A: The first thing you need to know is where the wrinkles form, not why. In most cases rejectable wrinkles form on a roller, even if the cause is upstream. This is no more difficult that just paying close attention. Two caveats: first, there may be a couple of rollers that initiate trouble, so each source must be identified. Second, the roller that initiates the wrinkle is usually, but not always, the first roller where you see the problem. However, wrinkles are unusual in that they are one of the few defects that can progress upstream if severe enough. In that case, observe the more modest occurrences to find the troublesome roller.

Once you know where the wrinkle starts, observe the angle of the wrinkle such as MD, Diagonal (Shear) and CD. There is little in common between these types in terms of solution and even less in terms of mechanics. I have written and taught much on this subject so I expect the reader to do some homework here. Briefly, even a small angle of the wrinkle indicates something is crooked. Thus, when you have the Diagonal Shear wrinkle you want to find out whether it is the web (bagginess, etc.) or roller (misalignment, deflection, diameter variation, etc.) that is crooked. If you are not absolutely certain, assume for the moment it is your roller and give it your best attention.

If the wrinkle is almost exactly in the MD or very slightly fan-shaped, the web wants to be wider. This major class of wrinkle has subcases that will not be listed here but are all easily diagnosed. You might choose to identify the root cause and reduce it. Alternatively, you may wish to employ effective spreading. This has to be done precisely at the location you just identified. Two rollers upstream will do no good. Two rollers downstream will be too late. There are many choices here, and again we will let the reader do his or her homework.

Other patterns can also be helpful. For example, a diagonal wrinkle on one side indicates a tipped or carrot shape in the system. However, diagonal wrinkles that are symmetric about the middle are chevron-shaped—which is a smile- or frown-shaped system in disguise. Thus, the cause of a wrinkle on one edge is probably quite different than identically appearing wrinkles on both edges.

Unfortunately, the least useful information, when the wrinkle occurs (grade or condition) is one most people latch onto. Often this is merely a severity factor rather than associated with the cause. We shouldn't ignore incidence, but we should pay more attention to location and angle.

Another simple view is that the location where the wrinkle forms is either incorrect or intolerant or both. Incorrect could include roller misalignment, excessive deflection or diameter variation. Intolerant could mean the roller has excessive traction or is too small in diameter. It could also mean that we have given a less-than-perfect web an excuse to misbehave, even if the roller is good enough or even perfect. In the case of intolerance, we should always bear in mind the first commandment of good web machine design: Minimum Roller Count.

There you have it. No fancy instruments are required. Just pay attention to where the wrinkles form and what their angle and pattern are.

David Roisum, Ph.D. Consulting Technical Editor 920/725-7671 drroisum@aol.com, www.roisum.com