pramodkotwal(at)yahoo.com
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 Posted: Fri Mar 21, 2008 4:35 pm Post subject: Nitriding a Black art ?.. not really, Science.. |
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I think it is time to get some basic concepts cleared.
"First of all the strength of a shaft is what it is,
whether it is nitrided or not, it is what it is."
If you mean that a given shaft will withstand only a certain number of load cycles at a given level of bending stress, you are absolutely right.
What nitriding, carburising and other surface hardening processes do is not change this particular property of the shaft but rather reduce the "effective" stress that the surface of the shaft sees under the same bending moment. As I have tried to explain, this is achieved by preloading the shaft with compressive stresses that work in the opposite sense to the bending stresses.
A properly
implemented fifth bearing design will reduce the
magnitude of stress imparted to the shaft and allow it
to perform under conditions that fall below, hopefully
well below the threshold of fatigue limit.
The bearing will eliminate deflections. It will perhaps alter the vibrational characteristics of the shaft. It will not reduce the bending stress produced by the connecting rod because stress is force divided by the cross section, which are affected by the introduction of the bearing.
If you want to increase the number of load cycles that the shaft will survive,
reduce the bending force,
reduce the effective bending stress by preloading the shaft
or increase the area over which the force is spread.
The lamentations about the limits of the Corvair design are well justified. Perhaps it is time to realize that it isa good idea to respect those limits and live within those boundaries.
At least, the fifth bearing will do no harm.
By the way, your back handed compliment about my understanding of the "black art" of heat treating are appreciated.
Pramod Kotwal
Ron Lendon <rlendon(at)comcast.net> wrote:[quote] --> Zenith-List message [quote][b]
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