The Research On Theory And Experiment Of Plate Shape Control For Multi-high Mill

In the strip rolling process, the plate shape control technology plays a veryimportant role in improving the product quality. Roll deformation theory is the core partof shape control theories, which includes roll flattening and roll bending deformation.The roll bending model based on influence function method and with high accuracy hasbeen widely used. However, the current roll flattening model has a low accuracy becauseof its defect theory, which restricts the strip production development. In order to improvethe calculation accuracy of the roll deformation, a new and more accurate roll flatteningmodel is proposed.Based on boundary integral equation method, an analytical model for solving afinite length semi-infinite body is established. The lateral surface displacement field ofthe finite length semi-infinite body is simulated by finite element method (FEM) andlateral surface displacement decay functions are established. Based on the boundaryintegral equation method, the numerical solution of the finite length semi-infinite bodyunder the distributed force is obtained and an accurate roll flattening model is established.Different from the traditional semi-infinite body model, the matrix form of the new rollflattening model is established through the mathematical derivation. Compared withsemi-infinite body model and Foppl formula, the result from the new model is moreconsistent with that by FEM especially near the edges. In order to improve the efficiencyof the new model, the numerical integration in the model is fitted by mathematicalpolynomial. By comparison between the semi-infinite model and the new model,quantitative relationship and the scope of semi-infinite body model are obtained.In order to analyze the influence of the new roll flattening model, the model isapplied in roll deformation calculation of4and6Hi mill, where the roll flattening, rollbending, the flattening between work roll and strip are coupled together, and the accuracyis verified by FEM. And then, the new model is compared with Foppl formula and semi-infinite body model in different strip width, roll shifting value and bending force, theinfluence laws are obtained. For the work roll edge contact in thin strip rolling process, based on the new model (finite length semi-infinite body flattening theory) in this paper,a new work roll edge contact deformation model is established. Based on the new rolldeformation model and coupled with the variational method (metal plastic deformationmodel), a new4Hi mill plate shape control model is established. At last, based on thecoupled model, the distribution law of rolling force and tension are analyzed by changingwork roll edge contact condition, work roll diameter, plate width, bending force, andreduction.The20Hi mill is applied widely in thin strip rolling process. But the rolls of20Himill are arranged as cluster, contact position and roll flattening are complex, the currentroll flattening model can not obtain accurate result for20Hi mill. For the reason above,based on the finite length semi-infinite body flattening theory, a new plate shape controlmodel of20Hi mill is established, which includes roll deformation model and metalplastic deformation model. And segmented roll contact are considered in the new model.Taking a20Hi mill in laboratory as an example, the effects of the first intermediate rollshifting and taper, ASU, tension, work roll crown and the second intermediate non-driveroll crown are analyzed.Rolling experimental study is carried out at the20Hi mill in laboratory. Because thatthe rolling force of20Hi mill is hard to measure, a new measurement method is proposed.Based on the rolling force measure method,0.4mm thickness strip as the raw material, arolling experiment is carried out by changing plate width, the first intermediate rolls andtaper, tension and reduction, the influence law of plate shape is obtain. The test resultsare analyzed by the new plate shape control model of20Hi mill, and the accuracy of thenew model is certified. Taking0.04mm thickness strip as the raw material, a rollingexperiment is carried out. By changing the first intermediate rolls and taper, reduction,the influence law of particularly thin strip shape is explored. Based on the new plateshape control model of20Hi mill, the influence factors are studied. As the result, areasonable method for particularly thin strip rolling process is obtained.