Reason for frequencies less than 1XRPM in planetary Gearbox

Hi Friends,

                  In one our planetary Gearbox we observing non synchronous frequencies below 1XRPM. The vibration at Gearbox i/p is varying from 15 mm/sec to 20 mm/sec and the mill is frequently tripping due to vibration.What could be  the possible reason for non synchronous frequencies and how to eliminate it.

Please find the spectrum for reference.

 

Sagar

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John from PA posted:

I see units of mm/s.  Are you using an accelerometer and integrating to velocity?  It might be something as simple as integration noise.  

Any details on the gearbox?  Drawing, tooth counts, etc.?  Are you certain it is a planetary arrangement, as opposed to a solar or star arrangement (see attached)?

Hi john,

               Yes,it is Planetary gearbox.Gearbox Model is CPNHX - 224.It is speed reduction gearbox and gear ratio is 82.87:1

the gear teeth details is as follows

Input RPM1489 
Input pinion25 
Wheel/helical stage52 
 1st Stage2nd Stage
Ring Gear Teeth13174
Planet Gear Teeth5327
Sun Gear Teeth2518

 

and as you said it might noise but am getting the same in other gearbox.Here the gearbox is used for raw meal grinding in cement plant.

How many planets are in each stage?

You didn't answer my question...are you using an accelerometer and integrating to velocity?  I'm still of the opinion that you are likely seeing integration noise further, IMO, the fact that you have it on another machine supports noise as opposed to ruling it out as you seem to indicate.  Just how does this machine feel?  6 mm/s (RMS) at 3.13 Hz is a displacement of almost 0.9 mm pp (34 mils).  That machine should feel very rough!  Note that I also used RMS velocity, it is even more if you are measuring peak units of velocity.

I have attached a summary of the anticipated frequencies based on your tooth counts and using a planetary arrangement.  Except for the helical stage pinion rotational matching your peak at 24.8 Hz I don't see any match on the lower frequencies of 3.13, 7.81 and 18.75 Hz.  They could however be sum and difference frequencies. 

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You may have already done this, but,......

Instead of a 2500 Hz Fmax, can you take data with a 0 to 200 Hz Fmax and 3200 lines of Resolution?

This data will not be an "expanded" spectrum from a higher Fmax setting, but an actual acquired spectrum with a setting of 0 to 200 Hz and 3200 lines.

Can not tell much about the data below the 1x peak, from this 2500 Hz Fmax, except it looks as though the data at the low end might be recovering from a "skislope"  pattern. A true zoom in of this area might reveal more.

Thanks and Have a Great Day,

Ralph

Zoom

 

 

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Hi John

Yes we use a accelerometer and it integrates to velocity.

coming to planets,in first stage we have three planets and in second stage we have four planets.This gearbox is a movable gearbox where some pressure is applied for grinding(Normally runs between 10 to 15 mm/sec vibration).

Kishore kumar posted:

Dear sir ,

What type of equipment connected to the Gearbox and the Vibration levels of that equipment and spectrum .Did you check decoupled condition Vibration spectrum of Gearbox to its equipment .

Please share ,so that we could understand the problem .

Hi Kishore,

                   The Equipment is roller press used for raw meal grinding.Motor is connected to gearbox via cardan shaft and gearbox connected to roller.Motor Vibration is 2.5 mm/sec in load condition and roller vibration varies from 5 mm/sec to 9 mm/sec.Roller DE spectrums are as follows.Decoupled condition means motor with gearbox ???

 

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Ralph Stewart posted:

 

You may have already done this, but,......

Instead of a 2500 Hz Fmax, can you take data with a 0 to 200 Hz Fmax and 3200 lines of Resolution?

This data will not be an "expanded" spectrum from a higher Fmax setting, but an actual acquired spectrum with a setting of 0 to 200 Hz and 3200 lines.

Can not tell much about the data below the 1x peak, from this 2500 Hz Fmax, except it looks as though the data at the low end might be recovering from a "skislope"  pattern. A true zoom in of this area might reveal more.

Thanks and Have a Great Day,

Ralph

Zoom

 

 

Hi Ralph,

              I have spectrum with 320 Hz,1600 lines in axial direction but not in horizontal.will take the data as you told once the machine starts.please find the spectrum for reference.

 

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vidya Sagar posted:

Hi Ralph,

              I have spectrum with 320 Hz,1600 lines in axial direction but not in horizontal.will take the data as you told once the machine starts.please find the spectrum for reference.

Thanks vidya,

The strange  peak below 1x does not appear to be there in this data, does it?

Have a Great Day,

Ralph

 

 

vidya Sagar posted:

Hi John

Yes we use a accelerometer and it integrates to velocity.

coming to planets,in first stage we have three planets and in second stage we have four planets.This gearbox is a movable gearbox where some pressure is applied for grinding(Normally runs between 10 to 15 mm/sec vibration).

You may want to request the anticipated frequencies from the manufacturer Eichoff.

Based on earlier information, the 2nd stage has ring = 74 teeth, planet = 27 teeth and the sun = 18.  If your tooth counts are correct, that may mean you have a non-factorizing gearset in the 2nd stage.

In a non--factorizing planetary gear train the the number of teeth on either the sun gear or ring gear is not evenly divisible by the number of planets.  In your case both the sun (18T) and ring (74T) are not divisible by 4.  A non--factorizing system is theoretically smoother and quieter than one that factorizes for torsional
vibrations, but will cause increased lateral vibration.  In a factorizing arrangement, the tooth actions of the various planets are synchronized, tending to produce a cyclic beat.  Having said that ANSI/AGMA states "The benefit from hunting and non--factorizing is theoretical, without experimental verification." 

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