Study On Elastohydrodynamic Lubrication And Noise Of Grease-lubricated Deep Groove Ball Bearings

Deep groove ball bearings are widely used in aerospace engineering,high-speed railway,mining machinery and other equipments.Residual deformation and residual stress can easily bring about fatigue peeling,wear and other failures to the bearing operating under heavy load conditions.However,few studies have been carried out on the plasto-elastohydrodynamic lubrication(PEHL)of the heavy-duty deep groove ball bearing lubricated with grease.In addition,material defects,improper heat treatment or severe impact can result in cracks occurrence on the bearing raceway.These cracks will inevitably affect the bearing's lubrication performance.However,the study on the lubrication performance of the grease-lubricated deep groove ball bearing with the surface crack has not been found to date.Apart from the need to improve the lubrication performance of the bearing,its noise is also urgently needed to be solved.However,the noise study regarding the deep groove ball bearing has not yet been found.The present work is sponsored by the National Natural Science Foundation of China(No: 51775067),which is named as “study on multi-body lubrication and thermal characteristics of high-speed rolling bearings considering rotor dynamic performance”.Based on this supportion,the PEHL performance of the heavy-duty deep groove ball bearing lubricated with grease,the bearing lubrication performance with the surface crack effect,and the bearing's noise considering the EHL effect are studied in turn.The above research is eager to provide a certain theoretical reference in improving the lubrication performance of the bearing and reducing the bearing's noise.The main contents of the present thesis are as follows:Firstly,the PEHL model of the heavy-duty deep groove ball bearing lubricated with grease is established.Moreover,the increment theory is adopted to solve the bearing's residual deformation,and the fast Fourier transform(FFT)method is employed to accelerate the deformation and stress calculation.Further,the PEHL performance of the bearing is studied.It is found that the concave residual deformation occurs at the center of the lubrication region of the heavy-duty bearing's outer raceway,and the convex residual deformation occurs at the lubrication region's edge and its surrounding region.Morever,the lubricated area between the most severely loaded rolling element and the outer raceway is larger at the PEHL state than that of the elastohydrodynamic lubrication(EHL)case,while the minimum film thickness and central film thickness for the former case are less than the corresponding results of the latter case.Under heavy load conditions,appropriately selecting the grease with large rheological index,reducing the bearing's radial clearance or improving the inner ring's rotational speed(for the fixed outer ring)are helpful to reducing the maximum film pressure,maximum residual deformation and maximum residual von Mises stress of the grease-lubricated bearing.Then,the lubrication model of the grease lubricated deep groove ball bearing with a surface crack is established,through which the lubrication performance of the bearing with the crack is studied.The results show that the crack can increase the maximum film pressure and maximum von Mises stress,and induce the von Mises stress concentration for the rolling element,compared with the case without the crack effect.Increasing the crack's length and depth both result in the increase of the maximum film pressure.With the decrease of the shortest distance between the outlet of the crack region and the center of the lubrication region,the maximum film pressure between the rolling element and the outer raceway gradually increases.When the mentioned distances along the all directions are equal to each other,the maximum film pressure with effect on the crack located at the lubrication outlet region is greater than that for the case with the crack located in the lubrication inlet region.Finally,the noise model of the deep groove ball bearing considering the EHL effect is established,based on which the bearing noise is analyzed.The simulation shows that the noise distribution of the bearing is symmetrical about the middle cross-section in the bearing width direction,and the noise gradually decreases from the middle cross-section of the bearing to it two sides.The area of the noise region in the loading region is lager than that of the non-laoding region.Moreover,the maximum noise occurs at the center of the lubrication region between the most severely loaded rolling element and the outer raceway.When the outer ring is fixed and the rotational speed of the inner ring increases,the maximum noise of the bearing first decreases and then increases,and there exists a critical rotational speed.Appropriately reducing the bearing load and its radial clearance,increasing the number of rolling element,and selecting the grease with the large rheological index all contribute to reducing the maximum bearing noise.