PURPOSE: To exactly control a reflux quantity of a molten metal, by controlling a blow-in quantity of inert gas for reflux so that both height of the molten metal surface in the upper direction of an ascending pipe and a descending pipe in a vacuum vessel, and its difference are not less than a prescribed value.
CONSTITUTION: In a vacuum degassing device 1 which leads a molten 3 such as molten steel, etc. in a ladle 2 into a vacuum vessel 11 from an ascending pipe 12 by blowing in inert gas such as Ar, etc., and executes degassing of the molten metal before returning it from a descending pipe 13, distances l1, l2 to the molten metal surface in the upper direction of the ascending pipe 12 and the descending pipe 13 are measured by distance measuring means 15A, 15B utilizing laser light, an acoustic wave or an electromagnetic wave, height L1, L2 from a molten metal level in each ladle 2, and L1-L2 are derived by an operating means Cal from said values, are displayed on a displaying means Ind, and in accordance with this display, a valve 16 is controlled manually or automatically so that L1, L2 and L1-L2 are not less than a prescribed value.
KOJIMA KATSUHIRO
NIIMI KIYOAKI
YOSHIMURA FUMITAKA
