Bearing Manufacturer Unveils Plans for U.S. Wind Energy R&D Center

High-capacity slewing-ring bearings featured in data sheet

The HS Series slewing ring bearings offer high load and thrust capacity for their size and are featured in a new data sheet from Kaydon Bearings Division. Outside diameters range from 20 to 47 in. (500 to 1,200 mm). Most HS sizes are available from stock and forgings are stocked for the rest.

HS Series bearings provide four-point contact in deep groove gothic arch raceways. With about twice the load capacity of Kaydon RK Series bearings (up to 139,900 ft-lbs.) in the same envelope, they are ideal for medium-duty to heavy-duty applications such as cranes, aerial lifts, digger derricks, chute swivels, lift truck rotators, and industrial turntables. A rectangular cross-section gives the HS Series even greater stiffness than the lighter RK Series, which reduces distortion and allows lower internal diametral clearance. Kaydon HS bearings are available with internal gearing, external gearing or no gearing. Standard features include two fittings for lubrication and integral seals to protect against contamination. The new HS Series data sheet is available for download at http://www.kaydonbearings.com/downloads.htm#other.

Kaydon Corporation Bearings Division
http://www.kaydonbearings.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

Special polyurethane improves abrasion resistance

The Timken UltraWind P1 Seal is a significant wind-turbine bearing seal with a polyurethane design that provides increased resistance to abrasion for longer wind-turbine service life and more reliable performance than most other commonly used sealing materials. “Seals have an integral role in maximizing wind-turbine uptime and productivity because they prevent lubrication leakage and bearing contamination,” said Hans Landin, director of Process Industries original equipment and wind energy at Timken. “However, over time the cumulative impact of abrasive forces caused by varying loads and speeds, as well as extreme temperature fluctuations, rain, snow, debris, and lubrication challenges, can significantly reduce seal performance in wind-turbines. The new UltraWind P1 Seal addresses the problem with the latest polyurethane technology.”

In addition to its durable polyurethane base, the Timken UltraWind P1 Seal contains a variety of other features, including:

• A flexible sealing lip that handles misalignment or run-out in the application of the bearing. The lip’s special profile also helps minimize heat generation and cone wear while helping to accommodate bearing deflections.
• A corrosion-resistant, stainless steel garter spring that helps prevent rust.
• A machined design for a broader, more diverse range of applications, plus ease of installation via stress minimization. This design also allows for multiple positions at the cone lip OD contact; and

The Timken Company
www.timken.com

Bearing take the load off offshore grout

An elastomeric spring bearing improves the stability of the 90-monopole wind turbine foundations at a wind farm off the U.K. coast. The steel and rubber bearings reduce stress on a grouted connection in the wind turbine foundation. Grout fills the gap between an inner-foundation pipe and outer-transition piece of the foundation. It must withstand the tower’s vertical weight and lateral loads. Foundations are a 50-m long, 5-m dia steel pipe piled 30m into the seabed. Below water level, a larger diameter transition piece pipe fits over the foundation for 7 to 8m and extends above water to a flange to attach the wind turbine tower.

Trelleborg Sealing Solutions
www.Trelleborg.com

Trends in bearings

Probably the most significant accomplishment in the bearing industry over the last ten years is the better understanding of what happens to bearings in wind turbines. Researchers and OEMs have defined their loading, vibration, temperature extremes, and identified a few peculiar hazards such as stray electrical currents. This information is driving several industry trends.

“For example, we need to consider main-shaft bearings as part of a complete unit that includes lubricant, a seal, and housing,” says SKF Strategic Technical Manager Dave Mikalonis. “Analyzing as an assembly improves the reliability of the bearing, which is another trend across the board: bearing reliability whether it’s on a main shaft, in the gearbox, or a generator. We’re better at understanding the influences of operation on the application enough to provide the most durable bearing to meet the turbine’s life expectancy.”

Another trend, says Mikalonis, is insulating bearings to protect them from stray electrical currents in generators. “The stray currents take a path of least resistance to ground which is often through a bearing where it can cause pitting and early failure. A couple solutions include coatings that insulate bearings from stray currents and hybrid bearings, those with silicon nitride rolling elements and steel races. The hybrid bearing provides natural insulation, and also provides benefits with lubrication because it can run for periods with poor lubrication.”

The industry is beginning to recognize the bearing’s role in turbine drive train efficiency.  “Bearing designs are becoming available with energy efficiency in mind through the use of improved internal geometries and cage designs” says Mikalonis.

In addition to bearings, how they are lubricated has also been improved with the use of automatic greasing systems that provide the proper amount of grease at the proper interval. “It’s much better to relube a bearing with small amounts more frequently, than with a large amount less frequently,” says Mikalonis. “Condition monitoring is another trend in the push for reliability. This equipment predicts maintenance problems before they occur and become costly by impacting the availability of the wind turbine.”
Other trends might be identified if manufacturers could review the bills of material from turbine OEMs. “They keep such lists close to their vests, so it’s difficult for O&M personnel to develop a strategic spare parts inventory for after warranty work,” says NTN America’s Joe Kahn. “Not long ago, O&M crews would reactively change bearings and stick with the manufacturer the OEM selected. Lately, we’ve seen a shift to search for bearings from a short list of trusted manufacturers, which gives others the opportunity to add value to repairs either through reduced bearing acquisition costs or improved bearing performance.  For generator bearings, some prefer ceramic-coated versions and some hybrid ceramic bearings.”
Kahn says many manufacturing plants worldwide gives companies like his a degree of flexibility. “That means bearings can be made where they’re consumed, which reduces the logistics and duty costs. In addition, inventories sufficient to support wind O&M has brought large inventories into our Midwest warehouse to ensure the right parts are in stock and ready to go before a turbine goes down and that expensive crane is on site.”

