Large Helical Gear Noise 1

[twitte]

Hello,

I am designing a piece of industrial equipment that requires (2) parallel shafts to rotate counter each other. The shafts are coupled via (2) 8.66" p.d. helical gears with a 22.5 degree helix. The gears are 10 N. D.P. and 1" wide. The problem I am having is that when running at 800 RPM, the gears are making a substantial amount of noise. The gears are lubricated with a oil bath of gear oil. Any suggestions on how to quiet the gears down would be appreciated.

Thanks

 

[L17Aurora]

Noise? - are they correctly meshing. Do they feel smooth when you turn by hand?
Try wiping dry & putting some bluing compound on the teeth. See if they are meshing over the full tooth.

 

[tbuelna]

twitte,

There's no simple fix. The noise you hear is due to the gears or housing structures vibrating in response to some excitation force. A 22.5deg helical gear mesh should be fairly quiet if designed and manufactured properly.

If the noise only occurs at a certain speed, it is likely due to the gear meshing frequency coupling with a natural structural frequency present in the gear body or housing.

If the noise occurs at a range of speeds, it is likely due to manufacturing tolerance errors in the gears or housings. Gear tooth profile, index and pitch line errors are the largest source of gear noise. Housings with inadequate mounting stiffness, misaligned or mislocated bores, or large dimensional variations with temperature can also lead to gear mesh inaccuracies that produce noise.

Correcting or reducing manufacturing errors in the gears or housings likely requires making new parts, which won't be cheap. But before you do that, you should carefully inspect all of your existing parts to check for mistakes. If you don't find any manufacturing issues, you should next do some analysis to see if you have any vibratory coupling modes between the various part structures.

Good luck.
Terry

 

[mfgenggear]

What is the AGMA quality & what is the method of gear manufacture. Hobbled gears cut at AGMA 6 vs. AGMA 10

Hobbed or/ Hobbed & Ground gears with a minus Involute at the tips will make for more quite gears.
other words a high pitch line Involute.

Control of the Total Composite error will help.
What is AGMA QUALITY?
The gear tooling must be special ordered.

Alternatively the manufacturing method & quality class can resolve some of the issues.

Hobbed, ground, honed, super finish.

 

[twitte]

Thanks for all the help. I did not specify an AGMA quality when I had these made, so I am not sure. I am going to check my backlash, I have a feeling that this might be a little tight. Overall finish, looks very good, I will have to experiment.

Thanks

 

[tbuelna]

twitte,

mfgenggear makes a good suggestion. Check your gears carefully for both face and profile errors, tooth-to-tooth and composite index errors, and pitch line runout to the bearing journals. Your pitch line velocity is only about 1800 fpm and you have a decent contact ratio, but your gears might benefit from some tip modification, which would reduce some of the dynamic mesh loading. As long as you don't remove too much case (assuming your gears are case hardened), you might be able to grind some tip modification into the existing gear teeth.

You can also correct some small amounts of index and profile error, as well as add some face crowning, with a rotary honing process on your existing gear teeth.

Your 10DP gears should have about 0.003 to 0.005 inch backlash at operating temps. You should check backlash at several mesh points.

Good luck.
Terry

 

[unclesyd]

In addition to the very good suggestions posted above I would also try one additional thing. I would change the gear oil to a nighy modified oil like the ones by Lubrication Engineers. On many ocassions I've corrected me overheating and noise problems simply by changing gear oils. LE doesn't promote noise reduction, but I've never seen a case where the noise wasn't suppressed when changing to their oil.

http://www.le-inc.com/productPages.jsp?productID=200