IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4,JULY 2004 2095 Dual In-Mold Electromagnetic Stirring in Continuous Casting Ryu Hirayama, Keisuke Fujisaki, Senior Member, IEEE, and Takahiro Yamada Abstract—We evaluate an effect of the dual in-mold electromag- netic stirring (M-EMS) which is arranged in series to control the molten steel velocity distribution using magnetohydrodynamic cal- culation. A stirring force ratio (SFR) defined as where is an electromagnetic force of upper M-EMS and is the one of the lower M-EMS is introduced as an index of input. The value of SFR at the optimal condition that meniscus velocity is almost zero, but some velocity is realized at lower M-EMS position. Especially, the SFR condition to have no velocity at free surface is extremely rig- orous. This means that it is very difficult to be stable at meniscus by the dual M-EMS system. The lower velocity hardly changes when the SFR changes. Index Terms—Continuous casting, electromagnetic analysis, electromagnetic stirring, magneto hydrodynamics calculation. I. INTRODUCTION M OST of the surface quality of the bar steel or steel code is almost decided at the billet mold in the continuous casting, since the molten steel becomes solidified. The molten steel is poured through the submerged entry nozzle, and it is cooled down to be solidified gradually. The M-EMS is used on commercial process line at the billet mold to obtain the high quality steel [1]. The M-EMS which is arranged outside the copper mold makes some electromagnetic force in the molten steel to obtain some velocity. Some velocity at the molten steel is useful for preventing to attach nonmetallic inclusions which cause the bad steel quality. Then some velocity is necessary at lower part of the mold to obtain the high inner quality. Since some powder is floating at free surface to make the casting operation smoothly, large velocity at the free surface causes the powder inclusion into the molten steel and then the surface quality becomes worse. Therefore, it is said that no velocity at free surface and some velocity at lower part of the mold are an important process condition for the M-EMS. If the one M-EMS could realize both conditions to be some velocity at the inner part and no velocity at free surface, the good quality billet would be realized. But, it is very difficult to realize both velocities by using one M-EMS, because of the velocity controllability. Dual EMS where two M-EMS’s are arranged in series in the casting direction and the stirring directions of upper M-EMS and lower M-EMS are different is expected to be a new process technology, because of being effective for the inner quality as Manuscript received October 15, 2003. R. Hirayama and K. Fujisaki are with the Nippon Steel Corporation, Chiba, Japan (e-mail: ryu-hirayama@re.nsc.co.jp; fujisaki@re.nsc.co.jp). T. Yamada is with the Nittetsu Plant Design Corporation, Chiba, Japan (e-mail: yama@re.nsc.co.jp). Digital Object Identifier 10.1109/TMAG.2004.832131 Fig. 1. Structure of dual M-EMS. well as the surface quality [2]. This system is controllable for the free surface velocity and the inner part velocity indepen- dently. We obtain the characteristics of dual M-EMS by using the magnetohydrodynamic calculation [3]. II. MOLD STRUCTURE WITH DUAL M-EMS Fig. 1 is a structure of dual M-EMS. The M-EMS is driven by the electrical power source of three-phase alternating current, and produces the traveling magnetic flux at the molten steel in y direction or direction. Then the eddy current generates in the molten steel in direction. For the Fleming’s left-hand rule, the molten steel receives the electromagnetic force in direction or direction. The M-EMS is made of many sheets of laminated silicon steel and stirring electromagnetic force is strong in front of the laminated steel. The operational frequency of M-EMS is very low such as less than 10 Hz, because the copper mold is arranged between the M-EMS and the molten steel to solidify the molten steel. As shown in Fig. 1, two M-EMSs are arranged in the Dual EMS process in series in the casting direction. The thickness of the laminated core of the upper M-EMS is considered to be shorter than that of the lower M-EMS . Since the purpose of the upper M-EMS is to realize the zero velocity at the free surface, it is enough that the stirring area of upper M-EMS is 0018-9464/04$20.00 © 2004 IEEE