Study On Coupled Vibration Of Tandem Cold Rolling Mill Excited By Multiple Sources

Rolling mill vibration is a technical problem that has plagued the iron and steel industry for decades.Once the rolling mill vibrates violently,it will have bad consequences,not only seriously affecting the product quality and accuracy,increasing environmental noise,reducing the life of the rolls online,but also threatening the safe production of mills,causing unnecessary economic losses and reduced productivity.Aiming at the vibration problem of a typical high strength thin strip in a cold rolling mill during high-speed rolling,this paper studies the vibration mechanism and vibration suppression strategy by combining on-site tracking test,numerical simulation and theoretical research.The research work in this paper has important theoretical significance and engineering value for the vibration problem of high strength thin strip rolling by tandem cold mill under multi source excitation.The main research work is as follows:(1)Field and comprehensive test and signal analysis of rolling mill vibration.In order to comprehensively control the vibration state of the cold tandem rolling mill,the state monitoring of the S5 stand with the most severe vibration is carried out,focusing on monitoring the vertical vibration speed signal of the top of the stand and the displacement signal of the force motor valve spool,the hydraulic cylinder output pressure signal and the vertical vibration signal of the rolling mill roll system.It is found that the stand will have severe vibration when the stand is rolling strip steel grades are S30Y,S40 and other steel grades below 0.496mm,and the rolling speed range is 17.5-20m/s.And the dominant frequency of vibration varies with the change of process parameters,and its range is 7585Hz.It is also found that the output pressure fluctuation of hydraulic cylinder and the displacement of valve core contain the same components as the vibration frequency of rolling mill.(2)Establish a rolling mill vibration model under multi-excitation and multiparameter coupling for simulation research.Based on the mechanical vibration theory and rolling theory,combined with field test data,establish a 9-DOF vertical vibration dynamic model of S5 considering multi-source excitation,rolling process dynamic rolling force model,vertical system electro-hydraulic coupled vibration model and the rolling millstrip coupled vibration model to determine the main factors that induce rolling mill vibration.The influence of strip excitation on rolling mill vibration,and the influence of rolling mill variable stiffness control and pressing system controller parameters in roll gap control system on strip excitation rolling mill vibration are mainly studied.The results show that reducing the excitation amplitude of strip steel,the dynamic stiffness control gain and the clamping system controller gain can suppress the rolling mill vibration caused by strip steel excitation.(3)Study on the influence of dynamic and nonlinear characteristics of force motor valve on rolling mill vibration.During the field experiment,it is found that there are frequency components related to rolling mill vibration in the valve core displacement and the pressure after the valve,but this component was not obvious in the pressure before the valve.It is speculated that the force motor valve and its control system have a great influence on the vibration of the rolling mill.According to the on-site drawings and data,the hydraulic pressing system model including the force motor valve and the vertical vibration model of the rolling mill were established.Based on the multi-scale method and the incremental harmonic balance method,the dynamic characteristics of the force motor valve under different parameters are analyzed.A series of nonlinear phenomena such as harmonic resonance,parameter resonance and low-frequency fluctuation modulation of the valve core displacement caused by the parameters of the force motor valve are explored.The mechanism of force motor valve inducing or amplifying rolling mill vibration under the conditions of internal feedback,external disturbance and load fluctuation is explained.(4)Research on vibration amplification and nonlinear characteristics of the rolling mill caused by radial clearance of the fault-free backup roll bearing.Aiming at the phenomenon that the new bearing can still generate periodic excitation,this paper establishes a four-row cylindrical roller bearing and a rolling mill vertical system dynamic model including the bearing,which theoretically explains the mechanism that the new bearing with assembly clearance can still generate periodic excitation.The influence of rolling speed,number of rolling elements and bearing structure clearance on the vibration of the bearing and rolling mill is analyzed,and the bifurcation phenomenon of the motion state of the bearing and rolling mill system caused by the damping change is analyzed.It is found that the nonlinearity caused by rolling mill stiffness change leads to energy transfer between different frequencies when the multiple excitation frequencies are close,thus amplifying vibration.(5)Corresponding vibration suppression measures are proposed,and a good vibration suppression effect is obtained.For the 75-85Hz vibration phenomenon of tandem cold rolling mill,through field test,theoretical research and simulation solution,the induction mechanism of vibration under multi-source excitation is discussed,and the corresponding vibration suppression strategy is proposed.For the pressure fluctuation excitation of hydraulic system,the dynamic characteristics of force motor valve can be changed to reduce its cut-off frequency and enhance the linearity of force motor valve spool system;For the strip steel incoming excitation,the dynamic stiffness control parameters can be reduced,the controller gain of the pressing system can be adjusted,and the excitation frequency of the strip steel can be adjusted;In view of the support roll bearing excitation,measures such as reducing the bearing radial clearance,increasing the vertical system damping,avoiding multi source excitation frequency approaching,and increasing the number of bearing rollers have effectively reduced the rolling mill vibration energy and achieved good vibration suppression effect.