PURPOSE: To prevent the oxidation of the inside surface of the body of the heat insulating furnace which insulates the heat of metal, such as aluminum, in a molten state and to improve the quality of the products produced by die casting, etc., by covering the inside surface of the body of the heat insulating furnace with carbon wool packed with graphite materials in its seams.

CONSTITUTION: The carbon wool 5 is fixed to the inside surface of the body 2 of the heat insulating furnace by using graphite dissolved with oil to a jelly form. The inside surface of the body of the heat insulating furnace is covered with the carbon wool 5 packed with the graphite materials in this way, and therefore, the direct contact of the aluminum 4 in the molten state with the inside surface of the body 2 of the heat insulating furnace does not arise. The oxidation of the inside surface of the body 2 of the heat insulating furnace by the aluminum 4 is thus prevented and eventually the degradation in the quality of the die cast product is prevented.