Surface Contact Fatigue Failure Assessment in Spur Gears Using Lubricant Film Thickness and Vibration Signal Analysis

Gears are very common machine elements that are used to transmit power. During power transmission, the gear teeth are subjected to high contact pressure, leading to wear and tear, even though adequate lubrication is used. When gears operate near their maximum load capacity, very high contact pressure occurs at the mesh interference. This may lead to partial breakdown of the lubricant film at the gear teeth contact surface, thereby triggering distributed faults on gear teeth, viz. scuffing, scoring, spalling, pitting, and mild wear. Currently there are three different approaches to the detection of faults in geared systems: vibration analysis, oil/wear particle analysis, and acoustic signal analysis. Generally, in an industrial environment, vibration analysis and oil/wear particle analyses are conducted independently, but of late there are requirements in the diagnostic world for more reliable and effective diagnostic information regarding fault growth in machinery components. In the present work, experimental investigations are carried out to assess surface fatigue wear on spur gear teeth of back-to-back power recirculation-type spur gearbox; in particular, vibration signal analysis using continuous wavelet transform is used in conjunction with specific film thickness studies. Specific film thickness analysis provided details of lubrication regimes in gear teeth contacts and corresponding wear propagation on gear teeth, and the vibration signals acquired from a gear pair are postprocessed using Morlet wavelet transform. Results obtained from the integration of specific film thickness analysis and wavelet transform provide better diagnostic information than the lubricant film thickness estimation alone for detection of gear faults.