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fburgos

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Hi, I have very little experience with large gearbox (more than one reduction stage), and none with setting up/monitoring low speed shafts we have 3 kiln output speed are around 10-11rpm, I only have "old analyzer data" 2-1000Hz 800 lines. Overall levels range from of 0.3  - 0.7 mm/s rms

I have more questions than a clear point of view. 

1) I don’t have any data about the construction of these gearboxes, only ratio, my textbook from Technical Associates of Charlotte, have a method to estimate intermediate shaft speed they suggest a "speed increment factor"

SIF = ratio^(1/m), m is the number of meshing gears inside the gearbox.

For me this sounds good to setup a textbook fmax of 200xRPM on each shaft.

Anyone have another method? I think hunting the GMF is going to take time and it’s going to be hard, I just want to be prepared.

2) TA seminar textbook for gearbox suggest to measure a "normal 120xRPM (shafts 600+ rpm)" and a "special" high frequency point for gearboxes 200xRPM 3200-6400 lines.

Why measure two sets, if I can have a "better" resolution with the “special”

3) What is a “normal” spectrum for less than 600 rpm?

4) On the slowest shaft (10rpm) “special” setup is fmax 2000rpm/33.33Hz and 3200 lines the collection time is going to be 96 seconds (1 average, for 15 revolutions I think is ok for the waveform)

What about vibration above 35Hz, is this the “normal” setup usage?

4) On the 10rpm even the BPFI is just 168.5 RPM, should I enable SST on my route data, do I need a 500mv/g sensor?

 

John from PA

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Reply with quote  #2 
Quote:
Originally Posted by fburgos

1) I don’t have any data about the construction of these gearboxes, only ratio, my textbook from Technical Associates of Charlotte, have a method to estimate intermediate shaft speed they suggest a "speed increment factor"

SIF = ratio^(1/m), m is the number of meshing gears inside the gearbox.

For me this sounds good to setup a textbook fmax of 200xRPM on each shaft.



I would use some caution with the TAC method for SIF.  It might get you close, might not, but on something like a quadruple reduction it probably is best to attempt to get actual tooth count, even if you have to look in an inspection port and count the teeth.  Sometimes alternatives exist, spare parts in a warehouse for instance. 

Let's say you have a motor input, 1000 RPM, and your output speed is 10.  That's a total ratio of 100.  Let's also assume I have a quadruple reduction.  So the expression should be 

100^1/4 which is 3.16.

That means input speed (1st reduction pinion) is 1000 RPM

1st reduction gear and 2nd reduction pinion = 1000/3.16 = 316 RPM

2nd reduction gear and 3rd reduction pinion = 316/3.16 = 100 RPM

3rd reduction gear and 4th reduction pinion = 100/3.16 = 31.6 RPM

4th reduction gear = 31.6/3.16 = 10 RPM

Pictorially, something like the figure below. 

arrangement.jpg   

Vibe-Rater

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Reply with quote  #3 
Hi John,

I've not seen that formula before but it makes sense.  I'll use it from now on if needed.  I just used to use 3 : 1 - in hindsight is quite close to your number.

fburgos,

So do your setup as per John, go and collect data measuruing input / output super accurately - lots of resolution.  I'd be gunning for at least 150 orders 3200 lines to start and until you figure it out.

I always use hunting the GMF and chasing it through the box going from both ends toward each other.  It is almost certain that you can identify the input gearmesh, then find rotational behaviour for the 2nd shaft.  Measure the output speed super accurately then look for a synchronous peak and work back the other way.

You mention SST so I assume you have CSI.  Do you have a Speedvue? That would be the tool of choice to measure 10 rpm accurately. Bit too slow for strobing.  I don't think you need a 500 mV/g.

On the suggestion of 2 sets TA usually recommends 3 1/2 x GM.  i think that is overdoing it because you can already see 3 1/2x on the mating pinion - the same mesh.

On completion of database setup and data collection.  Post here the *.rbm file and I'm sure a few (inc me) will be up to the challenge. rgds 

ps. Make sure you have at least 1 axial point per shaft, 1 point perpendicular and throw in a bunch of others. Depends on the gearbox layout.  A photo of it would be very useful.
pps. What brand and what are chances of chasing through OEM?  Sounds like a very important box so it surprises me that no info is available in someones filing cabinet.


