FEATURE FASTENINGS & ADHESIVES The growing adoption
of threadlocking adhesives by the wind farm sector is resulting in safer,
longer-lasting fastened
joints, which in turn supports the uninterrupted
Threadlockers: the adhesive solution for wind turbines
V
ibration and corrosion can lead to the catastrophic failure of conventional
mechanical locking devices such as spring washers, nylon ring nuts and flat washers. On wind turbines, fastener damage occurs most frequently on critical assemblies such as the blades, gearboxes, generators, drivetrains and brakes, all of which are housed in the nacelle. However, even when the blades are not
turning, a turbine can still be considered a moving structure. High winds, for example, will cause the tower and nacelle to sway, producing mechanical stress and vibration along the entire height of the structure. Furthermore, it is well established that several structural elements of wind turbines are subject to expansion and contraction as temperatures fluctuate – some turbines experience changes in temperature that extend from sub-zero during winter to more than 38˚C in summer.
THREADLOCKING SOLUTIONS The leading cause of threaded fastener loosening is vibration, as this can lead to a loss of clamp load and, ultimately, failure. As a consequence, clamp force must meet the design specification when the fastener is first assembled and stay at that value throughout its entire operating life. All the engineered components located in
the nacelle are a concern when it comes to fasteners, as are the stairs needed to reach them. Nacelle access on a large commercial wind turbine requires maintenance professionals to climb a series of ladders that can reach up to 90m. How the ladder and treads are secured into position therefore demands close attention. Aware of the dangers to both expensive
parts and personnel, a wind farm that recently erected its first turbine wanted to ensure that the bolts attaching the blade to the hub maintained the design torque and were protected from the corrosion that can occur with exposure to the elements. To meet the requirements, LOCTITE 243 threadlocking adhesive from Henkel was specified. This is not only helping to prevent catastrophic failure by
14 SEPTEMBER 2020 | DESIGN SOLUTIONS
resisting vibrational loosening but is avoiding thread corrosion and maintaining fastener torque in the wing-to-hub assembly.
PREVENTING VIBRATION A fastener’s ability to remain secure is compromised by the inherent tiny gaps present between the surfaces of the mating threads. These gaps permit micro movements to occur that, in time, loosen the fastener and result in a loss of clamp load. The growing popularity of threadlocking adhesives such as LOCTITE 243 results from their ability to completely fill the voids between interfacing threads, thereby preventing any opportunity for micro movement. In thwarting both vibration loosening and
corrosion, the adoption of threadlockers at the wind farm is circumnavigating the risk of fastener failure and will make disassembly easier if and when the necessity arises. A LOCTITE Engineering Solutions Expert from
Henkel helped the wind farm team remove the protective shipping covers from the exposed bolt threads and clean the steel fasteners. The team then inserted the blade into the main hub, applied LOCTITE 243 to the fasteners, torqued the blade-to-hub assembly in accordance with the specification, and mounted the hub to the generator drive system. Now, with corrosion-free fasteners
that maintain clamp load, and which are easily disassembled at a predictable break- loose torque, the wind farm is assured of safe, maintenance-free wind turbine operation until the next scheduled downtime for routine checks.
ONE-PART ADHESIVES Anaerobic threadlockers such as LOCTITE 243 are one-part adhesives that, in the absence of air, form into tough thermoset plastics when applied to metals. These products deliver 100% contact between metal parts, which contrasts greatly with a typical untreated nut and bolt assembly, where as little as 15%
/ DESIGNSOLUTIONS
supply of renewable energy as the world transitions to a greener future, as Henkel explains
metal-to-metal contact is commonplace. Typical wind farm applications for
threadlocking adhesives include the locking and sealing of dozens of fasteners on the yaw and main rotor bearings, as well as the nacelle panels. Available in a variety of strengths, threadlockers provide outstanding temperature resistance, fast fixture and cure speeds, and straightforward dispensing. Threadlocking adhesives also act as lubricants
during fastener tightening, so instead of dissipating torque as friction and heat, the conversion of applied torque to high clamp load is improved. Once cured, threadlockers offer a reliable seal and prevent effects such as galling and corrosion, which can seize threads. The latest breakthroughs in the stability
and reactivity of anaerobic chemistry have resulted in the availability of standard liquid and stick formulations to suit different applications. Moreover, high-lubricity anaerobic threadlocking adhesives effectively reduce friction, making them particularly suited to the large diameter, high-strength fasteners found on wind turbines. Such adhesives are also formulated to deliver enhanced oil tolerance, ensuring their suitability for use in turbine gearboxes and other moving parts exposed to lubricants. Another attribute is excellent performance
without activators. These formulations are perfect for use on plated and stainless fasteners because they eradicate the need for cleaning and cure rapidly.
Henkel
www.henkel-adhesives.co.uk
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