Manufacturing method of core and casting product using inorganic binder

A manufacturing method of a core using an inorganic binder, comprising:

• an original sand supplying step in which original molding sand is supplied to a muller;
• a mulling step in which the original molding sand is mixed and mulled with a liquid inorganic binder including water glass and mulled sand is prepared by the muller;
• a sand transferring step in which the mulled sand is transferred from the muller to a mulled sand hopper;
• a sand supplying step in which the mulled sand is supplied from the mulled sand hopper to a blowing head positioned under the mulled sand hopper;
• a blowing step in which the mulled sand supplied into the blowing head is blown into a core mold;
• a gas exhausting step in which the inside of the core mold is exhausted and depressurized;
• a curing step in which after the core mold is preheated, the inside of the blown core is cured and calcined;
• and
• an extracting step in which the core mold is separated and the cured core is extracted,
• wherein the inorganic binder includes the water glass of 40 to 70 parts by weight, nano-silica of 5 to 35 parts by weight, a Li-based water resistant additive of 0.1 to 10 parts by weight, an organic silicon compound of 0.1 to 10 parts by weight, and an anti-sand burning additive of 1 to 10 parts by weight.