Shape Difference And Control Strategy Of Different Strip Specifications In 2250mm Hot Strip Mill

Traditional flatness control strategy and profile control model for common specifications show defects during strips rolling in 2250mm hot strip mill,where the strips width range is 700?2100mm and thickness range is 1.2?25.4mm.In addition,the increase of strip mill width intensifies influence of asymmetry factors and the influence shows difference in strips with different specifications.In this paper,refer to WISCO 2250mm hot rolling production,the deform characteristics difference and shape difference of strips with different specifications is studied via combining of numerical calculation and industrial verification.Shape control strategies suitble for ultra-wide hot strip mill are proposed,with respect to flatness control,crown control,work roll contour prediction and asymmetrical shape control.The main work and achievements are reflected in the following aspects:(1)The results of numerical calculation on the metal transverse flow characteristic of strip with different specifications and its effect on strip flatness show that,because of the effect of metal transverse flow,the flatness is easier to control in strip with smaller width,larger thickness and reduction rate.In order to improve flatness quality of thin gauge strip,based on the relationship of metal transverse flow and similarity degree of profile,a method for strip crown setup in each stand is proposed via balanced allocation of residual stress difference at exit of each stand.(2)Study on rolling force transversal distribution during rolling of strips with different width,thickness and reduction reveals the influence of unit crown on rolling force transversal distribution.The strip crown regulation mathematical model is built,which integrates strip deformation and roll deflection characteristic.The model shows that during the rolling of strip with larger width in downstream stand,the crown transmissibility is stronger and " decrease " of crown regulating ability is more obvious.And the model provides theory and method support for high-precision crown control for all the specifications in ultra-wide hot strip mill.(3)The establishment of traditional work roll wear contour and thermal contour prediction model relies too much on engineering experience analysis and the precision of model decreases under large change of strip specification and process condition.To solve this problem,the work roll wear contour prediction model is built based on the rolling force transversal distribution and the work roll thermal contour prediction model where heat transfer coefficient change with the process conditions are established respectively,which are used to analyze the influence of strip specification on the work roll contour and crown of strips to be rolled.(4)The asymmetric degree of rolling mill and rolling strip in WISCO 2250mm hot rolling line is measured and analyzed.An asymmetry shape calculation model including roll deflection and strips deformation is established,via which influence of asymmetry factors on the shape of strip with different specifications is determined.This paper puts forward strategies about the allowable range of asymmetry factors and roll tilting for different strip specifictions.With some of the research results applied to industrial production,wedge qualified rate has been increased and flatness quality has been improved significantly.