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Filed under: Rollers, Traction --- Tim Walker @ 03:16 PM

I continue to run into applications where one side of a web can't be touched. Sometimes one side is freshly coated, another time the web is easily scratched, and recently, the web had a big part attached to it sticking out one side. It's hard to go over a roller with a big bump on your web.

The first choice in one-side contact is to design your line like a scroll. Place the unwind in the center of one side of the scroll and your winder in the other side of the scroll. If your roll loading is cantilevered (rolls go in and out sideways), you can form a pretty tight sprially path around the unwind, as many times as are needed for your tension, guiding, and processing plan. When your done with your unwind spiral, move over to the winder side and spiral inward as needed until you hit the windup (or sheeting, the more likely finale to the bumpy product. All rollers will rotate the same clockwise or counterclockwise direction.

For tension control, you can still have 2 or more zones, but driven rollers will likely have 90 degrees of wrap (and of course no nips). A rubber roller can support a good tension change with 90 degrees, but a vacuum suction roller can do even better (again use rubber for high friction, if possible). Tension feedback will likely be with a transducer roller, since most people prefer 180 degrees on dancer rollers.

Other tricks?

Continue reading"One-Sided Contact Web Handling"

Filed under: Rollers, Traction --- Tim Walker @ 07:23 PM

I've never seen where a groove is a problem because it is too small.

I have seen grooves that are too big, usually big meaning too wide, sometime meaning they are too deep.

I've never seen the math on this, but at some point a web will begin to fall into a groove. For films, this usually happens when the web thicknes is less than 0.002" for stiffer polymers or less than 0.004" for softer polymers. For these materials, I think 0.25" is definitely too wide. As you go thinner, less than 0.001" thick films, even 0.1" wide grooves may be too much. The groove sensitivity drops with lower tension and when the wrap angle is near zero.

How about really wide grooves? (continued)

Continue reading"When do roller grooves get to be a problem?"

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 11:58 AM

John Bastarache wrote in with an interesting question:

"I have a question about tension in the sheet. If a sheet is 100 inches wide and trimmed down to 80 inches wide, is there more tension in the sheet at the reduced cross direction of 80 inches. Keeping in mind, that the draw is a constant."

If the tension was created by a dancer roller or applied torque, then the tension would increase on a PLI (pounds per inch of width) or psi basis.

However, you've included that the tension is created by draw. If you read my last two columns from a pffc-online.com, you'll learn the fundamentals of draw control. Draw creates tension through the web's material property, modulus, relating stretch (or strain) to stress (or tension).

Tension (lbs/in) = strain x thickness (in) x modulus (psi)

Therefore, the tension created by stretching (or drawing) on a force per width basis is independent of web width. However, if you are wondering about the total tension force (lbs), this will go up with width.

Force of Tension (lbs) = strain x thickness x width x modulus.

You can think of the t*w*E (thickness x width x modulus) as the web's spring constant.

Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 11:44 AM

Mike Flanagan wrote in asking this great question.
The short answer is YES.

Here's Mike's question in whole "Are there not some dynamics involved in guiding that can create wrinkles downstream from guides that are improperly installed? Seems to me I have seen wrinkles show up on some steering guide applications that have to do with overly short entry spans. Is that the case?"

Many wrinkles are created by grossly uneven tensions across the web. Usually this is caused by misalignment, but any thing that overly bends or twists the web can do it. How can a guide do this?

1. A guide may be over steering. If a guide is poorly tuned or the geometry is off (like a edge sensor too far downstream) the lateral oscillation of the web at the guides output can be worse than the error it was meant to correct.

2. If spans are set short and corrections are large, the severe bending or twisting may be too much for the web. This can happen when two sequential guides fight each other or the web lines has a dominate pull to one side. If an unwind guide sensor is misplaced and guides the web to one side, the next correctly set guide will pull the web back, but if the correction is extreme, the result may be a wrinkle. A smart positioning of an upstream guide can reduce the work of a downstream guide and eliminate the problem. Usually guides don't talk to each other, but this is a case where teamwork among web guides can solve a problem.

3. Get the geometry right (cont'd)

Continue reading"Can a Web Guide Create Wrinkles?"

Filed under: Slitting, Cutting --- Reiny Schable @ 02:45 PM

THE NIP MUST BE CLOSED. In the rotary shear process, materials are slit in the nip between two overlapping, hardened metal disks that create stress in the shear mode sufficient to sever the product.

Continue reading"The open nip is a major cause of poor slitting"

Filed under: General Business Topics --- Tim Walker @ 06:18 AM

TJWalker reporting from IWEB '05 in Stillwater, OK.
This is the 8th International Conference on Web Handling held at Oklahoma State University, sponsored by their Web Handling Research Center.

About 110 attendees from 45+ companies and 6 universities, including several attendees from Asia and Europe.

What going on here? Besides some good BBQ and music last night with Oklahoma hospitality, the IWEB is the most advanced educational opportunity for web handling and winding technology. The attendees represent the top experts in handling paper, films, foils, nonwovens, and other continuous thin materials. At 100+ people, it's a relatively small conference, but for understanding why things wrinkle, scratch, vary their tension, or make bad rolls, it hard to find a better group to handle it.

Of course, much of it is over my head. Not the concepts and conclusions, but advanced calculus or computer modeling is not my stength. Can you learn something at IWEB without the math? Certainly algebra is required. If you can convert from the conference metric units into lbs and ft its a plus. The biggest gain is learning what is known and what isn't. What problems are understood and what aren't.

I'll file a series of posts on my highlights of the conference. Stay tuned.