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June 09, 2006
Do Rollers Reduce Unwind Tension Variations?
Question:
Does running a web through a 'z' pattern of rollers reduce tension variances? The 'z' pattern in question is made up of 4 rollers located immediately after the unwind.
Peter Krasucki
pkrasucki@rdspecialties.com
Answer:
Yes, to some degree, especially is the web had good friction on the roller (doesn't slip) and the rollers have modest to high inertia.
You can imagine a stopped web with stopped rollers. If you jerk on the web at the unwind and the web doesn't slip on the roller and the rollers don't turn, then NO tension shock would pass over the rollers.
A running web is different from this scenario. The tension or strain of the web travels with it. For a running web, if you change the unwind brake setting, the tension from the unwind to the next drive point will nominally go to the new level. So low frequency tesnion changes will pass through the system.
The benefit, if significant, will be in calming high frequency tension variations, where high frequency is relative to the span lengths (or the time to travel the span length). In some regards, longer spans will do more for tension noise attenuation than the rollers.
tjw
Posted by Tim Walker at June 9, 2006 08:10 AM
