Experimental Investigation of the Flow in a Continuous-Casting Mold under the Influence of a Transverse, Direct Current
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ication of various magnetic fields is considered for an effective flow control in the continuous casting of steel with substantial capabilities to improve the quality of the steel and to enhance the productivity of the process. For instance, alternating current (AC) magnetic fields are employed as electromagnetic stirrers (EMS) for a better homogenization of the melt and for a promotion of the double-roll flow pattern in the mold, which is supposed to decrease many slab defects and therefore improve the quality of the solidified steel strand.[1,2] Another approach to ensure high-quality slabs under high casting speeds is the use of direct current (DC) magnetic fields across the mold perpendicular to the casting direction as electromagnetic brake (EMBR).[3,4] Too high velocities of the flow discharging from the submerged entry nozzle (SEN) impair the cleanliness of the steel by the entrapment of bubbles and nonmetallic inclusions. The DC field should brake the discharging jet directly and dampen the recirculating flows that arise from the high-intensity jet pouring into the mold from the SEN. The main impact of the magnetic field is supposed to result in a uniform reduction of the velocity in the mold region. The EMBR technology had been invented already in the 1980s and was applied initially to continuous-casting plants in Japan and Sweden.[5] On the one hand, second and third KLAUS TIMMEL, Ph.D. Student, SVEN ECKERT, Group Leader, and GUNTER GERBETH, Department Head, are with the MHD Department, Forschungszentrum Dresden-Rossendorf (FZD), 01314 Dresden, Germany. Contact e-mail: [email protected] Manuscript submitted March 2, 2010. Article published online December 7, 2010. 68—VOLUME 42B, FEBRUARY 2011
generations of EMBRs are brought into industrial use (see, for instance, Reference 6). On the other hand, the electromagnetic braking of such highly turbulent and complex flows considered here is a complicated phenomenon and has not been understood fully until now. A multitude of numerical studies was carried out considering different magnetic field configurations[7–11] for the continuous-cast steel, but the reliability of the numerical results is confirmed only insufficiently by accompanying experimental activities. Experimental studies on industrial scale with hot metallic melts (T ‡ 900 K [600 C]) may require formidable effort and expense. The main drawback is the extremely limited availability of measurement techniques that can provide reliable quantitative data from the flow. Hence, a serious deficit of experimental data is noticed, which could be employed for numerical code validations. Various researchers[5,12,13] reported about EMBR tests in steel plants. Remarkable improvements to the steel quality were found and related to a distinct reduction in the flow velocity. However, the effect of the magnetic field on the flow was shown only roughly. The strain gauge method was used to measure the force acting on a ceramic rod immersed in the molten steel near the surface region. The obtained signals showed a reduction of fluctuations by the m
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