A thorough understanding of a fastener’s coating performance can ensure joint integrity, as well as improve field life and serviceability. Global acceptance and availability are also key considerations in choosing the right coating.

The Magni 565 coating allows formulating lubricants into the topcoat, usually eliminating the need for messy post-treatments. This non-electrolytically applied, zinc-and-aluminum-rich coating also eliminates concern of hydrogen embrittlement. The coating can be formulated in many colors. It also comes in several friction levels while providing good consistency across many bearing surfaces.

Advantages of fastener coatings
The importance of corrosion protection and lubricity in the wind industry differs from the building trades or the appliance industry. Varying demands have made it impossible to formulate one universal coating. A short list of what a coating should do includes:

• Improve appearance
• Add lubricity
• Protect against corrosion

Appearance
This is of lesser concern in most turbine joints, but it plays a key role when choosing a fastener coating in the building trades and appliance industry. Electroplated and electrocoated fasteners are predominant in these industries. Because such fasteners are often visible, it is essential to match colors and coat uniformly. Electroplated fasteners offer good uniformity and come in several different colors using different passivation systems, dyes, and a topcoat. Electrocoated fasteners also offer good uniformity but are typically available only in black.

Lubricity
Identifying a coating with the right frictional characteristics is probably the most crucial task. Erratic friction during assembly leads to either a loose joint or too much strain on the fastener. Either event can lead to a failed joint.

Two important components of lubricity are consistency and efficiency. Both are required to insure joint integrity and easy assembly. Proper lubricity assists the fasteners’ ability to efficiently reach its designed load at a prescribed torque. The torque-tension graphs (next page) demonstrate how properly integrated lubrication can improve joint consistency.

Some alloy platings also have improved lubricity but are typically more expensive than zinc plate or dip and spin coatings.

The three bolts on the left have been hot-dipped galvanized (HDG) and subjected to ASTM B117 for 500 hours. The three on the right, coated with Magni 565, have endured the same test but for 1,000 hours.

Corrosion protection
The harsh environments of wind farms have significantly increased demands on corrosion protection. The increasing demand on field life, as well as the use of aluminum and magnesium in other assemblies, emphasizes the importance of high-performance fastener finishes. Bimetallic assemblies often rely on coatings to reduce galvanic potential or insulate different materials in an effort to minimize corrosion rates. For this purpose, a duplex coating is becoming more prevalent.

Mechanics of corrosion protection
Although there is a myriad of finishes to choose from, there are only two basic types of corrosion protection: Barrier protection and sacrificial protection

Both protect the substrate from corrosion, but do so in distinctly different ways. To better explain these methods of protection, it is first important to review the corrosion mechanism. Iron corrodes by anodic, cathodic, and diffusion reactions. The reactions are described as:

Anodic reaction
Fe →Fe²⁺+2^e-

Cathodic reaction
4e- + 2H₂O + O₂ →4(OH^-)

Diffusion reaction
2Fe²⁺+ 4(OH^-) → 2Fe(OH)₂
Fe(OH)₂ + O₂ + H₂O → Fe₂O3 + H₂O

Corrosion prevention inhibits the rate of these reactions, with either a barrier or sacrificial coating to the substrate.

Zinc-coated bolts show high deviation in the torque required to get several to a 30,000-N clamp load.

Barrier protection
One way to protect ferrous substrates is with a barrier coating. Here, the coating works as a barrier between a corrosive media and the substrate. Such coatings, often organic and polymeric in nature, come in a wide array of colors and can be applied many different ways, including by electrophoresis (electrocoat). These can be extremely effective, but performance diminishes if the barrier (coating) is damaged during assembly. These defects, macroscopic and microscopic, are inevitable and give the environment access to the substrate. Once this happens, oxidation of iron, along with the cathodic reduction of dissolved oxygen, attributes to the generation of OH¯ (alkalinity). Generated alkalinity can react with the coating causing it to dis-bond or delaminate from the metal interface, ultimately causing coating failures.

