| Shape is one of the important quality indexes of cold rolled strip products.At present,most of the researches on shape theory are aimed at traditional regular wave shapes,such as middle wave,edge wave,quarter wave,and compound wave in edge.The traditional shape control mechanism and control system can only control the regular conventional shape defects,but there is little research on the special shape defects of strip,and there is also a lack of corresponding control means and control strategies.Because the oblique stripe defects seriously affect the subsequent coating and plating process,the theoretical research and treatment technology of oblique stripe defects have become an important issue for coldrolled strip producers to solve urgently.In this paper,a 1700 mm five-stand cold continuous rolling mill is taken as the research object,and the theoretical and experimental research is carried out on the oblique stripe defect of finished strip steel.The main research contents are as follows:Firstly,the initial load distribution is assumed and verified by finite element method,and the mechanical conditions leading to oblique stripes are analyzed.By analyzing the process of solving stress distribution of twill pre-buckling strip steel by variational method,solving critical load of twill post-buckling by Galerkin virtual displacement method and solving deformation path of twill post-buckling by perturbation method,the analytical method for metal plastic forming is studied.Several load distributions are assumed for the oblique stripe defects,and the corresponding buckling deformation results are obtained by the finite element method,and the load distribution causing the oblique stripe defects of strip steel is determined.Secondly,a three-stand two-roll continuous rolling model is established by using finite element software.By setting the rolling boundary condition of the upper and lower rolls crossing of the first stand and second stand on the finite element model,the roll crossing phenomenon in the cold continuous rolling process is simulated.Adjust the process parameters such as the front tension of the third frame,the rear tension of the first frame,the intersection angle,the reduction rate and friction coefficient of the first frame,and carry out numerical simulation.The influence law of each process parameter on oblique stripes is obtained,which provides theoretical support for establishing the control strategy of oblique stripes.Finally,the comprehensive control experiment of oblique stripes was carried out by a1700 mm five-stand tandem cold rolling mill.The stability of the 1st to 5th stands is calculated by using the stability theory of rolling mill.By adjusting the intersection angle,front tension,shape target curve and other parameters of 5 work rolls,the twill adjustment experiment of 5 stands was carried out,and the influence law of each process parameter on oblique stripes of 5 stands was obtained.By adjusting the work roll intersection angle of the first four stands,the twill adjustment experiment of the first four stands is carried out,and the influence law of the first four intersection angle on oblique stripes is obtained.According to the results of finite element simulation and twill control experiment,a comprehensive control strategy of diagonal stripes including front tension adjustment,roll intersection angle adjustment and target shape curve adjustment is established,which provides a reference for the suppression and elimination of diagonal stripes defects in the cold rolling process. |
