Research On Optimal Control Strategy For Key Process Of Linked Pickling And Cold-rollingTandem Mills

The automatic control system of linked pickling and cold-rolling tandem mills has been matured,and how to further improve the quality and efficiency of cold rolling products has become the focus.In this thesis,based on the optimization of the control system of a 1450mm linked pickling and cold-rolling tandem mills,which is the first and fully developed in China,the research is carried out concerning the extension rate control,the flow control of acid liquid,the high precision setting of the rolling force and the overall speed optimization strategy of the combined unit,The key process optimization control whose core is the product quality and quantity for linked pickling and cold-rolling tandem mills has been achieved.The main contents are as follows:(1)Automatic control system of linked pickling and cold-rolling tandem mills is analyzed.The main functions of the process automation control system are data management,material strip tracking and model setting.Object of the control system of the basic automation level control system is the execution equipment of the unit,mainly including the strip speed control,the inter stand tension control,the whole line seam tracking,thickness control,shape control and so on.On this basis,according to the problems to be solved at present,the optimization control strategy of the key process of linked pickling and cold-rolling tandem mills is studied.(2)Construction of high precision elongation control system.In view of the equipment componets and technological characteristics of the tension leveler,with elongation control as the core,the fuzzy control algorithm is combined with the conventional PID control algorithm,forming a fuzzy self-adaptive PID indirect elongation control system.The fuzzy control table is obtained by off-line fuzzy inference,and through on-line inquiry and control,the control error of the elongation can be reduced effectively,and the control precision and the anti-interference ability of the extension rate have been greatly improved,which has good dynamic and static performance and strong robustness.(3)Case reasoning method based optimization of pickling control system.A case based reasoning method is introduced into the pickling control system.The physical properties of the steel,the parameters of the acid liquid and the speed of the strip operation are comprehensively considered,and a case database of production process for pickling process is established.Through researching historical case which is similar to the current condition,the frequency conversion pump speed is reused and modified to control the acid flow rate according to the similarity.In the end,the variable pump speed of the acid flow control is ultimately controlled,improving the adaptability of the frequency conversion pump speed to the change of operating conditions.(4)Development of lever arm coefficient model of cold rolling mill.The lever arm coefficient is the core factor of the calculation of the cold rolling force energy parameters.A simplified three-dimensional elastoplastic finite element model is established to simulate the cold rolling process.Distribution state of the rolling pressure and the lever arm coefficient are obtained.Influence of the process parameters,such as the reduction rate,the front and back tension,the deformation resistance and the friction coefficient,on the rolling pressure and the lever arm coefficient is analyzed.BP(Back Propagation)neural network is applied to deal with the on-line measured data,and the mathematical model of the lever arm coefficient of the cold tandem rolling mill is obtained.(5)Modeling of high-precision force parameters based on energy method.The generalized Hooke’s law and the direct integral of polar coordinates are used to calculate the rolling force in the elastic zone.A simplified velocity field is proposed to calculate the power of the deformation,shear and friction in the plastic zone,and the influence of tension on the cold rolling process is considered.The analytical model of the rolling force which is simple and easy to apply in the field is obtained.The lever arm coefficient is obtained.On the basis of the model,considering the influence of roll squash,the analytical solution of the rolling force is obtained by cyclic iterative method,and the influence of the parameters,such as tension,friction coefficient and compression rate,on the parameters of neutral point and stress state coefficient are further analyzed.(6)Research on speed optimization control strategy.Aiming at the problem of manual operation being difficult to achieve the optimal condition,the volume change rule and the speed running characteristic of the looper are analyzed,and the evaluation function is set up on the basis of the tracking system of the strip,with the target of the speed balance,the maximum output and the stable equilibrium of the looper.Modified powell method is used to obtain the optimal value of the velocity of the different regions.The results show that after optimization,the average speed of pickling is greater than that of manual setting,which improves the operation efficiency and output of the unit.The relevant research results of the optimal control strategy for the key process of the linked pickling and cold-rolling tandem mills have been successfully applied to a 1450mm linked pickling and cold-rolling tandem mills,which effectively improves the quality of the products and the production efficiency,createing a good economic benefit for the enterprise.