I'm trying to analyze a gearbox that has high vibration. It is a Philadelphia gearbox size 6M-HPS-1 with an input speed of 3600rpm, an output speed of 1175rpm and an input/output ratio of 3.01:1.

I've been trying to find out the number of teeth on the gears to help me in my analysis, but the service manuals that our Shops have don't have that info. I've contacted the manufacturer, but so far haven't received a response.

My question: Short of opening the gearbox up, is there a way to determine how many teeth are on each of the gears in the box?

The predominate frequency in the spectrum (besides running speed)should be gear mesh frequency. For example if you have an output shaft with 37 gears rotating at 4200RPM the gear mesh frequency would be 2590Hz. 37x4200/60
Hope this helps.

Kevin,

Input speed = 3600rpm = 60Hz
Output speed = 1175rpm = 19.58Hz

Unfortunately you will need at least one more parameter to determine the teeth e. g.: one gear's teeth OR the gear mesh frequency.

The gearmesh frequency should be a characteristic dominant peak highly visible in your FFT. If you manage to find it, zoom in and look for side band frequencies spaced at either 60Hz or 19.58Hz, the side band frequency and pattern should lead you in the correct direction with regard to which gear is defective etc.

I think (from some calculation in an Excel spreadsheet) your gearmesh frequency should be approximatelly

960Hz which will give you an input gear with 16 teeth and an output gear with 49 teeth.
but more likely

1920Hz which will give you an input gear with 32 teeth and an output gear with 98 teeth.

In analysing the gearbox high vibration I suggest you pay particular attention to the gearmesh frequency and its sidebands as well as the timewaveform for signs of impacting or modulation etc.

Have fun.

Stefan

This message has been edited. Last edited by: M. S. Minnaar,