| 摘要 |
PROBLEM TO BE SOLVED: To efficiently restrain the spitting without lowering the oxygen efficiency in decarburization and to improve the yield by alternately arranging two kinds of Laval nozzles having different inclining angles in a circumferential direction in a top-blown lance and specifying the ratio of both nozzle diameters. SOLUTION: In the top-blown lance for refining by blowing the refining gas onto molten metal, a plurality of Laval nozzles are arranged to improve the oxygen efficiency in the decarburization. At this time, in the nozzles 1, two kinds of nozzles 2-1, 2-2 having different inclining anglesθ1 ,θ2 , e.g.θ1 <θ2 are alternately arranged, desirably at the equal interval in the circumferential direction. Further, the ratioα=d12 /d11 of the diameter d12 of the nozzle 2-2 having large inclining angleθ2 to the diameter d11 of the nozzle 2-1 having small inclining angleθ1 , is made to 2.0>=α>1.0, desirably about 1.8>=α>=1.2. In this way, the pitting caused by the jet from the nozzle 2-1 is reduced and the pitting caused by the jet from the nozzle 2-2 is increased, and the pitting in the vertical direction is reduced to reduce the loss of molten metal.
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