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Hi professionals,

in Press section,  the roll at Tending side is supported by 2 air billows (nearly 70 degree ). bearing housing has 2 pivots one on the billow and one at the machine structure.

i experienced very high vib. at  at 1x roll, 7 Hz ( 20 in/s !!), i think it is resonance.

i performed  bump test on the air billow construction , relieved 7 Hz natural frequency, we tried to change the pressure and the tension of the felt but did not help.

how to fix such problem, the roll is only one year in operation.

waiting your help

regards

Pizo

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@Registered Member posted:

Hi professionals,

in Press section,  the roll at Tending side is supported by 2 air billows (nearly 70 degree ). bearing housing has 2 pivots one on the billow and one at the machine structure.

i experienced very high vib. at  at 1x roll, 7 Hz ( 20 in/s !!), i think it is resonance.

Have you tried changing the speed from 7 Hz (420 cpm) to a slower speed maybe 5 Hz (300rpm) to see if the vibration decreases? This might help confirm a resonant condition is present, unless this is something that has just shown up in the last week or so. If there has not been any changes or maintenance done on this roll, which has been in the machine for a "year" with not problems, resonance should not be the problem. Has there been a CLOSE inspection to see if anything has broken, became loose (bolts) or a balance weight came off the roll.

Which direction is it moving, horizontal, vertical, axial, or perpendicular to the "billows" pressures, etc?

If the bump test on the billow construction shows 7 Hz, has this just now started showing? If so, this may mean something has failed on one or both of the "billows".

I guess what I am saying is, "if the roll has been running a "year", what has changed to cause a resonant condition to appear"?

Has the cover on the roll been inspected. (unless it is just a steel cylinder with no covering) ?

If it has a stub bearing shaft that could become loose, has it been inspected for looseness?

Thanks, Ralph

i performed  bump test on the air billow construction , relieved 7 Hz natural frequency, we tried to change the pressure and the tension of the felt but did not help.

how to fix such problem, the roll is only one year in operation.

waiting your help

regards

Pizo

Helo ralph,

billow and pressure have been inspected, nothing found

The dominant 1x,  50 in/s is perpendicular to the billows , the vib. in the horizontal relative to that is just 6 in/s. resonance is always very directional.

Drive side vibration is just 0.3 in/s vertical. if the a balance weight came off the roll, at least the drive side would be little higher, or ?

i did not bump the billow construction before to have a comparison.

i made bump without felt gave me 6 Hz, and with felt 7 Hz !

The Roll is a steel cylinder with no covering, looks god

"I guess what I am saying is, "if the roll has been running a "year", what has changed to cause a resonant condition to appear"? " ,,,, some people claim that the high vibration disappear when a new felt is installed ( sound strange and not documented)

If it has a stub bearing shaft that could become loose, has it been inspected for looseness?

there are no harmonics in the spectrum. but i will look.

if i changed the roll and the vib did not become better, they will kill me

Best Regards

Pizo

Hi Pizo,

it has been many years since I have been involved with paper machines but I seem to remember the air bellows used in this application where dampened with fluid inside in some cases? Also it there any restraint perpendicular to the air bags? Guide/tension/dancer roles are usually restrained perpendicular to the bellows so vibration in this direction should be less than that axial to the air bags. The restraint is usually a swing arm or β€œchannel” guides.

good luck.

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