It is so common that you might expect that the web will shift sideways at a roll change. However ordinary, it is no more desirable than the common cold. Whether this is a mere nuisance—or fatal—depends on the health of the raw material, the converting machine and the product being made.

It is important to understand that an outcome, such as a sideways shift of the web, can be a result of many distinctly different causes. This is not unlike a stomach ache, which is a symptom common to many different maladies. We should not expect that any single remedy would help in but a fraction of the cases. Most outcomes are not subject to a “magic bullet” medicine.

The best way to begin troubleshooting most problems is to first diagnose the single cause that is present in a specific case. Knowing this will readily yield ideas for treatments. Here we will list some general mechanics as a set of ideas to consider as working theories for diagnostics.

One cause for shifting at roll change is due to a change in bagginess, sometimes called camber. If, for example, you have three rolls cut from the full width of a producing line that had baggy edges, you would have variable tracking at roll changes. The A roll might consistently turn to the back side, the C to the front and the B to the center. Every web handler should know how to read the roll ID to tell where it came from on the upstream machine.

Astute operators will sometimes sequence the rolls to minimize this shift that would disturb registers for hundreds of feet. If I came on shift, I might cherry-pick from the warehouse all of the B or center rolls and let Charlie on the next shift deal with the end rolls. If I ran out, I might then find all the A rolls, so the path the web prefers would be similar across roll changes. Bagginess is a raw-material defect, so that the problem would lie mostly—but not entirely—with the supplier. (The customer is always responsible to have reasonable product tolerances and perhaps even good guiding in this case.)

It is possible that the winder has made the bottom of the roll different than the top, for reasons too numerous to list here. What we will say is that this supplier-caused issue on rolls whose appearance is decent is rare, except perhaps on very tender materials such as nonwovens. Thus, a good troubleshooter would not start looking there unless there were strong clues that the winder was connected.

Often a shift is due to less-than-perfect threading or splicing. Whether automatic or manual, the splice might have three different errors: pucker, offset or angle. The pucker or offset is easy to see and thus not so likely to be the cause if one pays attention and practices diligence. However, even the tiniest angular error will result in a centerline kink that will give the path or guide a kick to the side that will last dozens of web widths. In this case, the customer's equipment or operator would be the cause, so that a supplier remedy would not be expected unless it was the supplier who had made a mid-roll splice.

Lastly, changes in tension, a likely occurrence during roll change, coupled with any misalignment, could easily cause a momentary web shift even on perfect product. Again, a customer equipment issue that is not fixable by the supplier.

I hope this illustrates the importance of good information, good technical knowledge and even better troubleshooting skills.