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Wind turbine bearings benefit from Durotect B coating

Paul Boughton

FAG rolling bearings from the Schaeffler Group are found at the heart of many wind turbine installations around the world and, more recently, in wave and tidal stream systems. Used predominantly to support the rotor in wind turbines, these bearings are typically designed to have at least a 20-year operational service life.

Suitably designed bearings are critical in reducing wind turbine operator costs. For example, the design of low-friction bearings for the wind turbine rotor shaft and gearbox is a key consideration, as are the associated lubrication methods for the bearings, mounting and maintenance to ensure maintenance costs are minimised and service life is increased.

Schaeffler has worked closely with designers, manufacturers and operators of wind turbines for more than 25 years and more recently with manufacturers of wave and tidal stream systems. In a typical wind turbine drive train, FAG rolling bearings are used to support the rotor, gearbox and generator. In addition, plain bearings can be found in blade adjusters in pitch-controlled wind turbines and in geared motors that drive the tower slewing ring and pitch control. The significance of these rolling bearings will increase as larger, multi-megawatt class turbines are developed.

When it comes to the maintenance of wind turbines, the cost of replacing a bearing on the tower is more favourable than having to replace a complete gearbox due to a bearing failure. Over the next few years, it is predicted that MRO companies will increasingly have to carry out routine inspection and overhaul of gearboxes on wind turbines. This will inevitably result in the replacement of bearings that are deemed as being damaged or likely to fail imminently.

For this reason, Schaeffler has developed Durotect B, a new black oxide coating for its FAG range of cylindrical roller bearings. Field tests have demonstrated that significantly lower failure rates in wind turbine gearboxes are experienced if these units are fitted with Durotect B coated cylindrical roller bearings.

Durotect B is a matt black, mixed iron oxide layer that is produced in a dip solution. The surface structure, magnetic and electrical characteristics of the base material are maintained. The coating is highly resistant to bending and stress.

As well as excellent anti-corrosion protection, Durotect B also offers increased resistance to slippage and sliding, as well as during alternating, low-load conditions that are common in wind turbine and tidal stream energy applications. The coating also provides improved run-in behaviour. Geometrical interchangeability is also provided due to reduced thickness of the coating (between 0.4 and 2.0 um).

Schaeffler also recommends Durotect B for other types of roller bearings, including bearings for high-speed shafts and couplings, as well as for full-complement bearings.

For more information, visit www.schaeffler.co.uk

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