Two-dimensional model for twin-roll continuous casting
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I.
INTRODUCTION
I N recent years, a growing interest has been concentrated on the twin-roll continuous casting (CC) processes, which have many advantages over other existing methods. The rapid solidification process using twin-roll is promising because it is assumed that (1) it permits greater control over the internal material structure, such as establishment of microcrystalline structure and mechanical properties, and improves segregation; (2) it saves energy through a reduction of processes, such as the simplification of the hot rolling process, the manufacturing of difficult hot rolling materials, and the simplification of casting and rolling facilities. Although the twin-roll CC process is a promising one, it is more difficult to control because of the existence of the deformation of the roll itself, due to thermal expansion or thermal stress owing to the narrow roll gap. Further, if solidification is completed before the liquid reaches the minimum clearance point between the rolls, then deformation of the solid will occur when operating with fixed gap. The plastic deformation of the material then has to be considered in this case. For the above-mentioned reasons, it is necessary to develop efficient numerical tools to elucidate the complicated flow and heat transfer mechanism, which will be especially useful for designing optimum twin-roll CC systems. A complete solidification analysis in one dimension for the twin-roll CC including flow and heat transfer in the liquid and solid regions is limited, to the best of our knowledge, to the report by Miyazawa and Szekely m in which the heat transfer, the flow of the solid and molten phases, and the pressure distribution in the solid phase for the twin-roll rapid quenching of pure metallic materials were clarified. They discovered that there exists T. SAITOH and H. HOJO, Professors, and H. YAGUCHI, Research Associate, are with the Department of Mechanical Engineering II, Tohoku University, Sendai 980, Japan. C.G. KANG, Associate Professor, is with the Department of Mechanical and Precision Engineering, Pusan National University, 30 Jangjeon-Dong, Dongnaeku, Pusan 607, Korea. Manuscript submitted October 7, 1987. METALLURGICAL TRANSACTIONS B
a narrow range of casting parameters (i.e., the roll spacing, the angular velocity of the rolls, the feed rate of the material, and the physical properties of the material) that gives a stable mode of operation. The CC problems, including the twin-roll technique, have been reviewed by Szekely, [2] Ohnaka, ~31 and recently by Ohashi. t4~ This paper presents a thorough numerical methodology for the two-dimensional heat transfer and flow phenomena in the liquid and solid regions in a twin-roll continuous casting system with the fixed-gap operation. The mathematical model presented covers the wide range of casting parameters since the two-dimensional transport in both phases is taken into account. The present study differs from that of Miyazawa-Szekely in that the complete two-dimensional aspect in CC is clarified. II.
MATHEMATIC
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