AIMCAL's Web handling & Converting Blog, by David Roisum

The profile of most spreaders that are properly applied is flat. In other words, if you slit a uniform web and then spread, each gap would be precisely the same width if the slit widths were identical and proportional to width if not. Spreader profiles where people have made the most common error, overspreading for the available traction, will result in a spreader profile is frown shaped. You loose it on the ends first (which may cause wrinkling near the quarter points for reasons to involved to discuss here).
      However, some spreaders have an inherent profile. The expander rollers and the edge pull rollers have something like an 'M' shaped profile. We will leave it to the reader to study those spreaders and posit why. There is only one spreader, however, that has a profile that can be changed. By this I do not mean for example a variable bow spreader which you can alter the amount or level of spreading. Rather, the ability to target more spreading in one CD location and give up spreading in another CD location. That device is a rare type in the bent pipe spreader family. It is the D-bar that is used most commonly in spreading slits on a two-drum newsprint winder. Here, jacks spaced on perhaps 1 foot intervals allow the operator target a bit more here and a bit less there by distorting the shape of the bar very slightly from its nominal arc of a circle.
      Those in the know will use this type of thinking to look at spreading and wrinkling and roll run together type problems. First, what is the shape of the problem? More at the front, back, certain lane and so on. Second, what owns that shape? Is it the web or the spreader?

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Wed Aug 06 12:29:00 CDT 2008