Solar panels are obviously exposed to a variety of weather conditions, with wind sometimes causing enough vibration for the panel mounting bolts to loosen over time. Further, differential thermal expansion and contraction can also cause the loosening of threaded fasteners, and a recent example of an operator overcoming the possibility of this loss of joint integrity has emerged from Japan
Driven by the potential for downtime costs if the threaded assemblies worked loose, a Japanese solar power plant decided to take action to prevent it happening by specifying an adhesive thread locker that could be applied to the already-assembled nuts and bolts. The company chose to lock its threaded assemblies with an engineering adhesive rather than a mechanical device, (for example a spring washer), because it proved the most efficient for them. This was not only measured by the ease and speed application but also the extended service life of locked assembly, says Loctite.
The company adds that the adhesive proved the best choice as it is the only thread locking method that addresses the gap which exists between the threads of the nut and bolt. Although imperceptible to the naked eye, this gap is still large enough to allow side to side movement of the bolt within the nut when it is exposed to wind movement; regardless of whether a mechanical locking device has also been fitted. Further, says Loctite, the problem can be exacerbated by thermal cycling.
The adhesive thread locker completely fills the gap between the threads and solidifies into a tough thermoset plastic between the two metal surfaces in the absence of air, preventing any micro-movement. Generally, the adhesive is applied during installation or maintenance while the fastener is being assembled but as the Japanese energy company discovered, a wicking grade version gave them the advantage of securing all their threaded assemblies without having to dismantle them first.
The chosen product for this application was LOCTITE® 290 from Henkel, a liquid medium/high-strength thread locker for locking and sealing threaded fasteners. Because of its low viscosity and capillary action, the adhesive actively creeps in between the threaded surfaces. This meant engineers could apply the adhesive to the nuts and bolts in situ, saving significant maintenance time in the process and creating assemblies that were both long lasting and corrosion resistant.