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Hard to say exactly, but it appears that there is very low resolution in the orbit. To get a good timebase and orbit plot with asynchronous sampling, take a higher fmax (wider span). You can also decrease the number of lines. Basically, sampling for a lower resolution spectrum provides a higher resolution timebase. Some of these settings may need to be adjusted for your data acquisition system. If, for example, you are using a Zonicbook with EZTomas, then you need to use a high Fmax, but also to keep the number of lines high so that you can get decent spectral data, decent timebase data, and also make sure the analyzer catches the keyphasor pulse.

Also, I would set the plots up so that the timebase shows the same amount of revolutions as the orbits (5 in your case). That would make it easier to correlate the two plots.

Finally to really tell what is going on, you may need to compensate the data correctly and provide much more than a single orbit plot. Unfortunately with orbits you can't just take a wall chart approach. While there are some generalities, orbit patterns aren't distinct enough to say that a square pattern (or bow tie or banana or round pattern) means a certain fault. It could mean something, then again, it might be just the way it appears due to the glitch.
RM
Michael,

Here is the total number of rev orbit that matches the waveform. See attachment.

John,

It has been running 2 weeks. Spare rotor (rebuilt), new bearings. No change in the 2 week time frame.

Coupling is 2 shim paks with a drop-out spool, length, maybe 1 foot long, 2 at the most.

The data on the Inboard prox probs looks like all the problem is at the Inboard, coupling end.

The outboard prox probe is less than 0.5 mil, orbit is basically "circular" in nature, but not near perfect circular though. It does have some "sharp turns" during the rotation but not "square" in nature.

I thought maybe misalignment or coupling unbalance or coupling not installed at the original match marks to be in a "balanced" condition.

The casing reading, IB and OB are basically the same amplitude, 1.5 Mils horizontal. As are the vertical, IB and OB, the same, 0.5 mils. Looks like rotor unbalance from these readings.

The square orbit is my main concern. What could cause this, misalignment, coupling unbalance or what?

The original rotor ran 14 years with no problems. Failure was due to oil pump shutdown without warning, spare pump failed to start soon enough.

It will not be shut down right now, due to production loss, unless the trend changes.

Attachments

RM
quote:
Originally posted by Machine Survey:
I agree with Michael and Mascherama... I would really like to see the slow roll orbit. Would want to either confirm or rule-out whether it is a journal surface condition (ie glitch).


I know of an instance where a 4-jaw air operated chuck used on a journal grinder had a bad air regulator that caused substantial over pressure. This caused four work-hardened localized areas in the probe target area due to the excessive clamping pressure. The slow roll waveform was essentially identical to the full speed waveform. I can't help wonder if something like that had happened since you have near perfection in the 90Β° angular relationship.
RM
I would recommend inspecting the coupling with a tunable strobe with focus on the shim packs.

In addition, I would verify the prox probes output with casing measurements from portable instrumentation. This step is not to actually verify amplitude but to show that the vibration is not instrument generated by measuring it with an accelerometer that is immune to the possible glitches that are of concern. If you measure it with both, then it is probably real and not instrument generated.
RM
Thanks to all who have replied so far.

Danny,
Coupling is sealed in a recirculating oil bath. Can not see the coupling during running.

Casing readings showing 1.5 mils, both inboard and outboard in horizontal direction and 0.5 mils vertically.As compared to ~2 to 3 mils on the Inboard probes. Outboard probes less than 0.5 Mils.
Sleeve bearings,new.

Old rotor was showing less than 0.5 mils at 8,845 rpm blower speed in all directions.

In theory or reality, what should be the "ratio" of probe vs casing readings be?


Vibrant,

What other data would you need?

Will be rechecking it on Friday, tomorrow.
RM
Buddy,

There is no correct ratio of amplitude between prox probes and casing mounted accelerometer readings. The point is that an accelerometer won't pick up a burr on the shaft unless it is contacting something stationary. If the accel picks it up also, then it is a real tick and not an instrument glitch caused by a shaft irregularity. If the prox probes pick it up but the accel doesn't then it is likely a glitch.
RM
quote:
There is no correct ratio of amplitude between prox probes and casing mounted accelerometer


This is complicated. Before hand, this can be difficult to get correct, and that assumes you are doing the best modeling with modal testing to confirm.

However, with similar machines in operation in the field, this can be a valuable CM tool, because there is a transfer function that fits the machine or machine type. Even with a single machine, this can be valuable for CM. That transfer function needs a reason to change.

When I was supporting a monitor center for many machines, I established normal ranges for this relationship. The proximity probes were most of the time (vast majority of the time) a reliable gage of the rotor. However, when the velocity to shaft relative displacement went high - sometimes add a high or unusual shaft relative to the mix - something was odd. What was not right could range from piping supports to foundation issues such as stuck gib key or uneven cooling of the stationary parts or supports. Even when there were other bigger problems, I would get these corrected as part of the solution. Machines have a natural rhythm.
RM
Just to catch up on the more recent replies,

John,
quote:
Is there any tendency toward a similar orbit shape at the opposite end?


The other bearing is not showing this pattern. Looks like more of a random plot with no rhyme or reason why.

