The investigation and practical application of vibration theories to detect cup nicks on tapered roller bearings

摘要

Timken South Africa manufacture and assemble AP tapered roller bearings which areudused on rail journals. These are also assembled in numerous other facilities worldwide.udThe bearings are large and cumbersome to handle. On the assembly line there is noudmethod of detecting the presence of cup (outer ring) nicks during the assembly process. Audnick is a displacement of metal of very small size on the raceways. High spots of metaludalso exist. They are most frequently caused during the assembly of bearings. Cup nicksudare known for repeat customer complaints due to rough rotation. The presence of the nickudcan induce premature fatigue spalling on the raceways, thus compromising the life of theudbearing. Accelerometers were mounted on nicked and non-nicked cups and wereudanalysed by completing Fast Fourier Transforms and Power Spectral Densities (PSD)udwhile the assembly was rotated in a Lateral Machine. When analyzing the results with audPSD it was found that it was possible to define a baseline for a good defect-free bearingudat different sampling rates. These were then transposed onto the PSD’s of defectiveudnicked bearings and it was found that the nicked bearings could be distinguished asudhaving exceeded baseline limits. The frequencies at which this trigger occurred were notudthe associated bearing frequencies calculated for the ball pass outer frequencies. Theudenergy associated with the rollers rotating over the nicked portion of the raceway excitesudfrequencies with sufficient energy to transpose into the machine running frequency rangeudas well natural frequencies of the bearing components. Different severity nicks wereuddetectable as well as roller-spaced and non-roller-spaced nicks. The nicks with high spotsudexcited the most energy. Tests were performed to show that a cone (inner ring) nick wasudalso detectable by exceeding the baseline limit. Testing performed showed that the limitsudwere also applicable when the accelerometer was mounted on a machine component andudnot directly on the cup. Recommendations include the implementation of the testing onudthe production line to increase the sample size of acceptable bearings for the baselineuddefinition. The data analysis method can be fully automated to compare measured resultsudto set limits in a reasonable time frame to not compromise production output. Nicks areuddetectable as long as a whole spectrum of frequencies is considered in the baseline limits and detection is not reliant on one defined frequency.