Requirements for Seals in Wind Energy

Material classes HNBR, NBR and PU

Depending on whether the bearing is oil- or greaselubricated, different combinations of seal design and material can be used. In these applications, the sealing materials must demonstrate excellent lubricant compatibility and high abrasion resistance. Good elastic behavior at low temperatures is also essential for the sealing function – particularly under high dynamic shaft deflection.

Materials in the NBR, HNBR and PU classes deliver impressive sealing performance under these environmental conditions.

NBR stands for acrylonitrile-butadiene rubber, while HNBR is a hydrogenated variant of NBR. Hydrogenation makes the HNBR material class even better than NBR in terms of ozone resistance, thermal resistance and oxidation resistance. The hydrogenation also results in very good wear resistance.

The polyurethane (PU) material class is remarkable for its optimum lubricant and ozone resistance combined with very good low-temperature performance. Additional strengths of PU include high wear resistance and strong mechanical robustness.

Material class NBR

The preferred material class for blade-bearing seals is acrylonitrile-butadiene rubber (NBR). For these applications, NBR offers an ideal balance of lubricant compatibility and low-temperature elasticity. Its thermal and chemical resistance is also fully sufficient for this environment. The Ventoguard® range made of NBR, for example, features high mechanical strength as well as very low abrasion and compression set. These material properties ensure that the sealing solutions in blade pitch systems are highly stable and functional – which is absolutely essential. The reason: For optimal wind turbine performance, the blade angle must be continuously adjusted to wind speed through rotational movement at the blade bearing. This pitch adjustment in the rotor blade can be achieved via electrical or hydraulic systems.

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Material class PU

Polyurethane (PU) seals developed for wide temperature ranges have proven effective in demanding hydraulic environments. They maintain excellent sealing behavior even at low temperatures and under continuous vibration, while also delivering outstanding media resistance. By the way – as energy demand rises, sealing solutions in pitch cylinders are also evolving. Larger turbine dimensions lead to higher technical requirements and stresses on the individual components. This means that the seals also have to be adapted, as the conventional PTFE solution no longer achieves the required service life. Modern pitch-cylinder seals use PU as a more sustainable alternative to PTFE in hydraulic cylinders. PU also offers superior sealing performance in the operation of modern hydraulic systems.

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Material class FKM and NBR

Active electrical pitch control in pitch-regulated turbines makes it possible to adjust the angle of the rotor blades. This maximizes the energy output while protecting the system from excessive wind loads. A motor-gearbox assembly drives this adjustment. The assembly is sealed with Simmerrings made of FKM and NBR class materials. Due to the chemical structure of the fluoropolymers used in FKM, this material class offers excellent chemical and thermal resistance.

For gearbox sealing, the material must combine excellent lubricant compatibility with sufficient lowtemperature elasticity. Since the Simmerring® materials are the basis for lubricant compatibility approval under FLENDER specifications, they ensure compatibility with a wide range of industrial gear oils.

Material class FKM

Main-gearbox seals must provide high wear resistance and offer outstanding compatibility with industrial gear oils. The seal must maintain its return capability throughout the full service interval. At the same time, the high circumferential speeds at the sealing interface can lead to increased thermal stress. The material class of choice here is FKM. Due to the chemical structure of the fluoropolymers used here, this material class offers excellent chemical and thermal resistance.

When Simmerrings made of FKM are used in main gearboxes, they demonstrate impressive wear resistance and lubricant compatibility. This ensures robust sealing performance over a long service life.

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Material class EPDM

Static flat seals are used in the access area of the nacelle. This is where rubberelastic materials made from synthetic ethylene propylene diene rubber (EPDM) are applied. They offer very high resistance to heat and weathering. Seals made from EPDM also reliably withstand ozone, UV radiation and slightly alkaline saltwater over very long periods. These materials can be manufactured to customer specifications – providing flexible installation options across different mounting points.

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Material class NR

For this application, we focus on the high-performance NR substance group. The high-voltage cables and pipes that are used to connect floating wind turbines to the grid generally form the backbone of subsea power distribution. Buoyancy modules are installed at these points to keep tensile and shear stresses on cables and pipes as low as possible. At depths of 100 meters and descending into the kilometer range, every component involved in energy transfer is exposed to the harshest environmental conditions. For buoyancy modules, this means the material must remain seawater-resistant for more than 25 years, withstand pressures of 10 bar or higher and offer temperature resistance up to 80 °C. NR materials developed specifically for this purpose – and approved by the American Petroleum Institute under API 17L – offer very high pressure resistance and contribute significantly to stress relaxation in floating wind turbine applications.

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