Theory Research On Strip Crown And Shape Calculation And Pre-set Modeling In Hot Rolling

Hot rolled steel strip is an important type of steel product, which is widely used invarious fields of the national economy and has an important impact on technologicalprogress for the entire steel industry. With the improvement of mill equipment andadvance of modern rolling technology, the market puts more and more attentions on theaccuracy of hot rolled strip products. The geometry accuracy of strip includinglongitudinal thickness difference, transverse thickness difference and flatness three fields.Because of the complex influence factors of plate shape and crown, many problems in thebasic theory, shape detection and control technology have not been solved. So in thispaper, the basic theory of strip shape and crown, the relationship between the variousinfluence factors and the shape are studied systemically and deeply, and mathematicalmodels of shape analysis, forecasting and setting are established precisely.The theory of plate shape mainly includes two modules: metal plastic deformationand rolls elastic deformation. Variational method is used to solve the lateral flow of metalin the roll gap, and the lateral distribution of tension is obtained. Through the research ofthe range of the definite integral in the Euler equation, the calculation method is proposedto adapt to the hot rolling, and the accuracy of the lateral displacement is improved. Inrolls elastic deformation, for the errors of roll ends flattening calculated by traditionalflattening models, a new model is derived by using a combination of plane strainassumption and plane stress assumption, which improves the calculation accuracy of theflattening between rolls. Thermal crown and roll wear are also studied, and the impact ofthermal crown distribution caused by the work roll shifting is analyzed.Based on the theoretical analysis, a scientific off-line analytic system of plate shapeis established by using variational method to simulate metal plastic deformation, usinginfluence function method to calculate rolls elastic deformation, considering thermalcrown and roll wear. According to the research of the program iterative process, theiterative efficiency is increased and the calculation time is reduced by the improvement ofinitial value setting and matrix solving. Then, taking good shape as an important goal, a new optimization scheme of the rolls size and rolling schedule is proposed bymulti-objective optimization.In order to simulate the rolling process accurately, on the basis of others’ research,using three dimensional rigid plastic FEM base on Lagrange multiplier to analysis theplastic deformation of the strip, influence function method to analysis the rolls deflection,a coupled simulation system is developed by virtue of iteration scheme. Because of thelow efficiency of the finite element method, a rapid algorithm is proposed bycombination of the analytic model and three-dimensional finite element coupling model,and the iterative process is optimized based on the calculation accuracy.To verify the accuracy of the off-line computational models of plate shape, stripcrown with consideration and without consideration of thermal crown and wear arecalculated based on the experimental data of Baosteel2050hot rolling line. For detailedcomparison of thickness distribution, the rolling measurement experiment is conducted inBaosteel1780hot rolling line.Pre-set model of plate shape in Baosteel2050hot rolling line is studied, and theinfluence coefficients are modified by offline simulation, so the calculation errors isreduced. The original model only uses the quadratic curve to describe the lateraldistribution of rolling force and this will cause some errors. So, in this paper, by using thecoupled model to calculate the rolling force distribution and analyze the influence ofdifferent factors, a new model which has high precision is established to calculate stripcrown of pre-set model.An off-line simulation software of plate shape which has friendly interfaces andhigh-efficiency operation is developed by taking Visual Basic and C++as program tools.The software can simulate the strip crown and flatness in hot rolling, calculate theinfluence coefficient of rolls size, roll crown, bending force, tension, rolling force, stripinlet crown and so on, and offer an effective platform for mechanism analysis of shapecontrol and on-line shape model.