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FEATURE SPONSOR


OILS & LUBRICATION


The grease in your main bearing before and after flushing. Which would you prefer in your critical machinery?


SINGLE AND DOUBLE MAIN BEARING CONFIGURATIONS


Several different main bearing configurations exist. For the purpose of this article let’s discuss the single and double main bearing configurations most commonly used. In these bearings we will normally find two sets of spherical roller bearings running in two opposing bearing races. The upwind race nearer the rotor, the downwind race nearer the gearbox. The bearings are grease lubricated, an


auto-greaser being the preferred method of delivery. The auto-greaser pumps new grease into the bearing at a pre- determined rate, new grease forces old grease through the bearing to an exit point and waste collection. In theory the bearing always runs on fresh, clean grease.


REALITY


The reality, however, is that the new grease takes the path of least resistance through the bearing from ingress to exit, old dirty grease populates areas of the bearing not reached by the new. Over time old grease becomes heavily contaminated and compacted. The effectiveness of the lubrication is now compromised and the condition for boundary lubrication - metal to metal contact - occurs. Micro-pitting, macro- pitting and spalling are inevitable. The inexorable progress towards main bearing critical failure has begun and for many turbines there is nothing to be done to prevent it or manage it as no MBGF solution has been available.


CONSIDERATIONS


1. Would turbine owners accept a gearbox where there was no option to change the oil?


2. Would turbine owners accept gearbox exchange as the only option to contaminated oil?


Romax Gear and Bearing Engineering Model Showing the 3 Point Mount Drivetrain Configuration. The double spherical roller main bearing is directly behind the hub (hub mass is represented by the grey cylinder)


The answers are quite obviously no, so why is it that so many turbines are being manufactured with no option for main bearing grease flushing and the only maintenance option is replacement on the inevitable failure?


IS MAIN BEARING FAILURE REALLY A PROBLEM? SOME FACTS.


Over 12 months, 577 on & offshore Multi-MW turbines were monitored. The confirmed failures detected were as follows…


Main bearing


Gearbox Planetary Bearings Gearbox Intermediate Shaft Blade


Total Failures FAILURES


16 7 6 2


31


Of failures detected, 51% were main bearing related. Annually, the main bearing failure rate was 2.77% on windfarms only 20-25% into their expected life. The problem exists and occurs


relatively early in the turbine’s life. With expected life now 25-30 years, it’s time to change thinking on main bearings.


Dave Moss Commercial Manager Romax Technology


Surely it’s better to design a main bearing that could be easily flushed, cleaned and repacked with fresh grease up-tower?


PREVENTATIVE MAINTENANCE


Where possible, surely it’s better implementing main bearing grease flushing as preventative maintenance rather than an operation of last resort?


SCAN/CLICK


MORE INFO


www.windenergynetwork.co.uk


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