Last month we looked at the bilge or the round part of the roll. We concluded that gage profile is most problematic and often best read there. Now we turn our attention to the ends of the roll with a bold statement. If you care about your processes, if you care about your customer, then you must care about roll edge quality. The ideal is often referred to as "book end," though real book ends are not nearly good enough for many rolls. Rather, a better visual analogy would be roll ends that look like they were cut by a laser and polished.

Wound roll edge quality issues could be broken into performance and cosmetic categories. Some performance issues are rejectable. For example, web width could vary throughout the roll for many reasons. If, however, the customer makes 8½× 11 in. sheets, the width had better be close to 8.5 in. The width tolerance of many film and paper rolls may be 1/16 in. or even 1/32 in. In either case, the tape measures you find in hardware stores, even name brand, are not accurate enough for tolerances this small. Certified tape measures or rulers are required.

Curiously, the width of the body of the roll is wider than the top where measurements are taken. This is due to inviolate physics where interlayer pressure due to winding causes the width to grow because of the Poisson effect. This growth of the body width can be quite large on products such as nonwovens and textiles, but can also be seen on most other products if you look closely.

Another performance issue would be offsets. Here, a layer or layers are the proper width, but do not align adequately with their neighbors. This can cause problems with registration on the customer's machine if they do not have a guide. However, even with a guide, the offset may exceed the travel or rate of correction of the guide and pass some of the initial edge position error onto the final product. Another problem with offsets is that the roll edge is very much more susceptible to handling damage.

Other performance issues relate to the cut edge itself, rather than how they align on the wound roll. Perhaps the greatest sin in the paper industry is fuzzy edges. Not that fuzziness itself is a problem, but rather because fuzzy edges are usually accompanied by dust which fouls printing equipment. Thus, fuzzy edges are a proxy for the real problem of dust. In the film industry, it may be angel hair—which are tiny threads that got extruded by the blade rather than cleanly cut. Similar issues are found with the skippy cuts that are the bane of score cutting.

In truth, most features seen on the edge of a roll are cosmetic rather than performance-related. As a practical matter, however, it makes no difference whatsoever if the defect is "merely" cosmetic. The results will be identical. Customers are free to attach that appearance to any trouble they have, with or without sound reasoning. If you have any visible blemish, you put yourself at a competitive disadvantage, just as if you send customers a performance problem. Perception is the only reality here.

To those with a mechanistic world view, I will offer this as well: the roll edge is a good place to see process variation. Not just winder variation shows up on the roll, but also variations from forming or converting. If one edge of the roll is starred and the other is not, chances are good you have a caliper variation. If one side of a roll edge is rough, it may be a baggy lane crossing the slitter. If the roll edge has a bull's-eye pattern, it may be due to upstream oscillation. An offset could result from a tension upset or a forming upset.

What ever your job duty: mechanical, electrical, customer service, Q/A, operator, and so on, paying attention to roll edges is a good first step toward process improvement.

920/725-7671

DRroisum@aol.com, www.roisum.com