Patent ID: 8240524

Claim:
An upper nozzle configured for fitting into a discharge opening of a tundish or a ladle, the upper nozzle formed with a bore for allowing molten steel to flow therethrough, the bore comprising a bore surface having, as viewed in cross-section taken along an axis of the bore, a configuration which is a curve defined to have continuous differential values of r(z) with respect to z, between two curves represented by respective formulas: log(r(z))=(1/1.5)×log((H+L)/(H+z))+log(r(L)); and log(r(z))=(1/6)×log((H+L)/(H+z))+log(r(L)), wherein: L is a length of the upper nozzle; H is a calculational hydrostatic head height; and r(z) is a radius of the bore at a distance z from an upper end of the bore, and wherein: the calculational hydrostatic head height H is represented by formula: H=((r(L)/r(0)) n ×L)/(1−(r(L)/r(0)) n )(n=1.5 to 6); and the radius r(0) of the bore at the upper end thereof is equal to or greater than 1.5 times the radius r(L) of the bore at a lower end thereof.