New coating for cylindrical roller bearings
reduces gearbox failures in wind turbine applications

The Schaeffler Group has developed a new, mixed iron oxide coating for cylindrical roller bearings, which provides increased resistance to slippage during alternating, low load conditions, significantly reducing failure rates of wind turbine gearboxes.

Investment in renewable energy systems, whether wind, wave or tidal, requires significant financial commitment. Protecting this investment by ensuring maximum availability of the energy system is therefore critical.

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.

With the implementation of increased Megawatt wind turbines, higher capacity gearboxes are now required. The operating conditions for rolling bearings therefore involve highly dynamic forces with extremes of peak and minimal loads, sudden load reversals and widely differing operating temperatures. Schaeffler offers a wide range of rolling bearings with high static and dynamic load safety factors, including tapered roller bearings, cylindrical roller bearings, spherical roller bearings, deep groove ball bearings and four-point contact ball bearings.

Schaeffler's premium quality 'X-life' branded bearings offer increased operating life far beyond conventional limits. X-life bearings have improved product characteristics, including lower noise and reduced friction, easier maintenance and higher load capacities.

FAG spherical roller bearings are also playing an important part in several high profile European tidal stream energy systems currently in development. Here, FAG double row spherical roller bearings are used to support main turbine rotors with diameters up to 750mm. Schaeffler UK is also supplying spherical roller bearings and radial ball bearings for use on drive train gearboxes for tidal energy systems.

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 in a short time period.

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 of the bearing during 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 of the bearings. Geometrical interchangeability is also provided due to reduced thickness of the coating (between 0.4 and 2.0 µm).

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

In a wind turbine, virtually all forces and moments induced by the wind act directly on the rotor shaft. The rolling bearings are therefore subjected to highly dynamic loads and sometimes harsh operating conditions. This means that the design of the rotor shaft, as well as the bearings that support it, are critical.

A rolling bearing solution will typically comprise a locating/floating bearing design with spherical, cylindrical and tapered roller bearings. Spherical roller bearings, for example, can now be protected with another coating developed by Schaeffler.

Durotect® P is a dark grey coloured PTFE coating that reduces friction and provides improved anti-wear protection of main rotor bearings in wind turbines. The thickness of the coating is between 10 and 20 micrometers. The coating provides improved sliding capacity of the bearing outer ring, with a corresponding reduction in the friction factor to less than 0.1 under axial displacement of the bearing rings.

For further information, e-mail: info.uk@schaeffler.com  or view website: www.schaeffler.co.uk    Refer to next page

GE Energy expands in growing offshore wind sector

GE have completed the acquisition of ScanWind. With this move, GE has expanded its portfolio of renewable energy offerings to better serve customers. ScanWind is a developer of advanced drive train and control wind turbine technologies aimed at offshore deployment.

"The acquisition of ScanWind is an important step in our strategy to place GE in a strong position in the growing offshore wind segment," said Victor Abate, Vice President of Renewable Energy for GE Energy, at the European Offshore Wind Conference in Stockholm. "We are impressed by ScanWind's simple, solid, reliable design and by the team of people who developed it."

Headquartered in Trondheim, Norway, with a design-engineering centre in Karlstad, Sweden, ScanWind was founded in 1999 to develop and commercialise advanced drive train wind turbine technology that eliminates the need for gearboxes. ScanWind's 41 employees have designed and developed the 11 turbines operating on the Norwegian coast which are currently demonstrating the reliability and performance of this advanced technology. (Refer to the two pictures on the right).

The ScanWind turbine technology will join GE's family of wind turbines that includes the GE 1.5- megawatt series, the most widely deployed wind turbine in the world with more than 12,000 now in operation. The GE wind portfolio also includes the 2.5 MW series wind turbine, proven in European applications and now also available in North America.

Reliability and maintainability are of concern in every energy sector but are paramount in offshore wind applications. "This is particularly important for the growth of the offshore wind industry, where project economics are strongly affected by turbine design and reliability. The ScanWind design fits these requirements," noted Abate.

For the EU member states to reach their renewable energy targets by 2020, analysts predict major investments in European offshore wind projects. Industry experts predict a 20-fold global increase, from an installed base of 1.5 GW in 2008 to 30 GW by 2020. Stephan Ritter, General Manager of Europe and Offshore Wind for GE Energy's Renewable Energy business, will lead GE's offshore wind expansion and manage the integration of ScanWind. Ritter comments, "We look forward to taking ScanWind's proven technology and enhancing it, by leveraging our existing wind turbine expertise, our supply chain and our global research capabilities."

GE continues to invest heavily in driving innovation and research and development in the areas of clean energy and infrastructure - investing over $6 billion annually in research and development, of which $1.4 billion is focused on developing clean technology solutions. According to Abate "Our decision to buy ScanWind is part of GE's overall strategy to ensure that we're the innovation leader by developing new renewable energy technologies, collaborating with key players, and when appropriate, making key acquisitions."

GE Energy in profile
GE Energy is one of the world's leading suppliers of power generation and energy delivery technologies, with 2008 revenue of $29 billion. Based in Atlanta, Georgia, GE Energy works in all areas of the energy industry including coal, oil, natural gas and nuclear energy; renewable resources such as water, wind, solar and  biogas; and other alternative fuels. GE Energy has the resources and experience to help customers meet their needs for cleaner, more reliable and efficient energy. Many GE Energy products are certified under ecomagination, GE's corporate-wide initiative to aggressively bring to market new technologies that will help customers meet pressing environmental challenges. With more than 18,000 workers in Europe, GE Energy has plants in France, Germany, Austria, Spain and Hungary. A centre of excellence, GE Energy's plant in Belfort is the sole producer of medium and high-power gas turbines in France.

GE Energy in Europe
GE Energy has over 18,000 employees in Europe, with manufacturing sites in France, Germany, Austria, Spain and Hungary. The Belfort site in France is GE Energy's European headquarters with over 2,000 employees. Belfort is a worldwide centre of excellence for gas turbines, and the only producer of medium- and high powered gas turbines in France. The sites at Salzbergen in Germany and Noblejas in Spain are centres of excellence for the manufacture of new-generation wind turbines. Germany also has one of the GE group's four research and development centres near Munich. The Jenbacher site in Austria is the world headquarters of the leading manufacturer in the field of alternative gas engines, packaged electricity generators and cogeneration installations for the production of electricity. Many European countries also have sites for the manufacture of spare parts and the supply of services, including Hungary, Italy and Great Britain. GE Energy Europe has a university in Florence in Italy for training its staff and engineering centres in Warsaw in Poland and Moscow in Russia.

GE Energy in the UK
Headquartered in Bracknell, Berkshire, GE Energy employs 1,500 people in the United Kingdom. GE Energy offers global services to thermal, renewable and nuclear energy applications designed to help utilities, plant operators and manufacturers meet their operational goals and respond to environmental challenges. The United Kingdom is a launch pad for some of GE Energy's most pioneering technology including gas turbine inlet filtration, oil and gas plant optimisation and control solutions as well as Geospatial Information Systems and pipeline data management software solutions.

For further information contact, Frank Farnel, e-mail: frank.farnel@ge.com