| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve the secondary combustion ratio, heat transfer efficiency in a furnace and the sensible heat of exhaust gas and the heat transfer efficiency of arc heat and to prevent the conduction of large short-circuit current at the time of melting. SOLUTION: A DC are melting furnace has the capacity into which the whole quantity of scraps can be charged in one time, and in the case the arc voltage becomes a setting value or lower, a voltage lowering signal is transmitted, and in the case the arc current is higher than a setting value, a current conductive signal is transmitted. In the case of receiving both signals, a side arc judging part 47 transmits a side arc signal to an adjusting part 39, and in the case of receiving both signals while continuing for a prescribed time, the side arc judging part changes to a short-circuit signal and transmits to the adjusting part. In each, the adjusting part 39 is made so as to keep the movable electrode 12 as it is, or so as to rapidly elevate the electrode. Nozzles for secondary combustion in the furnace are set to >=3 pieces and the ratio (h/L) of a height (h) of the nozzles from molten metal surface and the free board length L, is made to 0.15-0.55 and gas blowing direction is regulated to <40 deg. opening angle to the electrode while avoiding the electrode. The ratio of the height in the furnace and the inner diameter of the furnace, is regulated to 0.6-1.4, and in the case of being 1.0-1.4, the nozzles are set to >=2 steps and >=3 pieces in each step.</p> |
