Multi-mode control of strip-finishing-temperature in hot-strip mills

Abstract

At present, hot-rolled strip manufacturing has gradually exhibited more diversity and process complexity. Using the single control strategy, the traditional strip-finishing temperature-control mode shows some defects and deficiencies, for example, low control precision, slow production rhythm, and great fluctuation in the strip-finishing-temperature curve, which cannot meet the requirements for high precision and high-performance product control. For use with domestic 2250 mm hot-strip mills, a multi-mode control model was developed on a quadratic programming algorithm for the strip-finishing temperature. The proposed multi-mode control model has three control modes to regulate the speed, inter-stand cooling, and coupled speed and inter-stand cooling. To obtain the best control effect, the appropriate control mode can be adopted depending on the different steels used and different working conditions in the hot-rolling process. At the same time, based on the cooling capacity of the adjustable rack and the calculated strip-finishing temperature, Newton-Raphson iteration and the acceleration calculation model were used to calculate the large acceleration region and the quadratic programming optimization method to optimize the on-line adjustment of different control modes to meet all the strip-finishing temperature-control requirements. The on-line application of the proposed multi-model realized a 99% hit rate or better on the strip-finishing temperature for three consecutive months, with a deviation in the strip-finishing-temperature control of ±20℃. A 97.2% hit rate or better was realized on the strip-finishing temperature for three consecutive months with a deviation in the strip-finishing-temperature control of ±15℃. These results show that the control model has the advantages of a fast response speed and high precision and meets the requirements of finishing-temperature control for different steels and different working conditions. As such, the proposed method improves the strip-rolling stability and the accuracy of the finishing-temperature control and enhances product competitiveness.

Keywords

• strip
• hot-strip mills
• finishing temperature
• multi-model
• quadratic programming method
• acceleration