Flatness control analysis of tension levelling process based on finite element method

Flatness is an important index to judge the quality of strip steel. The common flatness defects are edge wave,middle wave,quarter wave and so on,which is essentially the uneven distribution of residual stress in the bandwidth. Wave defects can be effectively eliminated by the joint action of tension roller, bending roller and straightening roller. In the straightening process,plastic elongation occurs on strip under the effect of tension which is below yield strength. The flatness and quality of strip can be significantly improved. However,in the design and application of the tension leveler,the adjustment of tension leveler parameters is mostly based on experience and lacks theoretical guidance. To quantitatively analyze the improvement effect of tension leveler with different process parameters on the straightening of wave defects and increase the straightening effect of tension leveler in actual production,the tension levelling process of strip steel in a 1 450 mm cold pickling-rolling line was analyzed by the finite element software ANSYS/LS-DYNA which based on the three-dimensional elastic-plastic finite element method. The influence of tension and roll-intermesh on the flatness of straightened strip with initial flatness defect was analyzed. The influences of intermesh and tension on the flatness of strip with initial edge wave or middle wave shape defects are consistent. The results shown that wave defects of strip steel can be significantly improved by tension levelling. The intermesh of straightening roll is the main influencing factor,with the increase of intermesh the type of strip defect changes from edge wave to straight,and with the further increase of intermesh for straightening roller,the edge wave defect appeared again. With the increase of inlet tension,the type of strip defect changes from edge wave to medium wave after tension levelling.