Good vibrations (Rail Engineer)

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“Wheelsets and their axle journal bearings are expensive ‘consumables’ on rail vehicles. Employing preventative maintenance regimes that make use of time or mileage drivers for the replacement for items that aren’t necessarily broken is wasteful and expensive. The objective, of course, is to avoid failures in service, which can be highly disruptive and costly through performance penalties or major incident repairs.

“Axle journal bearings might typically have an L10 [L subscript 10] life expectancy (the life that 90 per cent of the bearings can be expected to reach or exceed) of 1.5-1.8 million miles, but the default maintenance measure is to replace them at half that mileage. The graph of failure vs. mileage is not linear so, at half L10, a failure rate of 3.6 per cent might be expected.

“While early swap-out improves availability, it does not eliminate failures entirely. Bearings have a hard life and external factors such as wheel faults (flats, out-of-round, tread spalling), and damper failures can shorten their lives in unpredictable ways.

“Moving towards bogie maintenance interventions based upon condition monitoring and trend monitoring makes much greater economic sense. However, the ability and confidence to safely extend maintenance and overhaul periodicities requires the gathering of accurate empirical information on wear rates and fault progression.

“Analysing the acoustics produced by bearings enables the very early detection of defects and the trending of deterioration. Acoustic monitoring can be used without having to take the vehicles out of service and it allows bearing faults to be detected and monitored months, or even years, in advance of intervention…”

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Written by Long Branch Mike