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09/11/2001

 

Home Up Engineering Study

 

 

PLANETARY DEFECT CALCULATIONS

I have listed below the calculations of the frequencies that we look for when checking planetary drives. We have found that the third harmonic of the planetary fundamental gear mesh frequency is the best indicator of a problem, and exhibits the best side bands. We have found ring gear problems from the ring gear defect frequency with velocity; and enveloped Gs is a good way to find any defect change that is at a higher frequency. We have found sun gear side bands around the fundamental planetary gear mesh frequency which has indicated a serious problem. I will discuss this in a future newsletter. I would recommend setting up a basic Excel program to calculate the values and their harmonics with different numbers of teeth and different input speeds. Always take in to account if the ring gear is rotating or stationary.

 

 

 

 

 

Ns = Sun gear rotational speed.

Np = Planet gear rotational speed.

No = Out put shaft rotational speed.

Ts = Number of teeth on sun gear.

Tp = Number of teeth on planet gears.

Tr = Number of teeth on ring gear.

np = Number of planet gears.

Fm = Planetary fundamental gear mesh frequency

No = Ns/((Tr/Ts)+1)

Np = No(Tr/Tp)

Fm = Ts(Ns-No) = Tr X No = Tp X Np

Prominent gear mesh component = np X Fm

Defects are sidebands of the gear mesh frequency and the mesh harmonics.

NOTE: These sideband frequencies can also be separate frequencies and have harmonics. They are easily seen with Enveloped Gs Spectrums, and on standard spectrums if gear problems are present.

Fs = Sun gear sideband defects.

Fp = Planet gear sideband defects.

Fr = Ring gear sideband defects.

Fs = +/- np(Ns-No) = Sun gear sideband defects.

Fp = +/- (2 X Np) = Planet gear sideband defects.

Fr = +/- (np X No) = Ring gear sideband defects.

* CLICK ON THE ENGINEERING STUDY AT THE LEFT TO SEE AN IN DEPTH PROOF OF THESE CONCLUSIONS.

Notes:

  1. I would like to thank Mr. Dave Kadushin with SKF Condition Monitoring for his help with these calculations. www.skfcm.com
  2. I would like to thank Mr. Robert Jones at SKF Condition Monitoring for answering many of my questions during the last few years. He is now retired, but has helped me with many anomalies of vibration analysis.
  3. I also would like to recommend the training from Technical Associates of Charlotte www.technicalassociates.net or Full Spectrum Diagnostics http://www.fullspec.net.  The employees of Massey Technical Services have received their training from these two companies.

 

by: Larry Massey

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