Barrier protection works best when coating defects are kept to a minimum. Excessive coating damage diminishes the corrosion protection proportionally and leads to premature failures. Therefore, material handling is critical when this technology is used.

Magni 565 coated bolts provide better uniformity in the torque needed to produces a 30,000-N clamp load.

Sacrificial protection
Another corrosion protection option applies a sacrificial coating. These include electroplating-galvanizing, Hot Dip Galvanizing (HDG), along with inorganic-organic duplex coatings. Although the application method for sacrificial coatings can vary significantly, the protection mechanism is similar.

Sacrificial corrosion occurs when two dissimilar metals come in contact. The more active of the two metals in the cell becomes a sacrificial anode and cathodically protects the other. To protect steel fasteners from corrosion, they are often coated with metals of higher reactivity. Zinc-rich coatings, whether electroplated, galvanized, or non-electrolytically applied, offer cathodic protection for steel fasteners by letting the coating “sacrifice” itself in place of the ferrous fastener. This technology relies on the coating to preferentially corrode.

Sacrificial coatings are affected less by coating defects than barrier coatings. The coating, which contains a more reactive metal, still provides cathodic protection around small voids and defects. However, excessive material handling can diminish the performance of this technology as well.

Understanding how these two systems provide corrosion protection makes it clear why duplex systems, such as Magni 565, can offer high performance to conventional galvanizing. The topcoat’s resistance of a corrosive media’s coming in contact with a sacrificial coating delays the corrosion mechanism. In addition, these topcoats can be formulated to provide specific frictional characteristics. WPE

By:  Edward Koneczny, Windpower Market Manager, The Magni Group, Inc, www.themagnigroup.com

Windpower Engineering & Development

The company’s A2LA Scope of Accreditation allows ISO 17025 accredited torque calibrations up to 100,000 ft-lbs, pressure gauges to 20,000 psi, and Skidmore-Wilhelm calibrations.  A new calibration lab completed in January of 2012 lets the company perform in-house services including continued testing, repairs, certification, and calibration on many types of tools with NIST Traceable Standards.

Aztec Bolting

Scope of Accreditation

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The Flextec 650 is IP23 and Desert Duty rated, meaning it can operate in extreme field environments. Welding outputs are rated for extreme temperature operation up to 55° C. Tough PC boards stand up to dust and humidity, while the Fan-As-Needed feature reduces power consumption, dirt intake and damaging thermal cycling.

The recent high amperage Flextec 650 multi-process welder from Lincoln Electric delivers up to 815 amps of welding power. Its FLEXible TEChnology lets welders use a variety of processes – stick, Touch Start TIG (DC), MIG, flux-cored CV submerged arc and arc gouging – on numerous applications, including heavy equipment and transportation, construction, and welding education.

The inverter-based Flextec 650 is rated at 650 amps at 100 percent duty cycle with a robust amperage range of 10-815 amps, while weighing in at only 165 pounds in a case that measures only 21.83 inches high by 16.3 wide x 29.33 deep. Lincoln Electric Ready-Pak and One-Pak packages configured with Lincoln Electric wire feeders and accessories are structured for easy ordering. Job site-ready rack packages are also set for future release.

Welder features include:

• Flexible multi-process capability for handling the widest range of welding applications
• Low-power consumption resulting in operating cost savings
• Lighter in weight for easier transport
• Selectable hot start for extra starting amperage
• Faster arc response with variable arc control
• Remote control operated by a foot pedal or hand control up to 100 feet away

To request a copy of the Flextec 650 product literature, call (888) 355-3213 to obtain bulletin E5.96.

Lincoln Electric
www.lincolnelectric.com

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Power Team has launched a newly redesigned website with enhanced features that let users more easily search products and product specifications. The company manufactures high-force

SPX Hydraulic Technologies is a leading manufacturer of high performance, fluid-power equipment, bolting equipment, and railway products. Visit the new site at www.powerteam.com for a complete product listing, application stories, technical manuals, product specifications, a product selection guide, material safety data sheets, and more.

