Transient Fluid Flow during Steady Continuous Casting of Steel Slabs: Part II. Effect of Double-Ruler Electro-Magnetic Braking

Plant measurements and computational models of transient flow with and without electromagnetic fields are applied to investigate transient phenomena in the nozzle and mold region during nominally-steady steel slab casting. In Part II of this two-part article, the effect of applying a static magnetic field on stabilizing the transient flow is investigated by modeling a double-ruler ElectroMagnetic Braking (EMBr) system, under conditions where measurements were obtained. A Reynolds Averaged Navier-Stokes (RANS) computational model using the standard k–ε model is employed with a magnetic field distribution extrapolated from measurements. The magnetic field decreases velocity fluctuations and deflects the jet flow downward in the mold, resulting in a flatter surface level and slower surface flow with slightly better stability. The effect of EMBr on surface level and surface velocity, including the effect of the real conducting steel shell, falls between the cases assuming perfectly-conducting and insulating walls. Measurements using an eddy current sensor and nail boards were performed to quantify the effect of EMBr on level and velocity at the mold surface. Power spectrum analysis of the surface level variations measured by the sensor revealed a frequency peak at ~0.03 Hz (~35 seconds) both with and without the EMBr. With EMBr, the surface level is more stable, with lower amplitude fluctuations, and higher frequency sloshing. The EMBr also produced ~20% lower surface velocity, with ~60% less velocity variations. Finally, the motion of the slag-steel interface level causes mainly lifting rather than displacement of the molten slag layer, especially near the SEN. 1. Introduction To control surface level and velocity to avoid defects in steel slab continuous casting, many efforts have been made to optimize nozzle geometry and caster operating conditions including casting speed, submergence depth of the nozzle, mold width, argon gas injection, and ElectroMagnetic Forces (EMF), with the aim to achieve stable mold flow under nominally steady-state operation conditions. Application of a magnetic field to stabilize steel flow is an attractive method because the induced forces intrinsically adjust to flow variations. The field strength distribution depends on the magnet position(s), coil windings, and current. Electromagnetic systems are classified according to the type of field: static (DC current) or moving field (usually AC current). Static systems include local, single-ruler, and double-ruler (FC-Mold) ElectroMagnetic Braking (EMBr). Moving systems include ElectroMagnetic Level Stabilizer (EMLS), ElectroMagnetic Level Accelerator (EMLA), and ElectroMagnetic Rotating Stirrer (EMRS). EMBr is often used in slab continuous casting. Many previous studies …