Bearings enable precise adjustment of wind turbine blades

Paul Boughton
In order to optimise operating efficiency, wind turbines need to be aligned to wind conditions. In order to achieve this, the tower and rotor blades must be adjusted so that they make optimal use of the wind, while also ensuring that the blades are not subjected to excessive loads that could cause damage.
Developed specifically for wind tracking of the nacelle and adjustment of rotor blades on wind turbines, Schaeffler’s slewing rings are available with outside diameters up to 4,000mm, for use on wind turbines with outputs up to 5MW.
Due to their design, these slewing rings can transmit radial and axial forces, as well as tilting moments. The slewing rings are available as single or double row, four-point contact bearings, without gear teeth or with internal and/or external gear teeth, enabling precise angular adjustment at varying loads.

In order to control the output of the wind turbine, the angle of the blade must be continuously adjusted to the wind speed via the rotary movement of the blade adjustment bearing. Adjusting the blades therefore controls the speed of the rotor, which ensures relatively uniform electricity generation.
In some cases, very high forces are generated from the dynamic load of the rotor blades, which must be transferred securely via the bearing raceways and screw connections of the blade bearings into the rotor hub. For this, double row, four point contact bearings with or without gear teeth on the inner or outer rings are used.

Slewing rings are also required to adjust and optimise the position of the nacelle to the direction of the wind. The wind loads and the dynamic inertia forces are transferred via the bearing raceways and screw connections into the head of the tower. Here, single row, four point contact bearings with or without gear teeth on the inner or outer rings are primarily used.
Due to the company’s unique expertise in supplying bearing solutions for wind turbines – including zinc thermal sprayed surfaces, multi-layer painting, finished seal running surfaces and high-strength tempered steel (eg 42CrMo4V) – Schaeffler is able to offer slewing rings that offer the highest levels of reliability, rating life and protection against premature damage such as fatigue in the raceway and surface corrosion. Due to the bearing material with its protective surface coating, the slewing rings are suitable for temperatures down to -30 deg C.
By using state-of-the-art production facilities and the highest level of manufacturing expertise, Schaeffler is able to produce superior quality slewing rings, which are used in multi-megawatt class wind turbines across the world.

By using state-of-the-art bearing design and calculation software, Schaeffler is also able to ensure that the highest levels of quality and reliability for bearings and slewing rings are met.
Schaeffler uses its own in-house software, BEARINX, to model and calculate slewing rings. The external forces acting on the rolling bearings, internal loads in the rolling bearings, comparative stresses of the shafts and other critical parameters, can be presented in diagrams and tabular form. The internal load distribution of the bearing can be calculated precisely – including contact pressures taking account of the raceway osculation.
Based on individual rolling contact loads, BEARINX can also be used to determine the calculated bearing life more accurately than ever before. For more detailed analyses, FEA calculations can be used to determine how adjacent constructions affect the rolling bearings, and vice versa.
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