PURPOSE: To easily produce castings having good product appearance without generating defects, such as casting defects and surface roughness by volatilization defect, by coating the outside surface of a lost foam prototype for casting with a foam layer of a thermosetting resin. ;CONSTITUTION: The contact part of a sand mold with molten metal heats up to a high temp. and the foam layer of the thermosetting resin on the surface and the internal thermosetting resin foam are dissipated by volatilization when the molten metal is poured into the mold. The thermosetting resin foam in the lost foam prototype of the non-contact part is shrunk by radiation heat but the thermosetting resin foam does not shrink. In addition, the shrunk matter is held in the thermosetting resin foam layer in the surface part of the lost foam prototype and does not come into direct contact with the sand mold. The shrink matter is dissipated by volatilization together with the thermosetting resin foam layer when the molten metal comes into contact with the shrunk part of the thermosetting resin foam as the pouring of the molten metal progresses and the dissipation of the contact part by volatilization progresses. Then, the presence of the residual lumps, etc., of the lost foam prototype within the sand mold hardly arises after finishing of pouring the moten metal.;COPYRIGHT: (C)1995,JPO
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