Cyclic forward-reverse loading safety factor for spur gears. 4

[morris9791]

Dear Experts,

Can anyone advise me regarding incorporating a safety factor to account for forward and reversal loading of spur gears using AGMA standards. Is there any specific AGMA standard that deals with this?

More specifically, is there a K factor (or other) that takes this type of loading into account?

Any information will be greatly appreciated.

Kind Regards

Eddie

 

[dimjim]

There is.

 

[gearcutter]

If you're talking about reverse loading of a gear, such as an idler, then AGMA 2001-C95 suggests using 70% of the allowable bending stress number for steel gears.

If you're talking about oscillatory motion for applications such as robotics or yaw drives then I know of no AGMA standard that covers this.

You could do a search on their web site.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[morris9791]

Thanks Ron,

I have obtained the standard, it is quite useful. I am looking for data that plots the rim thickness factor against backup ratio for fully reversed gears. I have seen a plot in Ray Drago's Fundamental Gear Design book; however I need to interpolate the graph for a particular backup ratio. Do you know of any source I can get access to?

Any information will be appreciated.

Kind Regards

Eddie
Design Engineer

 

[gearcutter]

You could try a Google search.
I found many references including free PDFs on the subject.

Here is one from NASA you can download:

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA312521&Location=U2&doc=GetTRDoc.pdf

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

morris9791,

For the fully reversing tooth bending loads (ie. an idler gear) you are concerned with, you should check the fatigue S-N diagram for your particular gear alloy and heat treat. You should also know the total number of load cycles. I believe the stress (or strain) ratio R= minimum stress (or strain)/maximum stress(or strain).

In order to equalize the bending stress between a driver gear and idler gear, you can usually accomplish this by increasing the face width of the idler gear to increase the bending strength of its teeth. You don't need to increase the face width of the mating gears, since contact stress is not an issue. Just be sure to keep the face width 1D or less for spurs, and 2D or less for helicals/double helicals.

As for the effect of rim thickness, it is a very wise rule of thumb to have a rim thickness equal to at least one gear tooth whole depth. Any thinner than this and you will risk propagating a crack through the rim, instead of through the tooth, which would be a catastrophic gear failure.

Good luck.