Research On Vibrations Of Cyclindrical Roller Bearings Based On Contact Mechanics

Rolling element bearings, as a kind of basal components, are widely used in various rotary machineries and their working performances often affect behaviors of the machineries. However, the performance of a bearing is reflected to a great extent by its vibration which concerns with its structure, fabrication and assembly quality, and its lubricant. Therefore, the value of a bearing's vibration has become an important quality parameter for the bearing. With the trend of making quiet running bearings in today's world, domestic bearing manufacturers have to envisage the task to depress vibration or noise of their products. The study on characteristics and mechanism of vibration of rolling element bearings, presented in this dissertation, will contribute not only to fundamental theory on bearing vibration, but also to be available to quality estimation and fabrication guidance for depress vibration or noise of bearings. According to Chinese standard, the Rolling Bearings —Measuring Methods of Vibration (Acceleration) (JB/T 5314-2002), the vibrations of cylindrical roller bearings are studied based on contact mechanics and vibration theory considering both the Hertzian elastic deformations and the elastohydrodynamic lubrications. By means of introducing a structural damping and an oil film stiffness in Hertzian contact area, a contact mechanics model of the contact pair between roller and ring race is proposed comprehensively. And its dynamic load model is proposed on the assumption that there is a virtual roller in the cylindrical roller bearing. Moreover its dynamic stiffness and damping models are also proposed. According to the models, its contact mechanics characteristics are analyzed and the values of dynamic load, stiffness and damping are found to be unconstant and periodically variable with rotation of the bearing. Based on analysis on the contact mechanics characteristics, a Lagrange non-linear dynamic differential equation, as a simulation model for a cylindrical roller bearing, has been deduced considering both Hertz elastic deformations and elastohydrodynamic lubrication of the bearing. Then characteristics of bearing vibrations are studied based on this simulation model. The simulation results have firstly shown the varying compliance vibrations of a bearing under a radial load, even though the bearing is perfect in geometry and with ideal lubricant. In the similar way, the vibrations of both general bearings and bearings with defects have been simulated successfully. From the simulation results, it could be seen that the defects of bearing are the one of the main reasons caused its vibration. Through simplifying the simulation model mentioned above, a contact vibration model of cylindrical roller bearing is proposed based on contact mechanics and vibration theory. According to the model, radial vibrations of cylindrical roller bearings are analyzed. The analysis conclusions show that the basic frequency of the bearings under a radial load is unconstant and periodically variable with rotation of the bearing, and two peaks without frequency-doubling relation will appear in its spectrum. Aiming at abnormal vibrations appearing while testing bearing vibrations, which may cause abnormal sound, a defect vibration model of cylindrical roller bearing with initial fabrication defects is proposed, and a method is also proposed to detect quasi-periodic defects. According to the defect model, characteristics of the bearing with initial fabrication defects are analyzed. It has been opened out by the analysis and experiments that there are either separate or bunchy damped vibrations mixed in the vibrations of a bearing with initial fabrication defects. And a new kind of method to diagnose the eigenfrequency of the quasi-periodic vibrations of cylindrical roller bearing has been given in time domain by the high-frequency resonance technique and a low-pass filter. The experimental investigations have gotten the following results. It is testified by measured vibration of cylindrical roller bearing that there are two peaks without frequency-doubling relation shown in spectrum of the vibration. And the abnormal vibrations will always appear while the outer ring of a bearing has defects and whether or not the defects are in the contact region due to centrifugal forces of rollers. Also the contact mechanics model, the non-linear dynamic simulation model, the radial contact vibration model and the defect vibration model mentioned above are verified by the measured results. Researches in this dissertation are based on experiments and some new phenomena are found in experiments, which are explained in theories. The verification each other between vibration theory and its tests is well realized in this dissertation.