Research On The Vibration Characteristics Of Main Drive System When Hot Tandem Mill Rolling Thin Strip Steel

With the increase of automobile ship industries and aviation industries' serious demand on the high strength and thin strip steel products,the running speed of rolling mill is promoted constantly,which results in the frequent occurs of anomalous vibration.This kinds of abnormal vibration is prone to lead to production safety,fatigue damage of working components and worsen-quality products,which might cause great economic losses for steel mills.Therefore,it is of theoretical and technical importance to further study the vibration mechanism of rolling mills.Meanwhile,for the researches on the related problems of rolling mill vibration,owing to the too simplified model of rolling mill,it was not prone to research on the local characteristics of the rolling mill or the vibration characteristics of the subsystem under the overall influence of the rolling mill.What's more,the parameters of system dynamics model were mostly determined empirically,to recognize the system parameters with the actual vibration characteristic under the real world working conditions was seldom paied attention to.Therefore,it is necessary to study and analyze the vibration of the rolling mill subsystem from the perspective of the overall rolling mill model and determine the system parameters with the vibration characteristics under the actual working conditions.In this article,it is a base that a strong abnormal vibration,occurring in one 1580 mill when rolling in high strength and thinner steel,results in the failure of connecting rod of transmission oil collecting box and surface marks in product.And,the main drive system with serious vibration is taken as the emphasized subject.Meanwhile,the affection between both vibration features of the main drive system and the whole rolling mill,multi-sources excitation disturbance and the selection about the nonlinear structure parameters are taken into consideration.The serious vibration problem in main drive system of F2 mill,when rolling in high strength and thinner steel,is studied by means of experimental study,signal processing,finite element analysis and dynamics research.The main contents and works of this paper is as follows:(1)For the F2 units of one 1580 mill in which the serious vibration occurred,the field test and finite element simulation analysis were both conducted by taking the mutual affection between the main drive system and the whole rolling mill into consideration.The analysis results indicate that when rolling high strength thin steel strip products,the vibration of main drive system is expressed with obvious 38 Hz and 42 Hz frequency resonance,and relatively slight 79 Hz frequency resonance.In particular,the main mode of 79 Hz vibration is located at the oil collecting ring connecting rod,and 79 Hz is almost equal to the plus of 38 Hz and 42 Hz,which will induce the collecting ring fatigue fracture.(2)At the roller end,the vibrations of both in vertical and horizontal directions of the work roll are similar as the torsional vibration and its main frequency are 38 Hz,42 Hz,79 Hz ant their doubling frequency.Similarly,at the driving end of the main drive system,the driving torque current of the motor has the characteristics of 42 Hz and its doubling frequency.Those indicate that there are the torsional-horizontalvertical coupling vibration based on the roller in the load end and the electromechanical coupling vibration based on the motor at the drive end in the abnormal vibration of main drive system,(3)In order to further study the dynamic characteristics of the main drive system,the direct-connecting and nine-degree concentrated mass model under the free vibration was established to gain the linear stiffness parameters of the main drive system.Due to the difficultly solving high dimensional equation,the equivalent twodegree nonlinear dynamic model was set up,based on the equivalent principle.Combining the roll-bite free attenuation signal,the nonlinear structural parameters in the equivalent model were identified and the results show that the actual attenuation curve has a good agreement with the response cure simulated by recognized parameters,which benefits for the following study on the dynamics characteristics of drive system.(4)Based on that the main drive system factually is driven by the motor electromagnetic torque and the roll-end load torque,a nonlinear dynamic equations under multi-frequency excitations was established.The obtained parameters were used to analyse the amplitude-frequency characteristic of main drive system under some kinds of resonances,such as,super-harmonic resonance,sub-harmonic resonance and super-/-sub-harmonic simultaneous resonance.The analysis results show that under the different types of resonance,there are the similar amplitude-frequency characteristics,which means that with decreasing the linear and cubic damping coefficient and increasing the cubic stiffness coefficient,the response amplitude gradually are weakened.Based on the above discussion,adjusting the excitation frequencies of the motor electromagnetic torque and the roll-end load torque and optimizing the friction and lubrication conditions et al at the rolling interface for changing the damping coefficients are applied to shorten the strength of serious and abnormal vibration in main drive system.