Traction and Web Challenges FAQs
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Why is traction so important for an idler roller?
Traction is important because it is the only way to control the web as it winds its way through a machine. Without traction, a web is free to slide left and right and to slip over the roller. Printing registration is lost with side to side web movement and scratching occurs when the web slips over the slower moving roller.
What is Air Entrainment and how does it damage the web?
Air trapped between the web and the idler is one of the main causes of losing traction. The trapped layer of air acts like a lubricant which causes the web to slide over the roller rather than turn it. Once sliding occurs, traction is lost and the web is free to move left, right, and scratching occurs when the web slips over the slower moving roller.
How can I remove wrinkles from a web?
The WINertia AV roll with a reverse crown is a great way to spread a web and a very cost effective way to remove wrinkles.
How do Spiral Grooved rolls compare to lateral groove rolls?
Spiral grooves do not do an adequate job of eliminating air and hence, they lose traction at much lower speeds than a lateral groove roll. When the spiral grooves lose traction, the film tracks into the groove and drives the web toward the center. The WINertia AV lateral grooves are perpendicular to the web direction and the web cannot track down into the grooves. A video showing traction test results can be viewed on our resources page.
How can I prevent scratching on a web?
Using a WINertia AV roller which maintains constant traction is the best way to prevent scratching on a web. To some this might be counterintuitive as one of the myths of preventing web scratching is to use a very fine finish on a smooth roller. The problem with smooth idler rolls is that at higher speeds the web lifts off the roller which results in web scratching.
What is a spreader roll?
A spreader roll is any roller that spreads the web from the center out. Bowed and rubber covered spreader rolls can be effective but they are expensive to manufacture. The most cost effective spreader roll is the WINertia AV roll with a reverse-crown.
How does the idler alignment affect the web, even with slight contact?
Idler Alignment affects web skewing with greater wrap angles. The web needs traction with the idler in order to control it. Greater surface contact between the web and the idler minimize slipping. When wrap angles are less than < 15 degrees, there is so little contact between the web and the idler that misalignment of the idler becomes less of a factor. Slipping is very common with low wrap angles and causes web scratching. To maintain traction at low wrap angles use a WINertia AV roll or a WINtrac coated roll.
How does the wrap angle affect traction?
The higher the wrap angle the more surface area on the roller in contact with the web. This contact area allows the web to drive the dead-shaft idler roll. However, at web speeds over 300 feet per minute air entrainment still causes a loss of traction even with higher wrap angles.