Carlisle Brake & Friction
www.carlislecbf.com

Windpower Engineering & Development

Sealant Equipment
www.SealantEquipment.com

Windpower Engineering & Development

The test machine measures friction levels for a combination of seal material, shaft surface, and lubricant.

Nacelles become oily places when wind seals don’t work well. To find better seals, our companies developed a way to work in close cooperation with users to design tailor-made solutions that improve gearbox performance and life-seal predictions. Here’s what we learned.

A little background
Radial shaft seals are used in industrial gearboxes to prevent leakage and keep out contamination. The gearbox lubricant is usually selected according to the requirements of the gears and bearings, and not necessarily the seals. An equally important criterion for selecting the right radial shaft seal considers the influence of the lubricant on the wind turbine seal material along with load, speed, temperature, and life.

Gear oils are classified according to DIN standard 51 517/03 and, therefore, comply with considerable protection requirements against fretting and rolling bearing wear. Elastomer compatibility under static conditions is another consideration. However, practical experience has shown this is not enough to fulfill the multiple industry requirements regarding seal reliability and life under assumed operational conditions.

Industrial gear oils 
These normally consist of a mineral or synthetic-base oil. The base oil is 85 to 98% of the lubricant, complemented by additives. In Germany, 70 to 80% of gears are lubricated with mineral oil, while the remaining 20 to 30% use synthetic gear oils. Most wind-turbine gearboxes are filled with a synthetic lubricant.

Mineral oils have been the traditional basis for gear oils for decades. Additives normally dissolve well in these base oils. Elastomer (seal) compatibility is predominantly influenced by the additives selected.

Polyalphaolefins (PAO) are the most commonly used base oils for synthetic gear oils. They show better viscosity-temperature behavior, good low-temperature characteristics, and help reduce friction. Unlike mineral oils, elastomer compatibility with polyalphaolefin oils is influenced by the combination of base oils and additives.

Polyglycols (PAG) are another important group of synthetic gear oils. They have the same benefits of polyalphaolefins and like mineral oils, elastomer compatibility comes from the additives.

Synthetic esters offer the same advantages as polyglycols and polyalphaolefins. However, unlike mineral oils, elastomer compatibility is influenced by the different ester oil types and the additives.

Shaft seal materials 
Seals are usually made of rubber-like materials called elastomers. These long-chain molecules combine with additives to provide specific and technical material properties. Sealing materials based on butadiene-acrylonitrile and fluorinated rubbers are, with few exceptions, the proven and preferred wind turbine sealing materials used in industrial-gear applications.

Butadiene-acrylonitrile rubber (NBR) shows good swelling resistance in hydrocarbons along with high resistance to hot water, and inorganic acids and bases. However, when exposed to benzene, chlorinated hydrocarbons, esters, polar solvents, and polyglycol-ether brake liquids, considerable swelling occurs.

Fluorinated rubber (FKM) shows high temperature resistance, high chemical stability and good swelling resistance in hydrocarbons. Like NBR materials, FKM materials also tend to swell considerably when exposed to polar solvents and flame-resistant hydraulic fluids.

Interactions in the tribological system
The function of a radial shaft seal primarily depends on its geometry and the elastomer material. Radial shaft seals work like a small pump transporting liquids, gases, and dirt particles around it through the sealing edge. This effect is also used to pump small leaked amounts back into the sealed area. This intentional unmeasurable leakage is required for reliable lubrication and function of the radial shaft seal. It also has a considerable influence on its service life.

Leak-free sealing of the rotating shaft is ensured by the pressure of the sealing lip on the shaft. This force generates an asymmetric pressure distribution on the shaft dependent on the design of the seal-lip angle and tension-spring space. The pressure together with the elastic material properties cause the pump effect.
Considerable heat generates under the shaft seal’s sealing edge due to friction generated by the pressing force, the rotating speed of the shaft, and other factors,

Permanent interaction between the sealing material and lubricant is due to strong shearing forces combined with atmospheric oxygen. Therefore, it is critical to optimize the combination of shaft seal, lubricant, and shaft surface finish to ensure trouble-free operation.

Elastomer compatibility 
The chemical and physical resistance of the sealing material to the proposed lubricant must be considered along with the sealing material and operational temperature range. The behavior of rubber-like materials toward liquids is tested to DIN ISO 1817 in the specific medium or standard test liquids.

