Physical and Mathematical Determination of the Influence of Input Temperature Changes on the Molten Steel Flow Characteristics in Slab Tundishes S. LÓPEZ-RAMÍREZ, J. DE J. BARRETO, P VITE-MARTÍNEZ, J.A. ROMERO SERRANO, and C. DURAN-VALENCIA Transient fluid flow behavior in a tundish with two different arrangements, a bare tundish and a tundish using flow control devices, was studied using physical modeling and a mathematical model. The study places special emphasis on buoyancy effects, particularly transient buoyancy effects due to step change in inlet temperature. For the bare tundish case, the inertial forces are strongly dominant, while in the arrangement using flow control devices, tundish with turbulence inhibitor and low dams, the buoyancy forces are dominant. The results were compared to those representing the real behavior, considering temperature variations, for each tundish arrangement. This comparison made possible the determination of the probable implicit error that could be present in the estimation of the fluid flow characteristic behavior used for the design of the tundish geometry and flow control devices when the temperature variations are not considered. I. INTRODUCTION THE tundish is a vessel that receives molten steel from the ladle and distributes it to the molds through a submerge entry nozzle in the continuous casting machine. In addition, the tundish can be used as a reactor, where it is possible to (a) carry out chemical reactions to improve the quality of the steel, [1] (b) modify and control the temperature of the molten steel, [2,3,4] and (c) remove nonmetallic inclusions. [5] Evidently, before viewing the tundish as an extra resource, it has to work in an optimal manner by controlling the contact of oxygen- molten steel in highly turbulent zones, splashes, slag entrap- ment, and cooling zones. In order to remove inclusions in the tundish, it is necessary to have a good understanding of fluid flow behavior. Some- times, inertial or buoyancy forces may govern this behavior: [6] the inertial forces dominate the fluid behavior when the liq- uid steel stream coming from the ladle shroud promotes high turbulence, which is transmitted to the bulk of the fluid; and vice versa, when the turbulence is reduced, the buoyancy forces dominate the fluid flow behavior. Under this flow regime, the tundish has the highest possibility of allowing the inclusions to float toward the free surface of the liquid bath. [6] When the buoyancy forces are strongly dominant, the tem- perature plays a role of paramount importance. During a normal casting operation, the tundish inlet steel temperature continu- ously drops, due to the heat losses throughout the walls and the free surface to the surroundings of the ladle. During ladle change operations, the new and hotter steel is poured into the tundish and the inlet steel temperature is again increased. The buoyancy forces developed by the fluid density change con- tribute to the modification of the steel flow patterns. Further- more, the steel in the tundish also loses heat through the walls and the free surface. The common way to control the flow is by designing and placing devices inside the tundish; some of them are designed to reduce the turbulence promoted by the entry stream from the ladle shroud, for instance, turbulence inhibitors. This is commonly carried out experimentally using physical or using mathematical models. Two different techniques are normally applied when the design is made experimentally. The first method is based on the addition of a tracer as an impulse in an analogue water model; in this case, the tracer varia- tion with time is monitored at the tundish outlet, [6] and its response is a “C” type curve (RTD curve), which is then used for the evaluation of the flow characteristics. The sec- ond method is based on a temperature step input change in the ladle shroud of a water model (real behavior indicates that the inlet temperature drops; however, this situation is difficult to reproduce experimentally). Temperature varia- tions are also monitored at the outlet of the tundish model; in this case, a “F” curve type of temperature is obtained. [4] This F curve might be transformed into a C curve type; this method considers the influence of temperature on the molten steel flow. The two methods can be reproduced using a mathematical model. Generally speaking, for the design- ing of a tundish arrangement, it is necessary to look for the highest plug flow volume fraction with a minimum dead volume and perfect mixing zones. [7] The molten steel flow behavior characterized by water and mathematical modeling in the bare tundish and in the tundish equipped with a turbulence inhibitor and a pair of dams is the base for the development of this work. The main objective METALLURGICAL AND MATERIALS TRANSACTIONS B VOLUME 35B, OCTOBER 2004—957 S. LÓPEZ-RAMÍREZ, Researcher, is with the Molecular Engineering Research Program, Instituto Mexicano del Petróleo, C.P. 07730, México. Con- tact e-mail: slopezr@imp.mx or slopezr@prodigy.net.ax J. DE J. BARRETO, Professor, is with the Metallurgy Graduate Centre, Instituto Tecnológico de Morelia, 58120-Morelia, Michoacan, México. P. VITE-MARTÍNEZ, Post- doctoral Student, and J.A. ROMERO SERRANO, Professors, are with the Department of Metallurgy and Materials Engineering, Instituto Politécnico Nacional-ESIQIE, C.P. 07300, México. C. DURAN-VALENCIA, Researcher, is with the YNF Research Program, Instituto Mexicanodel Petr´ oleo, C.P. Ø7730, México. Manuscript submitted February 26, 2003.