Never use thread-lockers on electrical fixings: Page 2 of 3

May 29, 2018 //By Keith Armstrong
Never use thread-lockers on electrical fixings
‘Thread-locking’ means preventing threaded fixings from loosening due to vibration. There are many mechanical ways to do this, including split pins, locking nuts, special washers, etc. but the term ‘thread-lockers’ is usually applied to chemical products that glue a thread in place. 

For both electrical safety and RF bonding, I always recommend not relying on screw threads because of the likelihood of corrosion. Instead, the screw fixing should be used to press two conductive surfaces together to create the electrical, electrical safety, or RF bond.

Unfortunately, unless the amount of liquid thread-lock is precisely metered every time it is applied to an individual screw thread, there is the risk of it not providing sufficient protection from vibration – so people always over-apply it, to make sure that they get reliable anti-vibration. The result is that the excess insulating liquid just gets everywhere – including in-between the conductive surfaces that are being clamped together by the fixing! 

In a recent military project, I found that the over-liberal use of liquid thread-locker had caused it to squirt into a joint in a shielded enclosure at every screw fixing (and there were a lot of them!). It not only prevented the screw threads from providing RF-bonds across the shielding joint, but also prevented the two metal enclosure halves from making direct contact with each other. The shielding that was achieved by the enclosure was useless.

As conductive liquid thread-lockers don’t exist, what can we use for locking threads without having to use precisely metered doses or extra parts?

Well, Nylok nuts and bolts use a solid ring of nylon that is cut into by the thread to provide the thread locking function. They have been readily available for over 40 years to my knowledge and are available compliant with a huge range of military, avionics and aerospace specifications. Loctite offers a solid thread-locker that they call ‘Dri-Loc’. Unlike Nylok’s standard off-the-shelf fixings, Dri-Loc is applied by fixing suppliers as a custom solution (I assume under licence from Loctite or Henkel).

Another alternative is Stanley’s ‘Spiralock’, which achieves about 15% more torque than regular screw threads or coil inserts, and provides anti-vibration thread-locking without any additional materials.

Design category: 

Vous êtes certain ?

Si vous désactivez les cookies, vous ne pouvez plus naviguer sur le site.

Vous allez être rediriger vers Google.