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Web Handling & Converting

Blogmaster: Dr. David Roisum

12

I am having trouble figuring out what tension I have at the finish of my wind. I have a starting rewind tension of 80 N and my taper tension set is 35%. I had the idea that then we should end with a final tension of .35 X 80 N = 28 N, but is not that way, we have a final tension of 53 N. How can I figure it out?

Join the club. The concept and execution of winding taper should have long ago been buried. It was designed as a convenience for the lazy electrical engineer; not for any of the customers (operator or wound roll). With ubiquitous availability of PLC’s and computers, there is no reason to continue this taper nonsense. However, for those of you with old machines and lazy electrical engineers, let me offer a brief discussion of how to figure out finishing tension. From this you will see clearly why taper does not serve the customers (operator or wound roll) nearly as well as the straightforward four-point method that defines starting and ending tensions directly. This discussion is needed because these lazy electrical engineers at the winder machine builders not only gave you taper (gain) because it was easy for them, they also offered no instruction, no calibration, and no insight and what to do to maintain or use the taper controls.

On most machines, the percent taper is the amount the tension is reduced at the maximum diameter roll diameter of the machine. So, you need to know the wound roll size you are currently making and the capacity of the machine. So, let us assume 0.4m and 0.5 meters respectively. Then the tension would taper 0.35 x 80 = 28. However, you are winding only (for this example) a 0.4m roll and the tension tapers across the entire diameter range so for your roll that would be (0.4/0.5) x 28 or tapering down 22. This is subtracted from the original 80N for a final tension at the end of the roll of 80-22 = 58. Or, it is possible that the calculation for taper started at a zero diameter instead of core diameter.  Why did you measure 53 N on the load cell? Simple, something is not in calibration. See rant above.

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Comments

#123 Dhananjay
Saturday, April 16, 2011 8:39 PM
How taper tension can solve the problem of horizontal winding marks near core and after joints in winded laminate rolls? Web temperature can affect the winding impression & tunneling effect in laminate?
#125 Jay
Monday, April 18, 2011 10:03 PM
Well, after reading converting blog I did not have any clue on web or coil edge straightness problems any in industry is facing.

The problem I have now is thin(0.0012") aluminum sheets are wound to 5 feet dia. on 16" fibre core.

While sheet is travelling at a speed of 4000 FPM with 2000 psi tension, I see the sheet is steering on the on all rollers about an +/- 1/2" (bilateral steer) some time causing sheet to steer one side and werkc the coil while slitting.

All the rollers are checked for square and level looks good.

The edge guide system is in place to control the sheet to width movement towards the slitter.

Any feed back will be appreciated.

Thanks
JBB
#129 David Roisum
Saturday, April 23, 2011 6:35 AM
JBB,

There are several things that can cause the web to steer.

1) poor guiding
2) web bagginess
3) roller diameter variation across the width
4) roller MISALIGNMENT

You said that you checked alignment. I'd guess not. Hand tools are totally inadequate for aligment; more dangerous than useful. Optical methods that can read to 0.001" (or lasers or gyroscopes) are the ONLY measurements good enough for metal. You can calculate required alignment tolerances using the TopWeb program by Rheologic.
#131 David Roisum
Saturday, April 23, 2011 6:55 AM
Dhananjay,

Taper has no effect on this problem nor most any other winding problem (except one of five types of telescoping and one of seven types of starring). Instead, if I read you correct, the tail (or core) is marking the layers above. If so, wind as loose as possible at the core (without causing other problems) and use little or no taper. Also, make sure the first wrap is dead smooth on the core.
#189 timothy j walker
Wednesday, August 17, 2011 4:52 PM
Large diameter + 4000 fpm = super air entrainment and lubrication.

Are you using a nip roller at winding?

tjw
#191 David Roisum
Friday, August 19, 2011 7:50 AM
Great question. Nip rollers are a given in the paper industry at those speeds. However, foil is a mixed bag due to the possibility of marking the delicate sheet with a nip. Their rolls (intentionally and unintentionally) tend to football shape which helps air in the top few layers to escape, but it may not be anywhere near enough.

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Blogmaster

David Roisum photo

Dr. David Roisum

Dr. Roisum is a well-known authority in the area of web handling and converting. He has authored seven books, including Winding, Rollers and Web-Handling and has coauthored or edited several others. He was a technical editor for Converting Magazine with a monthly column entitled "Web Works." An accomplished professional speaker and instructor, Roisum has been praised for his skill at translating highly technical information into a common sense practical reference. Dave has been honored by TAPPI with their Finishing & Converting Division Award, Thomas W. Busch Prize and Finest Faculty awards and is a TAPPI Fellow. Dave received his Ph.D. from the Web Handling Research Center where he later became an Industrial Advisory Board member.

Dave has worked for the Beloit Corporation as a designer of winding machinery and later as a manager of research, and for Kimberly-Clark as a converting expert serving all business units. He is now a principal of Finishing Technologies Inc., providing consulting services to more than 300 clients who convert or manufacture: paper, film, foil, nonwovens, textiles and many other materials. He has accumulated much practical experience working in nearly 1,000 plants over the course of more than three decades.

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