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Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 10:00 AM

My last column in Paper, Film, and Foil Converter magazine was on how to drive a winding roll, comparing and contrasting surface and center winding. One main point I make is surface winding tends to make a looser roll.

This prompted the following advice from one of my past clients.

He said that I should be careful when I say that a surface winder winds a looser roll. He has a surface winder that can't wind a roll loose enough. The rolls are so tight on his thin film product that it magnifies the gauge bands to point where the customer rejects the product. The winder is a true surface driven winder with no drive on the core and the roll weight creates the surface winding nip pressure. (So as the roll diameter and weight increases, the surface winding nip pressure goes up.)

My reply:

But I’m still going to stick to my ‘surface winding will be less tight’ statement. If you compare winding the same roll on a pure surface winder and a pure center winder using the same winding tension and winding nip force, the surface wound roll will be looser. In surface winding, the nip load is the #1 variable to determine roll tightness for a given material and roll geometry.

Why are your surface-wound rolls extra hard? I believe it is due to excessive nip load. It sounds like the roll’s weight controls your surface winding nip load (pounds per inch of width that the roll presses against the surface driving roll). I’m guessing your surface winder has the core positioned on the top or 12:00 position of the surface drive roll. Sometime the top load surface winders will have a ‘rider roller’ that allows the surface winding nip to be set above the roll’s weight, but don’t really have an option to relieve the gravity effect or run a nip load less than the roll’s weight.

Another surface winder design loads the core from the side (the 3:00 or 9:00) position and pneumatically controls the load to the optimum value, independent of roll weight. In this design, the surface winding nip load can be less, sometime much less, than the roll’s weight.

What is too high in surface winding nip load? The first estimate of surface winding tension is the nip load multiplied by the web-web friction coefficient. So if you roll weighs 10 pounds per inch of width (say winding polyester, density of 0.05 lbs/in^3, on a 4-inch OD core to a 9-in final diameter), then the effective winding tension is 10 x 0.25 (typical PET friction coefficient) or 2.5 PLI. If this was a 3-mil film, no problem, but if you are winding 0.5 or 1 mils film, the 2.5 PLI is way too high.

Filed under: General Business Topics --- webmaster#1 @ 03:35 PM

A wine company out of Australia has introduced a revolutionary new solution that delivers the wine and a glass from which to drink it all in one package. Hardy Wine Company has unveiled a product it calls the "Shuttle," which reportedly is designed to be served in areas where glass is not permitted (makes sense); meet the needs of those who prefer "safe," sealed, single-serve containers in group situations (also makes sense); and enable quick delivery of large quantities of alcohol in crowd settings (kind of scary). But however you look at it, this product truly represents the innovation that characterizes the converting and packaging market. The delivery and usability of a product has become just as important as the quality of the product, and retailers are having to find ways to differentiate themselves to strengthen market share. I can just see the wealthy crowds picnicking at the symphony this summer with their wine Shuttles and single-serve string cheeses ...
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 11:38 AM

Question:
When web (PET) is wound after slitting, the winding tension should be changed in case of paper core and plastic core?

When winding PET on a paper core you may need a high starting tension than for the plastic core. It depends on what defects you are seeing. A plastic core is usually stiffer than a paper core and will usually create higher pressure near the core for the same winding conditions. A paper core may show more spoking or starring defects. A plastic core may show more core impression or blocking defects.

Filed under: General Business Topics --- khevenor @ 01:40 PM

An article recently in USA Today revealed Wal-Mart's plans to "go green." The company is putting in place a number of programs to encourage sustainability and motivate its suppliers to produce goods that do no harm to the environment. Part of this plan calls for smaller or reduced packaging and more recyclable content.
All this sounds good for the environment, but it will also be good for Wal-Mart. Part of the statement from the company says "Wal-Mart said Friday that it will start 'grading' suppliers on how well they do. Less, in this case, is more. When it cut excess packaging on its private-label line of toys, Kid Connection, the company estimates it saved $2.4 million a year in shipping costs, 3800 trees and 1 million barrels of oil. Downsizing a product's package is tricky, though. Products are sold on store shelves by volume. Bigger packages get more shelf space and can catch consumers' eyes better."
Is this good for the package printing and converting industry in the long run? I think that ultimately, we must all work toward what is good for the environment, even if that means an adjustment in our industry today. What do you think?
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 08:00 AM

Contributed by Tim Walker-

Question:

I have a three layers product of thin paper/LDPE/thin paper (extrusion laminated product). Our customer complains of sagging or bagginess at the product edges. I expected that PE thickness variation could be the cause, but what about other factors such as: 1) alignment between guide roller and nip roller, 2) temperature variation of cooling roller, and 3) wound roll stiffness.

For any cause of web sagging or bagginess, you must find a cause that fits the shape or location of the bagginess. Whenever I have a suspected cause of a defect, I try an experiment to see if I can make the defect intentionally or make it worse. To test the theory of whether (1), (2), or (3) contribute to bagginess, try making these worse or shifting them from side to side and see if the bagginess follows. If yes, then you have proven these as real bagginess cause.

Answer:

From my experience I don’t expect that guide or nip roller alignment will create bagginess, but it is simple to try an experiment with misaligned rollers and find out. I also don’t suspect that cooling roller temperature variations are the bagginess source. The wound roll stiffness or hardness variations should be directly related to the crossweb thickness variations. I do expect that there will be a strong correlation between thicker lanes and where bagginess forms. Also, tighter rolls will have higher stresses and lead to more yielding (and bagginess), looser winding conditions should reduce bagginess.

Another factor to consider with paper products is moisture. If you dry out paper, wind it, then expose the roll edges to a humid environment, then edges may become baggy relative to the center of the web. Try wrapping you rolls with a moisture barrier during storage and shipping and see if the bagginess is reduced.

Filed under: General Business Topics --- khevenor @ 08:47 PM

Earlier today, I had the opportunity to visit and tour Accord Carton in Alsip, Illinois. Still being fairly new in this segment of the graphic arts industry, this was my first experience in a package printing facility, and more specifically, in a folding carton plant. But having toured dozens of commercial printing plants over the past 15 years, I was struck by how smooth and calm the atmosphere was. I know that part of this is due to the excellent third-generation management of the Codo family, but I also think that to some extent it's because of some of the key differences between commercial printing and package printing. Much of the work in Accord Carton is contracted on a regular basis and involves fairly long runs, as opposed to the unpredictable flow of short-run, quick turnaround jobs that often flood a commercial printing facility. And also, the nature of packaging work means that the finishing and converting must be tightly integrated into the process to allow for a smooth flow from raw material to finished product. If Accord Carton is indicative of the typical package printing plant, then the industry has a bright future. Using a variety of equipment from Bobst, Nordson, Kluge, Creo (now Kodak), Akiyama, and a brand-new 56-inch Roland 900 press from MAN Roland, the company is well positioned to grow and be passed down to future generations of the family.
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 08:00 AM

Contributed by Tim Walker:

Question:
When I have web thickness variations, I see meandering at my nipped drive roller. How do I prevent this?

Answer:
Two things with nipped roller I almost always recommend will reduce this problem. First, make sure the web wraps one of the two rollers at least 20-30 degrees before reaching the nip contact point. Second, keep the span length ahead of the nip short. The web wrap and traction it creates between the web and roller will help to isolate the upstream span from the nip force variations. The short span will be stiffer than a long span and have less meandering for the same stress variations.