PFFC - October 2008 - (Page 12)

WEB LINES Do You Have a Need for Speed? F By Timothy J. Walker Contributing Editor aster, faster, faster. As you reach the designed capacity of your existing process, before buying new equipment, most converters will ask if they simply can increase speed to get more capacity and profitability. In an effort to increase profits everywhere, here is a checklist of what to consider as you think about moving to higher process speeds. Too much air lubricates web-roller contact, reducing the traction to drive the web and idler rollers or hold the winding roll together. Too much air entrained in the winding roll will bleed out slowly over roll storage time and turn a tightly wound roll into a loose structure impossible to transport or unwind. u How fast can you drive a roller or roll? Baggy webs may Theoretically, there is no limit to how fast you can drive a roller or roll. (Don’t you brace begin to yourself anytime a point starts with the word “theoretically”?) Motor speeds typically are maxed apart like a flag out at 1,750 or 2,000 rpm, but line speed is rpm times roll or roller circumference and can be in a magnified with gearboxes or pulley-belt systems to get as much surface speed as you want. u As you move to extreme rpms, you will need to bulk up your bearings, couplings, rollers, and u Beyond the web-only issues, the more likely other components to handle the speed increase. limit to increasing speed will be your processes. Just as an automobile can be designed to set Your extrusion or coating system is limited in land-speed records, a web line can be beefed pound or volume per hour. Your drying or curing up to meet just about any challenge. However, process requires time, so your process doesn’t you likely already have a web line, one that was have enough length-to-speed ratio to get the job designed for a given maximum speed. Simply done. Heating, cooling, and moisturizing all may changing the gear ratio doesn’t mean your line be time or length-to-speed limited. will function properly at high speeds any more u Web handling systems and components also than turning your ’65 Chevy Impala into a hot may be speed averse. Web guides will have rod will survive your drag racing dreams. increasing following error as lateral offset u In the paper industry, where speeds of 5,000, occurs over a short time. Rubber-covered even 12,000 fpm are not unusual, critical speeds rollers generate heat due to hysteresis and of all rotating elements must be addressed. need convective cooling, so high speed turns Most web handling processes never will rubber coverings into goo. Clutches, brakes, need to consider the critical speed of a roller, and differential winding shafts generate heat winding shaft, or core, but if you do, balance proportional to the differential speed. At and deflection play strongly into what speed high speeds, these components won’t have a rotating element will begin to whip and enough convective cooling, leading to thermal uncontrollably vibrate or buckle. You don’t ever expansion and failure. want to see your rollers or cores beyond their u The last consideration is operational issues. With critical speed because they will actually explode. increasing speed, unwinding rolls run out faster; winder roll transfers happen more frequently; So far, we’ve addressed equipment start-up and winder indexing waste will issues; what about the web? increase; quality sampling inspection will see a smaller percent of your u Air drag may create too much product; and 100% inspection tension drop. Baggy webs may systems will have to work harder. begin to flutter and tear apart like NIPS & a flag in a hurricane. Entrained air Beware of the plan to increase TRACKING pulled along by the moving web, speed, because as the old joke says: roller, or winding roll will grow We’re losing money, but we’ll make beyond the web or roller roughness. up for in it volume. tear flutter & hurricane. COMING NEXT MONTH Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 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 | OCTOBER 2008 WWW.PFFC-ONLINE.COM http://www.webhandling.com http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - October 2008

PFFC - October 2008 Contents First Glance Calendar of Events From the Editor Web Lines Process Management News Clips Narrow Web & Label Reporter Narrow Web & Label What's New Products Shrink Sleeves Carton & Box Reporter Carton & Box What's New Products Cover Story - Custom Coating Core Shafts Show Preview Flexo Printing Film Converting Static Control UV/EB Inks What's New Products Trade Show in Print Services Directory Classified Marketplace Equipment Buyers & Sellers Advertisers Index Experience Speaks

PFFC - October 2008

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