Tension calculation formula

Ask or answer questions related to the flexo pressroom environment

Moderator: Frank Burgos

Re: Tension calculation formula

Postby Randyskalba » Sat Mar 03, 2012 4:53 pm

Looking for more information for suggested tension settings,
We run a F & K 8 colour Wide Web and Print on Poly 1.00 to 1.50 Thick.

Everyone in our shop seems to have there own way to set tensions and im looking for feedback on what works best for anyone here.

Could you please provide me with how you would set your tensions for the following?

UNWIND:
INFEED NIP:
CHILL NIP:
REWIND:

Would you set the tension even across those 4 Tension zones?
Is it common to run more Tension at the Rewind of the press?
Any advice would be welcomed.
Randyskalba
 
Posts: 37
Joined: Wed Aug 19, 2009 8:18 pm

Re: Tension calculation formula

Postby SknyRussianHillbilly » Mon Mar 05, 2012 12:22 pm

Randyskalba wrote:Looking for more information for suggested tension settings,
We run a F & K 8 colour Wide Web and Print on Poly 1.00 to 1.50 Thick.

Everyone in our shop seems to have there own way to set tensions and im looking for feedback on what works best for anyone here.

Could you please provide me with how you would set your tensions for the following?

UNWIND:
INFEED NIP:
CHILL NIP:
REWIND:

Would you set the tension even across those 4 Tension zones?
Is it common to run more Tension at the Rewind of the press?
Any advice would be welcomed.


Hi Randy:
As you probably already know, PE is pretty extensible, and can likely run at a lower tensions than the .5-1.0 lbs per linear inch / per mil of thickness, that I issued as good initial numbers earlier. At 1.0 lbs PLI you could probably get a snapback on your print of 1/2" per foot on 1mil poly.
I generally run the lowest tension I can to maintain web control. Too low and you can get web weave and other things like wrinkes/creases...Too high and you distort your print length. If you are winding for final shipment, the roll has to be more critically wound than if you have a separate finishing wind. Winding tensions on press are also more critical if you slit on press. We generallly wind a little on the soft side and let slitting handle the finished roll because everything here hits the slitter.

We generally increase tension a little at each zone, and then decrease the tension in winding because the lay on rolls have a tendency to increase roll tightness by a nipping roll effect. If I were running paper or board instead of an extensible unsupported film, I would probably be running a higher tension in winding than through the machine. Too much winding tension on an extensible film and you can crush the core, or even cause ink transfer to the reverse side and block the roll.

To answer you with specific numbers I am going to use a 40" width 1.0 mil material through the press and .3 lbs per linear inch as the starting number and then adjust the others to the unwind. I would problably start at the same place for 1.25 or 1.5 guage PE material as well.
Unwind - 12 lbs.
Infeed nip - 13-14 lbs
Chill nip - 14-15 lbs
Rewind nip - 10 lbs with a 35-50% taper at 30" O.D. depending on the image.

1) first thing I would do is make sure that the web looks good through the press, no wrinkles, minimal weave, no bags. If we can drop tension a little, we generally do, and higher speed helps with web control. We go higher in tension only if we have to.
2) second, after setting print, I would check image repeats and make sure they fall in tolerance. Any modification to initial infeed nip and chill roll nip settings can change the print repeat.
3) We frequently need to make winding corrections based on ink coverages. A heavy continuous coverage will have the tendency to translate into a much tighter wind in the ink area vs. non ink area. Lay on rolls and pressures also have an effect. I wish that I had some hard fast numbers to use on winding, but I don't, it is sometimes on a case by case basis.

Hope I have been of some help to you.

Now can I impose for some help from you Randy?
You said that everyone in our shop seems to have their own way of setting tensions.
If you can expound on any of the methodolgies that you have heard, maybe one of us can get a trinket to help us out of a jam sometime.

