- September 01, 1995, Andrew R. Mykytiuk, PFFC Editor
Take a look at a single-station unwind/rewind stand and it appears relatively uncomplicated, right? After all, it does what its name implies—it unwinds and rewinds.
Unfortunately, unwinders/winders/rewinds, like most things in life, are not quite as simple as they appear to be. In fact, according to Dr. David Roisum, author of The Mechanics of Winding, winders have a critical influence on the creation of all kinds of roll defects, defects that can easily result in a roll being devalued, culled or scrapped. "I have seen a situation in which 20%-80% of all production from a winder for half a decade went into a landfill due to a single winding defect," writes Roisum. That situation, by the way, was quickly remedied when the company took Dr. Roisum's advice and changed the nip roller.
The laws of physics that govern these devices have been understood for more than a century. As computers became more powerful, researchers were able to create increasingly sophisticated modeling programs that used universally accepted mathematical formulas to benchmark winder/unwinder/rewinder performance.
What we now know is that winders, unwinders and rewinders, even when properly set up, will still impart great amounts of stress throughout the roll and are directly responsible for a variety of unacceptable defects, including corrugations, delamination, crepe wrinkles, stretching, wrinkling, blocking, cigars, bursts, out-of-round or eccentric cores, and the dreaded web break.
Understanding this technology and its limitations is more important than ever today, with the continuing trend toward thinner, lighter films, tissues and foils that have a tendency to stretch, wrinkle and entrap air.
John Shelton, adjunct professor at Oklahoma State's web-handling program, says the web-handling field is so vast that many aspects are still not completely understood. He says a winder can be tuned to work well with a certain web, but when you switch webs all the variables change.
"Ideally you'd have a computer program for each different kind of material and just punch in a code and let the machine do the rest," says Shelton.
Thomas Herold, head of technical sales for WTI International, Rockford, IL, explains that his company offers programs with menus and the capacity to save values. Computers store the parameters or values of a successful run and then help set up the machine to duplicate this success when the same material is wound or unwound in the future. This marriage of software and hardware, which has been perfected through years of testing, is becoming an increasingly popular option for short runs.
Shelton wants to make it clear that, while none can be classified as quantum leaps, he has been witness to many advances over the years: the move from mechanically controlled systems to electrically powered, digitally controlled systems; easier roll/core loading and unloading; more versatile computer programs; better cores; more tractable tension control; improved breaking; and increases in speed.
Shelton would like to see the development of inexpensive sensors to aid in the measurement of tension. If you know what the tension is, he says, you can control it, and he's convinced that if such sensors were available, perhaps we would soon see the big breakthrough in web handling that everyone is looking for. Until that time we must content ourselves with incremental improvements.
Richmond Industrial Corp., Richmond, VA, sells a yeoman winder equipped with splicers engineered to join material on the fly at 600 fpm. "The line does not have to be slowed down, and production keeps running unimpeded," says Brian Fatzinger, head of sales and marketing. The development is actually in the splicing technology.
Even though there haven't been any major leaps in winders and rewinders, today's equipment is built to be both rugged and precise, according to Fatzinger.
Shelton agrees and adds that there has been a return to engineering fundamentals: round rollers, free-turning idler bearings and precision machine alignment.
The company offers a range of winders from 250 mm to 8,500 mm wide with an extensive array of speed/diameter options. Features include adhesiveless start at reelchange; lay-on roller operating in gap or contact mode; automatic turret indexing under tension control; automatic reel change; programmable and precise tension control; and thread-up systems.