Research On Vibration Characteristics And Stability Region In Hot Rolling Process Under Asymmetric Factors

Horizontal vibration and torsional vibration occur frequently in the rolling process of hot strip mill,and the problem of horizontal vibration is more prominent in the production of high-strength and thin-gauge products.Rolling mill vibration not only causes product quality problems such as uneven thickness of the strip and surface chatter marks,but also causes frequent roll replacement and parts damage.In this paper,the hot strip rolling mill is taken as the research object.Considering the characteristics of structure and process' asymmetric features,the instability mechanism,stability region analysis and vibration suppression are systematic studied based on the theoretical analysis,the numerical simulation,the experimental verification.The main research contents are as follows:(1)The structural model constructed by the horizontal stiffness of the upper and lower roll system and the asymmetric characteristics of the roll radius of the work roll was coupled with the process model constructed by the asymmetric characteristics of roll speed,friction and temperature at the rolling interface,and the time-varying meshing stiffness of the transmission system is introduced.finally,the dynamic mechanism model of asymmetric rolling mill is established.The influence of asymmetric factors on the rolling mechanical parameters was analyzed,and the influence of the process parameters and the time-varying meshing stiffness on the inherent characteristics of the rolling mill system was studied,which laid a foundation for the identification of the vibration properties of the rolling mill and the suppression of vibration.(2)Based on the system stability theory,the system stability criterion was used to study the influence of asymmetric factors such as the horizontal stiffness and the radius of the work rolls of the upper and lower rolls,the upper and lower roll speeds,friction and temperature of the rolling interface on the stability region of the rolling mill system.The instability mode type of each instability region was determined by studying the characteristics of the instability frequency and the corresponding mode shape under its similar natural frequency,and the comparison and verification with the instability mode type judged by the dynamic response analysis were carried out,which revealed vibration inducing mechanism,instability critical condition during hot rolling.(3)The influence of typical process parameters such as friction coefficient.deformation resistance,front and rear tension,and reduction ratio on the stability region of the rolling mill system under typical asymmetric factors was discussed.On this basis,the degree of influence of each process parameter on the stability region of the rolling mill system was analyzed quantitatively by comparing the relative sensitivity factor of typical process parameters,which provided theoretical support for the dynamic optimization of process procedures and the instability vibration control strategy.(4)A method to determine the stability region of the system under time-varying meshing stiffness was proposed.The influence of time-varying meshing stiffness on the stability region of the rolling mill system under typical asymmetric factors was studied from the perspectives of different meshing stiffness states and parameter excitation caused by the time-varying meshing stiffness.The influence of characteristics typical process parameters on vibration instability the parameter excitation stability region was analyzed.According to the influence of different process parameters on the speed instability window,it can provide a important reference for the vibration suppression and rolling speed increase in the hot continuous rolling process.(5)The temperature difference between the upper and lower surfaces of the strip was tested by thermal imager,and combined with other rolling parameters,the stability of the rolling mill system at the asymmetric temperature is predicted.The comparison with the test signal verifies the influence of the temperature asymmetry on the stability region and the correctness of the law.By analyzing the influence law of Q235 plate and SPA-H plate on stability region at asymmetric temperature,the reasons of plate failure and container plate vibration were explained.Measures were put forward to suppress the rolling mill vibration by reducing the front tension,increasing the back tension and reducing the reduction rate.According to the site conditions,it is verified that the measure to reduce the reduction rate are effective in suppressing the vibration of the rolling mill.