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Web Handling & Converting

Blogmaster: Dr. David Roisum

06

Q: I am looking for a "cookbook" for winding different type of materials. Specifically, a book that would explain what tension and taper (%) as well as nip should be used for each material in order to make perfect rolls.

A: Unfortunately, there are no "recipes'"to make a perfect roll. To begin with, each defect requires a different 'strategy.’ Defects fall into one of four classes:  tight defects (reduce tension throughout the roll), loose defects (increase tension throughout the roll), taper defects (start tighter, finish looser) and other (a catchall for mechanical/control/operator defects that can’t be solved by changing the TNT’s on the winder). This part is simple enough because the literature describes generic solutions to specific defects. (see Roll and Web Defect Terminology; Winding Machines, Mechanics and Measurements and Web101). Here, you must be quite careful to get the right defect in order to get the right list of remedies. For example, the most common types of telescopes (type IA and IB) are taper defects while two others (the storage telescope and two-drum winder dishing) are tight defects. Same with core crush which has three subtypes: Tight (typical with stretchy materials), loose (typical with stiff materials) and other (rare, but seen on materials that shrink). With just a very few but key observations, you can determine which specific defect you have. Beware of superficial appearances and names people may give defects because they could be misleading or quite possibly incorrect. Here, it is best to literally go to school (such as my web and winding schools hosted by AIMCAL) because it will make the whole process much faster and much more reliable.

To this we must add the complication of constraints that depend on the specifics of the winder and material. For example, let us pretend we have a loose defect; any loose defect will do. What can happen is that we might be limited in our ability to increase tension because the material might not be able to withstand increased tension (common on light or brittle materials) or perhaps we don’t have enough motor to pull higher tensions (common on heavy materials). Alternatively, we could increase the nip except that maybe we have a center wind and thus have no nip knob to work with.

Things can get even more complicated when we have more than one class of defect (the norm). Continuing with the above example of a loose defect. Perhaps we have already maxed tension and we DO have a nip on our winder, BUT the profile is so uneven that we damage (wrinkle etc) the material at the gage bands.  In this example, we have tight AND loose defects at the same time; not so rare as you might think. In this case we must use techniques such as optimization to find the best place "between a rock and a hard spot." In some cases, materials may not even be windable at any reasonable level of trouble. Perhaps the most common reason is excessive profile variation; a quality control concern. Occasionally you may run into the material/physical property that precludes trouble-free winding; a DFM (design for manufacturability) or fitness of design issue. Cases of excessive profile variation or unusual material properties can sometimes have no winding solution.

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Blogmaster

David Roisum photo

Dr. David Roisum

Dr. Roisum is a well-known authority in the area of web handling and converting. He has authored seven books, including Winding, Rollers and Web-Handling and has coauthored or edited several others. He was a technical editor for Converting Magazine with a monthly column entitled "Web Works." An accomplished professional speaker and instructor, Roisum has been praised for his skill at translating highly technical information into a common sense practical reference. Dave has been honored by TAPPI with their Finishing & Converting Division Award, Thomas W. Busch Prize and Finest Faculty awards and is a TAPPI Fellow. Dave received his Ph.D. from the Web Handling Research Center where he later became an Industrial Advisory Board member.

Dave has worked for the Beloit Corporation as a designer of winding machinery and later as a manager of research, and for Kimberly-Clark as a converting expert serving all business units. He is now a principal of Finishing Technologies Inc., providing consulting services to more than 300 clients who convert or manufacture: paper, film, foil, nonwovens, textiles and many other materials. He has accumulated much practical experience working in nearly 1,000 plants over the course of more than three decades.