Novel Approach for Modeling of Nonuniform Slag Layers and Air Gap in Continuous Casting Mold
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HEAT transfer and lubrication behaviors in the mold are the key factors to maintain slab quality and productivity. It is known that the primary cause of cast surface defects is the inhomogeneous heat transfer from strand to mold during continuous casting, which leads to irregularities in the shell thickness profile or even surface cracking. In the continuous casting process, mold powder melts to form a liquid slag pool that is fed between onto the free surface of liquid steel and a solid slag film upon entering the freezing mold/strand channel against the water-cooled, copper mold. The solid slag film provides the optimum level of horizontal heat transfer between the shell and mold while the thin liquid slag film provides liquid lubrication to the shell. Along the casting direction, the slab shell forms and thickens gradually with the intense chilling action of mold plates. An air gap appears when the slab shell shrinks and separates from mold due to thermal shrinkage and phase transition. Among factors influencing the heat transfer of mold and solidification of slab, distributions and existing states of slag and air gap in
WANG XUDONG, Associate Professor, KONG LINGWEI, Master, and YAO MAN, Professor, are with the Department of Materials Processing, School of Materials Science and Engineering, Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian, 116024, Liaoning Province, P.R. China. Contact e-mail: [email protected] ZHANG XIAOBING, Chief Engineer, is with the Chief Engineer Office, Jiangsu Shagang Group, Zhangjiagang, 215625, Jiangsu Province, P.R. China. Manuscript submitted February 1, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
the channel between mold and slab are of utmost importance. Owing to the equipment asymmetry, clogging of the submerged entry nozzle, and liquid slag infiltration and air gap, the growth of the slab shell and its thickness are usually nonuniform, which is identified as the primary reason for longitudinal cracks and many other surface defects. Thus, revealing the characteristics of nonuniform distributions of slag and air gap in mold would play an important role in learning the variability and nonuniformity of a complex casting process. Until now, many mathematical models have been developed to investigate the complicated heat transfer and mechanical behaviors inside the mold.[1–3] Nevertheless, most of them have ignored the influence of measured data in the real casting process, and they have calculated with empirical heat flux equations as the boundary condition, which leads to the ‘‘uniformity’’ and ‘‘symmetry’’ distribution of slag layers and air gap. Therefore, the simulation results do not take into account the effect of nonuniform characteristics. On the other hand, published studies have mostly assumed that liquid lubrication exists in the whole mold, of which the solid slag film and solid friction are often neglected. Meanwhile, researchers seldom focus on the formation and evolution of the air gap in the mold and the results are mostly uniform.[4] Ne
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