Method for manufacturing cast product using breathable salt core

A method for manufacturing a cast product having a hollow part using a breathable salt core, comprising the steps of:

• forming the breathable salt core with powder by molding innumerable salt particles into a predetermined shape corresponding to the hollow part in which the breathable salt core has no groove for escaping residual gasses and so that the breathable salt core has a charging density subsequent to powder molding of 88% to 92% and in which the breathable salt core has an electromicroscopic gap is formed between the innumerable salt particles;
• placing the breathable salt core within a cavity of a gravity casting mold in an uncalcined state;
• gravity casting the cast product by flowing molten metal into the cavity thereby producing the residual gas at where branched flow of the molten material meets each other;
• making the residual gas enter into the electromicroscopic gap via a surface of the breathable salt core so as to retain the residual gas within the breathable salt core;
• and
• dissolving and removing the salt core.