METHOD FOR USING UPPER NOZZLE

摘要

In order to further limit the occurrence of accretions by adding a gas in-blowing function to an upper nozzle with a bore shape capable of creating a smooth (uniform) molten steel flow with minimal energy loss to limit the occurrence of accretions, a nozzle is used wherein, when the nozzle length is (L), the calculated head height is (H) and the radius at a distance (z) downward from the upper end is (r(z)), the shape of a cross-section of the wall surface of the bore through which the molten steel passes, the cross-section being cut along the axis of the bore, is a curve in which the derivative with respect to (z) of (r(z)) between the curves represented by log (r(z))=(1/1.5)xlog((H+L)/(H+z))+log(r(L)) and log (r(z))=(1/6)xlog((H+L)/(H+z))+log(r(L)) is continuous. The nozzle is configured so that the flow velocity (VL)(m/s) of the molten steel passing through the bore at the lowest end of the upper nozzle and the gas ratio (RG)=(QG/QL)x100(%), which is the volume ratio of the in-blown gas flow rate (QG)(NL/s) to the molten steel flow rate (QL)(L/s), satisfy the relationship (RG) <= 4.3 x (VL).