Air Entrapment
Entrapped air is a cushion of air between the web an the roll and is often found when rolls do not spin up to line speed. It becomes more of a problem as the line goes faster. Fox example, as plastic film has become stronger, it has been produced in thinner gauges. These lines can now be run at higher speeds, meaning air entrapment can become a problem.
When you get an air barrier buildup, the web loses contact with the roll. The roll then does not spin at the same speed. When it does make contact, it can skid and mark the web. This happens mostly with lighter tensions at high speeds. You get web flutter, side-to-side drifting, and lack of web control. If this happens on steering rolls, your web guide will quickly become ineffective.
In extreme cases of air entrapment, the web doesn't make any contact with the roll, and the roll speed is significantly less than the web speed. If all your rolls are wrapped or configured the same, and one isn't rotating, or it is rotating slowly, then suspect bearing drag. If the web is floating over numerous rolls, then suspect air entrapment.
Webex offers grooved or machined surface options that can help eliminate air entrapment, such as a spiral V-groove surface, a micro-groove surface and a diamond-knurled surface. A spiral V-groove design is specified most often for air entrapment problems. Other patterns are determined by specific application and type of web.
When considering solutions, think about what grooved configuration could be used without marking your web. If a standard V-groove won't work, you may need to use a micro-groove pattern, which is a much smaller groove but has a lot more of them. A diamond knurl and a micro-groove surface perform much the same. We can guide you though the various details of specifying the right surface configurations.
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