PURPOSE: To constitute the title furnace so that a gap formed between the fringe of a base part of a mold and a scattering preventive cover is made fixed even if the mold is tilted at the time of immersion, the scattering preventive cover and the mold are not interfered with each other and heating medium particles are not scattered outside, by a method wherein the scattering preventive cover is bent concentrically around a rotary center of the mold.

CONSTITUTION: A mold 6 for plastic molding is put on heating medium particles 3 with an inclination so that an air rich area is not generated and the mold is heated by the flowing heating medium particles 3. In this instance, the top of a furnace body 2 is covered with the mold 6 to be put on the heating medium particles 3 and scattering preventive covers 7a, 7b to be provided on the circumference of the mold 6. A high-speed air current blown upward toward a base part 6b of the mold from a projected part of the lower part of a mold main body 6a is sucked to a dust collector 12 and exhaust 11. In this instance, though the air is entered within a furnace body 2 from the outside at gaps 8a, 8b among the scattering preventive covers 7a, 7b and the base part 6b of the mold, uniform suction of the air with the fixed gap which does not depend upon an inclination of the mold 6 becomes possible, through which the heating medium particles 3 are prevented from scattering outside of the furnace.