Study And Application Of Pickling Process Control In Pickling And Rolling Line

Process automation control system is the important part of computer control system for pickling,and it is the most effective control method to ensure the product quality and production efficiency of cold rolled strip.Based on a building project of 1450mm pickling and rolling line,the study is carried out on the framework and function of pickling process control system,acid concentration and temperature setup models,speed optimization model,tension levelers tension setup model and so on.The software for pickling process control is developed and applied on line,which has exhibited good performance.The main work is as follows:1)Process control system for pickling was established.Taking the specific control and technological requirements of pickling process into account,the structure frame,data flow and call logic for the process control system have been designed,and the process functions such as data communication,data management,coil tracking,setup parameters calculation and speed optimization were developed.2)Based on the soft measurement,acid concentration prediction model was established.According to the fact that acid concentration online detection equipment and maintenance expensive,the acid concentration prediction model based on soft measurement was studied.The easy detection variables included acid conductivity,ferrous ions density and acid temperature were selected as auxiliary variable,the ferrous ions and hydrogen ions mass concentration were selected as main variable,the robust regression method based on M-Estimators was used to establish a predicted model which could calibration online.Compared with the traditional offline detection of acid concentration,this method could improve detection precision and real-time request efficiently,the cost decreased significantly due to the online detection equipment was not needed.3)Based on the case-based reasoning,acid temperature setup model was established.According to the problem that low setting precision of acid temperature influence the strip pickling quality,the acid temperature setup model based on case-based reasoning was studied.Mechanism setup model of acid temperature is rarely mentioned in the literature,however,there is a large amount of production data with good temperature setting precision,the temperature setup model was established with these production data and based on case-based reasoning technology,which have high setting precision and adaptive ability with condition changed.4)Speed optimization model based on multi-objective function was established.In order to reduce equipment wear and operators pressure,as well as to improve the production efficiency of the pickling and rolling line,four sections speeds should be automatically optimized to control the three loopers abundance,which include the entry loopers entry speed,pickling speed,trimming speed,and tandem cold rolling mill entry speed.According to the optimal speed principle,a new optimization algorithm was proposed based on multi-objective function.In the present work,Nelder-Mead simplex method is applied to find the optimal solution by minimizing the objective function.In addition,the calculation of four initial speeds are specified,especially the initial tandem cold rolling mill entry speed.The proposed speed optimization algorithm was successfully applied to a 1450 mm pickling and rolling line.The acceleration and deceleration are smooth and steady when welding,trimming or roll changing takes place in practice,the three loopers’ abundance are controlled in suitable range.Results show that the continuous pickling line unit could provide the material in maximum capacity to ensure that the tandem cold rolling mill unit’s production is efficient and the rolling yield is greatly improved due to the decrease in the number of stops.5)Tension setup model of tension-leveler was established.In the pickling and rolling line,elongation and tension were out of the precise control level when tension-leveler flying gauge changed or roll changed,which affected the pickling quality.To solve the problem,a new tension model was proposed,and the steady state error was put into the model to improve the tension-leveler model accuracy.The proposed tension model was successfully applied to a 1450 mm pickling and rolling line.Practical application results showed that average tension deviation of the first coil strip down from 4.477%to 1.798%after changing roll,which greatly improving the elongation control level.The generic solution of the steady state error in the tension model was provided.The proposed model was on-line used properly for a long time,and it was suitable for the industrial promotion.6)The self-development pickling process control system was practical applied.The main process and equipment parameters are introduced.Network configuration and software structure were illustrated,process control system,basic control system and human machine interface system were analyzed.The process control system have been applied successfully in a 1450 mm pickling and rolling line.It is beneficial to the development of pickling process control system with independent intellectual property rights in China.