Abstract

    The conditions of steel feed to the CCM mold are believed to be crucial factors affecting quality of continuous cast slabs. The greater kinetic energy inherent to a steel jet passing from a tundish to the mold is responsible for inducing powerful turbulent flows in the overheated steel. Modifications to the submerged entry nozzle design, namely the number and shape of its outlet openings, as well as optimization of contact angle with steel, would allow for fast and uniform growth of a solidifying shell, an increase in allowable lifetime of a SEN, and would promote separation of inclusions at steel-slag interfaces, thereby enhancing slag-metal reactions. Modern slab casters employ submerged entry nozzles of different configurations. Emphasis is placed on the design of a SEN lower part, since it specifies the pattern of steel outflow. In recent years, submerged entry nozzles supplied with “cleavers” and “traps” have been widespread, they produce different patterns of molten steel flow from the ladle through the tundish and into the caster. Clogging in continuous casting nozzles is a common operational occurrence that can result in change of fluid flow pattern, flow velocity and flow uniformity into the mold, which will in turn result in decreased productivity, increased maintenance expense, and decreased product quality.
    On the basis of experimental data and scoping calculations relating to the mode of depositions buildup in the interior of a submerged entry nozzle, it is reasonable to draw the following conclusions: alumina accretions are frequently observed when molten steel is deoxidized by the addition of Al in a process for continuous casting of aluminum-killed steel; alumina clogging is enhanced in the lower part of an orifice and is dependent on the nozzle submerging depth; the degree of clogging is also determined by a nozzle geometry [1-3]. Nozzle clogging is one of the most disruptive phenomena in continuous casting of steel. Nozzle clogs are suspected to adversely affect product quality in several ways. Mainly, the clogs may change flow patterns in the mold, which are usually carefully designed, and consequent mold level variations and unstable flow may cause casting defects due to inclusions of mold powder and bubbles. Hence, research aimed at optimization of SENs geometry must account for and be consistent with the optimization issues of circulation flow patterns in the mold. Here, effective clogging countermeasures include modifications to nozzle bores geometry, submerging depth in the molten steel, optimization of steel jet angle emerging from the orifice, argon injection through a stopper, etc. Physical and mathematical modelling methods are essential, as the data generated would aid in improved design and selection of steel making technique. However, transparent physical models are believed to provide with objective and unambiguous information as they enable to visualize the process flow [4,5]. The purpose of the present work is to examine thoroughly by physical modelling the process of turbulent eddies generation, to track their possible spread in the molten steel vessel with respect to submerged entry nozzle geometry. Extensive experimental results enabled us to develop optimal flow patterns, which are consistent with specific casting conditions. Incorporating an additional opening at the SEN bottom is employed in this study as one of the means for ensuring optimal fluid flow patterns in the nozzle and the mold.

REFERENCES

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