amount of about 8 to 10 parts by weight of Na2O and about 25 to 30 parts by weight of SiO2 with respect to 100 parts by weight of the binder and a oxide film in amount of about 0.1 to 0.3% by weight with respect to the total weight of the core composition;
• and
• a zinc oxide powder in an amount of about 0.4 to 0.6% by weight with respect to the total weight of the core composition.

A method for preparing a core for casting, comprising:

• preparing a mixture by mixing components of a core composition for casting, the composition comprises:
• molding sand, a binder that includes a water glass-based binder and an oxide film inhibitor and an additive;
• supplying the mixture to a core mold;
• and
• dehydrating the binder by supplying heat and hot air to the core mold supplied with the mixture.