Power Team
powerteam.com

Windpower Engineering & Development

A hydraulic wrench with compressor could weigh 70 lb and more when considering hoses and oil. One project manager remarked that a hydraulic wrench makes it necessary to get as close to a corresponding pressure reading as possible for the needed torque. Hydraulic torque equipment also tends to overheat requiring time to cool off, during which torquing operations halt. Lastly, hydraulic tooling means its testing and documentation is done by hand, which can lead to errors.

Electric torque wrenches allows setting torque values by supervisors before a day’s work begins. Techs on the site need only select the right job number to prep the wrench. The electric wrench allows setting six to eight different torque setting and locking them into place. This secures the torque amount and does not let others adjust the value without a key.

A lead wind project engineer at Wanzek Construction remarked that the margin for error is a lot less with an electric wrench because the tools can be “locked” to a particular torque value. Electric wrenches work with ±3% accuracy. In addition, torque limits on the wrenches can be set for several jobs at one time.

Controls and data-logging features for the E-RAD series of electric torque wrenches store in the 12 lb case.

In addition, more bolting work asks for accountability – knowing that each bolt is tightened to a prescribed level. More wind turbine manufactures require proof that each bolt has been installed and maintained at the appropriate torque specs to maintain the manufacturer’s warranty. Recent electric torque wrenches allow collecting such data. On-board data loggers report how many bolts have been torque along with failed torques and over torques. Also, the wind project engineer’s estimate is that electric torquing takes about 33% less time than does hydraulic torquing.

Shorter operations let tower-climbers “fly” in a next tower section and have flanges bolted before the ground guys are ready to bring up the next piece. This trims time for ground crew by letting tower workers get to the next section and prepped before another tower segment arrives. The durability of the electric torque wrench also helps reduce time.

The wind farm project manager adds that the calibration and testing capabilities exceed those of the hydraulic torque tools. Electric wrenchs, he says, let him digitally track all torque testing. When testing the electric wrench, data transfers to a program that logs it in a format that can be manipulated to fit one needed for the tower manufacturer’s specifications.

A few electric torque wrenches also let users tighten bolts to a torque or an angle. This simplifies work on GE rotors, says one engineer. For example, the tool could be set to 350 Nm plus 120°. Once bolt tightening begins, the gun automatically torques the bolt to 350Nm, stalls for a moment, and then move the nut 120°. This is vital to some torque procedures because it lets techs torque in a continuous motion without stopping to rely on someone’s eye to add the 120°.

A construction worker in a new nacelle puts the final torque on a rotor hub using an electric torque wrench from RAD Torque Systems.

The simple operation of the electric wrench helps eliminate mistakes when setting the torque value. The digital display on the electric wrench lets users change a torque value along with units in ft.-lbs or Nm. This removes calculation errors. What’s more, there is no oil changing necessary as with a hydraulic pump. Also, the only maintenance required would occur from normal wear and tear. Operating an electric wrench is as simple as hooking the torque gun to the box, plugging it in, turning the box on, setting the torque value, and starting the work. WPE

By: Aaron Johnson, Electronics Engineering Manager, RAD Torque Systems www.radtorque.com

Windpower Engineering & Development

Aztec Bolting celebrates 25 years of business with a new headquarters. Company president Larry Garza cuts the ribbon on the new facility while League City Mayor Tim Paulissen, to the right, hold the ribbon. City Chamber Member Shari Ferguson stands to the side of the mayor.

After completing a recent expansion to the headquarters in League City, Texas, with a new office facility and state-of-the-art calibration lab, Aztec is focused on demonstrating a commitment to remain a cornerstone in the torque and tension business. The facilities will allow for employee growth, expansion of outreach, and maintaining an extensive supply of inventory.

Another aspect of growth for Aztec is the pending accreditation of  ISO 17025 for the new calibration lab. ISO includes the tightest of technical requirements and reliability standards. It also ensures a commitment to streamline managerial focus of continued quality, consistency in techniques, and clear communication with customers.

Aztec Bolting Services consists of tooling sales, rentals, in-house calibration labs, industrial tool repairs, and qualified field services for all torque and tension requirements. The company represents several fine-standing manufacturers and suppliers providing the highest quality products and services that include Enerpac, Norbar, Skidmore, Stahwille, and others.

