Japanese solar plant turns to adhesive thread locking

2 min read

Threaded assemblies, subjected to load and vibrations, are often locked against self-loosening by either a mechanical locking device or an adhesive thread locker, or a combination of both.

The merit of this is easy to understand when the assembly is in a motor-driven machine where obvious vibration can cause an unlocked nut and bolt to gradually unwind.

It turns out that even completely static objects like solar panels need similar treatment, argues Loctite supplier Henkel. It points out that the variety of weather conditions and wind that panels are exposed to will cause enough vibration for the panel mounting bolts to loosen over time. Additionally, they are also subject to thermal cycling between periods of sunshine, shade and night-time temperatures, as well as seasonal variations.The metal bolts therefore expand and contract with the changes in temperature, leading to an additional loss of torque.

An (unnamed) Japanese solar power plant decided to take action to prevent this happening when it assessed the loss of revenue for the time that panels were out of commission and the increased maintenance costs involved in rectifying bolt failure. The solution was a specific adhesive thread locker that could be applied to already-assembled nuts and bolts. The company chose to lock its threaded assemblies with an engineering adhesive rather than a mechanical device, such as a spring washer, because it proved the most efficient. This was not only measured by the ease and speed application but also the extended service life of the locked assembly.

The adhesive’s unique advantage was its ability to penetrate the gap that 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. 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 it the advantage of securing all their threaded assemblies without having to dismantle them.

The product chose 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.