Screw locks – 5 ways to prevent the loosening of screws

tight screw connection

It can always happen that screws come loose from a thread.

This can not only be annoying, but in some places even life-threatening.

We explain to you why this happens and what screw lock options are available to prevent loosening.

Why screws come loose?

Screws can come loose when the so-called preload force decreases. In simplified terms, this is the pressure between the external and internal threads that is created during the screwing process. This can happen mainly for 3 reasons:

1. Vibrations in the component

Vibrations lead to minute friction in the screw connection. These "smooth", so to speak, the surfaces of the external and internal threads and cause the pressure between the elements to release, thus loosening the screw.

2. Corrosions

Rust can cause the material within the bolted joint to degrade, causing the bolted joint to loosen.

3. Setting the screw connection

The term sounds more complicated than it is. Put simply, the principle is the same as a metal spring that "wears out" when stretched over a long period of time. The tension between the male thread of the screw and the female thread of the component decreases over time due to deformation or. Adjust the elements according to.

How to prevent loosening?

There are several ways to make a bolted connection in such a way that prevents loosening as best as possible. Here are our recommendations:

Use of lock nuts

Lock nut

A locknut with a characteristic plastic ring

Locknuts visually resemble normal hexagon nuts – with a small but useful difference: they have a plastic ring inside the inner thread.

When a bolt is screwed into the nut, this ring deforms and gives the bolted joint an additional hold.

Attention: since the plastic ring deforms, lock nuts – unlike other nuts – can be used only once.

Fan discs

lock washer

Flap washers offer a particularly good hold due to their special shape

Fan discs catch the eye simply because of their striking shape.

They bore into the surfaces of the component and the bolt head/nut when the connection is tightened.

This significantly increases the frictional resistance.

Spring washers, clamping washers, spring washers, disc springs

All four, as well as the serrated lock washers, are located underneath the screw head or – depending on the design – underneath a nut.

However, they differ in their mode of action, which is not to increase the frictional resistance between the bearing surfaces, but rather to create additional pressure against the direction of the screw due to their inherently springy shape.

This increases the preload force and makes the fastener much harder to loosen.

Plastic washers

PLASTIC DISC

Plastic washer

It may not be immediately obvious at first glance why plastic washers are better at preventing the bolt from loosening than other metal washers do.

A quick comparison: imagine you have a plastic stick in your hand and you hit a hard object with it. In comparison imagine you do this with a metal rod.

The metal rod would resonate for a few seconds – the plastic rod absorbs the vibrations as far as possible. We find the same principle with plastic washers. They absorb vibrations in the construction, which in turn reduces friction between the inner and outer threads of the screw connection.

glue

Using threadlocker is also a good and especially easy option.

To do this, simply provide the screw thread with a little glue and turn them in.

This subsequently hardens and additionally secures the screw connection against loosening. Always pay attention to the required drying time. This can vary greatly from glue to glue.

Caution: depending on the glue and how hard it cures, you may not be able to undo the bond afterwards without using force to destroy the threads. So you should be sure when in doubt that the screw should stay there&

Helpful or not? Knowledgeable or boring? Your opinion counts. Click stars, done.

6 comments

Described in a very understandable and comprehensible way.

The following products have no locking effect, neither in terms of loosening, nor in terms of loosening. From a use with screws of strength class ≥ 8.8 must be discouraged!

Retracted standards
Spring washers (DIN 127, DIN 128, DIN 6905, DIN 7980)
Spring washers (DIN 137, DIN 6904)
Toothed lock washers (DIN 6797, DIN 6906)
Serrated lock washers (DIN 6798, DIN 6907)
Washers with external nose or. 2 rags (DIN 432, DIN 463)
Castle nuts (DIN 935, DIN 937 with split pins DIN 94)

These standards do not have a securing effect with screws of higher strength and are also not suitable as settling protection!

Locknuts function only as loss protection and have no screw-locking effect!

What Mr. Meyer writes is technically correct but does not show a solution.

As screw locking in metal construction can be used Schnorr discs or even better Nordlock discs.
When using machine screws to join wooden components (shrinkage due to drying), the only thing left to do is probably to use a good adhesive to secure the screws.

I am always annoyed by the screws of recliners, folding garden chairs, recliners, which always loosen automatically by opening and closing. I try it with glue or also with screws with plastic insert. Should actually be standard.

Only those are more expensive and increase the production costs often only centbetrage make up, with a Produktionszal of approx 50000 pieces per day……….

I just bought a SR Suntour parallelogram seatpost for my bike, used and therefore a little older. Advantage constructed from durable high-quality components, but screwing unfortunately not highly perfect. Problem: such saddle bars must withstand enormous forces, but still be flexibly adjustable. And as uncomplicated as possible. This has only one screw, with which one adjusts the inclination of the saddle, and at the same time fixes the saddle as a whole, and fixes the horizontal position – 3 in one. There work thus enormous forces in 3 ways on this one fast adjusting screw. This was meant to be practical, but probably hard to do in real life. The glue thing I consider unsuitable for my case, because the correct saddle setting is not a metric measurable once adjustable thing, but a longer try and error. That the screw is fixed with sticking, sounds first quite nicely, if one must never again loosen it – only that is not with Bikes so. The washer that clawed into the "screw matrial" may work – but in high-strength stainless steel screws? Don’t know … so after reading this exciting article, I am left with the flexible plastic washer. A) extremely cheap – B) reacts flexibly under pressure – C) hardly, if at all, impedes the attaching and reattaching function, i.e. opening and reclosing. The convenience of this solution depends, of course, on the type of plastic used. I will try and report ..

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