Vertical Vibration Mechanism And Simulation Of Four-Roll Mill With Compound Roll Bearing Defect

The mill vibration problem is a worldwide technical problem.With the improvement of requirements for rolling production speed and product quality,the vibration problem of the strip mill is becoming more and more prominent.The occurrence of vibration not only affects the surface quality of the rolled product,but frequent vibrations also accelerate the wear of the rolling equipment components,thereby reducing the service life of the rolling equipment.The roll bearing is an important rotating part in the working position of the rolling mill.Due to the wide variety of mill structures and operating conditions,different types of bearings must be used.Compared with general-purpose bearings,roll bearings have large working loads,large difference in running speed,and poor working environment.Therefore,in production,various types of failures are often prone to occur,which in turn causes vibration of the rolling mill and ultimately affects product quality.Therefore,it is particularly important to study the vibration characteristics of rolling mills with roll bearing defects.In this paper,three models of bearing defects are embedded into the vibration model of the four-roll mill.The vertical vibration characteristics of the two-degree-of-freedom strip mill vertical vibration model with the influence of the single-point defect of the work roll outer raceway bearing and three-degree-of-freedom strip mill vertical vibration model with the influence of the single-point defect of the inner raceway and the combined defects of the inner and outer raceways respectively are studied.Based on the actual parameters of the rough rolling mill of a 1780 hot strip mill in a factory,the vertical vibration characteristics of the work roll with different roll bearing defect frequencies and different degrees of roll bearing defects were analyzed by numerical simulation using MATLAB software.The study found,with different severity of failure,as the work roll speed changes,the rolling mill not only has the main reasonance,but also has the nonlinear vibration behavior like the superharmonic resonance excited by the roll bearing fault frequency and the fundamental frequency of the work roll.And for defects of different severity,the most severe form of all rolling mill resonance in all rolling mill vibration behaviors is also different.These findings provide a theoretical basis for further clarifying the effects of various failure modes of work roll bearings on mill vibration theoretically.The following points are the main research contents of this thesis:(1)A vertical vibration model of a two-degree-of-freedom strip mill considering the single point defect of the work roll bearing outer raceway is established.The influence of the area of the single-point elliptical defect zone of the work roll bearing outer raceway and the influence of the defect frequency on the vertical vibration characteristics of the mill are studied by simulation.(2)A vertical vibration model of a three-degree-of-freedom strip mill considering the single point defect of the of the work roll bearing inner raceway is established,and studied the influence of the area of the single-point elliptical defect zone of the work roll bearing inner raceway and the defect frequency on the rolling mill by simulation.(3)A vertical vibration model of a three-degree-of-freedom strip mill considering the compound defect of the inner and outer raceways of the work roll bearing is established.The inner raceway is a single-point closed elliptical pit defect,and the outer raceway is a partial recessed pit defect.The influence of two types of bearing compound defect on the vertical vibration characteristics of rolling mill with different defect severities and defect frequencies are studied by simulation.