Ladle Shroud as a Flow Control Device for Tundish Operations
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earch has been devoted to control fluidflow turbulence and to enhance flotation of inclusions in the tundishes of continuous-casting machines for steel. Other aims in tundish design, all related with control of turbulence, include thermal and chemical homogenization of the steel cast through all strands, the elimination of bypass flows toward the closest strands from the entry jet, closed areas of steel around the ladle shroud by the slag cover, and maintaining steady-state operations during casting. Traditionally, to attain a part, or all of these goals, various approaches have been employed such as augmenting the tundish volume to increase the mean residence time of steel in the vessel[1] or to use flow control devices (FCDs) such as weirs, baffles, and dams in order to alter and reorient the flows, and pour pads and turbulence inhibitors[2–5] to decrease input turbulence. Craig et al.[6] employed a set made of a weir and a dam in a single-strand tundish controlled by a stopper rod, reporting an increase of 26 pct of the steel’s mean residence time with respect to the bare tundish. Fan et al.[7] tried various internal arrangements of FCDs in the same type of tundish, using a dam, a baffled dam, a
KEN MORALES-HIGA, Graduate Student, and R.I.L. GUTHRIE and M. ISAC, Professors, are with the McGill Metals Processing Center (MMPC), McGill University, Montreal, QC H3A 2B2, Canada. R.D. MORALES, Professor, is with the Department of Metallurgy, Instituto Politecnico Nacional-ESIQIE, Col. Lindavista-Zacatenco, 07338 Mexico, D.F., Mexico. Contact e-mail: [email protected] Manuscript submitted November 5, 2011. Article published online October 23, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
reversed ‘‘L’’ dam, and a pouring pad with characteristics of a turbulence inhibitor. These authors found that the pouring pad reduced more the dead regions in the tundish compared with other FCDs, increasing the level of steel cleanliness. Since the usage of weirs and dams cannot prevent the formation of an open steel ‘‘eye’’ surrounding the ladle shroud, turbulence inhibitors combined with baffled dams have become popular during the last 15 years for that purpose. Bolger and Saylor[8] reported lower levels of total oxygen pickups during ladle change operations using these FCDs. The inhibitor reflects the incoming stream of steel upwards with a lower turbulence intensity thanks to the dissipation of kinetic energy by the overhangs, or ‘‘lips’’ around the periphery of this device. Morales et al.[9] and Lopez-Ramirez et al.[10] reported that the upward motion of steel in the pouring area provided by such an inhibitor is assisted by the buoyancy forces acting on the inclusions in a positive manner. Buoyancy-inertial regimes are defined through the ratio of the dimensionless number ratio Gr/Re2. After a ladle change, this ratio is larger than unity (due to the incoming hotter steel), and the buoyancy regime favors flotation of inclusions. There are other approaches to optimize the performance of continuous-casting tundishes, such as gas bubbling throug
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