Bearing R&D engineers, such as those at Timken, say they and other have identified the wear that limits the life of main shaft spherical-roller bearings, and it is not classical rolling contact fatigue. It’s mostly micropitting wear caused by an interaction of the raceway and roller asperities, leading to high stresses in the contact. Normal stress alone is not typically sufficient to initiate a crack at or near the surface early in a bearing’s life cycle. However, the addition of frictional shear stress increases the bulk contact stress values and brings the maximum values closer to the surface, allowing these localized stresses to become significant under the asperity contacts. This type of interaction typically occurs when the lubricant film is insufficient to separate the contacts and when there is relative sliding between the two contacting surfaces. This is known as low-cycle micropitting.

WPE

Space-saving slewing-ring bearings available from stock

Kaydon Corp. Bearings Division now stocks many models of its space-saving HS Series slewing ring bearings, units capable of handling moment loads to 139,900 ft-lbs. This is about twice the capacity of the widely used Kaydon RK Series bearings, and in the same envelope.

The considerable load and thrust with significant space savings makes Kaydon HS Series bearings ideal for a wide range of medium-duty to heavy-duty applications, such as cranes and aerial lifts.

HS Series slewing ring bearings are designed for four-point contact, with a rectangular cross-section, deep groove gothic-arch raceways, and maximum ball complement. This produces higher thrust and load capacities than the Kaydon RK Series, whose “L” cross-section saves weight while providing a flange for mounting. The HS Series has less internal diametrical clearance than the RK, and therefore greater stiffness. The two series also have several features in common: the same pinion, an identical gear, and equal race core hardness.

HS Series slewing ring bearings come in O.D.s from 20 to 47 in. (500 to 1,200 mm). Configurations include internal geared, external geared and non-geared. The gears are involute stub designs with 20° pressure angles, manufactured to AGMA Class Q5. All HS models feature two fittings for lubrication and integral seals to protect against contamination. Geared races have tapped holes, while non-geared races have through holes.

Kaydon Corp. Bearing Div.
www.kaydonbearings.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

Slewing ring bearings for wind power

Slewing-ring bearings in the DT series of Slewinfinite product line Kaydon Corp. Bearing Div., provides works in pitch, yaw, and gearbox applications in systems from 200 kW to 5.0 MW. The bearings are said to meet critical requirements and industry regulations such as those specified by Germanischer Lloyd’s Non-Marine Technology—Offshore Wind Energy.

The DT Series consists of the eight-point ball bearing originally developed to provide maximum load capacity for given envelope and bolt-circle diameters. It provides up to 80% increase in capacity over that of a single row four-point design, yet has a smaller profile than a three-row roller design. Maximum ODs are to 170 in (11,970 lb) with a bearing moment rating to over 8 million ft-lb.

A few design features include an internal configuration consists of two, deep-groove gothic arch raceways, each with a maximum ball complement, located in inner and outer rings. This results in a total of eight surfaces where the balls may contact at any time, providing exceptional moment, thrust, and radial load capacities. Through precise manufacturing, the raceways are closely matched to provide a high degree of load sharing. Integral seals are provided to assist in the exclusion of contaminants. DT Series bearings are made to order with a customizable hole pattern for bearing retention, and an internal or external gear or other drive mechanism. The series has been used successfully in heavy-duty applications including wind turbines and large cranes.

Complete specifications and drawings are in Kaydon’s Catalog 390, available for download at http://www.kaydonbearings.com/downloads.htm.

Kaydon Corp. Bearing Div.
www.kaydonbearings.com

Thin bearing manufacturer opens new website and message

Kaydon Corporation Bearings Division has unveiled its new website, www.kaydonbearings.com, and new brand. “The site was developed with customers in mind, providing more information in a clean, easy-to-navigate design,” says Kaydon Bearings marketing manager Brian Walters. “It features an improved search function, more product and market information, and additional drawings, specifications, and downloads.”

The company’s many solutions meet the specifications of the renewable energy, aerospace and defense, heavy equipment, industrial machinery, medical systems, and semiconductor manufacturing markets. Product category offerings include Thinfinite, Slewinfinite, custom, and remanufactured bearings and assemblies. Kaydon Thinfinite thin section bearing solutions, including Reali-Slim and Ultra-Slim bearings, save weight, create space, reduce friction, increase design flexibility, and provide excellent running accuracy in bore sizes from 1 to 40 in.

Company engineers can design custom bearings and assemblies when standard parts won’t solve a particular challenge. Custom bearings are available in an infinite variety of materials, separator options, cross-sections, internal fit up choices, lubricants, corrosion resistance options and contact angles. The company’s Bearing Remanufacturing Program returns bearings to service in the shortest possible time and ensures the highest quality workmanship on a cost-effective basis.

The website also introduces the company’s new brand message: Kaydon infinite bearing solutions. “Research showed that users value the company’s engineering expertise and a willingness to create almost infinite solutions for complex bearing challenges,” said Kaydon President Jeff Manzagol. “The new brand conveys that while also underscoring our position as inventor and leader in thin-section bearings and North America’s leader in slewing ring bearings.”

“Engineers also appreciate that we fill order volumes from one-offs to thousands and provide a wide range of product types, sizes, materials, and options,” adds Walters.

Kaydon Corp. Bearing Div.

www.kaydonbearings.com