PFFC - March 2009 - (Page 47) Applicable Converting Issues Ideally, crowns should be used in the design of rollers and equipment and not because of it. When the advantages of crowning rollers are carefully considered, the benefits add immeasurably to converting processes. Matt Menges has been president of Menges Roller since 1984. He has experience in every aspect, from manufacturing to roll engineering, since his graduation from college. His troubleshooting for customers inside their plants includes after-market and OEM manufacturing. Special expertise is in core and enduse application engineering. Matt Menges can be reached at 847-487-8877. (Contact the company for the complete Crowned Roller Report at www.MengesRoller.com). u Web is not tracking properly and/or moves back and forth | This usually is caused by uneven nip pressure or a wider nip area in one area of the web. The larger nip area pulls the substrate at a differing rate than the smaller area during nip lead in or nip lead out, which causes the web to move back and forth. u Excessive wrinkling or foldovers of the web or sheet | This is the same issue as above. An uneven nip pressure causes an unbalanced pull because of an unequal dwell time of the substrate in the nip. This wrinkling can be made worse by downstream pull rollers that actually pull the web as the uneven nip is holding the substrate, which creates wrinkles in the sheet. u Uneven coating weight or laminating films are ROLLER CROWNING baggy in the center or the edges | Because the nip is uneven across the face, coatings are immediately lighter in the middle. This problem usually gets worse as operators add pressure to the ends of the rolls, which causes deflection or bowing of the rolls. In laminating, the low center causes poor laminating film penetration, which can be a cause of wrinkles pulled into the sheet as the deflection causes greater and greater nip pressure irregularities. “Laminating is an art form,” says a roller user. “The nip pressure can be perfect, but other factors like humidity can drive operators crazy.” The point is that laminating will not tolerate uneven nip values. u Tracking or steering is the issue | Crowns can be used to align or steer. If you can picture a band saw, the blade runs between two large wheels with a steep crown. The blade stays perfectly centered on top of a steep crown. For example, steel mills utilize crowns to steer a difficult web of steel, which is stretched as tight as a piano wire through coil lines as long as a football field. u I crowned my rollers and I still have problems | A crown is a tool in your tool box. Used correctly, it will solve problems. However, it will not rectify a poor design or bad machine alignment. For example, a paper machine roll 25 in. in diameter and 40 ft in length can only be designed to work with crowning as an absolute preconceived notion from the start. Paper machine engineers don’t design their rollers to find out they have uneven nip pressures and then go back to the drawing board. ADVANCE PROGRAM YOUR EXISTING EQUIPMENT DELIVERING MORE WITH EQUIPMENT UPGRADES custom modifications new product capabilities CMR2000 replacement ENGINEERING SERVICES winding & slitting coating extrusion pelletizing systems integration WWW.PFFC-ONLINE.COM CONVERTING SYSTEM’S ADVANCE PROGRAM - it’s the way to use existing equipment to increase output or to make the new products the market demands. Let our team of engineers and product specialists help you to revise, update or upgrade your equipment at a fraction of the cost of a new line. | Converting Systems PFFC-ASAP 133 Converting Machinery www.bc-egan.com Fulton, NY 13069-1297 USA Tel: (315) 598-7121 Somerville, NJ 08876-0671 USA Tel: (908) 722-6000 MARCH 2009 | 47 http://www.MengesRoller.com http://WWW.PFFC-ONLINE.COM
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