Pneumatic trim-removal systems are something like industrial-sized vacuum cleaners. Even so, there are many things that can go wrong.

The first component—the inlet or trim chute— has had the least attention and is often the most troublesome. Here is where there is some true economic disparity. In the paper industry, these chutes may cost $20,000 each. It's difficult to describe in words their complex construction, so instead, imagine the air scoop and carburetor on a race car, and you get a rough idea. In converting, however, they may spend all of $2 to cut a flexible pipe to length. The operator may craft a precise positioning device using duct tape and baling wire. At the peak of creative effort, converters will sometimes put a funnel on the end.

The need for a serious trim chute is clear. You must have a dead flat and dead stable trim at the cut point. This may be a challenge considering the breadth of materials to be run. In paper, the trim may need to be pulled away at speeds of zero to 10,000 fpm. Speed ranges such as this usually require speed-programmable blowers which track winder speed. Pulling too hard at low speeds can break the trim intermittently. Pulling too little at high speeds can result in a nasty plug-up in the blink of an eye. Consider also that trim widths may vary from 1 to 10 in. and that calipers may vary on order of magnitude, and you see that the trim-weight itself may vary two orders of magnitude. Also, these variations mean that the trim chute must be quickly and precisely positionable.

Piping is the next place for trouble. All piping should be appropriately sized, have a smooth interior, an extremely generous bend radii, a constant cross section and so on. Sometimes static electricity or fouling by contaminants dictates the materials that can be used on the piping. The piping may be interrupted by devices such as injectors, eductors, choppers, inline fans, etc.

Somewhere in the system there's a blower, which can have three common problems. The most serious is to use a central blower to serve many machines. While the economies of scale sound attractive, instead of a separate blower for each machine, there are more ways this can fail than work well. The most common problem here is when one machine stops, the balance of air is disrupted for the others. A second problem is blower undersizing. You must do more than pull the trim away; you must pull hard enough so that a diagonal wrinkle is not formed in front of the trim slitter blade. Finally, the inlet and the blowers are noisy, which have a cost invisible to simple management metrics.

Lastly, we must separate the air (and possibly dust or other contaminants) from the trim. This can be done elegantly in a cyclone, but there are sometimes simpler methods. In any case, the sum total of all of the components that must work together over a wide range of conditions clearly indicates this is not a “do-it-yourself” project. There are only a couple of suppliers who specialize in web trim-removal systems, and we would rely on them for advice.

920/725-7671, drroisum@aol.com, www.roisum.com