Wind Turbine Rubber Parts: Isolation Mounts and Sealing Components Guide

A wind farm operations manager in Denmark was investigating an anomaly in the vibration data from one turbine in a 40-unit onshore farm. The turbine’s condition monitoring system was flagging elevated gearbox vibration at low wind speeds — an odd pattern, since gearbox vibration normally increases with wind speed and load. Remote diagnostics couldn’t explain it. An on-site inspection found the cause: two of the four main gearbox rubber isolation mounts had deteriorated severely — ozone cracking had progressed to the point where the rubber no longer provided meaningful isolation. At low wind speeds, the gearbox oscillated slightly on the partially failed mounts, generating vibration signals. At high wind speeds, the rigid metal-to-metal contact through the failed rubber transmitted load directly, masking the vibration in noise. The gearbox had been running with inadequate isolation for an estimated 8 months. Four new gearbox isolation mounts: €1,200. SCADA data loss of the anomaly pattern before it indicated any bearing damage: fortunate. The ozone cracking — typical of outdoor rubber exposed to industrial atmosphere — was entirely preventable with EPDM or CR compound specified for outdoor turbine environments.

Wind turbines represent one of the most demanding outdoor rubber applications: continuous duty, extreme temperature cycles, offshore salt atmosphere, UV exposure, ozone from electrical equipment, and very long service intervals (turbines are typically maintained at 6-month or annual intervals). Rubber components in wind turbines must provide service lives of 20+ years in these conditions.

This guide covers the critical rubber parts in wind turbine nacelles, towers, and foundations for onshore and offshore applications.

Need wind turbine rubber mounts and sealing components? Request a quote from Babacan Group — compound specifications for 20+ year service life.

Drivetrain Isolation: Gearbox and Generator Mounts

Main Gearbox Isolation Mounts

The wind turbine gearbox (in multi-stage geared turbines — the dominant technology in the 2-5 MW class) amplifies the low-speed rotor rotation (10-20 RPM) to generator speed (1,000-1,800 RPM). The gearbox is one of the highest-mass, highest-vibration components in the nacelle.

Gearbox isolation mount requirements:
– Load capacity: Main gearboxes in 2-5 MW turbines weigh 10,000-25,000 kg — each mount carries 2,500-6,000 kg
– Natural frequency: Must isolate gearbox meshing frequency (varies with gear ratio and rotor speed: typically 30-150 Hz at various load points)
– Temperature range: -40°C to +80°C for inland Nordic turbines; -20°C to +70°C for coastal and offshore
– Compound: EPDM for outdoor temperature and ozone resistance — the Denmark case above demonstrates that NR or standard SBR compounds fail prematurely in ozone-rich industrial and offshore atmospheres

The Denmark case: standard NR mounts showing ozone cracking after 8 months. EPDM compound for the same application would have resisted ozone cracking for 15+ years.

Main gearbox mount specifications:
– Shore A: 52-65 (moderately firm to support the heavy gearbox while providing compliance)
– Type: Conical rubber-metal mounts, sandwich-type, or housed mounts with steel housing for precise installation
– Service life target: 20 years minimum for main drivetrain components

Generator Isolation Mounts

The generator (in geared turbines, an induction or permanent magnet generator) runs at 1,000-1,800 RPM. Generator isolation mount requirements:
– Load: Generator assembly 3,000-8,000 kg (2-5 MW class)
– Shore A: 45-58 (softer than gearbox — generator has lower mass and lower vibration amplitude)
– Natural frequency: Target below 40% of generator operating frequency (1,800 RPM = 30 Hz, target fn below 12 Hz)
– Compound: EPDM or silicone for outdoor temperature and ozone resistance

Direct-Drive Turbine Mounts

Direct-drive turbines (no gearbox — Enercon, Siemens Gamesa with DD design) eliminate the gearbox but require precise isolation of the large-diameter permanent magnet ring generator:
– Generator diameter: 5-10 metres in 5-8 MW DD designs
– Mass: Very high (DD generators much heavier than equivalent geared generators)
– Isolation requirement: Very low frequency (generator runs at 10-20 RPM directly) — isolation mounts must target natural frequency below 5 Hz
– These applications often use steel spring mounts rather than rubber, as rubber mounts struggle to achieve the required static deflection at these load levels

Tower and Nacelle Structural Mounts

Nacelle-to-Tower Yaw Drive Rubber

The nacelle yaw system — which rotates the entire nacelle to face into the wind — uses rubber components in the yaw gear and yaw bearing seals:

