Flatness Analysis and Control of Strips with Different Thickness in 2250 mm Hot Tandem Rolling

Aiming at the flatness difference between thick strip and thin strip under the same flatness control strategy on a 2250 mm hot tandem rolling line, a flatness calculation model is firstly established in this paper. With the unknown variable-transversal flow of metal solved by finite element methods, the flatness calculation model is used to analyze and compare the flatness and longitudinal residual stress evolution during thick strip and thin strip rolling. The result shows that under the premise of the constant exit relative crown in the downstream stands, the distribution of metal transversal flow due to larger reduction ratio in F2 and F3 stand causes the flatness of thin strip differing much from that of thick strip. In order to improve the flatness quality, a crown setup method is proposed. Based on the relationship among the distribution of metal transversal flow, entry relative crown, and the change of relative crown obtained from the finite element model, the exit crown of thin strip at each stand is optimized by genetic algorithm with a restriction of achieving the target crown at exit of F7 stand and a goal of good flatness quality during rolling.