PFFC - May 2008 - (Page 12)

WEB LINES A Recipe for Scratching his month we’re having another session performance, reducing roller inertia, minimizing of “Do the Opposite.” I’m going to tell acceleration rates, and reducing tension differentials you how to make great scratches. The across driven rollers. solution to stopping scratches is to “Do Stress Concentration | Solid materials react to the Opposite.” Eliminate these factors, even just stress or force exerted over an area. High stress, one, and your scratches will be gone. which is easier to get when the area is small, There are five prerequisites to create a scratch is needed to cause abrading and scratching. or abrasive wear. All five are required to create the Debris, burrs, or other surface imperfections scratch. Let’s review them. act to focus normal Contact | The web forces as concentrators must be touching of available forces into The something—roller, any high stress. nonmoving equipment, Do the opposite: in stopping scratches or itself—in the winding Eliminate dust and or unwinding roll. debris particles from the is to stop relative Do the opposite: If you incoming web, roller don’t touch the web, you surfaces, and process motion by using can’t scratch it. Eliminate environment. Specify and inspect the incoming unnecessary rollers. Use web for cleanliness. air turns or air floatation nozzles in place of rollers. Prevent roller slippage roller surfaces. Use air or fluid to fully and associated debris lubricate the web/roller generation. Design interface. For narrow and processes and equipment stiff webs, use an undercut or dumbbell-shaped for cleanliness by eliminating debris sources or roller that makes contact only at the web edges. Use isolating the web from them. Ensure roller surfaces a tenter or edge nips to hold the web. are even and free of burrs. Force | The web must be pushing against the Relative Hardness | When abrasive wear occurs, scratch-causing surface with sufficient force. it is usually the softer surface that loses more Do the opposite: The normal load or pressure material. Diamonds are the top of the hardness is created by the tension web pull over a radius. scale and usually will cut or abrade anything else. Reduce pressure of contact by decreasing web Do the opposite: The first four factors will tension or increasing roller radius. Reduce tension lead to some nice scratching, with more severe in a scratch-sensitive area by reducing the roller scratching on the softer of the two rubbing diameter in that area. For example, if the coated surfaces. Change from steel or aluminum rollers to center of a web is most important, machine a rubber-covered rollers, or wrap the rollers with a profile into all coated-side contact rollers to have softer material such as masking tape, cheesecloth, smaller diameter in the middle and carry most of fabric, or paper. the web tension at the uncoated edges. In my experience, the top factor in stopping Relative Motion | Two surfaces with matched scratches is to stop relative motion by using rough surface speeds may cause a gouge or pick out, but or textured roller surfaces. Many converters wrongly they are unlikely to cause a scratch. associate high roller roughness with more Do the opposite: Ensure the traction likelihood of scratching. Roughness available is greater than the traction without relative motion does not create demand. Increase available traction scratching. Rough or textured roller with larger wrap angle, high surfaces include micro-grooving, tension, and higher coefficient of dimpled tape, plasma sputtering, traction. Prevent lubrication by and many roller wrap options, such IDLER increasing roughness, increasing as fabric or cheesecloth. ROLLER porosity, or increasing surface Follow this plan and you will BEARINGS texture or grooving. Decrease the have the opposite of scratched webs: traction demand with low drag bearing happy customers. T By Timothy J. Walker Contributing Editor top factor rough or textured COMING NEXT MONTH Web handling expert Tim Walker, president of TJWalker+Assoc., has 20+ years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; tjwalker@tjwa.com; www.webhandling.com. 12 | MAY 2008 WWW.PFFC-ONLINE.COM http://www.webhandling.com http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - May 2008

PFFC - May 2008 Contents First Glance Calendar of Events From the Editor Web Lines Process Management News Clips Narrow Web & Label Reporter Narrow Web & Label What's New Products Labels/Sleeves Cover - European Converting Drupa New Product Digest What's New Products Services Directory Classified Marketplace Advertisers Index Experience Speaks

PFFC - May 2008

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