Gap winding is many things to many people. A common arrangement is a centerwind with a lay-on roller where the lay-on roller has been lifted from the winding roll. The lay-on roller makes the wind tighter. Perhaps you don't want a tighter wound roll, so then you would lift the lay-on roller to loosen. Perhaps you do want a tighter roll, but the nip is causing troubles such as exacerbating gauge bands or causing wrinkles. We know that gauge variation across the width greatly reduces the window of trouble-free winding. Just when you want as many tools as possible in winding troubled webs you, in fact, have reduced tools because nips require near dead-level product.

The lay-on roller (now turned idler roller) in front of the now simple centerwind also improves roll-edge quality. Consider what steers the web on a simple centerwind with a distant idler roller in front. It is the wound roll whose cylindricity is quite poor which steers the web. On the other hand, with the “lay-on-turned-idler” roller right in front of the winding roll, it would be the very precise metal roller that steers the web.

Idler rollers which are big and slippery are quite resistant to wrinkling. This flattening effect is also desirable on the first roller after an unwind. The unwinding roll is geometrically troubled and just looking for the chance to misbehave. The first roller is the first opportunity. If you can get it by that roller, you may be home free. The roller just after an unwind and just in front of the winder both need to be big and slippery for wrinkle-prone applications.

Now let us consider the gap-winding mode. Here, we keep the roll and roller closely spaced, usually less than an inch, because this is most wrinkle-resistant winding mode. The clue to success is getting the web dead-flat on the gap (former layon) roller. We use our best spreading efforts in front of the roller; we use our best flattening efforts on the gap roller by making it big and slippery. If we get it flat on the gap roller, then it has too little time and too little space to go from flat to wrinkle.

Obviously there are some issues to consider in gap winding. 1) In gap mode, you have no lay-on roller so the winding roll will be looser, perhaps much too loose. 2) With thin, smooth materials like film, you can't wind very fast without filling the roll with air because you lack the best treatment for reducing air: the nip roller. Thus loose rolls and speed limitations make gap winding a bit of a niche mode. 3) Note mechanical and control challenges of moving the roll/roller to maintain a constant gap as the winding roll builds in diameter. Not a huge challenge so this mode is often provided as standard for many turrets and other centerwinds with lay-on rollers.

Finally, a centerwind with a lay-on roller has drive-control subtleties that must be addressed going into gap mode. The driven lay-on roller now off the winding roll interferes with the load cell to centerwind motor control. The motor can't simply be turned off. It must be run in no-load-motor-amps to exactly counter drag with an inertia compensation calculation. Together, these combine to make the roller “disappear” from the web as far as tension is concerned.

920/312-8466 drroisum@aol.com, www.roisum.com