• Yaw drive coupling rubber: Elastic coupling elements between the yaw motor and yaw ring gear. Must transmit high cyclic torque during yaw operations while protecting the gearbox from torque spikes. Shore A: 65-75 Shore A
• Yaw bearing lip seal: Excludes rain, salt spray, and wind-driven particulate from the yaw bearing raceway. EPDM or CR for outdoor weather resistance. Replacement interval: 5-10 years

Tower Flange Gaskets

Wind turbine tower sections bolt together at flanges. The flange gaskets:
– Seal the flange joint against water ingress (which causes corrosion in the tower bolts and flange faces)
– Distribute bolt preload across the flange face
– Compound: EPDM for outdoor weather resistance and long service life
– Service life: Must achieve 20+ year turbine design life — compound selection is critical

Flange gasket failure leads to water ingress at the flange joint, which can cause bolt corrosion and in severe cases, bolt stress corrosion cracking — a structural integrity concern.

Foundation Transition Piece Sealing (Offshore)

For offshore wind turbines on monopile foundations, the transition piece (the adaptor between the monopile and the turbine tower) uses rubber elements at various positions:
– Grouted connection rubber fenders and temporary positioning rubber (during installation)
– Sealing elements at the water-entry zone of the monopile
– Compound: EPDM with enhanced UV resistance for above-waterline exposure; neoprene for near-waterline applications

Blade and Hub Sealing

Pitch Bearing Seals

Variable-pitch wind turbine blades (all modern machines) use pitch bearings at the blade root — large slewing ring bearings that allow each blade to rotate about its long axis for pitch control. Rubber lip seals on the pitch bearing:
– Exclude salt spray, moisture, and contamination from the bearing raceway
– Must flex through the pitch bearing’s ±90° rotation without seal fatigue
– Compound: NBR or HNBR for compatibility with pitch bearing grease
– EPDM option for offshore applications with enhanced UV and ozone resistance

Pitch bearing seal replacement interval: 5-10 years in standard offshore conditions. Contamination in the bearing raceway from failed seals is the primary cause of accelerated pitch bearing wear.

Hub Cover Seals

The aerodynamic hub cover (nose cone) that encloses the pitch bearings and pitch motors uses rubber gasket sealing at its mounting interfaces:
– Compound: EPDM
– Temperature: Must maintain flexibility at -40°C (arctic offshore conditions in North Sea)

Cable Entry and Electrical Seals

Tower Cable Entry Gland Seals

Internal power cables and control cables enter the tower through cable entry glands with rubber sealing. These seals:
– Exclude water from the tower interior at cable penetration points
– Must maintain sealing at ±10 mm cable movement (thermal expansion)
– Compound: EPDM
– Temperature: -40°C to +70°C standard; arctic variants to -50°C for Scandinavian and Canadian offshore

Medium Voltage Cable Termination Rubber

Internal medium voltage connections (between generator output and the transformer) use cable termination components with silicone or EPDM insulating rubber. These components are safety-critical electrical insulation — compound and dimensional specification is as important as mechanical sealing.

Offshore-Specific Compound Requirements

Offshore wind turbines face the most demanding rubber environment:
– Salt spray: Continuous in exposed positions — EPDM and CR provide ozone and UV resistance with marine atmosphere compatibility
– Temperature range: North Sea: -20°C to +50°C (nacelle); Arctic offshore: -45°C to +50°C
– UV and ozone: Permanent exposure in outdoor positions — EPDM or silicone for exposed components
– Chemical compatibility: Hydraulic pitch systems use mineral oil — NBR for seals in contact with hydraulic oil

For general guidance on vibration isolation principles applicable to large industrial machines including wind turbines, see our anti-vibration mount selection guide.

Shore Hardness Testing in Wind Turbine Service

Wind turbine service intervals (typically 6-month or annual) should include Shore A testing of accessible rubber components:

Replacement Intervals

Conclusion

Wind turbine rubber components must deliver 20-year service lives in the most challenging outdoor environments — UV, ozone, salt spray, extreme temperature cycling. The Denmark case demonstrates that even a few months of operation on degraded rubber creates diagnostic ambiguity in the turbine’s condition monitoring data.

Key principles for wind turbine rubber component specification:
– EPDM or silicone for outdoor, UV-exposed, and ozone-rich environments — NR will fail prematurely
– Gearbox mount natural frequency must be properly specified, not just load rated
– Offshore turbines have shorter replacement intervals than onshore — factor this into maintenance planning
– Shore A hardness testing at each service provides the documented condition record that supports reliability centered maintenance

Babacan Group manufactures wind turbine rubber components under ISO 9001:2015 quality management, with EPDM, silicone, CR, NBR, and HNBR compound options for wind energy applications. Request a technical quote with your turbine model, component type, and site location.