Buckingham wear equation

[multiproducts]

We are experiencing pinion wear (channeling). I have analyzed the situation using the Buckingham equation for wear of gear teeth and we are nowhere near the conditions where we would experience wear. Does the Buckingham equation have speed limitations? The pinion is at 6200 RPM, hardness of 37Rc, 1.0 in-oz of torque, running against a gear of 58Rc. Could the hardness difference be a factor. Any help would be much appreciated.

 

[ivymike]

On the surface, I'm tempted to say "37 vs 58? um, yeah, that could be a problem." To be honest, though, I'm not particularly familiar with what you're describing.

 

[Philrock]

It would be a lot better if your hardnesses were switched - but you knew that. Depending on the geometry, it's possible you are experiencing scoring, rather than wear as predicted by the Buckingham equation.

Small number of teeth, high pressure, and high velocity all contribute to the liklihood of scoring. There is an appendix to AGMA 2001 that does an excellent job covering scoring.

 

[dimjim]

I agree with Philrock. I know some people want
to replace the pinion rather than having to replace
the gear and make it softer. I would increase
the hardness of the pinion either by carburizing
it or induction harden it to a higher rockwell.
Also curious if the pinion is a long addendum pinion
and have an arc of recess designed in it. I would
think at those high of RPMs that would have been
incorporated into the design.

 

[multiproducts]

Thanks,

I will take a closer look at the pinion tooth profile, in the meantime we will case hardend the pinion closer to the 58Rc gear.

 

[dimjim]

If the channelling is from involute interference or
too much approach action, the hardening issue may
help but just prolong the problem. This is a good
reference. I too am not familiar with the term
channelling. The chapter before the below listed
url should also be interesting to you. I assume
too that you are speaking of external gear and
pinion. If your pinion is not a long addendum
design, you might want to experiment with cutting
one less teeth on the same gear blank and see how
that helps.

http://www.mech.uwa.edu.au/DANotes/gears/failure/failure.html

 

[multiproducts]

It is an external spur gear. What we call channeling is when the gear wears down the teeth of the pinion. Our pinions are wider than the gear and the effect looks like a channel in the pinion. Our pinions are from extruded stock so I do not have the option of modifying the teeth without great cost. Thanks for the help, the chapter on the URL is very helpfull.

 

[dimjim]

Thanks for the explanation. Does sound like
excessive scoring or excessive wear. Now for
the old addage, what kind of lube are you using
on this. This has been a common reply for
wear, ie not enough lubrication.

 

[multiproducts]

we use Mobilith AW3 grease. Anything heavier steals too much HP. It seems to work well.

 

[dimjim]

If you are having that much wear why do you think
the lube is working well with such a light load
being applied?