See the attached plot.


Dan,
quote:
I'm guessing the 1.5 mils at 4X?


Dan Timberlake


The 1.5 mils is at 1x, not 4x.Confused


Danny and William C. Foiles,

So, are these casing readings and the probe readings (casing equaling 1/2 of the probe) seemingly real and correct as far as the movement of the shaft is concerned, and there is apparently no glitches involved, based on the readings?

Even though the outboard bearing has 1.5 mils casing, same as the inboard casing, and 0.5 mils probe (6 times less than the inboard probe)?


All,

As of now,after 4 weeks running with no change in the data, the machine is going to continue to be allowed to run until such time comes for our analyst to call for it to be shutdown or a scheduled shutdown is performed.

We have developed a series of things to "check" and perform the next time it goes down under a normal scheduled shutdown or with data analysis resulting in a suggested shutdown.

These are,
check alignment
check for match point alignment on the coupling, if there are any marks there.
If no match marks, then balance the coupling,
confirm the correct bearing clearances are within spec.

Anyone have any other suggestions?

Thanks to all. Smiler

Attachments

Images (1)
  • Blower_Outboard_Prox_Prob_Polar_Plot_November_28,_2014
RM
Buddy... you seem, to me, to be unresponsive to any of the suggestions that the reading is due to glitch? Do you have evidence that proves otherwise? I suspect your entire "check and perform" list could possibly be dismissed if there is slow-roll evidence during the coastdown that shows a square orbit similar to the operating orbit? John gave an insightful example in which a journal was work-hardened during machining which caused abnormalities in the probe reading. I would add another "check" item to check the slow-roll orbit during the coastdown...
RM
quote:
Buddy... you seem, to me, to be unresponsive to any of the suggestions that the reading is due to glitch? Do you have evidence that proves otherwise? I suspect your entire "check and perform" list could possibly be dismissed if there is slow-roll evidence during the coastdown that shows a square orbit similar to the operating orbit? John gave an insightful example in which a journal was work-hardened during machining which caused abnormalities in the probe reading. I would add another "check" item to check the slow-roll orbit during the coastdown...


Machine Survey,

I am wondering if I was not clear in my last post. If not, I apologize. Frowner

I do not assume anything and have responded to the "glitch" suggestions when I asked the question in my quote below, directed to Danny and Bill, concerning their response to the casing vs probe readings.

My entire sentence, in the quote below, is a question, not a statement. Sorry if it was not taken as such.

quote:
So, are these casing readings and the probe readings (casing equaling 1/2 of the probe) seemingly real and correct as far as the movement of the shaft is concerned, and there is apparently no glitches involved, based on the readings?


We will perform a coastdown orbit. We have talked about the "glitch" and I just failed to enter it in the list of "checks". Sorry.

I have not ignored your or John's suggestion and I truly hope it is a "glitch". Smiler

And I sadly say, I have no evidence proving anything at this time, concerning a glitch or not a glitch. Smiler

My apologies if I have offended you. Frowner
RM
Buddy
Absolutely no offense taken!... thank you for responding. Quickly written words in a blog, I believe, sometimes give unintended spin? Voice inflections and facial expressions are helpful, sometimes, to give the full message. I see, now, that my words may have indicated that offense was taken? Certainly not the case. Just hoped to emphasize my recommendation to look at the coastdown orbit before tearing into the equipment. Thanks for posting and responding. We all learn from your experience. Look forward to hearing results...
RM
John,

It looks like probes have been interchanged and a 90 degree rotation. If the probes(or if using an O'scope) this could easily occur, but this looks digital.

Look at it from the back side to change the 'orientation' or precession direction then rotate 90 degrees to get this. Or, there is something funny going on here.

Anyway this would occur if the probes were swapped on an O'scope - it does the orientation change and the rotation by 90 degrees if you like to think of it that way.
RM
quote:
Originally posted by William_C._Foiles:
John,

It looks like probes have been interchanged and a 90 degree rotation. If the probes(or if using an O'scope) this could easily occur, but this looks digital.

Look at it from the back side to change the 'orientation' or precession direction then rotate 90 degrees to get this. Or, there is something funny going on here.

Anyway this would occur if the probes were swapped on an O'scope - it does the orientation change and the rotation by 90 degrees if you like to think of it that way.


Bill, I 100% agree but the date/time tags are exactly the same (20-Nov-14 14:58:22), hence the reason I brought up the pecularity.
RM
quote:
Originally posted by Buddy Morris:
Just to catch up on the more recent replies,

John,
quote:
Is there any tendency toward a similar orbit shape at the opposite end?


The other bearing is not showing this pattern. Looks like more of a random plot with no rhyme or reason why.

See the attached plot.


In your early data you showed the DE orbit marked with the notation "5 Revolutions". I suggest you look at the NDE data but only view a single revolution. Step through the revolutions if possible to establish a clearer picture of the orbit shape. It might not be as random as you might think. When you view the attached, note the similarity of the DE orbit overall shape to the inside of the NDE orbit. What might prove interesting is a comparison of the DE and NDE single revolution orbits.

Attachments

Images (1)
  • DE_NDE_comparison
RM

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