Diagnosing Gearbox Noise

Diagnosing any noise issues in your equipment can be time-consuming and difficult to diagnose, and determining whether noise is coming from the gearbox within your system can be even more difficult without sophisticated vibration measurement tools. However, some general guidelines are as follows:

High Pitch Whine Noise

Gear noise from deteriorating gear set is usually a high pitch “whine”. This whine is generated by the tooth meshing frequency. For example, an input gear with 30 teeth running at 1800 RPM would have a meshing frequency of 900 HZ. Compare this to the shaft rotation frequency of only 30 HZ (1800/60)

Growl Noise

Bearings rotate at input shaft speed or some increasing or decreasing multiple.  The rotation frequency of the shaft is several orders of magnitude below the gear mesh frequency. Therefore, then noise produced by bearings as they fail is closer to a “growl” or at least a frequency much lower than gear mesh frequency.  In the advanced stages of failure, the balls or rollers may slide producing a screech.

Pinpointing Noise

Pinpointing the noise is easier said than done, especially on systems without torsionally tuned couplings.  Noise transfers via shafts and other rigid members, and often sounds as though it is coming from a gearbox when it may actually be transmitted there from another source.  A “listening rod” may be used to help locate the noise. Troublesome bearings usually generate excessive heat. Look for hot spots on the gearbox.

When it comes to finding out why there is noise in your equipment, don’t be certain that the gearbox is the culprit.  Take the time to follow the general guidelines to get you started on the right path.