Aztec Bolting Services Inc.
www.bolting.com

Windpower Engineering & Development

Aztec Bolting hydraulic bolting products for wind turbines.

One particular bolt design has an indicator cap on its head. If the cap turns easily by hand, the bolt is under tensioned. When difficult to turn by hand, the bolt is at its proper tension, a value set during manufacturing. Another design places a visual indicator in the bolt head. When the indicator is out of position, the bolt is under or over tensioned. The feature makes checking for tension a brief visual task.

Why torque control is a questionable way to achieve consistent pretension in structural bolts comes down to friction or what’s known as the k-factor. This is the relationship between the torque applied to a fastener assembly and the actual tension produced in the bolt. A short form of the relationship is:

Tension = Torque/kd

where: k = k-factor, and d = diameter

K-factors can range from 0.10 to more than 0.20 and vary from lot to lot, from bolt to bolt within a lot, and as a consequence of storage and lubrication. Also, consider the variability of the torque tool. Manufacturers of tension indicators say it is likely that when using torque control to govern bolt tension that actual bolt tensions will vary ±40% or more.

A preassembled pair of washers provides a structural, self-locking fastener that prevents bolted joints from loosening by shock or vibration in high-stress applications. The device consists of two preassembled (glued for easier handling) washer-shaped pieces. Each has an inclined cam on one side and a series of ridges on the other. On installation, the cam sides are mated and placed between nut and joint material. Under vibration, the nut tries to rotate loose but, because the angle of the cams is greater than the pitch angle of the bolt thread, the interlocking cams and the nonslip ridges of the washer work together to create a jam which prevents loosening. The washer pair can also be used on bolts in either blind-holes or through-holes. In blind-holes, the washer pair is placed under the bolt head, while through-hole applications use the washers beneath a nut.

Windpower Engineering & Development

One particular bolt design has an indicator cap on its head. Until the cap turns by hand with difficulty, the bolt is under tensioned. The device works by drilling out part of the bolt center and installing a tension indicator link to the cap. When tensioned, the bolt elongates, tightening the link and preventing the cap from rotating under finger pressure. Another design places a visual indicator in the bolt head. When the indicator is out of position, the bolt is under or over tensioned. The feature makes checking for tension a brief visual task.

Why torque control is a questionable way to achieve consistent pretension in structural bolts comes down to friction or what’s known as the k-factor. This is the relationship between the torque applied to a fastener assembly and the actual tension produced in the bolt.

The short form of the relationship is:

Tension = Torque/kd

where: k = k-factor, and d = diameter.

K-factors vary from lot to lot, from bolt to bolt within a lot, and as a consequence of handling, storage, and lubrication. K-factors can range from 0.10 to over 0.20. Also, consider the variability of the torque tool. Manufacturers of tension indicators say it is likely that when using torque control to govern bolt tension that actual bolt tensions will vary ±40% or more.

A preassembled pair of washers provides a structural, self-locking fastener that prevents bolted joints from loosening by shock or vibration in high-stress applications. The device consists of two preassembled (glued for easier handling) washer-shaped pieces. Each has an inclined cam on one side and a series of ridges on the other. On installation, the cam sides are mated and placed between nut and joint material. Under vibration, the nut tries to rotate loose but, because the angle of the cams is greater than the pitch angle of the bolt thread, the interlocking cams and the non-slip ridges of the washer work together to create a jam which prevents loosening. The washer pair can also be used on bolts in either blind-holes or through-holes. In blind-holes, the washer pair is placed under the bolt head, while through-hole applications use the washers beneath a nut.

Windpower Engineering & Development

The enhanced corrosion-protected anchor is one version of large diameter rock or soil anchors installed around the perimeter of a turbine foundation. The anchors require less excavation and a substantial reduction in the amount of poured concrete versus traditional reinforced concrete in spread footing foundations. Williams has designed other rock and soil anchors in various size and strengths such as 150-ksi grade bars or 270 ksi multi-stranded tendons.

