The Analysis Of Vibration Characteristics Of Multifactor Coupled Tandem Cold Rolling Mill Under Dynamic Roll Gap

Mill vibration called chatter occurs as a result of poor lubrication condition in high speed rolling of thin and hard strips.Mill vibration will seriously affect the quality of the strip,and voilent self-excited vibration will cause serious damage to the equipment in the mill house or strip break accidents,which poses a serious threat to the safety of personnel and instrument.Based on a 1450 mm UCM pickling and tandem cold mill,the cold rolling mill self-excited vibration characteristics were studied in this paper.The main work is as follows:(1)The main parameters and calculation method of deformation zone in tandem cold rolling process were analyzed.The rolling force model,deformation resistance model,forward slip model,mill jumping equation and tension equation used in Simulink simulation model are given.Moreover,the roll elastic flattening radius and the contact length in the deformation zone under a specially appointed rolling schedule are calculated by off-line method.The above work provides the theoretical basis in order to establishing the Simulink simulation model.(2)According to a 1450 mm cold rolling plant,the process of three-dimensional finite element modeling of UCM mill is presented,including establishing the geometric model of strip and roll system,defining material properties,meshing the geometric model,defining of the contact type and boundary conditions,loading etc.The finite element model of ANSYS/DYNA is utilized to calculate the stiffness coefficients of each roll in the roll system and the frame of stand,which lays a foundation for mill chatter characteristics analysis of cold tandem rolling.(3)In this paper,the classification of vertical vibration and the mechanism of vertical vibration in cold mill process is expounded.By using the first order Taylor formula of Bland-Ford-Hill simplified roll force calculation model,influence of the rolling process parameters,(such as the entrance and exit materials thickness of single stand,the front and back tension of a certain stand,and the friction coefficient of deformation zone in the roll gap)on the vertical vibration of the cold rolling mill are analyzed.(4)The dynamic coupling vertical vibration model considering the material hardening,work roll elastic flattening radius,dynamic roll gap,transmission delay between stand,coupling between stands,and other comprehensive factors,is established.By using this model the displacement fluctuation of roll deviating from its equilibrium position in vertical direction is expounded.In this paper,it is found that self-excited vibration occurs in the 4th stand of UCM mill under the speed of 25m/s when rolling T4 strip of 0.2mm;and when rolling 0.18mm T5 strip under the speed of 20m/s,self-excited vibration occurs in the 5th stand of UCM mill.The coupling of the tension,velocity,deformation resistance,thickness,and friction coefficient between stands reduces the stability of the system.All of the above findings laid the foundation for the subsequent research on the vibration mechanism of cold rolling mill and the stability of multi stand mill system.