Transient Fluid Flow during Steady Continuous Casting of Steel Slabs: Part I. Measurements and Modeling of Two-phase Flow

Abstract

Unstable mold flow could induce surface velocity and level fluctuations, and entrain slag, leading to surface defects during continuous casting of steel. Both argon gas injection and Electro-Magnetic Braking (EMBr) greatly affect transient mold flow and stability. Part I of this two-part article investigates transient flow of steel and argon in the nozzle and mold during nominally steady-state casting using both plant measurements and computational modeling. Nail board dipping measurements are employed to quantify transient surface level, surface velocity, flow direction, and slag depth. Transient flow in the nozzle and strand is modeled using Large Eddy Simulation (LES) coupled with the Lagrangian Discrete Phase Model (DPM) for argon gas injection. The surface level of the molten steel fluctuates due to sloshing and shows greater fluctuations near the nozzle. The slag level fluctuates with time according to the lifting force of the molten steel motion below. Surface flow shows a classic double roll pattern with transient cross-flow between the Inside Radius (IR) and the Outside Radius (OR), and varies with fluctuations up to ~50% of the average velocity magnitude. The LES results suggest that these transient phenomena at the surface are induced by up-and-down jet wobbling caused by transient swirl in the slide-gate nozzle. The jet wobbling influences transient argon gas distribution and the location of jet impingement on the Narrow Face (NF), resulting in variations of surface level and velocity. A power-spectrum analysis of the predicted jet velocity revealed strong peaks at several characteristic frequencies from 0.5-2 Hz (0.5-2 sec).

Measurements of Molten Steel Surface Velocity and Effect of Stopper-rod Movement on Transient Multiphase Fluid Flow in Continuous Casting

“…Displacement of the liquid slag layer is neglected in this equation, because the entire layer was assumed to be thin enough to simply rise and fall with the steel surface profile variations. This assumption agrees with recent measurements by Cho et al 38) The predicted mold level during the simulated 30.0 sec interval with stopper rod movements agrees reasonably well with the measured unfiltered mold level data, at the midway point between SEN and narrow face along the centerline, as shown in Fig. 14.…”

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

“…14,17) Part I of this two-part article presented models and experimental methods, and applied them to investigate twophase transient flow. 18) In Part II, the effect of double-ruler…”

“…18) The magnetic field applied by the double-ruler EMBr is shown in Fig. 2, and has high peaks in two regions: one centered just above the port, 250 mm below mold top and the other below the nozzle port, ~750 mm below mold top.…”

“…The equations and boundary conditions were solved with the finite-volume method in ANSYS FLUENT, as described in Part I. 18) …”

Modeling of Gas-Steel-Slag Three-Phase Flow in Ladle Metallurgy: Part II. Multi-scale Mathematical Model

“…Recently, Liu et al 11) and Cloete et al 12) coupled the VOF and DPM respectively for the immiscible continuous phases and bubbles with the standard k-ε turbulence model. For some other processes, also using the Lagrangian DPM for bubbles, Cho et al 13) investigated the transient fluid flow during continuous casting of steel slabs, Ling et al 14) investigated the effect of nozzle number on recirculation rate and mixing time in the RH process.…”