SUMMER 2019

64
THE DISTRIBUTOR’S LINK
COILOK FROM LIMIT LOCK LTD
38a Ahad Haam, Raanana, 4321120, ISRAEL
TOLL-FREE 1-877-343-2770 TEL 919-741-4860 EMAIL info@CoiLok.com WEB www.CoiLok.com
MAKING NEW & EXISTING BOLTED JOINTS
VIBRATION RESISTANT
Locking fasteners come in many shapes and sizes.
They all try to solve a long-time problem in bolted joints:
preventing unintentional loosening. Known solutions such
as split lock washers, double nuts, nylon insert nuts
or prevailing torque solutions have all been shown
to be useful in static applications, but to fail
vibration testing. Nevertheless, in the absence
of effective alternatives, these solutions are
used to prevent loosening under vibration.
An examination of the three main causes
of loosening in correctly torqued joints helps
assess fasteners used in critical bolted
joints subject to dynamic loads.
Mechanical Shock: Sudden impacts
- whether alternating or dynamic - are readily
caused by machinery, military applications, off
road transportation, etc. These sudden and
severe forces can cause a bolted joint to slip and
loosen. National Aerospace and Military Tests
NAS 3350/3354 and NASM 1312-7 test
the ability of a fastener system to withstand
this mechanical shock, and fasteners used
in joints subject to mechanical shock
should be shown to pass these
important tests.
Vibration: Over many decades,
vibration experiments on bolted
joints have demonstrated that small
but frequent transverse vibration between
the sections of a joint relative to the bolt head or nut
cause loosening. Repeated transverse movement works
loose the friction the bolt and nut use in holding the joint
together. Eventually, vibration causes the bolt and/or nut
to “turn loose”, causing the joint to lose its clamping force.
The Junker test was developed to test the performance of
fasteners in bolted joints subject to transverse vibration.
The standard for this test is DIN 65151.
Embedding: Normally design engineers will
account for the settling of a joint when it may relax
after installation. Embedding, which leads to
clamp load loss and joint loosening, can often
be observed in softer work materials such as
woods, soft metals or polished metals. It is
for this reason that manufacturers of wedge
locking washers and serrated washers/nuts
often recommend their products only when
the contact surfaces are as hard as the
washers.
To secure a joint in such a way that it
can withstand loosening is no small task.
A new product on the horizon is the CoiLok,
which accomplishes vibration resistance while
also providing versatility and reusability in
one cost effective package. CoiLok is
a small spring-like locking device that
screws over the bolted connection and
locks the nut firmly in place. It can be
used on new bolted connections or
retrofitted to existing connections.
CoiLok uses three working
principles to prevent loosening:
[1] Thread Wedge Effect (TWE): Solid wedging between
the threading of the bolt and nut threading,
[2] Axial compression of the bolt threading, and
[3] Radial compression on the bolt’s minor thread areas.
CoiLok is tested to withstand severe vibration, providing
effective bolting security resistant to loosening.
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COILOK