Optimal Design of the Cascade Controller for Reheating Furnace by Taguchi Method

Reheating furnaces are used to uniformly heat billets (blooms, billets, or slabs) to between 1000°C and 1300°C before hot rolling. Cascade control is widely used in temperature controllers of the reheating furnace. Unfortunately, the relationship between temperature indicator controllers (TIC) and flow indicator controllers (FIC) usually changes with a single slope. It means that temperature load disturbances cannot be effectively resolved. In this study, the relationship between TIC and FIC is proposed to be nonlinear with multiple slopes, which is used to accelerate the temperature response and increase the temperature stability under high or low load conditions. The temperature controller parameters are more diverse, so this study optimizes the temperature controller parameters and determines the characteristic curves between TIC and FIC effectively and quickly by using the Taguchi method. The performance of the multi-slope method and the single-slope method is evaluated in an actual heating furnace. The experimental results show that the proposed method in this study improves the mean square error and standard deviation by 33.76% and 22.44%, respectively. After commissioning, the parameter combination (including the characteristic curve) has a remarkable performance in the heating zone, which can be used to reduce temperature disturbance, accelerate the temperature response, and increase temperature stability in the reheating furnace.