PURPOSE: To prevent oxidation and cooling of molten metal by floating up a platy or granular floating material having heat resistance and sp.gr. smaller than that of the molten metal in a molten metal storing chamber, pouring chamber or molten metal receiving passage.

CONSTITUTION: The platy floating material 11 and the granular floating material 12 are floated in the molten metal storing chamber 3. These floating materials 11, 12 are composed of graphite or ceramic and has heat resistance and the sp.gr. smaller than that of the molten metal 1. The pouring chamber 7 and the molten metal receiving passage 4, too, use the floating material, but in the molten metal receiving passage 4 in some case, only the granular floating material 12 is used under consideration of spattering at the time of receiving the molten metal. By this method, surface of the molten metal 1 in the molten metal storing chamber 3, pouring chamber 7 or the molten metal receiving passage 4 is sufficiently shut off from gas with the floating materials 11, 12, and the oxidation and the cooling are prevented. As the sp.gr. of floating materials 11, 12 is smaller than that of the molten metal 1, this is naturally floated up on the surface of molten metal and as this has the heat resistance, thi.