Control of meniscus-level fluctuation by optimization of spray cooling in an industrial thin slab casting machine using a genetic algorithm

Meniscus-level fluctuation is a common problem during thin slab casting and can lead to breakout. Because meniscus-level fluctuation increases with increase in casting speed, it restricts high-speed casting. It is now known that the meniscus-level fluctuation is caused by fluctuation in bulging and decreasing the total bulging can control it. Increasing the spray cooling reduces the total bulging and hence the meniscus-level fluctuation. However, the increase in spray cooling poses other problems. The midwide surface temperature at the slab exit may fall excessively, requiring significant reheating and thus fuel consumption in the reheating furnace. Also, the temperature at the unbending point may fall below a critical value causing crack formation. Thus, an optimization procedure was adopted to find the optimum combination of spray cooling, which will minimize the total bulging, keeping the midwide surface temperature at the slab exit more than a minimum and user-specified value. To do so, a genetic algorithm was used in conjunction with a model for estimation of temperature at different locations of strand and total bulging in the strand (thermal-bulge model). Based on the results of optimization, the casting speed in a plant could be enhanced by more than 30%.