To determine static elastomer compatibility, S2 standard-test pieces and discs are punched from a 2-mm thick test sheet and stored in the test medium. For better correspondence between static and dynamic test results and practical conditions, Freudenberg increased the test duration for mineral oils from 168 to 1,008 h. After immersion in the test medium, test pieces are inspected with regard to changes in hardness, tensile strength, and ultimate elongation according to DIN 53504. Volume changes are determined according to DIN ISO 1817. Standard static compatibility tests were traditionally used for lubricant approvals, but it is now more representative to conduct dynamic seal testing as well. Dynamic oil compatibility tests following DIN 3761 and reducing friction deserve further discussion.

The illustration provides a closer look at the pump action or area of the seal. The tan arrows indicate lubricant circulation.

Flender AG developed the testing program. Dynamic seal testing is undertaken on DIN-standard test benches. The radial shaft seals are analyzed by measuring relevant functional parameters and by visual inspection. For approval, the variation compared to the original measurements is decisive. Visual inspection results are based on experimental values.
The friction between seal and shaft is an important indicator of the expected wind turbine seal life. It should be kept as low as possible because the friction heat generated by the sealing system influences gear efficiency and lubricant temperature. Temperature increases of only 10°C reduce the life of the radial shaft seal and gear oil by half.

The cooperative project, called Lube&Seal, focuses on determining the frictional moment, or power loss, for all wind seal and lubricant combinations as a function of speed, temperature, lubricant additives, and viscosity.

Initial findings on lubricant additives prove that different additives in the same base oil considerably influence the frictional moment and temperature in the shaft seal’s sealing zone. The example shows that the frictional moment and temperature are considerably higher with the lubricant polyglycol (PAG) 1 than with PAG 2 over the entire speed range, regardless of the oil sump temperature.

The cross section shows a typical elastomeric radial-shaft seal at work. The spring (circular detail) pulls it tight against the shaft.

Energy and CO2 emission reduction 
Basic research projects have shown that the right combination of radial shaft seal (material and shape) and lubricant can considerably reduce friction. A few rough calculations deliver the following figures, assuming a typical industrial gearbox with three seals and running for 5,000 hrs p.a. Then the power loss using:

-Standard radial shaft seals is about 90 W
-Optimized standard radial shaft seals is about 60 W

The potential energy-saving for an entire installation means a remarkable potential reduction of CO2 emissions. A gear manufacturer making one million gearboxes per year could reduce industrial CO2 emissions by about 25 tons simply through changing oil and seals (1 kW corresponds to average carbon dioxide emissions of about 500 g).
Industry requirements regarding tightness and reliability of radial shaft seals are ever-increasing. Elastomer compatibility of a lubricant, besides speed and temperature, is of particular importance to meet these increased requirements. Experience shows that testing only static elastomer compatibility is insufficient. Dynamic seal testing is indispensable because only these tests allow reliable conclusions on the long-term behavior of the shaft and seal tribosystem under lubricant exposure.

With an ideal combination of radial shaft seal, shaft, and lubricant, wind turbine seal life can increase three-fold and friction at the sealing lip can be reduced by up to 30%. As a consequence of this work, it’s also possible to considerably reduce CO2 emissions. However, the complex interaction between lubricant and sealing material must be thoroughly investigated to realize these reductions. WPE

By:
Erich Prem, Product Development Engineer Leadcenter Simmeringe, Freudenberg Simmerringe, www.Freudenberg-ds.com
Hermann Seibert, Head of Application Engineering, Klüber Lubrication Munchen KG, www.kluber.com

Windpower Engineering & Development

A WT 2000 replacement gearbox heads to testing.

The next generation of drivetrains will be large and operate in harsher environments (offshore) than those previous. They will have to be more reliable, easier to service, repair, monitor, and include effective diagnostics and prognostics. These Gen2 units will have to carry greater torque and rotor-bending moments, and show drivetrain dynamics with lower frequencies, for more durable machinery. Operational costs and financial risk must also come down.

The need for improved reliability has driven several efforts in the industry, including:

• A major revision to ISO 61400-4, “Design Requirements for Wind Turbine Gearboxes”

• The long running NREL Gearbox Reliability Collaborative (GRC)

• Stricter wind gearbox requirements in the 2010 edition of the Germanischer Lloyd “Guideline for Certification of Wind Turbines”, and

• Current revision efforts to AGMA 6006-A03, “Design and Specification for Wind Turbine Gearboxes”

The analysis is of a RomaxWind model of an NREL GRC drivetrain with a 750-kW gearbox. RomaxWind was released as a wind turbine specific version of the RomaxDesigner; software used by the automotive OEM’s for geared transmission design and refinement.

Engineering firms have been developing and improving design methods and software since the beginning of the wind industry. Manufacturers have been improving their product by implementing a range of tests such as full load end-of-line testing, off-axis load and dynamic development testing, 100% nital etching, stricter incoming material specifications and inspections, and improved techniques for the heat treatment of large components. Turbine designers have a better understanding of the loads and dynamics in the machinery.

