When should a web run higher or lower than the default recommended tension?
The recommended target tension is a starting point, but many factors may mean higher or lower tension is better.
The recommended tension of 10% of web damage is a starting point. Many factors may mean a higher or lower tension is better based on product or process factors, including:
Product mechanical behavior changes with temperature, moisture, or transformation (e.g., hot polymer films will yield at lower stress, so tension is usually reduced when the web is hot, a coated layer may become stiffer after drying or curing).
Tension may be increased:
- To pull out web bagginess, running straighter and avoiding wrinkles at nipped rollers.
- To create more roller traction to avoid scratching
- To make idler roller drag and inertial losses a smaller percent of average tension.
- To eliminate wrinkles by tension-induced stiffness.
- To improve concave rollers spreading.
- To reduce sag in horizontal web spans.
Tension may be decreased:
- To reduce roller deflection.
- To reduce web pressure against wrapped rollers.
- To avoid contact with air nozzles and or air turns.
- To eliminate wrinkles through reduced roller traction.
Tension may be increased or decreased to reduce the tension differential at a driven roller to maintain tension control.
Tension may be increased, decreased, or tapered to optimize winding and roll structure.