Advanced condition monitoring of tapered roller bearings, Part 1

A new condition monitoring technique is under development which is based on electrostatic charge. This was originally employed for the detection of debris in the gas path of jet engines and gas turbines, and is now being developed for lubricated systems. Previous investigations have demonstrated the viability of this technique in dry and lubricated tribo-contacts using laboratory-based equipment. This paper reports on the evolution of wear during a tapered roller bearing test, using a suite of condition monitoring techniques, that incorporated electrostatic wear-site sensors to identify charge during surface wear and oil-line sensors to detect debris in oil scavenge lines. The multi-sensor arrangement also included a vibration accelerometer, thermocouples, inductive and ferromagnetic particle counters. Additionally, oil samples were taken during various stages of the test and were analysed for sub-100 μm debris content. Off-line debris analysis included optical particle counting, ferrography, spectrometric oil analysis and electron microscopy. Further tribological assessments included mass loss calculations and photographic evidence of damage. During the initial 7 h, running-in wear was identified by dynamic wear site charge, acceleration and temperature. Also at this time, increases in oil-line charge correlated with debris detection by the inductive sensor, optical particle counter and ferrographic analysis. Following running-in, benign wear was indicated by a reduction in wear site charge, acceleration and temperature, as well as reductions in oil-line charge, inductive and optical particle counts. Around 42 h, increases in inductive and optical particle count were considered to be an early indicator (or precursor) of the impending wear out phase. At 53.5 h, wear out was identified by increases in wear site charge, acceleration and temperature. Evidence of wear debris was shown by increases in oil-line charge, inductive and ferromagnetic particle count. The debris was further corroborated by optical particle count, ferrography and spectrometry. The test was then stopped after 63 h and post-test analysis confirmed outer race and roller spallation.