Steve,
Shot peening induces residual compressive stresses into the surface of the
pin.
It is Tensile stresses that lead to fatigue cracks.
The residual compressive stress has the effect of reducing the level of
tensile stress that the pin sees in service.
Shot peening is not done to increase the abrasive wear resistance of steel,
but increasing fatigue resistance.
Erich
----- Original Message -----
From: "Steve Laifman" <SLaifman@SoCal.RR.com>
To: "Tim Morin" <tigert@ktc.com>
Cc: "Alpine list" <alpines@autox.team.net>; "Tiger list"
<tigers@autox.team.net>
Sent: Saturday, October 13, 2001 12:26 PM
Subject: Re:
> 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 >
> B9472289 < important in your life >
> < and don't let it get away!>
> <SLaifman@SoCal.RR.com>
> <http://www.TigersUnited.com/gallery/SteveLaifman.asp>
>
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