Heat-transfer and solidification model of continuous slab casting: CON1D
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9/11/03
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Heat-Transfer and Solidification Model of Continuous Slab Casting: CON1D YA MENG and BRIAN G. THOMAS A simple, but comprehensive model of heat transfer and solidification of the continuous casting of steel slabs is described, including phenomena in the mold and spray regions. The model includes a one-dimensional (1-D) transient finite-difference calculation of heat conduction within the solidifying steel shell coupled with two-dimensional (2-D) steady-state heat conduction within the mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid interfacial slag layers, and the effect of oscillation marks. The model predicts the shell thickness, temperature distributions in the mold and shell, thickness of the resolidified and liquid powder layers, heat-flux profiles down the wide and narrow faces, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of the nonuniform distribution of superheat is incorporated using the results from previous threedimensional (3-D) turbulent fluid-flow calculations within the liquid pool. The FORTRAN program CONID has a user-friendly interface and executes in less than 1 minute on a personal computer. Calibration of the model with several different experimental measurements on operating slab casters is presented along with several example applications. In particular, the model demonstrates that the increase in heat flux throughout the mold at higher casting speeds is caused by two combined effects: a thinner interfacial gap near the top of the mold and a thinner shell toward the bottom. This modeling tool can be applied to a wide range of practical problems in continuous casters.
I. INTRODUCTION
HEAT transfer in the continuous slab-casting mold is governed by many complex phenomena. Figure 1 shows a schematic of some of these. Liquid metal flows into the mold cavity through a submerged entry nozzle and is directed by the angle and geometry of the nozzle ports.[1] The direction of the steel jet controls turbulent fluid flow in the liquid cavity, which affects delivery of superheat to the solid/liquid interface of the growing shell. The liquid steel solidifies against the four walls of the water-cooled copper mold, while it is continuously withdrawn downward at the casting speed. Mold powder added to the free surface of the liquid steel melts and flows between the steel shell and the mold wall to act as a lubricant,[2] so long as it remains liquid. The resolidified mold powder, or “slag,” adjacent to the mold wall cools and greatly increases in viscosity, thus acting like a solid. It is thicker near and just above the meniscus, where it is called the “slag rim.” The slag cools rapidly against the mold wall, forming a thin solid glassy layer, which can devitrify to form a crystalline layer if its residence time in the mold is very long.[3] This relatively solid slag layer often remains stuck to the mol
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