Effective sealing is a critical but, at times, overlooked component of effective bearing lubrication in wind turbines. In many cases, seals are the differentiating factor that impacts overall bearing and system performance.
Consider that most wind turbines experience some amount of lubrication leakage. These occurrences are relatively minimal for onshore turbines but can pose an environmental risk for offshore wind turbines. Undetected or excessive leakage can lead to a wide range of costly problems and repairs.
Additionally, water ingress can compromise lubricating greases and oils when bearing seals break down or are unsuitable for their intended task. Moisture is a strong contributor to white-etching cracking (cracks within the microstructure of a bearing), which lead to early failure of roller bearings.
Bearing seals should be given careful consideration at the wind-turbine design stage. The market offers a variety of options for meeting the extreme demands of main-shaft turbine bearings, including:
- Single lip seals: All-purpose seals available in a wide range of sizes that are suitable for most applications.
- Dual lip seals: Used for difficult sealing applications involving the separation of two fluids or exclusion of foreign materials.
- Single lip split seals: Engineered for ease of installation on large shafts (requires no costly teardown to replace seal).
- Bearing isolators: Keeps bearings protected from contaminants and debris in applications where long life is paramount.
- Protector seals: Used in highly contaminated operating environments to protect bearings on both rotating and stationary shafts.
Bearing seals are typically made from special elastomers and PTFE materials. Over time, the cumulative impact of abrasive forces caused by varying loads and speeds, temperature fluctuations, moisture, debris, and lubrication challenges, can drastically reduce seal performance in turbines. For these reasons, it is advisable to speak with a bearing expert to determine the optimal sealing arrangement for a given application.
A bearing isolator, for example, may employ a labyrinth seal design that uses an intricate pathway to exclude debris and retain lubrication. This can essentially eliminate seal torque, resulting in less frictional forces in the bearing.
Bearing seals play an integral role in maximizing turbine uptime and productivity. And while proper lubrication remains top of mind for wind-farm operators, more turbine owners are beginning to appreciate how seals can positively impact their bottom line