| 摘要 |
PURPOSE:To decarburize a molten metal down to an extra-low carbon region without extending the time for refining by detecting the molten metal level position of the molten metal in a vacuum degassing vessel by a rangefinder and controlling an evacuation device in accordance with the detected value to control the molten metal level position so as to be kept in a prescribed range. CONSTITUTION:The inside of a degassing vessel body 11 is evacuated and maintained under the reduced pressure by operating the evacuation device 40 to rise the molten steel 17 in a ladle 18 into the body 11 via a riser 12. The molten steel is then returned via a downcomer 13 into the ladle 18. The molten steel 17 is decarburized by bringing the oxygen and carbon therein into reaction. Gaseous Ar is blown to the molten steel 17 via a supply pipe 16 to relatively reduce the weight of the molten steel 17 in the riser 16. The molten metal level position of the molten steel 7 is detected by the rangefinder 20 provided in the upper part of the body 11 and the detected value thereof is outputted to a process controller 30 in the above-mentioned operation. The process controller 30 outputs a control signal to the evacuation device 40 in accordance with the signal of the detected value to control the rate of discharge, by which the molten metal level position of the molten steel 17 is feedback-controlled. The molten metal level position is thereby maintained in the prescribed range and the need for extending the time for vacuum refining is eliminated.
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