Tips

How do you control tension off your unwind? How do you control tension at your rewind? Unwind and rewind rolls constantly change diameter and require constant adjustment of torque to maintain proper web tension. Remember the simple equation - torque = tension X roll radius, which mean tension = torque divided by roll radius.

If the roll radius is constantly changing (getting smaller off the unwind and getting larger at the rewind) we must change torque, linearly to maintain constant tension. Constant tension is always desirable off an unwind station and may be desired at the rewind (the rewind may need taper tension - but that's another discussion).

So, let's go back to my original question - how do your machine operators (or you if you are the machine operator) control tension in your operation? Are manual adjustments made to torque as roll diameters change? If you are adjusting torque manually a good option for you may be to add a simple open loop tension control, like an ultrasound control. Ultrasound controls measure roll radius and automatically make adjustments to torque to maintain linear tension control.

Ultrasound controls are relatively inexpensive and easy to install. Improvements made to your process, eliminating the need to manually adjust a brake or drive, will prove very fast return on investment.