Improvement of steel billet cleanliness and thermal responses of multiple strands through fluid flow control

Abstract

Fluid flow of liquid steel in a six-strand billet tundish using a simple squared advanced pouring box (APB) promotes the formation of heavy skulls, particularly in the corners of the vessel, and heterogeneous product cleanliness and thermal responses in the strands. To improve the flow patterns, two other APBs were designed and tested through water model tracer injection techniques, ultrasound velocimetry and mathematical simulations. The first APB is the actual design. The second APB maintains the same geometry but is equipped with two circular orifices with zero angle respect to the horizontal at each lateral side placed toward the tundish back wall. The third APB geometry is also squared with elliptic orifices with double upward angles also oriented to the tundish back wall. The first two devices induce long shearing–circulating flows, leaving stagnant regions inside the fluid bulk and particularly in the four upper corners of the tundish, which explains the existence of skulls in the actual tundish. The third device provides a long recirculating flow that eliminates all stagnant regions. Mathematical simulations have indicated that this flow carries energy, through convection mechanisms, toward the upper bath surface, indicating the elimination of skulls. Trials at the caster proved that all skulling problems were eliminated, and thermal and metallurgical evenness was reached using this simple flow control device.