Gear- standards

[Skyhawk989]

Hello,
My questions:

1) i have read agma 2OO1 c95 and find the geometry factors somewhat confusing. Difficult to analyze without a computer program or well defined gear tooth profile. Would it be safe to assume that the previous standard agma 218 would still be acceptable? why did they introduce such a tedious method of determining critical points, etc... ?

2) The agma 2OO1 introduces stress concentration factor. For static strength analysis, can i remove this factor? Considering that the root is case hardened, i dont want to remove the factor due to the brittle behavior of the case.

3) is there much difference between specs agma 2OO1 c95 and dO4?

4) The agma stress equations give the stress at the root of tooth on tension side...how about the compression side?
I noticed a very high compressive stress on compression side, especially at larger pressure angles. Should a FEA be performed to assess these stresses? i notice that geometry factor takes this into account to reduce the tension stress, which can be quite abit:
eg. pressure angle = 25, the compressive component (in addition to bending compressive stress) will be tan25* Wt = .466*Wt (which to me is significant even if the case can handle large compressive stresses)...do we simply rely on minimum case depth at root...similar to what Dudley recommends to ensure adequate compressive strength?


thanks

 

[israelkk]

Normally the tooth fails in tension/bending fatigue. More than that under compression the material can endure approximately three times the stress in tension.

AGMA formulas are based on empirical tests for many years either for bending and pitting.

The case is brittle therefore, you can not remove the factor. The case is mainly to resist the Hertz compressive stresses which are causing pitting and not to resist the bending stresses of the tooth. For static use you can remove the factor even for a tooth without the case. You basically can use the short beam bending formula.

AGMA standard apply only for dynamic stresses at a well lubricated tooth where lubrication film exists. If the lubrication film is broken then the formulas do not apply.

FEA will give the stresses including the factor due to the small radius at the tooth bottom.

As

 

[carburized]

To answer your question first if there is a difference in 2001 c95 or 218. In my opinion 218 still works good. 2001 goes little bit more in detail and the accuracy you get with that is not enough to justify spending that much time in it. Concentration factors which you are asking for, I will not remove them. Your concerbn is justified case being brittle. Generally there is hardness gradient, as you go towrads the center of material, hardness is less. Now, teeth usually fail in tension. The reason is carburized gears have large compresive stresses. If you are ok with tensile stress, you definitely ok with compressive. Pr angle 25 definitely has more forces but makes tooth stronger in mechanical ratings. But, of course you need to use better rated bearings with 25 degress as comapred to smaller pressure angle.

 

[dimjim]

I have often wondered about the reduced
fillet radii in the higher pressure
angle systems. Also the higher contact
radii produce greater contact stresses.
I often wonder if using 20 degree pressure
angles and using 50 percent long addendums
is not a better solution. You end up
having greater operating pressure angles
this way and many shops may find it easier
to produce these using standard 20 degree
pressure hobs or cutters.