Research On The Shape Evolution Of Strip And Its Comprehensive Control Technology During The Continuous Annealing Process

In recent years,with the plate and strip gradually from low-end to high-end,the quality requirements of plate and strip products become higher.The cold rolled steel sheet can not be directly stamped and processed.It must be annealed to nucleate and recrystallize so as to reduce lattice defects and facilitate further deep processing.At the same time,not only the properties of cold rolled strip will change,but also the shape of strip will change after continuous annealing process.The exit flatness of continuous strip rolling mill is the inlet flatness of temper rolling mill.Its shape directly affects the shape quality of finished steel strip.In the past,the cold rolled exit strip shape was often regarded as the inlet strip shape of continuous strip flattening,but the influence of continuous annealing process on the strip shape was neglected,which resulting in poor strip shape accuracy.In this way,how to determine the evolution law of strip shape in continuous annealing process and formulate the corresponding control technology and realize the conscious control of strip shape in continuous annealing process have become the focus of field technical research.This article based on the equipment and process characteristics of the continuous annealing unit and fully considering the influence of incoming strip shape and non-uniform factors in the furnace(such as roll shape,transverse temperature difference of strip steel,installation error of roll etc.),the strip is processed in an organic whole along the transverse direction,taking into account the shape of the strip between the upper and lower units.A set of transverse distribution model of tension stress in strip during continuous annealing process is established.The difference between strip shape inside and outside the strip is studied.The corresponding calculation model of strip shape inside and outside the strip is proposed.The evolution law and influencing factors of strip shape in continuous annealing furnace are analyzed quantitatively,which laid a theoretical foundation for the control of the flatness of the continuous annealing unit.According to the working conditions of the furnace roller in the continuous annealing furnace,and the contact state with the steel strip,the temperature field and the thermal profile model of the furnace roll were established.The numerical solution and distribution law of the temperature field and the thermal profile of the furnace were studied and the influence of the temperature difference between the strip steel and the furnace on the thermal profile of the furnace roll is given.The calculation process of the furnace rolltemperature field and the thermal profile model is given,and the corresponding calculation software for the thermal profile of the furnace roll in the continuous furnace is compiled.Finally realized the simulation calculation of multiple working conditions and products on site.Taking the control of the strip shape quality and the stability of the plate as the goal,combined with the equipment and process characteristics,starting from the optimization of the plate shape target curve,the comprehensive optimization of the tensile stress set values of each process section,and the furnace roll profile of each process section,a set of integrated plate-shaped control technology suitable for the continuous withdrawal unit was established,which realized the accuracy of the plate shape control in continuous annealing process while taking into account the stability of the plate.Taking a 1550 continuous annealing line as the research object,a set of virtual shape meter suitable for continuous annealing line has been developed by using the related research theory and mathematical model described in this paper,which have been realized the dynamic display,on-line prediction and closed-loop control of the flatness of all units under different working conditions.Furthermore,the relevant shape control technology mentioned in this paper is extended and applied to the unit,and the effect is analyzed.The results of field test and tracking show that the prediction error of the model is less than20% after the application of the virtual shape analyzer,and the prediction results are basically consistent with the trend of the measured data to meet the needs of field engineering.After the application of the integrated shape control technology,the overall shape sealing rate of the unit has been reduced by 35.65%,the peak shape has been reduced by 24.3%,the incidence of thermal buckling and deviation has been reduced by27.8%,and the occurrence rate of strip breakage has been reduced by 50.4% due to buckling and deviation,this not only effectively reduces the defect rate of finished strip,improves the quality of products,but also reduces the time of fault treatment caused by strip breakage and improves the production efficiency.