Coordinated Optimal Control of Secondary Cooling and Final Electromagnetic Stirring for Continuous Casting Billets

Secondary cooling and final electromagnetic stirring (F-EMS) are both key technologies for continuous casting. These parameters are usually optimized and controlled separately which caused internal quality fluctuations in unsteady conditions. In this paper, a coordinated optimal control strategy based on a multiobjective particle swarm optimization (MOPSO) algorithm is proposed for the parameter optimization of secondary cooling and F-EMS, which is solved based on multiobjective particle swarm optimization (MOPSO) algorithm. The solidification and heat transfer model are developed for the computation of billet temperature and the solidification, and the adaptive grid method is used to improve the diversity and robustness of optimal solutions. The secondary cooling water and F-EMS’ stirring current are dynamically controlled based on the optimization results. The results of field trials showed that the maximum carbon segregation and other quality indexes of billets can be improved significantly.

Effect of Final Electromagnetic Stirring Parameters on Central Cross-Sectional Carbon Concentration Distribution of High-Carbon Square Billet

The effect of final electromagnetic stirring parameters, with current intensity increasing from 300 A to 400 A and frequency increasing from 4 Hz to 12 Hz, on the electromagnetic forces and carbon concentration distribution of the central cross section of a 70 steel square billet have been studied. Along the center line of the liquid core zone, current intensity of 400 A and frequency of 8 Hz achieve the maximum electromagnetic force at the position 48 mm away from the billet edge among the 10 groups of stirring parameters. Nevertheless, along diagonal of the liquid core zone, the electromagnetic force near the diagonal center is the greatest and the current intensity of 280 A and frequency of 12 Hz obtain the maximum electromagnetic force. The optimal final electromagnetic stirring (F-EMS) parameter to uniform the central cross-sectional carbon concentration and minimize the center carbon segregation of 70 steel billet was obtained with a current intensity of 280 A and frequency of 12 Hz. Under this stirring parameter, the area ratios of carbon concentrations of 0.66 wt%, 0.70 wt% and 0.74 wt% in the middle of the billet cross section reached 28.5%, 56.9% and 10.9%, respectively. Moreover, the carbon segregation indexes for all sampling points were in the range of 0.92–1.05.

Numerical Simulation of Electromagnetic Field in Round Bloom Continuous Casting with Final Electromagnetic Stirring

A 3D mathematical model was developed to simulate the electromagnetic field in Φ600 mm round bloom continuous casting with final electromagnetic stirring (F-EMS), and the model was verified using measured data for the magnetic flux density in the stirrer centre. The distribution of electromagnetic force and the influence of current intensity and frequency were investigated. The results show that the Joule heat generated by F-EMS is very small and its influence on secondary cooling heat transfer in the stirring zone can be ignored. With an increase in current frequency, the electromagnetic force density at R/2 and R/3 of the Φ600 mm round bloom first increases and then decreases, reaching a maximum at 10 Hz.