Development and calibration of a karman vortex probe for measurement of molten-steel velocities
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I.
INTRODUCTION
Requirements for high productivity of clean steel in continuous casting processes have become increasingly severe. In order to reduce defects originating from nonmetallic inclusions, mold powder, and small Argon bubbles for high casting speed, the steelmaking industry is trying to control molten-steel flow in continuous-casting molds by using electromagnetic devices such as electromagnetic braking[1–5] or by changing the nozzle design.[6] In addition, attempts have been made to predict the molten-steel flow in continuous-casting molds, in order to determine optimum casting conditions, through the use of water-model experiments[7,8,9] and numerical simulation.[10,11,12] Because of these efforts, flow patterns in continuous-casting molds and the behavior of nonmetallic inclusions, mold powder, and Argon bubbles are qualitatively predictable. Unfortunately, due to lack of direct measurement methods for molten-metal flow velocity at very high temperatures, the effectiveness of the change in nozzle design and the use of electromagnetic braking, as well as the adequacy of the numerical predictions, have not been examined precisely. The main purpose of this study, therefore, is to develop a velocimeter capable of directly measuring the moltensteel flow velocity near the meniscus in actual continuouscasting molds.
II.
DEVELOPMENT OF KARMAN VORTEX PROBE
A. Previous Work Much effort has been devoted to developing velocimeters for measuring molten-steel flow in continuous-casting molds. The most popular velocimeter is a reaction probe.[13–17] Its measurement principle is based on the unique relation between the molten-steel velocity and the drag force acting on a two-dimensional or three-dimensional body immersed in the molten-steel flow. A circular cylinder or a sphere made of refractory has usually been used as a representative body. The drag force (FD) is represented by[18] FD 5 CD Arv 2/2
where CD is the drag coefficient, A is the area of the body projected to a plane perpendicular to the flow direction, r is the density of molten steel, and v is the molten-steel flow velocity. The drag coefficient CD is a function of the Reynolds number, defined by Re 5 vD/n
METALLURGICAL AND MATERIALS TRANSACTIONS B
[2]
where D is the diameter of the cylinder or the sphere and n is the kinematic viscosity of the molten steel. For example, the projected area A for a circular cylinder is given by A 5 DH
MANABU IGUCHI, Professor, is with the Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Hokkaido, 060-8628 Japan. HIROAKI KOSAKA, General Manager, and ATSUSHI HAYASHI and YUKIO TERAUCHI, Researchers, are with the R&D Division, Heraeus Electro-Nite Japan Ltd., Osaka, 569-0835 Japan. HIDEO MIZUKAMI and MASAHITO HANAO, Researchers, and MASAYUKI KAWAMOTO, Manager, are with the Steelmaking Process Research Department, Corporate Research and Development Laboratories, Sumitomo Metal Ind., Ltd., Ibaraki, 314-0255 Japan. HIROTOSHI KAWABATA, Senior Technician, is with Graduate
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