Simulation of slab solidification in the mold of a continuous-casting machine

Abstract

The mold is a key component of continuouscast� ing machines. Its function is to extract heat from the melt and to create a reliable crust at the surface of the nascent billet, capable of withstanding the ferrostatic pressure of the liquid steel after the billet leaves the mold. The economic efficiency and viability of continu� ous casting largely depend on the performance and, in particular, the working life of the mold, which is deter� mined by its structure and the materials employed. The mold's working life also determines the repair fre� quency and hence the productivity of the continuous� casting machine. The state of the mold's working cav� ity and the cooling conditions affect the surface qual� ity of the continuouscast billet. Improving billet cooling in the mold zone will enhance the surface quality of the cast slab, extend mold life, and increase the productivity of casting. The mold design has the greatest influence on the heat transfer between the ingot and the mold. In the upper part of the mold, the liquid metal is in direct contact with the cooling wall. Since the solidifying crust is still thin and pressed tightly to the copper wall, the heatflux density is a maximum. With increase in thickness and cooling of the solid crust, thermal and phase shrinkage of the ingot is observed (especially at the broad face). Consequently, the ingot moves away from the mold wall to form a gap. As a result, heat transfer slows and the ingot crust becomes hotter. In the lower part of the mold, on account of the increased ferrostatic pressure of the liquid steel and the increase in temperature of the crust, it expands, and the ingot approaches the wall. In these conditions, increase in heat transfer is facilitated by a design of the mold's copper walls that ensures contact between the ingot's solid crust and the mold's working surface with minimum gap. To find such a design, we need to know the linear shrinkage of the ingot and, hence, the temperature at all points of the ingot's cross section.