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RustyCas

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Found a pump the other day with very high 2X on the motor which was replaced in February. The baseline data (February) was normal.  So why did vibration suddenly spike to 0.75 ips from 0.06 ips?

Apparently this hub has been under a lot of stress. I'm guessing the hubs are jammed tightly against the rubber element.  Not sure this would account for all the cracks though.  I'm constantly amazed that you can extract so much information from a machine running 1800 rpm with just a digital camera.

P4041253 (Medium).JPG

P4041279 (Medium).JPG 


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John from PA

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Quote:
Originally Posted by RustyCas
I'm constantly amazed that you can extract so much information from a machine running 1800 rpm with just a digital camera.
 

Rusty, was the photo taken while the machine was operating?

By the way, 2X has been known as an indicator of a cracked shaft.  The crack introduces asymmetrical stiffness so you get a "snapping" twice per revolution.
Walt Strong

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"By the way, 2X has been known as an indicator of a cracked shaft.  The crack introduces asymmetrical stiffness so you get a "snapping" twice per revolution."

Perhaps true for a near mid-span crack, but the cracked coupling hub is at the END of the shaft!

Walt
Noknroll

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Good pick up Rusty, might have to get myself a decent camera,dont think my old nokia brick phone would cut it
John from PA

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Quote:
Originally Posted by Walt Strong
"By the way, 2X has been known as an indicator of a cracked shaft.  The crack introduces asymmetrical stiffness so you get a "snapping" twice per revolution."

Perhaps true for a near mid-span crack, but the cracked coupling hub is at the END of the shaft!Walt


Walt, the company I previously worked for had about 125 documented cases of shaft crack. These are cases that are fully brought to closure, i. e., the shaft was positively determined to have a crack.  I am aware of at least two cases where a crack was suspected and both cases had the crack immediately behind the coupling, basically at the keyseat.  One was a high speed gearbox and the other a centrifugal compressor.  In the instance of the gearbox the shaft extension literally fell off the machine as it was being moved to a repair center!  In both of these cases 1X and 2X were high, with changing amplitude and phase.
RustyCas

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Walt, I am thinking that the crack in the hub at the setscrew caused the hub to be loose and rock back and forth causing the 2X.  

John, yes photos taken with machine running.  I just set the zoom and poke it in the opening at the bottom of the coupling guard. Camera is 18-24" away from the coupling.  (OBLIGATORY WARNING: Keep you hands clear of spinning stuff!)   Any digital camera with a flash will do this, though the clarity is probably better with a better camera (higher MP, better optics, stronger flash).  

I use an Olympus TG-3 (TG-4 is the current version) which is shock/water/dust proof.  It also has a "microscope" mode which will zoom to 44X and works great with their Light Guide, like a ring flash, but uses an LED (which you can also use instead of the flash).  It's a little heavier/bulkier than I'd like, but the little Canons I used to used only lasted 3-6 months because of the dust/moisture.



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Danny Harvey

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Although I didn't measure phase, I found high 2 x turning speed on a newly installed felt roll shaft journal and called it bent or cracked. Dye pentrant test confirmed the crack. Closer inspection showed that there was no radius at the step to relieve stress. Further ndt found similar cracks in several other new rolls.

Rusty,

Were the cracks visible when not running? 

We have one pump that uses a Woods Sureflex (same as lovejoy) Size 12 with an E sleeve too. It had a very high 2 x. We aligned it and found a badly distorted sleeve which took a sharp turn at 180 degrees on each half.

I wish I could say that we replaced it and the 2 x went away but I can't.  Instead, they let it run for 4 years, then replaced the coupling element.  Things changed, but damage was done. The center hung pump now has a high degree of axial movement. I haven't seen the latest data yet but I believe that we aligned it again this week so we might have some data to show.  

I may need to get a look at it with a strobe running if I can't get all the permits.

 
RustyCas

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Danny, this was just last week on my regular rounds so I don't have any feedback on what they found.  I suggested the pump be shut down until they had a chance to replace the coupling, which they probably will.  
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Danny Harvey

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Rusty,

A couple of comments I forgot to include:

1. The crack at the set screw may be from repeated overtightening which is probably due to the key looseness you suspect.

2. Stock bores on this type of coupling are at least .0005" over and as much as .002" over from TB Woods.

3. Sleeve damage like I encountered could have caused the damage you witnessed, especially if there is corresponding damage 180 degrees to what you caught.  

I think you should take several thousand more pictures like that until you get lucky enough to catch the opposite side.
RustyCas

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"several thousand more pictures".... [rolleyes]  I usually only take a burst of 8-10 pics to get what I'm looking for, which the camera does automatically, but I suspect someone as old and slow as you are would have to take a lot more.  [tongue]

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Walt Strong

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Reply with quote  #11 
John,
If you want to put the cracked coupling hub at the end of the shaft in the same category of your many experiences with cracked shafts, this is fine with me; no further argument.

The photo indicates the possibility that the coupling hub is loose on the shaft. Rusty's and Danny's comments also suggest a good possibility that the coupling hub is loose on the shaft. We will just have to wait for the all-important maintenance feedback that Rusty will provide.

Walt
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