Characteristic Analysis And Control Of Complex Strip Flatness In Ultra-wide Cold Strip Mill

As a high-end product of steel industry, cold rolled strip is widely used in the construction, automotive, home appliances and other industries. With the improvement of requirements for flatness quality, enhancing control precision of cold rolled strips attracts more attentions from the producers. New problems are originated from flatness control of ultra-wide tandem cold rolling mill. The flatness errors of ultra-wide mills have more buckling areas and components, thus more flatness actuators should be involved besides roll bending, shifting and smart cooling.Using field-flow, thin-plate vibration, plate buckling, statistics, finite element simulation, numeric analysis and other theory and methods, flatness measuring process, flatness characteristics analysis of strip, flatness control performance assessment of ultra-wide mills and solution of complex flatness errors is researched in this thesis. The major research and innovative results are as follows:(1) A flow field model and a plate vibration model are established to analyze the relationships between distribution of exciting force and flatness measuring result. Attenuation rule of the excitation force is calculated by the model. Then the compensation method of flatness detection errors at the strip edge is derived. By analyzing strip temperature, the compensation method of temperature stress is given, and the setpoint curve setup method is also determined. The method of flatness errors tracking and analyzing is introduced, the reliability of SI-FLAT measuring result is proved, at the same time, tracking results show that the flatness errors of2180mm rolling mill are mainly composed of edge-center waves and central buckles.(2) Flatness index calculation method is modified considering the distribution of flatness detecting sensors, which made the flatness index more comparable between mills with different sensor distribution. Flatness errors of ultra-wide mill are analyzed by pattern reorganization method considering cubic basic flatness pattern, and calculation results are the same as the tracking results. Then clustering algorithm based on density and grid is introduced to detect the flatness characteristics, more flatness information is retained. Taking advantage of the clustering algorithm, more significant local characteristic of strip edge flatness in2180mm cold strip mill is found, and then a function is proposed to describe this characteristic.(3) Based on rolling parameters of2180mm cold strip mill, the working condition is described. A FEM model has been built to calculate the deformation of the roll stack and strip. Roll gap adjustment area method and effect function method are used to analyze the results from the FEM model, and the control performance assessment of ultra-wide mills is carried out. The reason of difficulty in complex flatness control is lack of actuators which have high similarity effect with the flatness error, providing guidance and new method for solving the flatness problem.(4) On the basis of studies and analysis in this thesis, a roll contour design method applicable for the ultra-wide cold rolling mill is presented. A new intermediate roll contour which has the ability to control edge flatness error is proposed. After applying the new roll contour in industrial test, a remarkable effect is achieved, also the feasibility and effectiveness of the roll contour design method is proved.