Rotating machinery specialists such as Romax Technology have been involved in these activities along with the development of the next generation of wind-turbine gearboxes. To date the company has developed 14 multi-MW models ranging from 1.5 to 5.5 MW, which are used by 10 different turbine manufacturers, most of which are installing turbines in the Far East. “We won’t design a wind gearbox for a manufacturer unless they go through certification either by GL, DNV, TUV or an equivalent,” says Romax Director of renewables Andy Poon. “This along with our own due diligence on the prototype development and manufacturing helps ensure high-quality manufacturing for our products.”

The company is working on improving the installation and serviceability of the high-speed stage of the wind turbine gearbox. This stage in any wind-turbine gearbox is most susceptible to wear and premature failure, given the high number of cycles and high inertia of roller bearings in larger gearboxes. The company is also developing a diagnostics capability for damage and wear in the gearbox, with condition monitoring equipment and specialized software. If wear in the high-speed stage is detected early enough, then an up-tower replaceable cartridge can be easily fitted by a technician. The high-speed cartridge is easy to assemble. The technician simply removes the whole unit and replaces the high-speed-stage bearings and pinion in the new cartridge. Bearing preload is preset in the factory to ensure good performance. Double helical gears are used in several models on the parallel stages in combination with the high-speed cartridge. This negates the requirement of the axial constraint to resist the load due to gear helix. Then the high-speed bearings need only react to radial loads. It eliminates the problem of double row, taper-roller bearings being unloaded in reverse torque situations.

An easily changed high speed cartridge is designed for a proposed 5-MW gearbox. A recent condition-monitoring product, Romax IDS, can detect wear early enough to allow, if necessary, a planned and orderly replacement.

Another recent significant development is a new way of adapting the high-speed bearing to many common wind turbine gearboxes in service. The concept of this new design was developed after evaluating many offshore machines. Most bearings are manufactured with high quality material, to high tolerances and surface finishes, and then fitted with no real idea of the actual preload,” says comapny Test Team Leader Richard Smith. “Industry falls down on the last 10% of the job. A new approach to retrofitting the high-speed stage takes aim at setting accurate bearing preload, which results in longer bearing life than the previous practice.”

Another feature of the recent gearbox is a split-torque design with rotating ring gears and a dry sump. This removes a common problem of debris accumulating in the 6 o’clock position of the stationary ring gear and the early failure of this gearing. Gravity feeds oil into a sump below the gearbox, so the gear stages need retain no oil. Churning is minimized so less aerated oil returns to the cooling system and drag losses drop.

In addition, the company has an advantage because it has been a long-time developer of commercial engineering software for designing gearboxes as well as being a large wind turbine gearbox design firm. Gears and bearings are designed with microgeometry, and clearance and preload settings after accounting for whole system structural deflections, non-torque loading at the rotor, and the effect of thermal expansions and off-nominal tolerances.

Romax software shows strong validation with extensive gearbox measurement data provided by the NREL GRC, and the software is certified by Germanischer Lloyd for gear contact analysis and rating. The analysis allows for improving function, performance, weight, and cost of gear trains.

The planet carrier provides an example of lessons learned. Generally, manufacturers use cast-steel carriers to meet strength requirements. However the steel has high scrap rate, can be a difficult to work with, and has stringent requirements for nondestructive testing.

Careful analysis has led the company to a suitable lower cost and lower weight (sometime by 1,000 lbs) cast-iron planet carrier. “We worked with GL to approve GJS 400 spherodal graphite cast iron for the planet carrier,” says Design Team Leader Dave Saysell. “By careful analysis and rearrangement of the structure, we can achieve equivalent deflections, strength, and fatigue life with this lower-cost material. Critical attention is paid to strength near the planet-pin fit and the carrier wind-up.” Environmental considerations are important because the material is more suitable for warmer climates. WPE

By: Ashley Crowther, VP Engineering, U.S. Wind Technology Center, Romax Technology Inc., www.romaxtech.com

Windpower Engineering & Development

The Eco Wisper mount on a hinged tower that has been lowered to access the 20-kW turbine. The 30 blades are said to rotate almost without noise.

Renewable Energy Solutions Australia (RESA) is the owner of what it calls the world’s most advanced silent wind turbine for mid-sized applications, about 20kW. The turbine features a 30-blade design that is almost silent and up to 30% more efficient than traditional 3-bladed designs. The Eco Whisper Turbine stands 21.1-m high and can produce high energy in low or high winds with a footprint of only 21 m². In comparison, the same output from solar panels would require 250 m².

