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Schaeffler’s slewing rings have been developed specifically for nacelle wind tracking and for the adjustment of rotor blades on wind turbines.

According to the company, wind turbines need to be aligned to wind conditions in order to optimise operating efficiency.

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.

Schaeffler’s slewing rings are available with outside diameters up to 4,000mm for use on wind turbines with outputs of up to 5MW.

The slewing rings can transmit radial and axial forces, as well as tilting moments.

They 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 the 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.

The company – which supplies bearing solutions for wind turbines, including zinc thermal sprayed surfaces, multi-layer painting, finished seal running surfaces and high-strength tempered steel (such as 42CrMo4V) – is able to offer slewing rings that offer high levels of reliability, rating life and protection against premature damage such as fatigue in the raceway and surface corrosion.

Thanks to the bearing material, with its protective surface coating, the slewing rings are suitable for temperatures down to -30C.

Schaeffler’s slewing rings are used in multi-megawatt-class wind turbines.

The company 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 before.

For more detailed analyses, finite element analysis calculations can be used to determine how adjacent constructions affect the rolling bearings and vice versa.

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