Improvement of Built-In Electromagnetic Stirring in the Molds of Bloom Continuous-Casting Machines
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IMPROVEMENT OF BUILT-IN ELECTROMAGNETIC STIRRING IN THE MOLDS OF BLOOM CONTINUOUS-CASTING MACHINES S. I. Shakhov,1 K. N. Vdovin,2 R. I. Kerimov,3 Yu. M. Rogachikov,4 and D. S. Shakhov5
UDC 621.746.27:537.812
We study the equipment developed at the AO AKhK VNIIMETMASh and intended for the built-in electromagnetic stirring in the molds of bloom CCM performed with an aim to improve the quality of manufactured tubular billets. Keywords: continuous casting machine (CCM), electromagnetic stirring, electromagnetic brake, mold, steel grade, quality of billets.
In order to improve the structure of continuously cast blanks, it is customary to use the method of intense electromagnetic stirring (EMS) in the process of crystallization of the metal. However, in the zone of meniscus, it is necessary to change the requirements to character of stirring [1]. Thus, the optimal velocity of motion of the metal must satisfy several conditions. On the one hand, it must be higher than a certain minimal level at which slag and nonmetallic inclusions start to centrifuge to the axial zone of the meniscus. On the other hand, this velocity should not exceed a certain maximal level because the swirls formed in the metal of the meniscus may become so deep that it would be impossible to remove slag from the surface. The presence of simultaneous too high intensity of stirring may lead to the appearance of negative liquation, formation of pores along the front of crystallization, and generation of the surface defects of the billet caused by the instability of the meniscus (scabs, bleeds, shrinkage cavities, etc.) [2]. In the case of too intense motion of the melt near the meniscus in the process of casting “to a level,” the protective slag mixture can be also drawn into the metal, which would lead to an increase in the score by point inhomogeneity and a decrease in the quality of macrostructure of the billets. In addition, in the zone of meniscus, the procedure of intense EMS may lead to the washout of submerged cups [3]. In the case where EMS is used in a mold in order to get a “quiet” meniscus, then the stator should be placed as low as possible. However, in some cases, e.g., due to the specific features of the structure of molds or the case of application of a short sleeve of length 700 mm, it is impossible to remove the stator from the meniscus for the required distance. Most often , this happens in the production of round billets with large cross sections. Therefore, the possibility of independent control of the flows of melt near the meniscus is an important factor affecting the quality of the billets. Note that it is also possible to use two-level stirring devices guaranteeing the possibility of independent control over the process of stirring in different domains of the mold [1–8]. This is realized by combining two sets of induction coils in a single EMS system, one of these sets is placed in the lower part of the mold and the other is 1 2 3 4 5
“A. I. Tselikov VNIIMETMASh,” Moscow, Russia; e-mail: [email protected].
“G. I. Nosov Mag
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