Helical gear noise reduction
Helical gear noise reduction
(OP)
We have a 20deg pressure angle helical gear-pinion set (17deg helix angle), AGMA 12 quality, with pinion rotating at 9000rpm, causing an annoying noise frequency ~3700Hz.
Any pointers on noise reduction? Our housing is aluminum. We've been told that perhaps 14.5deg pressure angles would reduce the noise...can anyone concur? Thanks.
Any pointers on noise reduction? Our housing is aluminum. We've been told that perhaps 14.5deg pressure angles would reduce the noise...can anyone concur? Thanks.





RE: Helical gear noise reduction
Firstly, how many teeth are there on the gear/pinion - knowing this would allow the gear mesh frequency to be determined - this in turn will provide a little better information of the source of the noise at 3700Hz.
I would guess that you are looking at some sort of gear mesh related noise. In general, if you can hear this noise then the gears are unlikely to be rolling smoothly over each other (in an old gearbox, this noise is often a symptom of gear wear)
Poor gear mesh can result from misalignment between the gear shafts, so that is something that might need to be checked.
One possibility for consideration is that you have a resonant gearbox casing, where the a surface/panel resonance is excited by an acceptable/normal level of gear meshing vibration.
Have you measured gear mesh vibration and assessed against recognised standards?
Have you tried a contact (blueing) check of the gear teeth?
RE: Helical gear noise reduction
The ~3700Hz frequency corresponds to our calcs for fundamental frequency on this pinion (24tooth,9000rpm). We also have multiple needle roller bearings in the system, but their fundamental frequencies dont appear to correspond to this noise frequency occuring and thus we've narrowed it down to the helical gears. After assembly, the noise level begins to occur, ie it is not wear related. We will try the blueing procedure, thanks. The 14.5deg was suggested by a manufacturer as a recourse to sound reduction, but we wanted to get some feedback before maybe attempting this change.
RE: Helical gear noise reduction
I would also do a high resolution frequency analysis and/or a demoduated spectrum analysis of the sound/vibration to identify side-band frequencies around the gear tooth frequency. This could indicate which of the two gears are misaligned or have loose bearing fit.
I simply can't imagine going from 17-degree to 14.5-degree helix (assuming same gear quality) would reduce sound, but I'm always willing to learn something new.
Walt
RE: Helical gear noise reduction