Dry lube bearing says goodbye to grease

SKF DryLube Bearings eliminates need for grease relubrication while performing reliably and almost maintenance-free over a wide temperature range. These next-generation high-temperature bearings especially suit hostile and extreme-temperature applications.

SKF DryLube Bearings are filled with a dry lubricant based on graphite or molybdenum disulfide with a resin binder. The dry lubricant is injected into the free space of the bearing, bonded to the cage, and cured until it solidifies. During bearing operation, the dry lubricant maintains a thin film on the bearing’s raceways and rolling elements to protect against metal-to-metal contact and potential damage caused by solid contaminants.

The bearings can lubricate applications up to 350ºC (660ºF), achieve higher speed capabilities than standard graphite-cage counterparts, and exhibit minimal lubricant loss over time. They also improve worker safety by reducing fire risks, eliminating slippery surfaces, and contributing to “green” operating objectives when compared with many oils and greases.

SKF Inc.

www.skfusa.com

Good news for gearboxes: Roller bearing improves reliability

Separable High-Capacity Cylindrical Roller Bearings support high-speed shafts and high-speed intermediate shafts in wind turbine gearboxes. These reliable bearings have a higher load-carrying capacity and eliminate risks of roller-to-roller smearing and adhesive wear in service. Exchangeability with standard counterparts allows fitting them to existing design envelopes whether in initial designs or replacement upgrades.

The compact bearing combines and builds on the advantages of conventional and SKF High-Capacity Roller Bearings. Key features and benefits include a lightweight brass cage to promote lower inertia to reduce the risk of roller smearing, cage guidance on the inner ring (shoulder) contributes to reduced roller slip, reduced risk of smearing, and higher reliability. In addition, the right amount of play between rollers and cage bars provide greater safety and reliability, and black-oxidized rollers improve running behavior and oil-film buildup for more stable running conditions.

During maintenance, especially up tower, the separable design promotes quick and easy dismounting and mounting to help reduce operating, maintenance, and lifetime costs/kWh.

SKF USA Inc
www.skfusa.com

One main-shaft bearing does work of two

Switching to a particular double row, tapered-roller bearing is one way to reduce total turbine weight while increasing component service life. The design, called Nautilus from SKF Bearings, carries all rotor loads on a single bearing rather than on a traditional two-bearing arrangement, one that separately carries radial and axial loads. By doing the work of two bearings, say SKF engineers, the Nautilus lets designers build it directly between the machine frame and hub, eliminating the main shaft. As a result, only rotor torque transmits to the drivetrain.

In the Nautilus bearing, two rows of tapered rollers, arranged back-to-back, lock the unit axially and provide an extremely high stiffness. The company adds that the large number of rolling elements allows extreme precision between raceways and provides extremely high load carrying capacity. Capable of being preloaded, the bearing has a large diameter that makes it strong enough to withstand yaw and tilt moments. Only torsional forces reach the generator or gearbox.

Benefits include significant reduction to nacelle weight and dimensions along with friction and energy losses. The company says component reduction and the bearing’s rugged design combine to lessen drivetrain loads and improve reliability.

This single bearing carries all rotor loads, forces, and movements, and allows transmitting only rotor torque to the drivetrain. This results in longer drivetrain service life and higher turbine reliability.

Without a main shaft to contend with, engineers have more room to design other innovative design features. The company says Nautilus bearings are compatible with a range of geared and gearless turbine designs. Oil lubrication works well when the bearing is mounted inside a gearbox. Units mounted outside the gearbox can come in a sealed, grease-lubricated arrangement that provides high performance under the most extreme offshore or cold climates.

In addition, the Nautilus cage, made from an polyetherehterketone polymer (PEEK), is segmented to make it more flexible, and minimize contact forces and friction. The segmented cage also means there are no additional cage forces to add to normal internal bearing forces. Hence, it can operate in a flexible environment with pre-load, lending stiffness to the drive train and the surrounding structure. Segmentation also improves roller guiding, providing optimized load distribution among the rollers. In addition, the PEEK cage has extremely low friction and makes the bearing less sensitive to inadequate lubrication conditions, resulting in less wear. Therefore either grease or oil can lubricate the Nautilus bearing.  SKF adds that the bearing is operating in multi-megawatt models worldwide and it will meet future needs of multi-megawatt size turbines, onshore or offshore, with or without gearboxes.

SKF Bearings Inc.
www.skf.com

Hybrid bearings work longer in turbine generators

XL hybrid bearings from SKF are aimed at wind-turbine generators and engineered to provide insulation against electric currents.  Their use can almost eliminate the risk of premature bearing failures due to erosion from electric currents. In addition the units can maximize lubricant effectiveness for long-term performance, even under poor lubrication conditions.

These bearings benefit from a deep groove ball design combining steel rings and bearing-grade silicon nitride (ceramic) rolling elements.  The units are lighter, harder, less dense, and more durable than all-steel bearing counterparts, and they conform to standard bearing boundary dimensions.

Resulting benefits include higher reliability than conventional bearings along with reductions in life-cycle costs, total operating costs, and maintenance requirements. The bearings can upgrade existing wind-turbine generators without redesigning them.

The bearings are available in many sizes. Custom designs are also possible.

Cylindrical roller bearing now handles greater loads

Compared with traditional cylindrical roller bearings for wind-gearboxes, SKF USA, Kulpsville, Pa., says its design carries greater load. SKF high capacity cylindrical roller bearings are improved for higher load ratings, for a higher safety factor, extended service life, and a higher power density.

Compared with full complement bearings the company is eliminating the risk of roller-to-roller smearing. Other design improvements reduce the risk of cage slip, fretting corrosion, ring creep, and flange fracture. These improvements result in enhanced reliability.

Also, these bearings are designed for improved lubrication with better oil film build up, resulting in reduced smearing risk and wear. The company lists these benefits for the recent design:

• Exchangeable with standard bearings
• New steel window-type cage
• Possibility for SKF Explorer class (PEX)
• Higher load carrying capacity
• Downsizing possibilities
• Extended service life
• Possibility for inspection of roller and cage assembly
• High cage strength due to shoulder guidance
• Lightweight cage in comparison to brass cage executions
• Reduced risk of smearing under light load conditions

Automated lube lengthens life of bearings and seals

Maintenance crews acknowledge that frequent lubrications with small quantities extend the working life of bearings and seals. But long hours of hub crawling is physically and mentally demanding work. A better idea is a centralized and automatic lubrication system for wind turbines. One instance, the WindLub from SKF USA, Kulpsville, Pa., provides a cost-saving design for lubrication tasks in the wind turbine, including the main shaft bearings. As a plus, the equipment reduces lubricant consumption and refilling the grease pump is simple and quick. SKF says the centralized lubrication system reduces turbine operating costs, increases operational reliability, and extends service intervals.