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THE DISTRIBUTOR’S LINK
FASTENER EXPERTS MENTOR GROUP MIKE ROBINSON: IS MY PART UP TO IFI STANDARDS IF IT LOOKS BAD? from page 122
For those of you that are on the manufacturing end of
our fasteners you know how many variables are calculated
and come into play daily. Whether it is the using
quality material, new tooling, heat treating at specific
temperatures, and many others. Even a subtle change
in just one of these variables can cause a big change in
the fasteners being manufactured. Bursts are a perfect
example of this. If the material has impurities, inclusions
or inconsistencies in composition it weakens the material
which can cause Burst during the forging process. If the
dies on the press are not controlled properly (misaligned,
worn, etc.) it can cause internal stresses that create
microcracks that turn into Burst. If your heat treatment
has a variation in temperature or time, it can heat the
material unevenly and leaves the potential to create
bursts. Many times, burst and shear burst are some of
the ugliest discontinuities you can come across. These
are usually an open break in the metal on the fastener.
Cosmetically these can look so bad that I instantly follow
my gut and start the rejection process before QC hits the
breaks on me and helps do our due diligence. Even though
it looks awful, doesn’t mean that its integrity has been
compromised. With bursts there are many factors you
need to consider when evaluating them. On hex heads if
the burst extends from the flats to the crown or from the
flats to the bearing surface, it is an immediate rejection.
If it reduces the WAF (width across the flats) below the
minimum requirement, there will also be an immediate
rejection. They still leave room for plenty of acceptable
bursts, if they are under the measurements allowed by
ASTM F788.
Much like burst, seams are also a result because of a
change in one of the many variables in
the manufacturing process. Whether
the consistancy in the material
chemistry, tooling or speed on a press,
or one of the hundred other variables,
seams on your fastener are created
because of this. These are quite
prevalent within the fastener world
and are not a reason to immediately
reject a part. A majority of the time
you will see a seam on the shank of a
bolt/screw/stud, but occasionally you
will find them extending into the head
or flange as well.
CONTINUED ON PAGE 161