Page 31 - Industrial Technology October/ November 2020 issue

Prevent nuts and

bolts self-loosening

WHEN THREADED BOLTS, SCREWS AND NUTS
COME LOOSE, IT CAN NOT ONLY COMPROMISE
THE PERFORMANCE OF YOUR MECHANICAL
EQUIPMENT BUT COULD ALSO POSE A SAFETY
RISK. WE ASKED THE EXPERTS AT HENKEL
ABOUT OPTIONS TO PREVENT SELF-LOOSENING

enerally, the reason threaded
assemblies fail is through
loss of bolt tension, the main
Gcauses of which are relaxation
and self-loosening. Self-loosening is
caused by any type of dynamic load, such
as vibration or changes in temperature,
insufficient clamp load and poorly fitting
parts. These load changes lead to short-
term frictionless situations where the bolt which completely fills the gap between
unwinds from the nut. The sum of these the threads. This is an engineering
very small movements ultimately results adhesive that solidifies into a tough
in the loosening of the threaded assembly. thermoset plastic between the two
There are several different methods metal surfaces in the absence of air and
of addressing the issue of vibrational prevents any side to side movement.
self-loosening. Most of them include the Secured in this way, the bolt will be
use of additional mechanical devices to completely vibration proof and stay in
lock the threaded assembly and place forever – if that’s what you want.
maintain the desired clamp load. If not, the assembly can be easily Remove bottlenecks
Split washers are one of the most dismantled with hand tools, for repair or
common mechanical devices used for maintenance. Additionally, liquid thread
this purpose. The washer is squashed lockers will seal the threads from and simplify your
flat when the nut is tightened against humidity penetration and, in that way,
mounting surface so that its sharp prevent corrosion.
edges dig in to prevent the threaded processes
fastener unwinding. But while it might Correct selection
delay the length of time it takes for the There is now a huge range of thread
bolt to loosen, but it will not locking adhesives available, offering
permanently prevent it. differences in viscosity, strength,
The main reason is that the split temperature resistance, cure speed and
washer does not solve the gapping harness/flexibility. To determine the best
issue, the free space remaining between one for the job ask yourself three main
the threads of the nut and the bolt. questions: What’s the fastener size?
Additionally, being metal itself, a split Which strength do I need? And how
washer can cause damage to contact frequently will the assembly need to be
faces and corrode in place. serviced? Make your adhesive and dispensing processes more
Another common solution is a Typically, on smaller size fasteners, productive with process-optimising materials & systems
double nut. While the second nut does lower strength grades will work well
increase the surface of interfaced enough regardless of what kind of • Improve speed and accuracy • Get fast, homogenous mixtures
threads, it does not eliminate the gaps vibrational loads they may be subjected of dispensing with dedicated of liquids, powders and pastes
dispensing robots with mixing and degassing
between them, and the loosening will to. Also, if you have a high servicing machines
still inevitably happen. The additional frequency requirement, you’ll want to • Reduce work in progress with
nut also doubles the amount of surface use a lower strength grade as well. For fast UV light curing materials • Achieve more consistent
that can corrode – and that’s a nasty assemblies that get dismantled less • Improve process simplicity with bonding results with plasma
surprise when you come to dismantle frequently, a medium strength product process-convenient materials surface treatment
the piece. Out of all the mechanical is recommended. It’s also possible to packaging
locking devices, the nuts are also the secure a threaded assembly that has Could you reach your productivity potential by improving some
heaviest, and if you use several double already been assembled, using a of these areas? Read more at intertronics.co.uk/productivity.
nuts to secure your bolts, you’re adding formula with wicking properties that will
more weight. creep into the assembly and between 01865 842842
The only way to address the gap the already torqued threads.
issue is to use a liquid thread locker MORE INFORMATION: www.henkel.com info@intertronics.co.uk
intertronics.co.uk/productivity
October/November 2020 • INDUSTRIAL TECHNOLOGY