Greases

Main rotor bearings: low starting torque

The greases used to lubricate rotor main bearings are normally based on a lithium soap grease and a mineral or polyalphaolefin base oil. However, because wind power plants are now being built in all climatic zones of the earth, the use of greases based on synthetic oils is becoming more and more widespread. As with gear oils, the compatibility of the base oils with elastomers and paints must be ensured.

The miscibility of greases is a criterion to be observed if, during a lubricant changeover, different types of thickener and/or base oil come into contact: if they are not miscible, the resulting mixtures may harden or soften.

Important to know: rolling bearing greases are frequently classified according to DIN 51 825. This standard governs water resistance, anticorrosive behavior and high and low temperature characteristics. As the rotor bearings rotate very slowly, but with high loads, the antiwear behavior of the greases used is of particular interest. This can be tested on the FAG FE test rig.

For operation at low temperatures, low friction start-up torque is essential in the wind power stations. For this reason, the pumpability of greases in centralized lubrication systems must be tested, as well as the starting torque attained with them in rolling bearings, as is laid down in standard IP 186.

Kluber developed the special grease in Kluberplex BEM 41-141 for this application, which has helped attain excellent results in practice.

  • Klüberplex® BEM 41-141 (PDF brochure)
    • Very good lubricity at both very low and very high operating temperatures
    • Low starting torques also at extremely low ambient temperatures
    • High resistance to ageing allowing long relubrication intervals. Consequently less disposal and other costs.
    • Optimum protection against corrosion and hence prevention of bearing damage.

Blade bearings: problem-free function ensured

Greases used in rotor blade bearings are based on lithium or calcium soap and mineral or synthetic oils. Care must be taken that the greases are compatible with the elastomers and paints used and, if necessary for lubricant changeover, that they are miscible with the previously used grease.

Other than rotor main bearings or generator bearings, the blade bearings do not rotate but are only moved by several degrees when the blades are adjusted. But just like the main bearings, a low starting torque is required for operation at low temperatures.

When the rotor is in operation, the vibrations of the blade are taken up by their bearings. The grease in the bearing is therefore required to form a protective lubricant film in the narrow space between the raceways and the rolling elements to prevent wear arising from the vibration.

Whether or not a lubricant is up to this job is measured by the Roth Erde rippling test developed by the Machine Elements Institute of the RWTH Aachen University if Technology. With the right lubricant, wear can be reduced to a minimum.

  • Klubersynth BEL 34-52 - This special grease was specifically developed for the slow oscillating motion of rotor blade bearings. It has passed the Rothe Erde ripping test with very good results and has been approved by Rothe Erde.

  • Klubersynth BEL 34-52
    • Long service intervals and low relubrication quantities due to high shear resistance
    • Excellent operation of rolling bearings thanks to high load resistance also at vibration and oscillating motion
    • Protection against corrosion even at high air humidity and in a saline atmosphere
    • No negative effects on typical sealing elements
    • Reliable operation thanks to low friction torque at low temperatures

Generator bearings: protected against wear

For the lubrication of generator bearings, lithium soap greases based on mineral oil or a polyalphaolefin are most commonly used. Care must be taken with these applications that the greases are compatible with the elastomers and paints used and, if necessary for lubricant changeover, that they are miscible with the previously used grease.

Another important aspect: the high bearing speeds and the heat generated in the generator cause high thermal loads to act on the greases. Operating temperatures of 70 to 90 degrees Celsius, and peaks up to 120 degrees Celsius, are not unusual.

Relubrication normally takes place after six months, i.e. after 3.000 to 4.000 operating hours. As access to the nacelle, and hence maintenance, is impractical, long lubrication intervals are highly desirable. The suitability of a grease for long-term use can be tested on the FAG FE9 machine.

  • Kluberplex BEM 41-132 - Kluberplex BEM 41-132 was developed on the basis of synthetic hydrocarbons, mineral oil and lithium complex soap and has been successfully used in the generators of various wind power stations for many years.

  • Kluberplex BEM 41-132
    • High aging resistance enables long relubrication intervals
    • Suitable for centralized lubricating systems
    • Pronounced antiwear effect in rolling bearings protects against premature bearing failure also at high peak loads

Please contact our sales department for pricing.

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