[TheForge] Re: Shot-peening article- history and usages

[David E. Smucker]

Shot-peening makes the surface harder, only in the way it adds cold work to 
the surface layer.  If you shot-peen or for that matter "pack" the surface 
before heat treatment all or most of this effect will be lost in the heat 
treatment.  The key to shot-peening is that it is cold working the surface 
layers AFTER heat treatment, not before.  The great benefit as noted in the 
article is that the result is very high compressive stress that is locked 
into the surface layer.  For failure to occur you first have to exceed this 
compressive stress and then add the required tensional stress to reach a 
point of fracture.  It is not unlike the used of high preloads on bolts to 
prevent them from seeing cyclic stresses.  Shot-peening is very useful on 
parts hat see high cyclic stress or parts that failure is very critical 
item.  (Airplanes falling out the sky is not a good thing.)

Great article thanks for the URL.

Dave Smucker
----- Original Message ----- 
From: <schade at acegroup.cc>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>; <mspencer at tallships.ca>
Sent: Wednesday, January 10, 2007 3:56 PM
Subject: Re: [TheForge] Re: Shot-peening article- history and usages


It was an interesting article and seemed to support the idea that
packing or "peening" in this case would harden the surface...

http://www.americanheritage.com/articles/magazine/it/2007/3/
2007_3_51.shtml

"Shot peening prevents this kind of metal failure because it
pre-stresses
a part’s surface with permanent compressive stresses. These counteract
the tension stresses that result from loading the part. In addition, the
shot-peening process nullifies stress risers because it applies a layer
of
compressive stresses to the total part’s surface. This prevents a
failure
crack from starting."

But if I remember right from the last ten or so times this subject came
up packing (forging at a dark red of black heat) did not harden the
surface.

Am I dreaming again?

Bob
___________________





On Jan 10, 2007, at 2:18 PM, Mike wrote:

>
> That a good piece.  Thanks for posting the URL.
>
> They had a shotpeen tower at the Hamilton Standard aircraft plant near
> Hartford, Conn. where I had a summer job circa 1960.  They shotpeened
> the propeller blades, about 5' or 6' long, that I subsequently glued
> deicers and rubberized fabric to.  Made a terrific racket when it was
> running.  I didn't realize at the time that it was Hot Stuff.
>
>
> - Mike
>
> -- 
> Michael Spencer                  Nova Scotia, Canada       .~.
>                                                            /V\
> mspencer at tallships.ca                                     /( )\
> http://home.tallships.ca/mspencer/                        ^^-^^
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