Computational Modeling of Temperature, Flow, and Crystallization of Mold Slag During Double Hot Thermocouple Technique E
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MOLD powder is widely used in modern continuous casting of steel, where it melts to form a liquid flux layer above the molten steel and infiltrates into the mold/shell channel. Mold flux functions are (1) to protect the steel from oxidation, (2) to insulate the steel and avoid meniscus freezing, (3) to absorb inclusions, (4) to lubricate the shell from sticking to the mold, and (5) to moderate the heat transfer in the mold. The crystallization of mold flux is regarded as one of the most important properties of mold flux because it greatly influences both heat transfer and lubrication.[1,2] Therefore, it is important to understand the crystallization behavior of mold slag. It is difficult to observe slag behavior directly in the mold due to the high temperature production environment that makes visualization and measurement difficult. Furthermore, the mold adds complications involving powder melting, mold oscillation, transient fluid flow, complicated chemical reactions with the steel and atmosphere, and other phenomena. Thus, several LEJUN ZHOU, Graduate Student, is with the School of Metallurgical Science and Engineering, Central South University, Changsha 410083, People’s Republic of China, and also Visiting Scholar with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green Street, Urbana, IL 61801. WANLIN WANG, Professor, is with the School of Metallurgical Science and Engineering, Central South University. Contact e-mail: [email protected] RUI LIU, Graduate Student, and BRIAN G. THOMAS, C.J. Gauthier Professor, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign. Manuscript submitted December 3, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
different laboratory technologies have been developed to study the fundamental crystallization behavior of mold flux, including the double hot thermocouple technique (DHTT) and the single hot thermocouple technique (SHTT). The DHTT and SHTT were first developed by Kashiwaya et al.[3,4] for in situ observation of mold flux crystallization and are favored by many other researchers due to easy visualization as well as high heating and cooling rates.[5–10] However, only the temperature of the mold slag adhering to the thermocouples can be measured, making important effects on crystallization, such as spatial variations in temperature and fluid flow inside the mold slag sample, difficult to quantify. Moreover, fluid flow in the small, lump-shaped DHTT sample is dominated by natural convection and surface effects driven by Marangoni forces. This is very different from the real process, where the mold slag is shaped in the form of a large, thin sheet that is squeezed in the gap between an oscillating mold and a moving steel shell. Thus, it is problematic to apply the experimental results directly to the real casting process. Fortunately, computer modeling offers a powerful tool to investigate these effects. Such models can be used to develop more fundamental property data. After the model s
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