John from PA

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Quote:
Originally Posted by Vibe-Rater

On the suggestion of 2 sets TA usually recommends 3 1/2 x GM.  i think that is overdoing it because you can already see 3 1/2x on the mating pinion - the same mesh.


Can you clarify that statement?  

TA recommends that you look at 3X of mesh, plus some margin, because 3X is an early sign of distress like pitting, spalling, etc. at the mesh.  I don't particularly like this generalization, since I've seen it applied all too often to high speed gearing; stuff where mesh can  commonly be 3 kHz to 5 kHz.  But looking out to 15 kHz is an altogether different game than looking at 1 kHz in something like a kiln drive.  
fburgos

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Reply with quote  #5 
I dont have speedvue.

we have 3 of this vakoma and two old falk,

Im using this one to learn, because I had a small oportunity to do a sketch and count the number of teeth but some are missing and confirmation of gmf in fft (couple of quick spectrums, missing data) only on the input and output gears, attached my excel file



Vakoma 4640 V-V-2.jpg

 


 
Attached Files
xlsx HS2 - VAKOMA 4640V-2-2.xlsx (62.10 KB, 18 views)

Vibe-Rater

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Reply with quote  #6 
fburgos,

Looks like you are doing a very good job there. Almost got it.  Big box, very important because it will stop the kiln no doubt.

Plenty of room, at least on the non drive end for Horizontal, vertical and axial on all shafts, hopefully the same on the other sides.  That's what I would do and include Peakvue.  Also the output will have a separate pinion driving the kiln girth gear if I am seeing that correctly.  So you should find that in the data as a separate gearmesh.  You might also be able to count that pinion.  You've done a lot of work already and should be able to pin point the 4th shaft through chasing the gearmeshes.  Try to find a 24x on the 4th shaft working in one direction and the 62x inn the other direction.  The key is that on all your 4th shaft data the 2 meshes should be synchronous. I would be working in orders on the frequency axis which makes finding the 2 synchronous sets much easier in my opinion.  CSI makes that easy with allowing speed corrections (X shortcut to find harmonic sets and rotational sidebands, and R shortcut to reset the spectral speed - think of this as stretching or allowing an elastic band to contract and is why good resolution data - even if the speed is guessed - can be massaged until it all works out.

You can also pretend the 4th / unknown shaft momentarily does not exist.  102*80*62/30/23/24 = 30.5507.  Divide that into overall ratio 99.81727 and you get 3.26726.  So your 4th shaft speed needs to be 3.26726 x output speed.  Set that up in your database and you should be very close to spot on allowing you to find the geartooth counts with the X function.  Again they should both be synchronous which will be easy to spot with X shortcut and frequency axis in orders.  Let us know how you go. rgds
fburgos

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Reply with quote  #7 
I'm thinking that z23 on shaft 2 is wrong, I found a 22 with harmonics but resolution is not best on the sidebands, tomorrow ill do a route and increase the number of lines and see what happens, also wrote an email to oem hope they are helpfull.
John from PA

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Reply with quote  #8 
Quote:
Originally Posted by Vibe-Rater
fburgos,
You can also pretend the 4th / unknown shaft momentarily does not exist.  102*80*62/30/23/24 = 30.5507.  Divide that into overall ratio 99.81727 and you get 3.26726.  So your 4th shaft speed needs to be 3.26726 x output speed.


Some possibilities for 3.26726.  Keep in mind that some of the possibilities are less than desirable due to multiple assembly phases, but still could be used.

possibilities.jpg 

  
Danny Harvey

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Reply with quote  #9 
Did you try to contact Vakoma to get the information from them?

If you post the Falk model numbers someone here may have those. I have never had much trouble getting info from Falk.
Vibe-Rater

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Reply with quote  #10 
Quote:
Originally Posted by John from PA


Some possibilities for 3.26726.  Keep in mind that some of the possibilities are less than desirable due to multiple assembly phases, but still could be used.

possibilities.jpg 

  
Hi John, although if z23 is not correct will throw the calc out because z23 is part of it. rgds
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