Proper lubrication is the lifeblood of wind turbine operation. It minimizes friction between moving parts, reduces wear and tear, dissipates heat, and helps keep components like bearings, gears, and shafts operating optimally. With the extreme conditions turbines often face, including high winds, fluctuating loads, and varying temperatures, high-quality lubrication can mean the difference between uninterrupted operation and costly downtime.
Lubricants generally fall into two categories: oil and grease, each with distinct properties and applications.
The liquid lifeline
Lubricating oils consist primarily of two main components: base oils and additives. Base oils make up 70–95% of the lubricating oil. Mineral oils, refined from crude oil, are widely used due to their affordability and versatility. Synthetic oils, engineered for specific properties, perform well under varying temperatures and extreme conditions, providing superior stability and reduced friction. Natural oils, such as those derived from rapeseed or castor oil, are less common but valued for their biodegradability, making them suitable for environmentally sensitive applications.
The remaining 5–30% of lubricating oil consists of additives that improve its performance. For example:
- Antioxidants prevent oxidation, which can lead to sludge formation and deposits.
- Anti-corrosion agents protect metal surfaces from rust and corrosion, preserving structural integrity.
- Extreme pressure (EP) additives help the oil handle high loads and prevent cold welding in heavily loaded bearings.
- Anti-wear (AW) additives form a protective layer on metal surfaces, reducing friction and wear under moderate to high loads.
Viscosity, a fundamental property of oils, plays a key role in their performance. It determines the oil’s ability to form a lubricating film and is heavily influenced by temperature. For instance, mineral oils typically experience a tenfold drop in viscosity when the temperature rises from 40°C to 100°C, whereas synthetic oils maintain more consistent viscosity levels. Oils used in wind turbines must also withstand high pressures that increase viscosity to prevent film collapse, thereby maintaining effective lubrication. The ISO VG (viscosity grade) classification is widely used to specify the kinematic viscosity of oils at 40°C, aiding in the selection of suitable oils for different turbine requirements.
Oil is primarily used in systems that require continuous lubrication, such as enclosed or high-speed components. In wind turbines, these are primarily the gearbox and hydraulic systems.
The art of long-lasting lubrication
Greases, consisting of base oil, additives, and a thickener (typically less than 30%), blend the fluid properties of oils with the semi-solid consistency needed to stay in place and provide prolonged lubrication. This composition makes them indispensable for applications requiring both adherence and durability.
While additives like antioxidants, anti-corrosion agents, EP additives, and solid additives such as graphite (MoS₂) contribute to the performance of grease, the choice of thickener has the greatest influence on its overall characteristics and suitability for specific applications.
Investing in lubrication is the ultimate high-impact, low-cost strategy.
Thickeners can be classified into metal soap and non-soap varieties, each offering distinct advantages. Metal soap thickeners include lithium-based options, valued for their general-purpose versatility, shear stability, and water resistance. Calcium-based thickeners, on the other hand, excel in water resistance but have a limited temperature range. Advanced formulations, such as metal complex soaps — exemplified by lithium-complex and calcium-complex thickeners — perform well in higher-temperature environments and provide enhanced stability. Among these, calcium sulfonate-complex thickeners stand out for their exceptional performance under pressure, strong anti-wear properties, and effective corrosion resistance.
Non-soap thickeners cater to specialized lubrication needs, making them indispensable for niche applications where conventional options may fall short. For example, polyurea thickeners excel in high-temperature environments due to their organic composition, offering reliable performance under extreme heat. Similarly, clay-based thickeners are valued for their ability to maintain consistent performance across a broad temperature spectrum, thanks to their stability and lack of a drop point. Meanwhile, PTFE thickeners provide unparalleled thermal stability and chemical inertness, making them ideal for applications involving very high temperatures or harsh chemical conditions.
Greases operate through mechanisms like oil bleeding (releasing oil to lubricate surfaces), shearing (spreading grease across contact points), and bulk motion (movement caused by vibration or rotation). And just like with oils, temperature plays a key role in how greases perform. At high temperatures, greases may show increased oil bleeding, oxidation, and evaporation, which can reduce their effectiveness. At low temperatures, greases may stiffen, restricting flow and leading to poor lubrication. This makes temperature management an important consideration in grease applications.
In demanding settings such as wind turbines, specialized greases are developed to meet specific requirements. For example, SKF LGWM 1 is made for low-temperature applications, offering good pumpability, corrosion protection, and water resistance. SKF LGEP 1 is designed for large bearings under high loads and low speeds, providing strong mechanical stability, fretting protection, and water resistance.
Choosing the right lubricant
Proper lubrication is key to keeping equipment running smoothly and cutting costs. For the best results, operators should consider factors like temperature changes, heavy loads, and exposure to dirt or moisture. Finally, following the manufacturer’s recommendations helps maintain equipment reliability and peak performance.
