STUDY ON THE BEHAVIOUR OF BUBBLES IN A CONTINUOUS CASTING MOLD WITH Ar INJECTION AND TRAVELING MAGNETIC FIELD

Abstract

Steel flow control in a continuous slab caster mold is effective for preventing entrapments of both mold power and argon gas bubbles and maintaining high slab quality.The steel flow control technology that utilizes a traveling magnetic field to optimize the flow of steel in the mold has been developed and applied.The moving magnetic fields can induce accelerating flow(electromagnetic level accelerator,EMLA),decelerating flow(electromagnetic level stabilizer,EMLS) and rotating flow (electromagnetic rotary stirring,EMRS) according the travel direction of the fields.EMLS mode applies a low frequency alternating magnetic field that moves from the narrow face of the mold to the mold center below the nozzle exits.In this study,the model experiments were carried out using liquid alloy of Pb-Sn-Bi and argon gas to study the two-phase fluid flow in the mold with a low frequency traveling magnetic field.The resistance probe was applied to measure the distribution of gas bubbles below the liquid surface and in the deeper liquid phase in the mold.The effect of various parameters such as magnetic flux density,casting speed and argon gas flow rate on the movement and distribution of argon gas bubbles in the mold was studied.The results indicate that the quantity of gas bubbles near the narrow face increases with increasing argon gas flow rate and casting speed.With imposed traveling magnetic field,the quantity of gas bubbles near narrow face at deep position in the pool was decreased,so the possibility that gas bubbles were entrapped into the solidification shell of the steel can be decreased,and the asymmetrical floating of bubbles along the width of mold for a higher casting speed was depressed,so higher disturbances at the free surface in the mold caused by excessive floating of gas bubbles locally can be avoided.The investigations on the floating of big bubbles revealed that the coalescence and flotation of bubbles can be enhanced with imposed traveling magnetic field,and the floating of big bubbles along the width of mold get more uniformity at 0.12 T.