Research On On-line Roll Changing Technology And Dynamic Rolling Theory Of Endless Strip Rolling

Hot strip rolling is a typical process industry,and its ultimate goal is short process and high automation.However,in the process of short process,equipment technology is prone to excessive rigid connection,resulting in low flexible adaptability between equipment process and products and lack of flexible regulation ability.For example,the roll wear of ESP finishing mill is a bottleneck problem that seriously restricts its technical development.Aiming at the latest hot spots and common problems in the short process of hot strip continuous rolling,the on-line roll change technology and dynamic rolling theory of endless strip rolling are studied.Aiming at the endless rolling line represented by ESP,this paper studies the formulation of on-line roll change strategy and the establishment of adjustment model,the establishment of dynamic rolling model and the simulation analysis of on-line roll change process.Comprehensively considering the characteristics of ESP and other endless rolling production lines,the"5+1"mode online roll change method and the"5-1"mode online roll change method are proposed,and the advantages and disadvantages and application conditions of the two methods are analyzed.Considering the influence of the wedge-shaped zone on the stiffness of the rolling piece between the stands,the tension control model of the online roll changing process is established.Considering the unequal flow rate of metal per second in the deformation zone of the dynamic rolling process,a roll speed control model for the online roll change process is established.Based on the above-mentioned models,the online roll change strategy under the"5+1"and"5-1"modes based on the casting speed of the continuous caster is proposed.Considering the influence of the changing speed of the roll gap on the flow velocity of the roll,the length of the deformation zone,the exit position and the average deformation rate during the roll withdrawal process during the on-line roll change,corresponding models are established respectively.Based on the above models,considering the influence of shear strain on plastic deformation,the energy variation method is used to solve the total rolling power functional of the roll withdrawal process,and finally the rolling torque and rolling force models of the roll withdrawal process are established.The parameter of roll gap change speed is successfully introduced into the rolling force model,which also considers the influence of roll gap change speed on the deformation rate of the rolled piece and the length of the deformation zone.Subsequently,the validity of the model was verified through the factory measured data and the finite element model.Based on the above-mentioned models,the influence of the changing speed of the roll gap on the rolling force,the position of the exit of the rolled piece,the position of the neutral point,and the second flow rate of the metal in the deformation zone are analyzed.This lays a theoretical foundation for the calculation and analysis of force and energy parameters in the roll withdrawal process.The roll-in process is more complicated than the roll-withdrawal process.The input process leads to additional deformation zone II.At this time,the velocity field,boundary conditions and integration interval when the rolled piece is deformed are quite different from the roll-withdrawing process.The dynamic flow velocity model,boundary condition model and average deformation rate model of rolled piece are established in deformation zone I and deformation zone II respectively.Considering the influence of shear strain on plastic deformation,the energy method is used to solve the total rolling power functional in the roll input process,and finally the rolling torque and rolling force models in the roll input process are established.The model also considers the influence of roll gap change speed on the deformation rate and the length of deformation zone.The validity of the model is verified by carrying out dynamic hot rolling experiments.The reason for the abnormal phenomenon that the rolling force decreases with the increase of the rolling speed during the roll input process is analyzed,and the proportion of the influence of the change of the deformation zone length and the deformation rate of the rolling material on the dynamic rolling force during the dynamic rolling process is analyzed.The dynamic rolling model established by the energy variation method is complicated and slow to solve,and cannot calculate the distribution of unit rolling pressure along the deformation zone.Based on the Orowan equilibrium differential equation,this paper considers the influence of the front and back tensile stress,and also considers the influence of the roll gap change speed on the average deformation rate of the strip and the length of the deformation zone.The dynamic rolling unit pressure equation and the dynamic neutral angle formula are established.And the dynamic stress state coefficient model,and finally get the analytical solution of dynamic rolling force.The accuracy of the model was verified by hot rolling dynamic experiment.Based on the above model,the distribution law of the unit rolling pressure along the contact arc is analyzed during the on-line roll change roll withdrawal and roll-in process.At the same time,the influence law of the front and back tension on the rolling force during dynamic rolling is also analyzed.Combine the online roll change strategy and adjustment model with the dynamic rolling theory model.The simulation calculations were carried out by taking the F₆stand replacing the F₅stand and the F₅stand being put into the rolling process as examples.The results show that the tension between the racks before and after the roll change does not fluctuate greatly under the guidance of the roll change strategy in this paper,and it is relatively stable during the entire roll change process.The simulation results of replacing the F₅stand by the F₆stand show that the thickness fluctuation of the finished product produced by the roll change process is less than 1%.The"5+1"roll change strategy can theoretically eliminate the wedge-shaped zone in the thickness direction of the finished product.The research results of this paper will lay the preliminary theoretical foundation for the ESP online roll change technology,promote the release of the technological potential of the strip endless rolling equipment,equipment upgrades,and product expansion,and improve the flexible production level of the strip endless rolling process.In addition,the theoretical basic model of dynamic rolling established in this paper can be applied not only to the online roll change process,but also to the research of dynamic hot rolling processes such as the production of hot-rolled plates with variable thickness and the vibration of the hot-tandem rolling mill.