Thanks a bunch,
Bill
SknyRussianHillbilly
 
Posts: 104
Joined: Tue Apr 21, 2009 3:45 pm

Re: Tension calculation formula

Postby Brian » Mon Mar 05, 2012 5:56 pm

There's a great article titled "Web Handling - A Challenge" in Flexo Gravure Int'l dated 3/2011. Good enough for me to laminate and hang in our shop for all the operators. It goes over, in detail, the calculations used for deriving the proper tension values. If you can't find it i can scan it in and e-mail to you.....or to Frank and he can e-mail it on.
Brian
 
Posts: 4
Joined: Tue Sep 25, 2007 4:26 pm

Re: Tension calculation formula

Postby Frank Burgos » Mon Mar 05, 2012 6:01 pm

Yep. I'll be happy to forward. Please send me one, Brian. I receive that magazine, but I don't have that issue.

Thanks,
Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

Re: Tension calculation formula

Postby dkelley » Tue Mar 06, 2012 8:02 am

I would also like a copy of the magazine article
dkelley
 
Posts: 263
Joined: Fri Jan 08, 2010 12:26 pm

Re: Tension calculation formula

Postby Dirtyworm » Wed Sep 19, 2012 10:54 am

A formula that I have learned years ago, and is a great starting point is........web width x web thickness x .2.....on a 30" 1.5mil web......30 x1.5 x.2 = 9lbs. That is a good starting point. I usually run 10% more in tunnel and 10% less on rewind with 30-35% taper for extesible, less taper for non-extensible
Dirtyworm
 
Posts: 2
Joined: Tue Sep 18, 2012 10:04 am

Re: Tension calculation formula

Postby angelius » Mon Sep 24, 2012 5:21 pm

Hi, I would also like a copy of the magazine article and the calculator whenever you have time, thanks a lot.
angelius
 
Posts: 6
Joined: Mon Sep 24, 2012 5:16 pm

Re: Tension calculation formula

Postby Frank Burgos » Tue Sep 25, 2012 8:14 am

I sent you the calulator by email.

Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

Re: Tension calculation formula

Postby widewebflexo » Sat Dec 15, 2012 3:59 pm

Hey, I would also like a copy that article and tension calculator, if you have time to send it.
widewebflexo
 
Posts: 2
Joined: Sun May 06, 2012 11:57 am

Re: Tension calculation formula

Postby Frank Burgos » Sun Dec 16, 2012 12:45 pm

I just sent you a couple that I had. I know that one is in process, but it gives you an idea of the inputs.

Regards,
Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

Re: Tension calculation formula

Postby Frank Burgos » Sun Dec 16, 2012 12:46 pm

I just sent you a couple that I had. I know that one is in process, but it gives you an idea of the inputs.

Regards,
Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

Re: Tension calculation formula

Postby Ferrarista » Thu May 09, 2013 12:09 pm

Can somebody sent me the calc. or to upload and share the link. Thanks
Ferrarista
 
Posts: 19
Joined: Thu Mar 14, 2013 6:16 pm

Re: Tension calculation formula

Postby Frank Burgos » Sun May 12, 2013 10:25 am

Dear Ferrarista,

I have sent you two calculators. They are a work in progress and I don't recall where they are in development. Please let me know if you have any questions.

Regards,
Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

Re: Tension calculation formula

Postby jmhorwitz » Tue Jun 11, 2013 6:08 am

Hi Frank
I would like to get Tension Calculator too.
How do I calculate unwind and rewind tensions?
We use several materials on our lines, but the one that is giving the most problems is 12 microns Metalized Polyester glue laminated to 43 grams per sqm of paper. Tolerances here are very tight, and we get a lot of variations on eye spot distances
Thanks
jmhorwitz
 
Posts: 2
Joined: Mon Jun 10, 2013 9:45 pm

Re: Tension calculation formula

Postby Frank Burgos » Tue Jun 11, 2013 7:08 am

Hi JM,

I'm on the road, right now, but I'll hook you up when I get back to my hotel room.

Regards,
Frank
Frank Burgos
Site Admin
 
Posts: 1039
Joined: Wed Dec 31, 1969 8:00 pm
Location: North Carolina

PreviousNext

Return to Pressroom

Who is online

Users browsing this forum: Google [Bot] and 5 guests

cron