Thermal criteria for tundish nozzle or taphole blockage

Abstract

A formulation is presented to describe the rate at which a solidified crust is formed (and possibly remelted) on the inside walls of a nozzle through which molten metal is being poured. The molten metal stream is considered to be turbulent and in the formulation allowance is made for transient heat conduction in the skull and in the refractory walls, together with the time dependent mass flow rate due to the presence of the skull. The resultant differential equations are solved numerically and computed results are presented for conditions that are thought representative of some tundish pouring practices. It was found that the growth and possible remelting of the solidified crust would take place very rapidly, in a matter of seconds. The effect of several parameters was examined, including the role played by the nozzle diameter, the superheat of the steel and the preheating of the nozzle walls. It was found that the nozzle diameter was the most critical variable; nozzles less than about 1/2 in. in diam were likely to freeze rather readily. The superheat of the steel was found important in affecting closure, but the preheat of the nozzle appeared to be less significant a variable, provided the nozzle was brought within about 500‡F of the freezing temperature of the steel.