PFFC - December 2007 - (Page 12)

WEB LINES Differential Winding Limits: Part II D By Timothy J. Walker Contributing Editor internal shaft. Each individual disk or “doughnut” has a mechanism, usually cam-lock buttons or bearings, to grab the core. A radially loading system should be used on slit rolls so narrow that two rolls would be locked on one element. All radially loading shafts will have easy core positioning and adjustment, but how the core stays in its position varies by design or supplier. The slip-core systems may contain a core lateral Axial-Loading Systems motion with the torque elements outside the core’s Axial-loading differential shafts stack alternating width; they may have adjustable pins or bearings; cores (or cores with special inserts) and keyed spacers or some operations may default back to using a on slotted shafts. The well-known limitation of spacer or core between winding rolls, such as axial axial-loading is that each core receives nominally loaded systems. The cam-lock systems don’t have the same torque, which isn’t good when winding a problem with lateral position, since the locking different widths on the same shaft. The second, mechanism restrains the core laterally. less obvious limitation of Regarding deflection, core-spacer stacks is their since a core-lock sensitivity to core width cross-shaft may be as variations, especially at much as 7 ⁄8 in. smaller narrow slit widths. If core than the core’s inner diameter, they will see width is slightly off, the more deflection-related stacking error creates a defects such as dishing, slit-to-core misalignment collapsed rolls, or shifted that’s nearly impossible to layers with heavy rolls or compensate for. high nip loads. On the plus side, the side contact between the Other Limitations cores (or core inserts) and Dust can be a problem spacers reduces lateral for any differential shaft; some will create core wander and core twisting. Since the shaft is both dust, and others will fail if core or product dust solid and the maximum possible diameter to fit within the core’s inner diameter, these systems will gets inside them. Differential shafts should have have the least shaft deflection, especially important good overspeed control to reduce heat and wear. All differential shafts work better when cores are for heavier rolls or high winding nip loads. neither too large nor too small. Core-lock shafts may fail to lock onto hard plastic or metal cores. Radially Loading Systems Differential winding after a well-wrapped surface In radially loaded shafts, the torque applied to a core is proportional (or nearly so) to the number of drum or several idler rollers will have limited ability to pull out anything, but they have the elements that grab the core, and each core receives torque as a function of width. Most radially loading most extreme bagginess at slitting. If differential shafts are turned up to a torque beyond the differential shafts are slip-core or capacity of the driving motor or clutch, core-locking. they won’t slip differentially and you’ll Both designs adjust air pressure be winding on the world’s most within the shaft to radially pushing expensive lock shaft. out on slipping elements to transmit I’d like to thank three differential torque to the winding core. The slipwinding experts for valuable core designs have small, nonrotating DRIVE ROLLER discussions that helped in preparing elements, often less than 1 ⁄8 in. wide, TRACTION that push against the core. The corethis two-part column: John Pretto OPTIONS locking system uses a series of disks (Goldenrod), Sean Craig (Tidland), 0.5–1.0 in. wide mounted on a smaller and Dan Cain (Tekkote). ifferential shafts are great tools, but like any tool, they have their limitations. Last month I covered the complexity of a differential shaft’s actual applied torque. This month we cover more differential shaft limitations. My goal isn’t to put down differential shafts but to avoid the frustration that occurs when delivered results don’t meet expectations. All differential shafts work better when cores are neither too large nor too small. COMING NEXT MONTH Web handling expert Tim Walker, president of TJWalker+Assoc., has 20+ years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; tjwalker@tjwa.com; www.webhandling.com. 12 | DECEMBER 2007 WWW.PFFC-ONLINE.COM http://www.webhandling.com http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - December 2007

PFFC - December 2007 Table of Contents First Glance From the Editor Web Lines Process Management News Clips Narrow Web & Label Reporter Narrow Web & Label What’s New Products Carton & Box Reporter 2008 Calendar of Events Materials Testing Pilot/Lab/Technical Facilities What’s New Products Services Directory Classified Marketplace Advertisers Index Experience Speaks

PFFC - December 2007

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