Study And Application On Strip Shape Control Technology Of Hot Strip

Based on the project of "Research on Improving Shape Control Accuracy of 1700mm Hot Rolling Mill" in Ben Steel Hot Rolling Plant, the project of "Development of Strip Shape Control System for Ganglu 1250mm Hot Rolling Mill" and the project of "Digestion and Absorption of Control System for Shougang 2160mm Hot Rolling Mill", the theory, mathematical model, control strategy of the strip shape control system and the roll contour optimization were researched systematically in the paper. The main works are shown as follows:(1) The roll deformation theory of the shape control was studied. The mathematical model of roll elastic deformation was set up by the influence function method, the influence functions of work roll flattening and flattening between rolls were improved, and the analytical software on roll elastic deformation was developed. The roll wear model was established by taking into account the main influential factors, and the forecast program of roll wear was complied. The roll thermal expansion model was set up by the two-dimensional finite-difference method, the boundary condition was handled by the heat balance method, and the forecast software of roll thermal crown was complied.(2) The shape control mathematical model of specific physical meaning was set up. Roll contour factors which impacting the roll gap were summarized into two parameters through the unload roll gap crown model to simplify the shape control model structure. The uniform load gap crown was influenced by rolling force, roll bending force, strip width, elastic modulus of the roll, roll diameter and unload roll gap crown. The uniform load distribution roll gap model was developed to describe the relationship between the roll elastic deformation and the influencing factors. The method was provided for determining the uniform load distribution roll gap model coefficient. Based on the volume conservation, the strip shape forecast model was deduced by considering the material transverse flow and secondary deformation between mills. The shape discriminant model was set up by considering the effect of the potential shape defect and the tension. (3) The control strategy of the shape control system was researched. Due to ignoring of the potential shape defect and the absence of strip crown control by the downstream stands, the traditional crown strategy had reduced the hit rate of the strip crown. A new kind of shape control strategy was proposed to enhance the hit rate of the target strip crown under the condition of guaranteeing the strip flatness quality. The new strategy can increase the shape control capability to utmost extent. The setup calculation mathematical model of each shape control actuator was established. According to the relationship between the shifting position of the work roll and the roll gap crown, the iterative calculation method was established to determine the shifting position of the work roll.(4) The on-line shape control system was developed. Smith prediction control method, whose regulator employs the integral form, was introduced to the flatness feedback control in order to eliminate the influence of time lag and velocity fluctuation in traditional flatness feedback control; the sample length tracking of the strip was acted as the event-triggered interruption in the feedback control.(5) The optimum design methods of the CVC-plus work roll shape curve and the backup roll contour were studied. Taking the minimum of the axial force as the objective function, the design method of the CVC-plus roll shape curve was deduced, and the optimum design software was developed. The effect of the backup roll contour and the roll thermal wear on the load distribution between rolls and the exit strip crown was studied. Taking the uniform load distribution between the rolls and the fine shape between the stands as the target, the optimum design method of the backup roll contour was developed by distributing the strip crown reasonably in every stand.The main research content of the paper, which was of great practical application value, was focused on the online control of hot strip mill. The flatness feedback control system was improved; the shape control system, which contained the mathematical model of specific physical meaning and the new kind of control strategy, was established; and the optimum design methods of the CVC-plus shape curve and the backup roll contour were introduced. The backup roll contour optimum design method and the shape control system have been employed in Tangshan Ganglu 1250mm hot strip mill. The application results show that the rolling weight was increased, and the shape quality was enhanced.