Rotor, blade and tower bearings are fundamental components of a wind turbine. The functional reliability of these bearings is critical to the long term, efficient and defect-free operation of the wind turbine installation.

The varied and often extreme loads on a wind turbine require a carefully matched combination of bearing design, lubrication and bearing sealing. This means that a packaged solution for each bearing position is required, which is optimally matched to the specific application.

Wind turbines are now installed in locations with a wide variety of climatic conditions, both onshore and offshore. Operating temperatures expected of a wind turbine can range from -30°C in Arctic regions to 60°C in sub-tropical climates.

Depending on location, the installation is exposed to varying levels of ozone, UV light, sand, dust and salt water. To ensure maximum availability of a wind turbine, robust, durable bearings are required. This can be achieved, for example, by using seals that protect the system from different weather conditions.

The Wind Energy Business Unit at Schaeffler combines rolling bearing know-how with comprehensive systems knowledge of wind turbines, built up over more than 30 years as both a supplier and development partner.

With assistance from a network of high performance seal suppliers, bearing seals are now being developed that represent the optimum combination in terms of functional performance, service life and cost.

Application development engineers at Schaeffler ensure that the specific details of each customer installation are considered. For example, the change in the seal gap of the rotor bearing arrangement in a 3MW installation can be calculated using design calculation software.

In addition to other parameters, the gap dimensions determined for various load cases form the basis of calculating the optimum design of a bearing seal.

Rotor bearings: rotary shaft seals

Rotary shaft seals are the preferred choice for sealing the rotor bearing. The integrated, corrosion-resistant steel spring in the sealing element ensures effective sealing over a long operating period. An additional dust lip can be added to provide even greater protection from ambient media. Under the operating conditions, elastomer materials such as HNBR offer outstanding resistance to ozone, debris and ageing.

The flexible, fabric-reinforced, outer part of the rotary shaft seal enables easy mounting and dismounting. Sealing rings can be replaced easily by simply cutting and bonding into place using a special adhesive set during onsite mounting. Moulded, single-piece rotary shaft seals can now be produced with shaft diameters to 3000mm.

Blade and tower bearings: profiled seals

I believe that for blade and tower bearings, double lip type profiled seals are most effective. The inner seal lip retains the lubricant within the bearing, while the outer seal lip prevents the ingress of ambient media.

Compared to the rotor bearing design, seals for blade and tower bearings undergo lower sliding speeds and so are subjected to only minimal thermal strain. In this case, NBR elastomer fulfils the requirements with respect to ozone, debris and ageing resistance over long operating periods.

A method for vulcanising the end faces of profiled strands enables the economical production of sealing rings of any diameter required.

The advantages of the optimised bearing seal are:

•  Extended bearing life

•  Reduced maintenance work

•  Reduced grease leakage

•  Easy to replace

Schaeffler has introduced a Wind Power Standard (WPOS) for its bearings for wind power applications.