Influence of rolling reduction, strip shape and asymmetry factor on the strip curvature

摘要

In order to improve the quality of plates, an asymmetric rolling process can be introduced, which will help reduce the total roll separating force and increase plate flatness and decrease thickness deviations along the width and length of rolled strip [1÷3]. By introducing asymmetric rolling, a disturbance of the equilibrium in the roll gap occurs, which changes the lengths of particular zones and the position of the neutral zone on each roll's side. A negative effect of this process might be bending of the strip beyond the roll gap, which can make it difficult to run the rolling process in a failure-free manner. The application of the asymmetric rolling technology under industrial conditions requires therefore a lot of theoretical research to be carried out in order to determine the permissible ranges of asymmetry factors, with the remaining process parameters being variable, for which a strip either being perfectly flat or having only a slight curvature will be obtained. Within this study, the effect of the strip shape factor, h0/D, on the magnitude of strip curvature on exit from the deformation zone has been determined. Many authors hold the view that one of the most important parameters influencing the strip curvature magnitude is the roll gap shape factor, ld/hav [4]. From tests carried out it has been found that the influence of the ld/hav factor is ambiguous. For different strip shape values and the same values of the roll gap shape factor, different magnitudes of strip curvature on exist from the deformation zone are obtained. The tests were carried out for steel S355J2G3. To determine the actual work-hardening curves of the S355J2G3 steel for the deformation conditions and temperatures prevailing in the real plate rolling process, the Gleeble 3800 device was used. Then, the work-hardening curves, determined for this steel grade, were implemented in the material database of the FORGE 2008? program [5].