Gear crowning 1

[Compositepro]

I just read an interesting article about gear crowning, a practice of which I was not previously aware.

http://www.pddnet.com/blog-fred-you...nment-problems-012710/?wnnvz=1750,01285302538

How common is this practice? It must reduce the gear's load capacity but the article says it is used on highly loaded gears (I guess because the load causes misalignment).

 

[tbuelna]

Compositepro,

Gear crown and lead correction are used quite commonly to optimize face profile contact in high-performance gear meshes.

But contrary to how you seem to perceive the effects of crown, it actually improves the load capacity of a gear mesh that is subject to axial misalignment at the tooth contact. A mesh that has axial misalignment will tend to edge load and create excessive localized contact stress. Proper crowning will mitigate this condition. The same is true for lead correction and torsional wind-up.

It is true that all other things being equal, a crowned gear tooth will have less capacity than an unmodified gear tooth under perfect alignment. But you should also remember that if the gear mesh was not subject to axial misalignment, crowning would not be required.

The optimum degree of crown and lead correction depends upon many variables such as torsional stiffness of the gearshaft, L/D ratio of the gear teeth, and stiffness of the bearings and housings the gear is mounted in.

Finally, face profile mods (ie. crown and lead correction) will help with contact load distribution, but not so much with noise. Noise is more effectively addressed by optimizing factors such as contact ratio, index errors, and by using appropriate profile and tip modifications.

Hope that helps.
Terry

 

[Tmoose]

Even with perfect alignment the edge of a cylinder ( or gear tooth)contact brings a stress concentration. Subtle curvature can improve the stress distribution a lot, with a big boost in fatigue (service) life. Cylindrical and needle roller bearings often use a subtle crown.

http://www.digitalmetrology.com/images/RollerProfiles.jpg

Real world misalignment could make more severe crowning necessary, but would seem to make it possible to avoid presenting a hard edge to the mating surface

 

[Spurs]

Crowning if done properly can provide for longer running gears and quieter gears.

Crowing can be both in lead and in profile.. although profile crowning is usualy referred to as tip relief.

Lead Crowning allows for the less than perfect alignment of the gears to still provide smooth motion without really affecting load carrying capacity.

Profile Crowning (tip relief) usually allows for some tooth deflection under load without impacting in a non-conjugte way due to the tooth deflection.

Both are used extensively in heavily loaded gears or where noise is to be minimized.

 

[Clyde38]

Compositepro,
You may find this article interesting. .

http://www.designfax.net/enews/20100216/feature-1.asp

[link

http://www.linkedin.com/in/clydehancock

]

[/url]