Center-wind torque assist is the third knob in the TNT's of winding: Tension, Nip, Torque and speed. It is the least common, most expensive and is easily the most misunderstood. Center-wind torque assist always requires two motors. One motor is attached to the winding roll. The other motor is attached to the roller. The roll and roller must be nipped together.

The sum of the two motors (minus drag) creates simple ingoing web tension. The difference between the two motors creates the torque (center-wind torque assist.) This motor application is unusual in that the motors may be opposing each other. In other words, one motor may be turning +20 amps and the other may be regenerating at -10 amps. Perhaps the only other common application for motors fighting each other is in curl control on dual-drive laminators. The mechanics are quite similar.

To make the roll tighter, put more power into the winding roll and drag with the roller. To make the roll looser, put more power into the roller and drag with the winding roll. For this reason, center winds with an undriven layon roller will wind slightly tighter than a surface wind even for the same tension and power input. On two drum winders, the roll is made tighter by shifting torque to the front drum and looser by shifting torque to the back drum.

What does all of this do? Quite simple. Tension makes the roll tighter. Nip makes the roll tighter. Torque makes the roll tighter (and looser). In other words, at the end of the day when all is said and done, all of the knobs do just one thing: affect roll tightness. Thus, while the winding MACHINE may have as many as four knobs (TNT's), the winding PROCESS has only one knob (wound-roll tightness).

Why would you need all of those knobs if they all do the same thing? After all, these knobs cost money and greatly increase the complexity of the process. The answer is to extend the range. What if the nip is giving you trouble, such as damaging material at a gage band? You can back off on nip and increase tension in its place and the roll will end up equally tight. What happens if tension is giving you trouble, such as necking or web breaks? You can back off on tension and increase nip, and the roll will end up equally tight. What if you need a really tight roll? Increase both tension and nip.

So why a third knob (torque) when you already have two (tension & nip)? Perhaps your first two knobs are maxed and you still need more tightness. Perhaps your first two knobs are in the mud and the roll is still too tight. Thus, the third knob extends the range to super loose or super tight. An equally valid answer is that the nip knob is not effective on compressible materials over an incompressible surface (core). Thus, some materials will wind looser for the first inch or two because the nip is not effective. Thus, torque can take up the slack (excuse the pun) at the start of winding.

Is there a moral to all of this? Perhaps it is caveat emptor. Know what you are buying, why you are buying it and how you are going to use it. More knobs don't necessarily increase efficiency. They may just increase confusion.

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