Study On Modeling Of Rolling Mill's Nonlinear Vibration And Its Dynamic Characteristics

The rolling mill is one of the key and core equipment in modern iron and steel industry.In recent years, as the development of modern steel industry towards to large-scale, highload, high-speed direction, the nonlinear factors of rolling process are progressivelyincreasing, which makes various nonlinear vibrations of rolling mill frequently occurredunder perturbation of rolling conditions or parameters in rolling process. The vibration ofrolling mill is always the major technical problems in steel industry. The vibration ofdrive system and frame system not only affects the stability of rolling process, butreduced the quality of product and productivity of production, especially severevibrations will cause the instantaneous destruction of device and lead to huge economiclosses. Therefore, in order to improve rolling productivity and product quality, reducerolling costs, the analysis on the characteristics and mechanism of rolling mill's nonlinearvibration have been an increasingly important task.The project was supported by the National Major Research Topics for 11^th-5-year Planof China (Grant No. 2007BAF02B10) and the Hebei Natural Science Foundation (studyon nonlinear dynamic behaviors of torsional vibration system on rolling mill. Grant No.F2008000882). Considering nonlinear factors in rolling process such as nonlinear friction,hysteresis stiffness and piecewise stiffness and so on, the dynamic response of rollingmill under nonlinear factors and external excitation is analyzed by using the theory ofnonlinear vibration, and the resonance characteristics and bifurcation behaviors of rollingmill are studied from inner relationship of the system. It provide the theoretical basis forfurther revealing the mechanism of nonlinear vibration and characteristic of rolling mill.Firstly, considering the nonlinear factors such as nonlinear friction of roller surface,hysteresis force of shaft, the nonlinear dynamic models of rolling mill's torsionalvibration system are modeling by generalized dissipation Lagrange theory; consideringthe continuous distribution of mass and clearance of rolling mill's drive system, thecontinuous dynamic model of torsional vibration with clearance and no clearance areestablished, respectively.Secondly, according to the structural and mechanical characteristics of rolling mill, the nonlinear dynamic models of roller system's vertical vibration are established whichconsidering the effect of piecewise stiffness, nonlinear stiffness with cubic item andnonlinear friction. Based on these models, nonlinear vibration dynamic behavior ofrolling mill can be analyzed further.Thirdly, the approximate solution of dynamic response of nonlinear vibration modelsunder periodic excitation and no excitation are studied by means of KBM method andaverage method, respectively. On the basis of dynamic response, the amplitude frequencyequation of main resonance, ultraharmonics resonance and subharmonics resonance areobtained, and the influence of resonance characteristics under nonlinear parameters areanalyzed. The dynamic characteristic of resonance and response of rolling mill areobtained.Fourthly, the stability of nonlinear autonomous system of rolling mill nearby singularpoint are studied by using the stability theory of singular and the topology under differentparameters is obtained. Then the bifurcation characteristics of nonlinear non-autonomoussystem are studied by using singularity theory and the transfer concourse and topology ofbifurcation function are obtained. The global bifurcation is studied by using numericalsimulation and, the conditions of periodic motion, period-doubling motion and chaos areestablished. These theoretical solutions offer base for avoiding or suppressing nonlinearvibration of rolling mill.Finally, the torsional vibration of drive system and vertical vibration of frame systemin 1780 rolling mill of Chengde Iron and Steel Company are designed and tested. Thefeasibility and effectiveness of studied were verified about mentioned related theoryabove.