All successful wind projects begin with strong foundations. Larger wind turbines naturally call for taller towers and larger foundations that consume enormous amounts of concrete and rebar. To handle variations in wind turbines, the current state of practice includes spread-footing foundations, “tensionless” pier foundations, and hybrid foundations that use rock anchors and micropiles to resist overturning turbines and compressive loads. A brief review of foundation designs shows the advantage of the hybrid foundation.

Spread-footing foundations are most common. Large gravity concrete pads, hexagonal in shape, use about 400 to 500 cubic yards of concrete and a truckload of rebar. The load transfer from the tower is accomplished with high capacity, post-tensioned threaded bars connected to an embedment plate near the foundation bottom. Bars are sleeved through the foundation to transfer loads generated by the turbine from the tower base all the way down to the embedment ring in the foundation bottom. Enginneers traditionally specify a preload for the anchor bolts that is higher than the tower service loads, thus eliminating fatigue and impact factors. Post-tension bars use clever cold-rolled “knuckle” threads, which are more durable than regular NC (National Course) threaded bars necessary for ease of tower installation.

Hybrid foundations are one way to reduce concrete and rebar, and are becoming more common. In them, a shorter (shallower) and smaller diameter concrete “cap” is constructed with blockouts – recessed holes – to allow drilling through the constructed

foundation. Contractors then drill a small, about 8-in. diameter, hole to a depth dictated by geotechnical reports (typically 30 to 40 ft), place an anchor in the hole, and completely fill it with a grout-a neat cement. Anchor features include a no-bond zone (also called a Free Stressing Zone) at the upper 10 ft of the anchor, so the load transfers deep into the ground. Good practice requires a load test on every anchor, as well as an extended “creep” test, one that evaluates the anchor movement over time, on a sampling of the production anchors. The anchors are then locked off at loads higher than anticipated service loads.

Long ground-anchor bolts, 40 ft in some cases, allow using smaller diameter and shallower foundations for wind turbines.

As turbine and tower technologies change, so must foundations. What was common 10 years ago is no longer the standard, and a decade from now the foundations on wind farms will continue to evolve to meet higher loads and stricter design standards. WPE

By: Tom Bird, Vice President, Western Division of Williams Form Engineering Corp.

Windpower Engineering & Development

The pins use a 2¼ coil cross-section to make them self-retaining pins that compress when installed into a host component. The company says they are the only pins with uniform strength and flexibility after insertion.

The company suggests those seeking a custom fastener might be interested in the its Optimal Application Engineering program. This is a five step procedure for designing and delivering the fastener more useful than one off the shelf. Step one, with the client, defines product performance, assembly, and commercial objectives. This includes gathering sample components, the drawings of the individual components, and assembly-level drawings. This stage also defines commercial objectives such as a target product cost, product packaging and labeling, and delivery requirements.

Step two calls for a comprehensive engineering evaluation after gathering product, assembly, and manufacturing objectives. Spirol says its application engineers can help find a best solution for the particular application.

In step three, the company provides a formal technical and commercial proposal, including prototypes for evaluation in the client assembly. The proposal will detail other products considered for the application, and why the recommended part is the best design.

Step four: When installation equipment is involved, Spirol can design a fixture to hold and align components during insertion. The company also builds, tests, installs, and certifies the machine, and educates operators and maintenance personnel.

Dowel bushings and spring dowels, other company products, can maintain alignment and are used to locate components with respect to each other. These roll-formed, hollow alignment dowels have lead-in chamfers that facilitate insertion into the holes of both mating components.

In step five, the company plans production to meet client-delivery requirements and will ship certified products anywhere in the world. Spirol says it provides a formal technical and commercial proposal, including prototypes for evaluation in an assembly. The proposal will detail other products that were considered for the application, and ultimately why the recommended part is the optimum solution. The brochure is available at the URL below.

Spirol International Corp.
http://www.spirol.com/library/main_catalogs/SPIROL_Corporate_Brochure_us.pdf

Windpower Engineering & Development