Hello all. I have a problem with a suction press roll on a tissue machine. The rotational speed of the roll is 450-550rpm. The roll is 35700lbs., rubber covered with through drilled vacuum holes. A fabric runs with the roll and is nipped to a Yankee dryer (16'D) at 450pli. The roll itself is mounted on glycol bags for loading purposes and is driven by a motor gearbox arrangement through a large universal shaft. The vibration signature is dominated by 1x rpm regardless whether the roll is loaded or unloaded. The vibration level increase with speed up to .5ips at 520rpm. That's the highest we've gone before returning to an acceptable level of .24ips at 495rpm. The roll was balanced to G1.6 with .560mils ds and .111mils ts residual at 6000fpm which is about 550rpm on the roll. I have attached some samples of data from different planes including pivot pin data. If you have some time and can offer your opinion it would be most appreciated. Also, let me know if you need any more information. Thanks.
This message has been edited. Last edited by: vibbase,
On a next stop of the machine, check the roll for a possible detachment of the rubber cover. Begin to inspect on the NDE area of the roll where the vibration amplitudes are the highest.
Looks there is too big of an amplitude change (10X higher) from loaded to unloaded at the 520 rpm speed. At 475 rpm the amplitudes are almost the same loaded and unloaded.
I would look for a "knot" or "hard" place on the TS end of the roll since there is such a great difference in the loaded and unloaded amplitudes at 520 RPM.
What does the "nip" direction (contact point of the yankee and pressure roll) data look like?
Originally posted by Alec: On a next stop of the machine, check the roll for a possible detachment of the rubber cover. Begin to inspect on the NDE area of the roll where the vibration amplitudes are the highest.
We ruled out cover problems. The TIR is good. The cover is new and has been ground and checked for delamination.
ensing-dot-ron-at-irvingtissue-dot-ca
Posts: 450 | Location: Great White North | Registered: 21 February 2005
I would look at the drive shaft as well just to rule out over lubrication or something like that.
How about an inner race crack on the TS bearing? We had one that was caused by a misfit, ran for a while with very low bearing amplitudes and was undetected. I believe it started out as a 1X, until it started spalling.
Also, what do you have on your roll? Steam sparger? Misaligned catch pan between the felt on the backside of the roll? Anything touching that you just haven't looked at yet?
Posts: 16 | Location: Marcus Hook, PA | Registered: 11 March 2005
Bite my tongue from my previous post..Looks like radial readings are much higher than the axial readings.. that, from my past experience, would likely rule out the drive shaft universal joint problems.
Posts: 211 | Location: ALABAMA | Registered: 28 February 2005
Unloaded Vs Loaded? If you can unload the roll why not unnip it. That would answer the cover question. If it goes away I would starting looking at the U-joint. I've seen the u-joint type failure push in the axial, or show up in the radial. The only differance I can remember was the motor offset was greater in the failure that pushed the roll axial.
However, I have also seen where they had a defect in the cover. During a sheet break a wad had been forced through a set of rubber cover rolls. You couldn't see the damage with the naked eye. It would bump as long as the roll were nipped, loaded or not. The damaged spot was easy to see with an IR camera. It showed up as a hot spot about 2 ft in diameter. However, the waveform you supplied doesn't appear to have a bump type signiture which is strange in either case unless it's a balance issue.
What are the delt peaks out at around 25 to 35 HZ? I've seen something like on covers with loose spot. Sounds like you've got a good learning problem on your hands. Happy Hunting! Waylon
Posts: 146 | Location: Lafayette La | Registered: 01 March 2005
What is your definition of "unloaded"? Waylon's and mine and maybe your's may be different. Mine is simply unloading the bags so the pressure roll is not touching the yankee and allowed to run solo.
And yours is---------?
What are the airbags doing during the high vibration? Bouncing like crazy?
Next time you go down try an impact test in the horizontal direction on the roll. I know the roll is heavy, but a good 4 foot 4X4 timber should excite something. What about one on the doctor blade mounting mechanism also, with the transducer on the roll and also on the doctor mechanism horizontal and vertical? Sounds far fetched, but I know from a case history where the doctor blade mount was resonant at particular FPM speed and made the pressure roll bounce baddddddd.
Another question------ Why is your low end cutoff so high? Looks like it may be set at 300 CPM.
The roll is away from the nip (1" gap)not touching.
quote:
What are the airbags doing during the high vibration? Bouncing like crazy?
They are still and quiet, no movement.
quote:
Another question------ Why is your low end cutoff so high? Looks like it may be set at 300 CPM.
The dataPAC 1500 does not do well with a lower cutoff. The default is 21.6cpm and the ranging time is excessive and unreliable. I have used digital (RSS) cutoff at 30 cpm with some success but in this case, 318 is the default and is suitable because the dominant vibration is 1x which is around 500cpm.
ensing-dot-ron-at-irvingtissue-dot-ca
Posts: 450 | Location: Great White North | Registered: 21 February 2005
could anything have happened that changed the balance of this roll ? such as weights coming off, being removed, etc.?
good luck... i am betting you get to bottom of this soon, could be after this roll removed and new roll installed you find problem while this roll is being rebuilt.
This message has been edited. Last edited by: MikeH,
Posts: 211 | Location: ALABAMA | Registered: 28 February 2005
Hey Mike; I can't look at the cardon shaft it's covered completely. We are now looking at resonance of the supporting frame(?) since two different although similar design rolls behave in the same manner in this position. The supporting structure/loading system was previously only run up to about 4500f/min until we rebuilt this machine with a larger dryer. So, we're going to run another test with the roll unloaded and see if we can get past the resonance zone (if it exists ).
ensing-dot-ron-at-irvingtissue-dot-ca
Posts: 450 | Location: Great White North | Registered: 21 February 2005
Originally posted by vibbase: Hey Mike; I can't look at the cardon shaft it's covered completely.
not that this is your problem, but we learned to cut out the guard around the cardon shaft to allow us to inspect on the run with a strobe light, installed a hinged flap with snap lock to hold secure while running, has helped on several occasions to identify a worn out U Joint.
Posts: 211 | Location: ALABAMA | Registered: 28 February 2005
We tried to run the machine up through the "problem" speed but had to quit because of problems with a slack felt. It's still on the agenda. I'll keep you posted.
ensing-dot-ron-at-irvingtissue-dot-ca
Posts: 450 | Location: Great White North | Registered: 21 February 2005
The latest. With the advice of the OEM, we tested the roll bearing by wrapping it with a chain and placing a jack in between the housing and pivot arm similar to what is shown as the green bracket in the attached drawing. The result was a decrease in 1x vibration from .163ips to .025ips. This was at 495 rpm but we need to run it up to speed to confirm. The idea was to dampen the support for the roll which is assumed to be in resonance by increasing the stiffness of the system. This bracket as shown in the attached drawing would also be installed on the drive end of the roll. The only problem is we haven't actually been able to confirm resonance because as we increas speed, the vibration increases. We need to run the roll up to 550 rpm at least and see a drop in vibration to prove resonance. Either that or do an FRF or bump test.
ensing-dot-ron-at-irvingtissue-dot-ca
Posts: 450 | Location: Great White North | Registered: 21 February 2005
