The Importance of Running Centered

The other day, someone asked me the following questions that I thought my loyal blog fans might appreciate:

How important is it to run centered on anti-wrinkle/spreading rollers?

My student asked further: I know we should control a web to run in the center of these rollers, but is there any acceptable range for the web to run off center?

Further still: What problems occur if the web is overly off center on spreader rollers?

These are good questions. No one has ever asked these questions before, and I don't know of any research on non-centered use of spreader rollers.

Running off center on a spreader will tend to pull the web more off center. The nature of spreaders is to try and pull the web to the left and right. An off-center web would have unequal pulling left to right, leading to a lateral shift in the web even more off center.

Pulling the web laterally will bend and shear the web like a misaligned roller. What I don't know is when is the roller's spreading benefit lost due to this added bending.

Bending that creates shear wrinkles is often quite small, only 1–2 mm (40-80 mils) of lateral shifting. Based on this and my experience, I'd say a web could be misaligned by up to 2% of web width without a problem, off center by 1 in. on a 50-in. wide web (25 mm for a 1200-mm web), but I'd be concerned for misalignment of over 5% (more than 2 in. for a 50-in. web or 50 mm for a 1000-mm web).

I think this would be an interesting experiment to try.

Tim Walker



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