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Danny Harvey

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Reply with quote  #1 
it's been a while since I did analysis on a Dry Calendar stack but what I am seeing is very familiar.

All 5 rolls show vibration at 825 cpm with sidebands of 63 cpm. I'm afraid that I'm not certain of running speed. According to my measurements, the speed of the bottom roll is 75 rpm but that is based on a ten second count of revolutions. The speed is the same for three of the rolls and about 90 for the two smaller diameter rolls.

The highest amplitude is in the drive side of the bottom roll.

As I recall, this  might be something that is touched off by a speck of paper attached to the face of one of the rolls and that the 825 is the natural frequency of the roll that it impacts on.  This is then transferred through the entire stack because of the contact between the rolls.

I forgot to add:  The highest amplitude is on the Drive Side bearing on the bottom roll in the AXIAL direction.

Does anyone have another explanation?
David Eason

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Reply with quote  #2 
Danny,
Could one of the rolls be barred? 825/75=11 bars and 825/91.6=9 bars. The sidebands at 63 makes me suspect that there is a roll running at 63 that is barred, is that possible?

David Eason
Danny Harvey

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Reply with quote  #3 
David,

I had considered that possibility with this being 11 x running speed but I normally associate barring with a pneumatically loaded roll such as a press roll on a Yankee or a suction drum rather than a hydraulically loaded calendar. I'm not really sure about how this is loaded, though. All the Couch Rolls on the wet end have had the air bags removed and use counter weights so there have been some serious modifications of this machine over the years. I would think that the higher pressure from hydraulic loading would result in a much higher stiffness coefficient and a resulting much higher spring frequency.

Not knowing the exact roll speed further reinforces my belief that if you don't know running speed, you are guessing.

Thanks for the input and I'm certainly not eliminating that from the possible causes. I'll try to get a more precise speed, roll diameters and bearing id's next trip.
Aubrey

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Reply with quote  #4 
Hi Danny,

In a paper mill I used to work, we had a terrible issue with barring on our hydraulic stack.

The site was never able to get the barring under control. They changed out the stack every 6 weeks.

That was almost a decade ago. I haven’t heard from any of the guys lately about it.

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David Eason

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Reply with quote  #5 
Danny,
Is this stack within the paper machine, or is it away from the machine? Does it have a king and queen roll? If so, could one of them be running at 63? What are the rolls made of? The stacks that I used to deal with were influenced more by the size ratio of the rolls. Often, 3 revs of one roll would closely match 2 revs of the nipping roll. Life was always short in these cases. You said that you don't know the exact speed, but suppose the speeds you quoted were dead on. 3 revs of the 75-rpm roll is 2-1/2 revs of the 90-rpm roll. A 3 rev cycle of the 75-rpm roll would make 2 marks 180º apart on the 90-rpm roll. I'm chasing the "roll ratio rabbit" but the sidebands make me really curious about what's running 63 rpm. 825 is 13 orders of 63 too.

David Eason
Danny Harvey

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Reply with quote  #6 
Aubrey and David,

I'll address you both because some of the same info applies.

The only other similar machine I have worked on had a wet and a dry stack. The Wet Stack was immediately outside of the Dryer and the Dry Stack was about another 10 feet away.  The Wet Stack never showed any hints of this behavior but the Dry Stack did it quite often.  From my recollection, (long story but I temporarily don't have access to my server with RBMWare on it) there was always something that didn't quite work out mathematically on that one, too. It has 5 rolls. the two on the bottom are the same diameter, them two smaller and another of the first diameter on top. I might have a picture and an infrared image if I can get to them. The rolls are steel shells with journals and outboard bearings mounted in a slide block, pressed by a hydraulic cylinder on each side. I think it's fairly typical of what Black Clawson made for lined board machines.

I was pretty certain about the speeds.  I had to check all the roll speeds with a stopwatch/count and repeated the several times so the math David suggests might be right on the money. 

I'm starting to believe that this may be barring as opposed to a sticky bit of paper and grease on the roll face. I wonder if unequal pressure from the cylinders might be a contributor since this is a great deal more apparent on the drive side. 

Any ideas on why it might be axial? To me, axial movement in just about any center hung rotor means something is bent. But that's axial movement at running speed, not 11 x running speed or whatever this is. 

Thanks for the ideas.

As far as I know, nothing is running 63 anywhere near there.  There is a sheeter about another 10 feet down the line and it clunks along at about 560 cpm despite hardly ever being used. I don't know if you've ever seen one of these contraptions but it's a real contraption and I wouldn't be surprised to find 63 cpm in there but I didn't see it on the Black Claswon drive that feeds all the other works. I can't go any further than that without getting chewed up in the works.
Vibe-Rater

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Reply with quote  #7 
Danny, synchronous averaging if you can get tape on each roll and you have a suitable tach. If you still have access to CSI then a Speevu is perfect.  Plenty of averages. As well. rgds Oh I can see now no rbmware sorry.

OLi

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Reply with quote  #8 
If you have like 11xRPM and some axial and you have the same number of bolts in the end plate of the roller..... It happened a Friday afternoon in a press I think many years ago and it was maybe not 11 but it matched and the bolts were found to be loose..... We also checked with a eddy probe axially as we could do that while running and it was significant so everything is possible. Your rolls may be different but anyway just some crazy thing that happened.
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Sinski

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Reply with quote  #9 
Only thing I could add would be that it being evident axially could be a sign of uneven loading of the hydraulics from front to back and therefore any cover issues could be evident axially. I would be getting accurate speeds of each roll if that was possible as I think this will help narrow it down.
David Eason

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Reply with quote  #10 
Scissoring might be a possibility for the axial movement too.

David Eason
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Reply with quote  #11 
Hi David,

They should be doing regular nip impressions to avoid that. rgds
Danny Harvey

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Reply with quote  #12 
David,

I had considered the possibility of a misalignment between the bottom two rolls if that's what you mean by scissoring. I would not eliminate the possibility that this got a roll of paper dropped on it or run into by a lift over the years.

Vibe,

Yes, they probably should be, but I wouldn't guarantee that they do.  I don't know what the test lab is like.

Sinski,

From front to back, you mean Drive Side to Tending Side, right?  Pressure in the two cylinders is one of the things that I want to check.  Like Vibe said though, it seems like it would show up in the paper.
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Reply with quote  #13 
Danny,

Sinsk and I come from the same mold so I can confidently say he means front is tending side and back is drive side. rgds
Sinski

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Reply with quote  #14 
Danny

Yeah it would show up as different caliper from front to back of the sheet.

Yes front is tending side and rear is drive side.
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