Following two years of development and testing in Australia, the turbine is ready. It’s first commercial installation is in Tullamarine. The turbine was a finalist in the 2011 Australian Cleantech Awards and was recently awarded a $250,000 commercialisation grant from the Australian government.

The Eco Whisper Turbine can offset medium to large energy requirements. It is suited to commercial, manufacturing, and industrial sites and other applications. It also works on and off grid application with a particular focus on remote communities and diesel replacement.

Other plusses are that it collects wind more efficiently and there are no turn away losses, it delivers more energy from more common wind speeds than three bladed designs, and it performs well in all wind conditions (lower start up speed compared to competitors)

Eco Wisper Turbines

Windpower Engineering & Development

The FusionDrive combines a gearbox and PM generators into one unit.

Wind gear manufacturer Moventas and generator manufacturer The Switch, have announced the delivery of the first commercial order for FusionDrive, a gearbox and generator combination. The first delivery is going to Germany-based DeWind.
“We think FusionDrive is the next big thing for the wind industry. It includes the benefits of a hybrid drive, but Moventas and The Switch have taken the integration even further,” says Dr. Sungkon Han, Managing Director of DeWind Europe.

The developers say FusionDrive is the answer to the challenge of turbines needing to be bigger in size and power, while the race is on to lower the cost of energy. The developers say FusionDrive is the smallest and lightest combination of gearbox and generator. Studies have confirmed that it is a technically optimized solution to limit rotational speed. More important to turbine manufacturer and energy provider, the unit provides the highest energy yield and the best serviceability in the market, say the two companies.

The unit requires minimal maintenance, say the companies. The gear and generator can be split, and all components are changeable in the nacelle enabling best serviceability in the market.
Moventas

Moventas.com

Windpower Engineering & Development

The MAG Megaflex is cutting a 18,144-kg spherical hub that measures about 3.6 x 3.6 m and has a blade bolt circle of about 2.5 m.

Astraeus Wind Energy’s MAG Megaflex machining system has passed its initial supplier qualification by completing “Operation 20″ metal-cutting processes in record time on a Clipper Windpower C96 turbine hub, one of the industry’s largest. The system simultaneously machines all three blade faces, which lets it complete the qualification hub in less than one shift, a first in the industry. “Completing hundreds of features on this hub in such a short time, and meeting the extreme tolerances required, is a world first for U.S. manufacturing technology,” said Astraeus President Jeff Metts. “We should be able to do the industry’s simpler hubs in even less time,” Metts added. “This is, without a doubt, world-leading technology that no one else can compete with. The system is operational now and we are taking orders, forecasting a capacity of about 1800 hubs per year.”

The 18,144-kg (40,000-lb) spherical hub was about 3.6 x 3.6 m (12 ft x 12 ft), with a blade bolt circle of about 2.5 m (8.2 ft). Operation 20 for this part included milling the blade faces, drilling and tapping or counter-boring more than 60 39-mm (1.5 in) holes per face, boring and drilling the blade-pitch gear mounting surfaces, and cutting various other features. Tolerances on the part, which was laser inspected after machining, include 0.05 mm (0.002 inch) true position on holes and ±1 degree on angles.

Look closely and you can see two of the spindles. The third is behind the hub.

Conceived by MAG in 2009, Megaflex development was funded in part with grants from the Michigan Economic Development Corporation (MEDC), which audited and approved the progress of Astraeus in meeting its performance requirements. MAG developed the entire system on a turnkey basis, including the process concept, programming, machine systems and tooling package. The patent-pending Megaflex design, which is based on three MAG FTR 5000 floor-type boring mills surrounding a B-axis rotary table, simultaneously machines all three blade faces on a wind turbine hub in one setup, a concept widely used in mass-production of automotive components and small parts. “This is automotive machining technology scaled up an order of magnitude,” explained Pete Beyer, MAG Director of Product Development. “We are using multiple spindles, specialized tools, and clever process technology to finish a part in one setup, in the shortest time possible, while maintaining the flexibility to process a family of different hubs.”

Concepts borrowed from the automotive industry include offline setup and quick part loading, using a fixture interface plate and a lifting bracket for the workpiece. The interface plate is bolted offline to a locating feature on one side of the casting; the plate then mates with a locating feature on the worktable for fast part setup. The lifting bracket attaches to the top of the part to allow a single crane to transfer the part in and out of the workzone safely and quickly. “These are classic part handling techniques on a gantry-type automotive line that we have adapted for very large parts,” said Beyer. “We can setup the next part offline on an interface plate, and quickly exchange a completed part to maximize utilization of the spindles.”

