We have a dryer gear vibration developing on one of our paper machines. It is a 1970s Beloit design with 76 tooth gears on the dryer cans, 80T idler between top cans and 51T driving We We have a dryer gear vibration developing on one of our paper machines. It is a 1970s Beloit design with 76 tooth gears on the dryer cans, 80T idler between top cans and 51T driving bottom can. Basically there is a gearmesh frequency being modulated at the 80t gear turning speed, in turn beating at the HTF between the 80T and 76T gears. See Attachment. My best guess is an 80t gear with damaged teeth around part of its circ running against an eccentric 76T gear. This vibration comes and goes (possibly depending on draw) but is getting worse slowly. Has anyone seen this or similar before. Any help is appreciated.
Cheers

PM3_gear_data_MP26112007.pdf (254 Kb, 80 downloads)

Planty,
I believe you have a serious problem with this gearbox. From plots on pg. 3,4, and 5 it looks like a classical example of damage on every 4th tooth of the 80T and 76T gears. Also looseness and eccenticity on 80T gear. It will help if you can take 2-3 revolutions TWF ( in g's and velocity) with high resolution on the 80T gear. You may see impacting on certain teeth mesh.

In summary, an inspection is warranted, IMO.

It will also be helpful to acquire peakvue data.
Fmax=1000 HZ, HP=1000 HZ

I dont work in mm/sec so I may have this all wrong, but I will give it a shot. Correct me if you see errors as it helps me to learn.

From your numbers, you have a Largest Common Factor of 4 between your 80T and 76T gears, so it would be normal to see 1/4 gm between these gears. Especially if you dont mark them before pulling them, then reinstall them. The repeat tooth order will change and you will likey see the 1/4x gm show up.

You dont have that factor between your 80T and 51T.

Converting your numbers to in/sec I get:
Spectrum at 1110hz fmax - .246in/sec overall
Confused of your rotating speed from the two plots:
2nd plot shows 4th dryer input shaft @ 227rpm
3rd plot shows 80T idler @ 227rpm
Wondering how 2 differently identified pts have the same RPM??

Assuming these are 60" dryer cans, then 1146mpm = 3759fpm, or 239rpm ( 3.98hz ) LOTS FASTER THAN I AM USED TO !!!

What frequency does your waveform capture. It shows transient of 60 seconds in time, and I am not sure if this is a really low fmax waveform that causes the 60secs of time or if the transient feature is allowing 60seconds of time on a higher fmax waveform.

What is your pk-pk g's if you captured a waveform of 300 orders that would capture out to 3x your gm frequency?

Would also like to see a 75 order / 1600line spectrum of your 2nd plot to see if that is really 1/4 gm or possibly a bearing.

From my experience making calls on dryer gears, I would compare the PK-PK G's of all your dryer cans, and if this one is 3x to 4x higher than the rest you probably have a worn or loose gear.

ps. I have found dryer gears can get pretty darn bad before they cause a runability issue. I would also suggest as David_G did to acquire peakvue data to help analyze any bearing issues.

Mike

This message has been edited. Last edited by: MikeH,

Thanks all for your advise. We have looked at a fairy high res waveform and could not see impacting but every 4 cycle was a bit higher. We may need to collect a higher res to see the impacting if any.
MikeH, The text with the attachment incorrectly said the 76T was the modulator. We now believe it is the 80T, although only 0.2hz separates the turning speeds of these gears. Again more res reqd to be sure. All the plots are taken on the 80T as the signal is clearer I think? (I am not taking the data, I used to be a VA tech about 10 yrs ago, boy things have changed since the old 2115! I am just helping out now). The 80T gear is also the input gear. The 76T gears are the dryer can gears. The 60sec wavefore was captured useing the CSI transient program so doesnt really have an Fmax. I think you just input a duration and resolution? I will try to get more data collected as suggested. Today the gears were quiet, as I said it seems very sensitive to changes in draw etc.Speed wise, yes the old donkey has been up to 1160m/min. We had to increase the diameters of the hitch rolls to get there and the machine seems to settle above 1100m/min. yes 60in cans. Again thanks for your help.
Cheers

quote:

Today the gears were quiet, as I said it seems very sensitive to changes in draw etc.

I would guess you probably do not have an urgent concern, based on what you are saying about the noise to quite changes you are getting. I have seen this many times with the "draw" more or less "dragging" one section of dryers which causes the gears to be under a no load or very near no load condition and this causes a lot of banging and clanging of the gears trying to catch up the "slack" from a backlash position to loaded position.

There may be some excessive backlash present that, under the draw condition, and is rattling and could over time cause some gear damage, which may have already happened with the machine being 37 years old.

I would suggest the operator try to run this section under load until inspections can be done.