Modeling and optimal compensation of the deflection of roller levelers for flat-rolled steel products

This work is concerned with the mathematical modeling and the optimal compensation of the deflection of a roller leveler for flat-rolled products. In a roller leveler, residual stresses and flatness defects like ski-ends, wavy edges or center buckles of flat-rolled products are reduced by means of plastic deformation. For that purpose, the product is alternately bent between the work rolls of the leveler. The process forces can reach several meganewtons and may lead to an elastic deformation of the leveler of several millimeters. An effective automatic operation of roller levelers requires thus that the roll gap or intermesh profiles of the work rolls are precisely controlled. However, measuring the work roll profiles, the product shape, or the load distribution is expensive. Hence, accurate models of the deformation of the leveler and the plate are required to optimally automate the leveler. In the first part of the work, a deflection model of the leveler is developed. For the validation of the model, a new experimental design is presented. Special test plates were prepared with eddy-current distance sensors. This sensor setup allows for a direct measurement of the roll intermesh. Based on the validated deflection model, reference values for the adjustment variables are calculated that optimally compensate for the deflection and control the desired curvature profiles of the product in a feedforward sense. At the same time, overloads of the leveler are avoided. The hydraulically actuated bending mechanism of the leveler is addressed in more detail. Limit cycles are thoroughly discussed that are caused by load-dependent stiction in the joints of the mechanism. Countermeasures, by means of control and mechanical design, are provided.