SUMMER 2023

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THE DISTRIBUTOR’S LINK
Guy Avellon
Guy Avellon has been in MRO and Fastener Distribution for over 30 years, in such positions Sales
Engineer, Chief Engineer, Manager of Product Marketing, Product Engineering & Quality and
Director of Quality & Engineering. He founded GT Technical Consultants where he performs failure
analysis, lectures on fastener safety, works for law firms and designs/audits Quality systems. He is a
member of SAE, is Vice Chairman of the ASTM F16 Fastener Committee, Chairman of the F16.01 Test
Methods Committee and received the ASTM Award of Merit in 2005. Guy can be contacted at 847-
477-5057, Email: ExpertBoltGuy@gmail.com or visit www.BoltFailure.com.
WHAT DISTRIBUTORS NEED TO KNOW
ABOUT TORQUE IN ASSEMBLIES
While torque may seem universal there are three
specific industries that apply torque differently; structural,
maintenance and mass assemblies.
In a bolted joint, torque is measured in two different
planes that are perpendicular to one another. Torque is
a combined relationship between force, times distance
and tension. Torque measures the reaction of rotational
movement of the fastener, while tension measures the
longitudinal movement of the same fastener. There are
many assembly devices that analyze these forces.
The amount of energy that is applied to the bolt from
rotation to create tension is determined by the energy
losses due to the friction between the surfaces of the
rotating parts and the joint. Therefore, the assembled
parts need to be new, no deformities and clean. The
relationship between the applied torque and the tension
generated in the joint is the torque-tension
relationship.
The mass assembly of products include the
automotive, truck and bus industries to name a few,
excluding the electronics industries because vehicles
experience heavy loading, vibration and shock. Also,
vehicles can become very dangerous to life and property
if something breaks or loosens.
Recently Rivian automotive has recalled approximately
13,000 of its vehicles for a loose steering assembly. It
was reported that the fastener connecting the front upper
control arm and steering knuckle “may not have been
sufficiently torqued.”
The question to be asked is, why wasn’t there
CONTRIBUTOR ARTICLE
sufficient torque applied? How was the assembly
tightened? Is there a torque calibration issue? Was the
output data not interpreted correctly?
Automotive assembly lines use a variety of
programmable, digital power tools for assembly that will
transmit data, such as torque and angle, to the data
processor for error-proofing. The torque-angle measurement
is a most accurate tool used for solid and stiff joints. In
most cases the turn will negate friction variables, which is
why a pre-torque is first applied to establish a hard base
without any further joint compression.
Some programmable nut runners and power screw
drivers will operate on an X-Y-Z axis that will locate the
next screw or nut to be tightened and will not allow
another part to be tightened until that prior task has been
completed. This action greatly aids with proper tightening
sequence as the clamp load is criss-crossed so the load
is evenly distributed.
It must be realized that with all of the torque aids, it
will not always mean that the preload has been achieved.
This depends upon how the data is monitored and
interpreted and if the parts tightened are within tolerance.
If the torque and angle have been achieved within a
certain per cent window, then the joint is good.
However, if the torque angle goes significantly
beyond the expected tolerance window to achieve the
proper torque, this means the joint was not solid and
there was interference between the joint, such as a burr,
unexpected lubrication or even a non-conforming part that
produced compression or resistance.
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