Doug Lascarbeau, Anaerobic Technology Director
Ed Fisher, Senior Market Application Engineer
Damage and mechanical failures on wind turbines happen most often on blades, in gear boxes, on generators, drive trains, and brake assemblies all of which are housed in the nacelle. Access to these areas on a large commercial turbine requires that maintenance professionals climb a series of ladders that can take them more than 300 feet up.
So how the ladder and treads are secured to the tower deserves close attention. For instance, it should perform as a part of the tower assembly and not a series of separate parts added after tower construction. Maintenance workers can fall if the ladder is not unitized, sturdy, and stable. Such a fall would mean certain injury and possible death.
Why threaded assemblies fail
Thermal cycling, movement, and vibration can cause threaded fasteners to loosen over time. The normal contact area of mating threads presents a problem because it is a surprisingly small percent. Without appropriate protection, fasteners can fail.
Even when its blades are at rest, a wind turbine is a moving structure. High winds that rotate the blades also sway the tower and nacelle, generating mechanical stress and vibration that affect the entire structure from the tip of the highest blade down to the base. In addition, structural elements expand and contract when subjected to operating temperatures that range from sub-zero to more than 100°F.
Vibration is the number one cause of threaded fastener loosening. Failure occurs when clamp load is not maintained. Clamp force must be adequate at the time the fastener is assembled and remain at that level throughout the useful life of the fastener.
In addition to vibration, a fastener’s ability to stay tightly fixed is impared by the natural existence of gaps between the mating thread surfaces. These tiny gaps allow micro movements that eventually loosen mated parts and result in a loss of clamp load. Clamp load must be maintained over the life of the assembly.
How to prevent failure
Anaerobic threadlockers are single-component adhesives that when applied to metals cure in the absence of air into tough thermoset plastics. Threadlockers completely fill the voids between interfacing threads, preventing the micro movements that lead to loosening. Threadlockers provide 100% contact between metal parts while a typical untreated nut and bolt assembly can have as little as 15% metal to metal contact. These adhesives maintain clamp load on the fastener until the bond is intentionally broken.
Threadlocking adhesives are the most reliable method to ensure a threaded assembly remains locked and sealed for its entire service life. Available in a variety of strengths, they offer excellent temperature resistance, rapid fixture and cure speeds, and easy dispensing.
Now consider the nacelle. Bolts there hold the panels together, letting this important enclosure endure vibration and exposure. Inside the nacelle, hundreds of threaded fasteners secure moving parts on generator components.
Threadlockers also act as lubricants during fastener tightening, so instead of dissipating torque as friction and heat, the adhesives improve the conversion of applied torque to high clamp load. Once cured, threadlockers provide a reliable seal and prevent leaks, galling, and corrosion that can seize threads.
Advancements in threadlockers
Recent advances in the stability and reactivity of anaerobic chemistry have resulted in gel, stick, and tape formulations. Semi-solid sticks and tapes work well in difficult areas, such as vertical and overhead applications where liquids could be too messy or could migrate. Dry-to-the-touch and packaged on a roll, tape threadlockers can be pre-applied to threaded fasteners for future use or applied during maintenance operations.
Recently developed high lubricity anaerobics effectively reduce friction and reliably convert torque energy into increased clamp load. These are especially effective for large diameter, high
strength fasteners that provide high clamp load. WPE