Detection of gear pitting failure progression with on-line particle monitoring

Macroscopic pitting is one of the most common gear flank failure modes mainly caused by repetitive Hertzian contact stresses of the mating surfaces. This may cause fatigue cracks initiating from the surface or nearby subsurface leading to the detachment of a macropit. In studies the determination of gear pitting life is done experimentally and the formation of macropits is typically followed by regular visual inspections and photographing of tooth flanks. Visual inspection is pretty time consuming and gives information only from one time moment. It is also challenging to estimate proper inspection intervals.

In this study, the progression of gear macropitting failure was detected with on-line particle monitoring from lubricating oil and it is correlated to the corresponding results obtained with vibration monitoring from the test gearbox and with visual inspection documented by photographs. The tests were carried out with modified FZG gear test rig with real gears and operating conditions. The on-line particle monitoring system was implemented to the test rig having pressurized circulating lubrication. Particle sensor of the analyser is based on inductive measurement principle and it detects ferromagnetic metallic particles larger than 70 µm and non-ferromagnetic metallic particles larger than 200 µm. The results show that the concentration of metallic particles in oil corresponds well with the severity of macropitting failure obtained from the visual inspection. It is also shown that vibration acceleration descriptors indicating peaked signal correlate with the wear of gear contact, but the correlation is not as strong as in wear particle monitoring.