4.4 Tension Zones

As I said above, the two-zone web line should be the starting point for any web process. But when is 3 or 4 or 13 tension zones the right answer?

The two tension zone line is designed to compensate for the diameter changes and process needs of unwinding and winding, but in web lines, we usually do more than just rewind, we have processes with their own tensioning needs.

Adding a fourth drive point creates a third tension zone potentially independent of unwinding and rewinding. As more processes and rollers are in the web path from unwinding to winding, more tension zones and drive points may prove beneficial.

 Here’s how to decide on more than two tension zones:

1. Divide your web line into process steps, including unwinding and winding as process steps.
2. For each process step, define the tension requirements of that step, including the nominal tension need (high, med, low) and the sensitivity to tension variations (high or low).
3. Look for compatibility between consecutive process steps. If two or more steps are compatible in nominal tension and sensitivity to variations, group them together as a single zone.
4. Add drive points as needed where high inertia components will take too much from web tension to be web driven. Consider both single component inertia and the inertia from a group of elements, such as a large number of idler roller in a drying or curing oven.
5. Select a master (based on guidelines above).
6. Select tension control method for each zone.