fastening & assembly solutions and technology - Approved Business

HOW TO: FASTEN SECURELY
Nuts, bolts and screws – in fact, any
threaded fastener - provide the
clamping force in a whole host of industrial
assemblies. This force is generated
by tightening the threaded components
until adequate tension and friction is created
within the fastener in order to check,
at least in theory, any movement of the
clamped parts. In reality, however, the
dual circumstances of shock and vibration
can reduce this tension and, therefore,
permit loosening to take place.
As soon as this initial releasing occurs,
the tension of both the fastener and the
clamping load is lost. The result can be
component and machinery failure – with
all the resultant problems of down time,
warranty claims, the expense of new
parts and loss of confidence.
These engineering adhesives, commonly
known as threadlockers, are generally
anaerobic products that can be
used on any threaded surface. Applying
the adhesive and bringing together the
two threaded parts of the fastener forces
out air from the joint and thus fill all the
inner spaces between the threads. A
chemical reaction then takes place which
causes the liquid adhesive to harden to
form a solid thermoplastic of a known
strength.
By employing different grades of
adhesive, the strength of the bond can be
varied to provide the essential break
loose torque. However the locking action
of the adhesive does not depend on the
force, a relatively low strength threadlocker
will still produce exceptional
resistance to vibration. And, to carry out
maintenance, the parts can be readily separated
using normal hand tools.
Independent assessment
But it is not necessary to take an adhesive
manufacturer’s word for the reliability of
engineering adhesives. In a spectacular
test, a threadlocker was tested on a
Junkers machine used by both the
aerospace and automotive industries.
This trial was specifically conceived to
test anaerobic threadlockers against traditional
locking means such as spring
washers, patch bolts, distorted lock nuts
and nylon rings. During the test, a fastener
was assembled in the machine and
tightened down to the required tension.
Once the air hammers were activated a
record was made of the time taken before
the fasteners vibrated loose.
These were intense tests, but the
results showed conclusively that adhesives
provide the most effective protection
against parts working loose under
FAST OCTOBER 2011
Engineering adhesives
ensure fastener security
Engineering adhesives used on fasteners will ensure their efficiency in even the most demanding of
circumstances. Colin Chapman explains how threaded fasteners can be safe and secure even under
great pressure
Colin Chapman is with the marketing
department of Henkel, maker of Loctite
brand adhesives
Threadlocking adhesives ensure that bolts are secure –
even under the most demanding conditions
extreme pressure. In fact, all other methods
failed within less than a minute of the
trial starting.
Of course, discussions – even laboratory
testing - involving threadlockers are
all very fine, but the proof of their effectiveness
is in usage. A few examples will
prove the point.
Take, for instance, the maker of fork
lift trucks who had a requirement to
secure joints between jack cylinders and
the bearing carrier, and to connect the
cylinder to the end plug. Prior to trying
adhesives, welding had been considered
the only way of achieving the needed
assurance. However, not only was this
process time consuming - but also there
was an on-going risk of damage to the
cylinder.
By switching to an adhesive not only
was damage prevented, but also a more
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