Research On Work Roll Wear And Process Parameter Optimization For Hot Strip Skin-pass Mill

Hot skin-pass rolling is the final forming step that determines the shape of hot-rolled finished products,and its role is to apply a small deformation of approximately 1%-4%to the finished products cooled to room temperature to ensure the shape quality and improve the mechanical properties and surface quality to some extent.The general trend of"hot-rolled strip substituting cold-rolled strip"and "energy saving and emission reduction"strongly requires hot-rolled thin strips,especially for strips with specifications below 2.0 mm.Regardless of the use of conventional hot rolling mill or compact strip production,different degrees of flatness defects are detected in the current production of thin strips;thus,skin-pass rolling must be carried out to ensure the shape quality of the finished products.Due to the particularity of the roll stacks structure and the working condition for hot skin-pass mill,the uneven wear of the work rolls is very serious,which will not only deteriorates the shape accuracy of the strip after rolling but also decline the performance of skin-pass mill in terms of shape control.However,the current theoretical research on the wear law of work rolls is scarce,and the periodic axial movement of work rolls and process parameter optimization,which are the main means to reduce the uneven wear of the work rolls,mainly rely on field experience.The thesis achieved some research work based on the 1580 mm hot strip skin-pass mill.The main contents and research results have been obtained:(1)Based on the theory of elastic-plastic mechanics,the elastic-plastic finite element method(FEM)is adopted to establish a rolls—strips coupling model of hot skin-pass mill.In the model,the strip length is considered as infinite,and the strip is divided into three parts along the rolling direction,i.e.,head stability section,tail stability section and skin-pass rolling section;among these parts,head stability section and tail stability section are very long and are not rolled,while skin-pass rolling section is short and is rolled.The finite element model is highly efficient and versatile,and can truly reflect the elastic deflection and elastic flattening of the rolls,as well as the elastic-plastic deformation of the strip.(2)The formation and development mechanism of work roll wear is analyzed based on numerous measured wear contours and wear characteristics of the work rolls.The established rolls-strips model for hot skin-pass mill is adopted to analyze the effect of the work roll contours of different wear stages on the the contact presssure between the work roll and the strip,and the wear evolution law of work roll is revealed.The wear evolution law is quantitatively expressed,and a wear prediction model that meets the actual production conditions of the hot skin-pass mill is constructed.The calculation accuracy of the model was verified by field test.(3)The established rolls—strips model for hot skin-pass mill is used to quantitatively analyze the effect of the work roll shifting values on the skin-pass rolling stability with the different wear stages of the work roll.Combining with the problem that the length of work roll body can not be fully utilized to homogenize roll wear under the fixing parameters shifting strategy adopted in the field.A varying stroke cosine roll shifting strategy for conventional work roll contours is proposed,which takes into account the skin-pass rolling stability and wear uniformity.The three-population particle swarm optimization and differential evolution algorithm with the global convergence properties and local search capability is introduced to optimize the roll shifting strategy parameters.Long-term industrial field application has verified the advantages of varying stroke cosine roll shifting strategy in improving uneven wear and skin-pass rolling instability of work rolls.(4)A comprehensive optimization calculation method of skin-pass rolling process parameters including the roll contours optimization and skin-pass rolling process parameters optimization is proposed.On the basis of the established mathematical model for comprehensive optimization of process parameters,a satisfactory optimization method based on Thr-PSODE algorithm is used to optimize the roll contour parameters,which takes into account the optimal strip shape quality after skin-pass rolling and the optimal lateral distribution of contact pressure between rolls under initial grinding contour and wear contours in different stages.On the basis of roll contour optimization,the Thr-PSODE algorithm is used to optimize the rolling force and the front and back tensions of strip,which takes into account the optimal stability of skin-pass rolling,the minimum roll consumption of working roll and the optimal shape quality of strip after skin-pass rolling.