| Spherical roller bearings (SRBs) are widely used in low speed, heavily loaded equipment, such as paper machines, mining machines, steel rolling machines. The contact between crowned roller and spherical raceway is different when the SRB works in different loading conditions, which results in a complicated status of its mechanical and thermal analysis. SRBs are mainly lubricated with lubricating greases. It is still a difficult issue to predict grease service life and bearing’s performance in the field of grease lubrication. By taking the double-row SRB as the research object, the mechanical performance, roller-pocket lubricating performance, thermal behaviour, grease ageing process and grease life prediction are investigated in details in this dissertation.The main contents and conclusions of the dissertation are in the following aspects:(1) Based on the bearing’s mechanical analysis, a mathematical model is developed for calculating the roller’s load distribution and bearing’s axis center orbit of the radially-loaded SRB with considering the effect of off-sized roller. Effects of single off-sized roller and multiple off-sized rollers on rollers’ load experience and axis center orbit of SRB are numerically analysed; (2) A mathematical model is established for calculating the hydrodynamic lubrication performance between crowned roller and straight-sided cage pocket of SRB on the basis of quasi-static model of radially-loaded SRB. The hydrodynamic pressure distribution and oil film thickness distribution of the lubricant in the roller-pocket clearance can be obtained by numerically solving the 2D Reynolds equation describing the lubricant flow in the roller-pocket clearance in the model. Effects of inner ring rotating speed, radial load, bearing’s geometrical parameters are numerically analysed with a calculating example; (3) A mathematical model for accurately calculating heat generation rate in a grease-lubricated spherical roller bearing is established by adopting the local heat source analysis approach, which involves in calculating heat generation rates of roller-raceway contact, cage and inner ring land contact, roller and cage pocket contact, and power loss of roller churning. Effects of inner ring rotating speed, radial load, working temperature, bearing’s geometrical parameters on grease lubricated spherical roller bearing are numerically analysed by using a calculating example; (4) Based on the accurate calculation of heat generation rate of grease-lubricated spherical roller bearings, a transient thermal model for a grease-lubricated SRB-shaft-bearing housing system is developed by using thermal network method. The transient thermal model for the grease-lubricated SRB-shaft-bearing housing system is numerically solved and the results show a good agreement with the experiment results. Effects of some parameters on the temperature rise of grease-lubricated SRB are analysed, including inner ring rotating speed, radial load, ambient temperature, SRB’s geometrical parameters, grease filling ratio and grease type; (5) A test rig is set up to simulate the ageing process of Al-complex lubricating grease in a radially-loaded spherical roller bearing working in different conditions. The worked grease sample is analysed with FTIR and SME to show the ageing process of grease in the test bearing; (6) Based on an empirical formula involving steady temperature, a modified grease life prediction formula is derived by analysing different factors affecting service life of grease working in bearings. On the basis of testing data of SRB outer ring temperature rise, a new life predicting method for Al-complex grease is developed by proposing a new concept of grease average shearing intensity.The research and conclusions obtained in this dissertation can provide some theoretical foundations for further research and optimization for spherical roller bearing, and offer some new ideas and methods on life prediction of lubricating greases. |
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