MQL, another automotive machining technology little used elsewhere, eliminates need to control splashing and misting coolant in the shop. “MQL is a green and sustainable technology that saved the initial and ongoing cost for pumps, filters, energy, regulatory compliance, and coolant acquisition and disposal,” Beyer explained. “MQL also produces dry chips, which do not have to be cleaned or treated, but can go straight into the melting furnace.”

Unique features on the boring mills include a specialized tooling package utilizing numerous extension tools, and a servo-controlled tilting A-axis on the W-axis ram. The tilting A axis allows the ram to be positioned for a normal approach angle to the work face. This is required because the blade face of the hub is not always perpendicular to the hub’s axis of rotation, but may be two to three degrees off, depending on the manufacturer. “The tilting ram is much stiffer than other solutions, such as a multi-axis A/C head, and it eliminates the need to interpolate axes,” Beyer explained. “The tooling package allows efficient machining of the challenging features on these parts, such as the back bore on most of the bolt holes.”

As part of the Megaflex design, each machine has a latch-plate interface to accept attachments from a head changing rack. However, for cost economy, the system currently has only one attachment rack, which can be moved for use by any of the machines. Rotation of the worktable allows the machine using the attachments to access all three faces of the part. Synchronous/asynchronous processing is then used to balance out the cutting times and cutting forces of the three spindles when doing similar and dissimilar operations.

“MAG delivered on the concept for a purpose-built system in terms of the budget, major reductions to cycle time and future flexibility,” Metts added. “Customers who have seen it say it never occurred to them to create a multi-spindle system with giant machines. When it’s running, it’s like watching an orchestra play. This sets the benchmark for the rest of the world and helps level the playing field with low-cost countries. Now that the U.S. has the tools to regain the lead in wind turbine manufacturing, it’s vital for Congress to extend the wind energy production tax credit to invigorate the industry, which is already softening. In addition, we believe there is an ideal opportunity for a forward thinking company to open a foundry nearby to cast hubs to feed this system.”

MAG
www.mag-ias.com

Windpower Engineering & Development

The onshore turbine is similar to the 6 MW offshore unit. LM Wind Power supplies the wind industry with operations from 13 manufacturing facilities worldwide, and more than 140,000 blades produced since 1978.

LM Wind Power’s 73.5-m blades became the first 70+ meter working blades to be installed when Alstom inaugurated the largest offshore wind turbine in the world on March 19 at Carnet in the Loire-Atlantique region of France.

The impressive composite structures have been developed specifically for Alstom’s Haliade 150-6MW wind turbine in a close collaboration between the two companies to boost energy capture while keeping loads down. The innovative blade design has already been through several rounds of testing before being installed on the turbine in France.

“It was great to see LM blades mounted on the newest and biggest turbine in the world as well as see the excitement this technological leap has made in the offshore world,” says LM Wind Power VP Sales & Marketing Ian Telford. “Our technology lets us design and manufacture relatively lighter glass fiber and polyester blades for the length, but above all, the company has proven ability to handle the industrialization of these blades, which is not easy.”

Alstom’s Haliade 150-6MW turbine has been EDF-EN / Dong Energy’s choice developed in response to a call for tenders launched by the French government that aims to install 3 GW of wind turbine power off French shores by 2015. Depending on the results of the tenders, Alstom and LM Wind Power plan to establish a blade manufacturing facility in Cherbourg with capacity to produce up to 100 sets of 73.5 meter blades per year. Production is planned to start in 2016.

LM Wind Power
www.lmwindpower.com

Windpower Engineering & Development

D C Connection Inc.
For more information, call 800-435-9346.

Windpower Engineering & Development

The filter element captures particles at 3 micron absolute (β3≥200)

Hydroguard hybrid breather can stand up to a wide variety of industries and applications. The breather is outfitted with an expansion chamber to isolate lubricants from all levels of ambient humidity. A clear, rugged polycarbonate casing allows for viewing desiccant as it changes color, indicating that the breather should be replaced. Check valves ensure no excess pressure/vacuum builds. Des-Case hybrid breathers attack the source of contamination, allowing your equipment and lubricants to run longer and harder. As wet, contaminated air is drawn through the unit, multiple 3-micron polyester filter elements remove solid particulate and the color-indicating silica gel extracts moisture. The diaphragm allows for expansion and contraction of the air in the casing as a result of temperature variations during steady-state operations. When air is expelled from the container, the top foam pad prevents oil mist from contacting silica gel or entering the atmosphere. The hydrophilic agent is partially reactivated by the dry air passing back through.

DES-Case
www.descase.com

Windpower Engineering & Development