Thickness Distributions of Mold Flux Film and Air Gap in Billet Ultra-High Speed Continuous Casting Mold Through Multiphysics Modeling

Abstract

The thicknesses of mold flux film and air gap are significant factors that affect the high-efficiency heat transfer, the strand lubrication and mold taper design of billet ultra-high speed continuous casting mold. Therefore, this paper established the three-dimensional fluid flow, heat transfer and solidification model, interfacial heat transfer model and two-dimensional stress-strain model to conduct multiphysics modeling. Thereby the thickness distributions of liquid slag, solid slag and air gap in the ultra-high speed billet continuous casting mold were obtained, and analyzing the effects of melting temperature of mold flux and mold taper. The results indicate that the thicknesses of liquid slag and solid slag increase and decrease respectively along the casting direction, and air gap mainly concentrates near the mold corner. The maximum thicknesses of liquid slag, air gap, and solid slag at the mold outlet are respectively 0.18 mm at the center of the strand surface (x = 0 mm), 0.28 mm at the strand corner (x = 80 mm) and 0.67 mm at x = 74 mm. The lower melting temperature of mold flux, the greater the liquid slag thicknesses and ascend from 0.14 to 0.18 mm, and conversely the maximum air gap thicknesses descend from 0.31 to 0.28 mm and existing ranges also get smaller, which is more favorable for the strand lubrication. To eliminate the air gap, the appropriate linear mold taper is 0.45% m−1 at the 6.5 m/min in casting speed.

Review of Testing Methods on the Heat Transfer Characteristics of Mold Slag Film

“…The liquid slag typically disappears at a location of 300-450 mm below the meniscus as it infiltrates into the air gap. [69][70][71] The temperature and cooling rate of the slag film constantly change along its movement direction, representing a continuous nonsteady process. Particularly, there are more complex variations in temperature and cooling rate of the slag film at the meniscus region.…”

“…Nevertheless, accurately determining the cooling rate of the slag film in a mold poses challenges due to the intricate thermal-physical state and nonuniform distributions, both longitudinally and circumferentially, of the slag film and the air gap. [69][70][71] Thus, the cooling rate of the slag film has often been disregarded in previous studies focused on the heat transfer of the slag film.…”

The Effect of Mold Structure and Cooling Parameters on Heat Transfer during Billet High-Speed Continuous Casting

“…However, compared to conventional casting speeds, the heat flux in the billet mold significantly increases and the solidification time of molten steel is shortened under a high casting speed, resulting in a reduction in the solidified shell thickness and its poor growth uniformity, leading to billet cracks and steel leakage accidents [4]. To achieve high-speed continuous casting, it is necessary to ensure efficient heat transfer in the mold area to avoid steel leakage due to a thin shell thickness at the outlet.…”