Physical and Mathematical Models of Vortex Flows During The Last Stages of Steel Draining Operations from a Ladle

Abstract

Slag entrainment during steel teeming-drain operations from a steel ladle impacts negatively steel cleanliness and quality. In the present work water modeling and mathematical simulations using a multiphase model for momentum and heat transfer were employed to understand the mechanisms of vortex funnel drain and sink drain flows. The critical bath height for vortex development increases with steel throughput and valve gate opening. Six stages during vortex development are identified, passing from a dimple formation on the bath surface until sink drain which begins when the bath level has the same magnitude as the nozzle diameter. This later drain pattern is independent from any other teeming-draining variable being only a function of the bath height and nozzle diameter; when they are about the same the metal-interface collapses. The temperature gradients originated by the heat losses of the ladle to the surroundings provide buoyancy forces that are large enough to influence liquid motion in the ladle. At large bath levels steel observes long-vertical recirculating flows and at low bath levels these flows change to horizontalcircular recirculating flows that become a seed for later vortex development. These buoyancy forces increase the critical height for vortex development and slag entrainment.

Study of Tundish Slag Entrainment Using Physical Modelling

“…Following partial results of works [8][9][10][11][12][13][14][15][16] a trend was found to increase the critical level with the application of liquid with lower density.…”

“…Critical levels for vortex creation were compared and discussed in the paper [14]. when the paraffin oil was applied, the critical level for vortex creation was at the height of 191 mm, when paraffin oil with low viscosity was used, then the height was 195 mm.…”

“…There are a lot of works [8][9][10][11][12][13][14][15][16][17] concerned the problem of the physical modelling of slag entrainment in the metallurgical aggregates. These works mainly focus on setting and adapting the theory of similarity for the case when liquids with various density and viscosity have to simulate steel and slag.…”

New Process with Argon Injected into Ladle around the Tapping Hole for Controlling Slag Carry-over during Continuous Casting Ladle

“…Hammerschmid et al [1] and Andrzejewski et al [6] reported that the vortex formation depends strongly on the state of initial rotation. However, Morales et al [7] and Dubke et al [8] reported that the initial rotation had little or null influence on the vortex formation. The vortex formation is also affected by the eccentricity of the draining nozzle [1,4,9,10], the steel throughput [5,11], the slag thickness [12,13], the ratios of viscosity as well as density between steel and slag [14], the diameter ratio of the outlet nozzle and the ladle [2,15], and so on.…”

“…A drain sink is always present at the end of the process and takes place when the bath height of the steel is approximately equal to the nozzle diameter [4,6,16]. Several researchers claim that there was no vortex formation and slag carry-over was caused by drain sink in the teeming ladle [4,8], while more researchers reported that vortex was formed prior to the drain sink formation [1][2][3]7,17].…”