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for securing threaded fasteners against
self-loosening. The washer is squashed
fl at when the nut is tightened against
the mounting surface so that its sharp
edges dig in to prevent the threaded
fastener unwinding.
In practice, a spring washer may
delay the length of time it takes for the
bolt to loosen, but it will not
permanently prevent it. The main
reason is that the split washer does not
solve the gapping issue, the free space
remaining between the threads of the
nut and the bolt.
On a typical threaded assembly there
is just 15% effi cient metal to metal
contact between the threads.
Everything else is empty space that
enables plenty of side to side
movement for the bolt. Additionally,
being metal itself, a spring washer can
cause damage to contact faces and
corrode in place.
For the Australian mining operation,
this problem was exacerbated by the
size of the bolts. The bigger the bolts,
the bigger the gap between threads
which leads to more vibrational impact
on the assembly. This realisation
resulted in the company changing to
adhesive thread locking with Henkel’s
Loctite 270.
FASTENING
This is a high strength formulation
that completely fi lls all gaps between
the thread and prevents any
movement of the bolt within the
nut. Secured this way, the assembly
is completely vibration-proof but
can still be easily dismantled with
hand tools for repair and
maintenance. Additionally, the
liquid thread locker seals the threads
against humidity and dust,
preventing corrosion and surface
erosion.
This simple adjustment to working
practice has not only underpinned
productivity but contributed to a safer
working environment. It is economical
too as one 50ml bottle of liquid thread
locker is suffi cient to secure around
850 M10 bolts but, unlike spring
washers, can be used on any bolt size.
To demonstrate how a threaded
assembly can self-loosen with
devastating eff ect, Henkel has
created a powerful video which
shows two identical loads,
suspended 40m in the air, vibrating
at the same rate. The fi xture on one
crane is locked with an adhesive
thread locker to prevent vibrational
loosening, the other is unsecured.
The result is sobering. MADE
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