SPRING 2012

34 THE DISTRIBUTOR’S LINK
Guy Avellon
Guy Avellon has been in the MRO and fastener distribution industry for over 30 years. He began his metallurgical
engineering career at Republic Steel Research Center in metal coatings and has since held positions as sales
engineer; Chief Engineer; Manager of Product Marketing, Product Engineering and Quality and Director of Quality and
Engineering. He founded GT Technical Consultants where he performs failure analysis, presents lectures on fastener
safety, worked for law firms and designs and audits Quality systems.
He is a member of SAE and is Vice Chairman of the ASTM F16 Fastener Committee and Chairman of the F16.01 Test
Methods Committee, since 1988. He also received the ASTM Award of Merit in 2005.
Guy and his wife, Linda currently reside in Lake Zurich, IL and may be reached at 847-477-5057 or visit his website
at http://www.BoltDoc.com.
TORQUE VARIABLES AND LIABILITY
When is it safe to recommend torque values
Earlier articles have cited how to calculate torque
values, how variables can affect the pre load and
different techniques employed for installing the fastener.
We spoke of material grades and components and a few
applications.
But what does this mean
to a distributor Of course they
should be knowledgeable
about fasteners; however
when it comes to
recommending torque values,
how great is your liability
Many times the customer does
not reveal all of the details of
the application. It takes a
trained individual to be able to
dig into what the customer is
using and how. This is
because there are many
variables to consider when
tightening a simple fastener.
The incorrect answer could
cause a great failure and it still
boils down to “the man with
the wrench.”
First, let’s list some of
those variables:
1. Bolt or Nut:
Grade: Does it match the other components being
used together Does it match what you are replacing
Is the Nominal diameter in tolerance Is there a proper
fillet radius
Threads: What was the manufacturing process
Hot formed, cold formed How is the fit, form,
engagement Plating or coating thickness: any thread
interference Is there proper
and complete thread tapping
of the nut Are the threads
cut or rolled Is the thread
run-out adequate
Surface: Any corrosion
present Surface voids or
bursts Was it hot headed
Any lubricants present What
is the type and coefficient of
friction.
Bearing surface: Is it free
from nicks, gouges and
bursts Is the surface area
sufficient for load contact and
perpendicularity How is the
surface roughness and/or
lubrication
2. Washer:
Style: Flat, lock, star, DTI,
etc. Is the hardness
compatible with the expected
bolt and joint loads Is the
size correct; not too small or large an ID or OD Does
it properly seat the entire bolt head or nut Is it coated
and treated for hydrogen embrittlement Any lubricant
present What type
please turn to page 192