- September 30, 2004, Timothy J. Walker TJWalker & Assoc. Inc.
Antiwrinkle rollers, like antiperspirants and anti-inflammatories, have a name that implies a cure to your problem.
But as with most remedies, read the directions and check for side effects. Here are some of my general directions for use of antiwrinkle rollers.
- Don't use an antiwrinkle roller if a standard idler will solve the problem. My first approach is always to try and resolve wrinkling by optimizing standard idler rollers. Remember that friction, wrap angle, span length, misalignment, and deflection are all wrinkle contributor or enablers. Subtle adjustments in any of these variables may solve your wrinkle problem with minimal expense or upset to your process. For a new process, I often don't recommend any antiwrinkle rollers, but be prepared to install them on a need basis.
- Apply to upstream wrinkles first. Always fight wrinkles by eliminating the farthest upstream wrinkle first. Wrinkles flow downstream. Antiwrinkle rollers are designed to prevent wrinkles, not pull them out. This is a remedy, not a bandage.
- More is not better. Use only the number of antiwrinkle rollers needed. If an antiwrinkle roller works, don't try to make it work “better” by modifying it for a stronger effect. More diameter change, more bow, and more stretch all lead to diminishing or detrimental returns.
- Try tape collars first. The secret weapon of an expert web handler is knowing how to apply simple masking tape bands on the edge of an idler roller to eliminate wrinkles. After doing this trick for years, I'm still amazed to see it work and get a process back up and running. The biggest limitation of this trick is working with width changes. A concave roller mechanism works by concentrating tension at the edge. A web width change moves the edge positions, eliminating or reversing the tape roller or concave roller benefits.
- Know the best traction for your antiwrinkle roller. Bowed rollers, flat expanders, flexible expanders, and edge nips rely on the parallel entry rule. Concave rollers use induced bending and the parallel entry roller to drive the web to lateral tautness. Both types of antiwrinkle rollers need good traction. Conversely, the mechanism behind hyper-crowned rollers and D-bars counts on slipping traction. Whether relying on good or poor traction, an antiwrinkle roller will lose or reverse its benefit if the traction condition switches.
- High line speed or air lubrication may negate an antiwrinkle roller's benefits. Air lubrication is the top source of antiwrinkle-negating traction loss, especially with high line speeds, large diameters, low tension, and the antiwrinkle killer — smooth surfaces. If you have line speeds over 300 fpm, I advise a textured or rough surface for any traction-dependent antiwrinkle roller. Concave rollers are the most dramatically dependent on good traction. Without good traction, they reverse their mechanism, becoming web wrinklers, not spreaders. Some flat-sleeved expanders are known to “balloon” at speeds over 100 fpm, transitioning from flat expanders to crowned wrinklers.
- Bowed and sleeved expander rollers often are set up to wear out. Both have a rubber sleeve that stretches laterally as the roller turns. If the web and sleeve stretch together, no problem. To avoid slip and abrasion, the web-roller friction must be higher than what is needed to stretch the web. Any sleeve stretching over 2% — 3% while in contact with the web probably is spreading and abrading.
- Antiwrinkle rollers increase lateral shifting. An antiwrinkle roller pulls the web left and right but rarely in perfect balance. The pulling imbalance will vary with tension, bagginess, and friction variations, creating an unwanted web wander.
Use antiwrinkle rollers ahead of nips. Many converters have found by experience that their process or the quality of their input material requires antiwrinkle rollers before slitting, coating, laminating, winding, and other nipping process steps. Getting a baggy web through a nip is one of the top challenges of web handling. An antiwrinkle roller may not guarantee success, but it will lower your baggy web intolerance.
- Use antiwrinkle rollers when the web grows widthwise. If you know the web expands in your process due to heating, moisturizing, tension changes, or viscoelastic recovery, antiwrinkle roller spreading to prevent wrinkles is a good idea.
There's one more thing I'd put on the side of the antiwrinkle roller's box — consult your web handling “doctor” before using.
Timothy J. Walker has 20+ years of experience in web handling processes. He specializes in web handling education, process development, and production problem solving. Contact him at 651/686-5400; email@example.com; tjwa.com.