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May 31, 2005
Why Align Your Rollers?
Here's a Top 10 reasons to align your rollers.
#1 keeping the web on centerline.
The parallel entry rule makes the web want to track parallel to the directing a roller is spinning (which is perpendicular to its axis of rotation). Parallel rollers, with good traction, keep a web tracking parallel to the machine's centerline.
#2 Reduce wrinkles
Roller misalignment is a big cause of wrinkles, especially in thin webs. Wrinkle causes are additive. So if you have misalignment, it may not create a wrinkle by itself, but it will lower your threshold to wrinkling from cause X.
#3 Reduce breaks
Misaligned rollers create web path variations between lanes of the web, shifting the tension from average across the width to high on one or both sides. The reason I advise running web handling tension at 10-20% of bad tension (the load to break or yield the web) is to provide a safety factor against misalignment-induced tension variations.
More...
#4 Uniform Nip Pressure
An nipped process, whether coating, extruding, calendaring, embossing, printing, winding, or other, relies on parallelism of both rollers to create a uniform contact footprint and pressure.
#5 Nip Winding Roll Cylindricity
I advise that all winding nips should be designed to hold parallelism (vs. articulating with the roll's shape). This puts the squeeze on high spots, lets air into low spots, and promotes a cylinder-shaped wound roll.
#6 The Neutral Position of Adjustable Rollers
Some rollers have are intentionally twisted out of alignment with other rollers. This may be done to tighten a loose edge. I always advise that adjustable rollers have a clearly marked "trammed" position, so when the adjustment isn't needed, the roller can be returned to parallel.
#7-#10 OK, so far I have a Top 6. I'll have to see if four more reasons come to me. I could add "to keep roller alignment folks in business" or "my boss told me to", but I don't think that's a good enough reason.
Posted by Tim Walker at May 31, 2005 09:14 AM
Comments
We impregnate hot melt epoxy resins into carbon fibers in a web process. We have polymer covered pull nip rolls to pull the film and fiber webs into and through the line. We have found that if the polymer covered nip rolls are not aligned with each other, we get a differential advancement of the web through that station thereby inducing a camber into the web.
Posted by: Tommy VanHorne at July 11, 2005 01:43 PM
