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Re:

To: Tim Morin <tigert@ktc.com>
Subject: Re:
From: Steve Laifman <SLaifman@SoCal.RR.com>
Date: Sat, 13 Oct 2001 12:26:06 -0700
Tim,

This is old memory, an may be flawed, but as I recall the shot-peening
process was subjecting the part to multiple impacts of hard steel BB
sized shot. This did, indeed harden the steel, but only the surface. It
is used for keeping the major cross section ductile, but hardening the
surface for wear resistance. Of course grinding was necessary to get the
surface to the size and finish required.

 The helicopter example is, however, a good one where the flexibility of
the hinge pin was a requirement, as well as the surface hardening of the
bearing surface. The overall strength was unaffected, however, but the
wear surface was hardened.

I do not think this process would be of much value when the entire
cross-section of the fulcrum pin is failing, and the surface that is
subject to wear abrasion is lubricated in bushings.

I could be wrong, and willing to hear from others with direct
experience, but this is my recollection. We stopped using the process,
at least decades ago on our rockets, with the advent of so many good
alloys, and the lack of any cost saving requirement. Saving a $1 that
could risk $100 Million worth of hardware wasn't very important. Hardly
anything "moves" much on a rocket but hot gases and fluids. The turbo
pumps on the liquids did rotate at extremely high speed, but torsional,
rather than bending loads were more important, as well as good bearing
support along the length of the shafts.

Steve



Tim Morin wrote:
> 
> Listers,
>     My two cents worth!  With all this talk about
> fulcrum pins, that have cracks and breakage.
> 
> Has any of these fulcrum pins, been Shot peened??
> 
> Maybe, everyone should Shot peen their pins.
> This process adds strength plus flexibility. Military
> uses this process on all Helicopter main rotary
> hinge pins.
> 
> Tim Morin


--
Steve Laifman        < Find out what is most    >
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