Mathematical simulation of fluid dynamics during steel draining operations from a ladle
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I. INTRODUCTION
DRAIN of liquid steel from a ladle is one of the most dangerous operations for a steel clean production. Completely draining steel from a ladle implies slag entrainment due to the vortex formation in the outlet nozzle. Slag detectors, either magnetic or mechanical vibration devices, record the first appearance of slag but are unable to detect vortex development and to quantify steel dirtiness. Moreover, for economic reasons, steel casters will always look for very small metal residuals in the ladle, continuing draining even well after the first slag in the nozzle has been recorded, without any apparent loss of steel quality. Nevertheless, after the fifth or sixth heat in a casting sequence, such operation will increase the number of slag particles in the tundish and this will result in decreasing steel cleanliness. Consequently, in order to determine a final solution to the problem of slag entrainment during steel draining operations, it is necessary to gain a deep understanding of the nature of the fluid dynamics when steel goes toward the nozzle and flows through it in a ladle located in the turret of a casting machine. As may be expected, various aspects of the problem at hand have been addressed by other researchers. For example, experimental findings using water models indicate that critical height of the liquid bath at which the formation of a vortex starts to decrease when the draining nozzle changes from a centred position to an eccentric one.[1,5] This critical O. DAVILA and L. GARCIA-DEMEDICES, Graduate Students, and R.D. MORALES, Professor, are with the Department of Metallurgy and Materials Engineering, National Polytechnic Institute-ESIQIE, Mexico D.F., CP 07338. Contact e-mail: [email protected] and [email protected] Manuscript submitted April 19, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
height, or bath level as is also called here, decreases with the eccentricity of the draining nozzle, and this certainly explains that it has eccentric positions in most of the steel plants. Other authors claim that the critical height increases as the steel throughput increases until a maximum value from which this height starts to decrease.[2,3] Transport properties of slag and steel also play an important role on the formation of a vortex as increases of viscosity ratio steel/slag and density ratio slag/steel lead to increases of the critical bath height for vortex formation.[3,4] Standstill times, after filling a water model, are also an important variable according to Porto et al.,[5] who reported that with long times the critical height becomes smaller for a centric outlet nozzle, and the opposite is observed for an eccentric position. Initial bath height does not influence the critical height for vortex flow. The diameter ratio of the outlet nozzle and the ladle, d/D, is also important according to some researchers,[6,7,8] who claim that this ratio and the critical height for vortex formation are proportional. For a constant d/D ratio, the critical height becomes larger w
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