FASTENING & ADHESIVES | THREADLOCKER
B LTS FROM THE BLUE While it may seem a humble player in
any given design, liquid thread locker
can have huge impacts in terms of
e ciency, productivity and safety.
When designing a new
machine or system,
it’s not always new
technology that wins
market share. Proven product
reliability is a powerful selling point
and it can often be signi cantly
boosted by taking a fresh look at
basic assembly methods. Preventing
the early failure of the humble
threaded fastener is a good case in
point.
Threaded bolts that self-loosen
during the machine’s operation
can cause all manner of problems
from increased maintenance and
downtime to quality issues and lost
production. So, when customers of
an East European manufacturer of
screen printers began reporting bolt
failures on its machines, the company
went back to basics.
In operation, these large-scale
printers generate a lot of vibration and
heat, both of which were causing the
threaded fasteners to self-loosen. The
manufacturer was swift to act on eld
reports and resolved the problem by
applying a wicking-grade adhesive
thread locker to the threaded bolts
on installed printers. It also adopted
adhesive thread locking as a standard
assembly method in the factory to
eliminate self-loosening at source.
In a typical assembly, there is
as little as 15% thread to thread
surface contact. The remaining
space allows movement of the bolt
within the nut, ultimately resulting in
it loosening after just a few machine
cycles. Changes in temperature
have a similar effect, causing micro
expansion and contraction of the
metal components leading to shortterm
frictionless situations
where the bolt unwinds
from the nut.
A common antidote
to the problem is
the application of a
mechanical thread
locking device
such as a spring
washer or a
double nut.
Both help delay
the onset of selfloosening
but
ultimately failure
is still inevitable
if the assembly
isn’t frequently
re-torqued.
By
comparison,
the liquid thread
locker lls all
voids between
the mating
threads and
solidi es to
form a
thermoset
plastic that
unitises the assembly. It effectively
stops the micro-movements that lead
to self-loosening and, at the same
time, seals the assembly against
corrosion and air borne contaminants
such as dust.
These adhesives are available in
a choice of strengths in easy owing
liquids or semi-solid form to suit the
application; all allow disassembly
with hand tools for repair and
maintenance.
The adhesive thread locker the
printer manufacturer chose for
bolt assembly is, Loctite 243 from
Henkel. It is a single component,
medium strength thread locker that
has recently been upgraded to offer
good bond strength on contaminated
surfaces, provide higher temperature
resistance and perform well on
passive metals without an activator.
Failure of a threaded assembly
through self-loosening not only risks
lost production but also worker safety.
This was the situation an Australian
mining operation faced when M36
anchor bolts threatened the collapse
of the jaw crusher equipment frame.
The bolts had been locked by
spring washers which simply could
not rise to the challenge of securing
bolts on a piece of equipment
subjected to continuous vibration
and high shear forces. This resulted
in the loosening – and ultimately the
breaking off – of anchor bolts and the
collapse of concrete footings.
Spring washers – also known as
lock or helical spring washers - are
one of the most popular mechanical
devices for securing threaded
fasteners against self-loosening. The
washer is squashed 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
28 WWW.EUREKAMAGAZINE.CO.UK | FEBRUARY 2021
/WWW.EUREKAMAGAZINE.CO.UK