GOALI: Online Dynamic Control of Cooling in Continuous Casting of Thin Steel Slabs

An online control system is being developed of secondary cooling for continuous casting machines in commercial steel plants, in order to maintain desired temperature setpoints in real time. This is important to optimize the quality of continuous-cast semi-finished steel shapes, which are used for 96% of the 100 million tons of steel produced in the U.S. each year. The system features a fast, accurate transient computer model of heat transfer during the solidification process that serves as a "software sensor", to provide feedback to a control system. Operating conditions are input from the level 2 automation system and the spray-water flow rates in the secondary cooling zone of the caster are continuously adjusted, in order to maintain the desired temperature profile throughout the steel. The system is being calibrated, using thermocouple and optical temperature sensors, tested and implemented at an operating U.S. thin slab caster. In the second year of this large project, progress has been on several different subprojects. The transient finite difference model, CON1D, has been optimized to run in an online environment and serves as the software sensor. A new control system has been developed using CON1D and has been demonstrated to be capable of stable tracking of the setpoints in real time, using a robust control algorithm that features anti-windup. Testing has shown it outperforms the existing control system used at the steel plant. It is currently being subjected to further rigorous testing under plant conditions. An ambitious experimental program to measure pray cooling coefficients has begun, including a novel induction-heating system that is capable of measuring heat transfer rates at constant surface temperature. Pyrometer measurements have been made at the steel plant to validate the temperature predictions. Finally, related work is proceeding on controlling fluid flow in the mold and in understanding of defect formation, in order to facilitate setpoint generation, so that cracks and other defects can be minimized. Future improvements to this novel model-based control system could revolutionize the control of continuous casting spray systems, with improved steel quality, and will have beneficial impact on related scientific fields and commercial processes.