Winding converts flat web into roll form and typically there are 3 types of winding as the following:
Among them, center wind method is the commonly used one.
Winding problems
- Telescoping
- starring
Taper tension control
There are four ways to control web tension:
- Constant tension. Tension remains constant during whole tension control process. The problem is the outmost layers of the wound roll is too tight which might lead to starring defects (internal stress)
- Constant torque. Under this mode, the outmost layer can be too loose which may lead to telescoping defects.
- Linear taper tension control
- Hyperbolic Taper tension control
Tape tension control can mitigate the above problems; the key is to control the tension profile and the internal tangential stress as a result, as shown below schematically.
Taper tension equations
t is the taper and its value is between 0 and 1. The following is the tension taper profile for the four cases:
accordingly the internal stress distribution are
Taper tension control is a trade-off between constant tension and constant torque; it indeed mitigates telescoping and starring defects; however isostress is still not achieved by simple lineal or hyperbolic taper tension control as shown in the above picture.
Advanced taper tension control
If Alfa=1, it is linear tension taper profile and it is hyperbolic if alfa is 0.
- For small rolls (R/R0<2), linear taper tension is effective in controlling telescoping
- For large rolls (R/R0>2), hyperbolic is better in controlling internal stress.
- Therefore alfa should be close to 0 for small rolls and 1 for large rolls.
Rule of thumb in tension control
It is recommended to set taper larger than 40% for large rolls (R/R0>2) and set taper less tan 40% for small rolls (max roll diameter/R0<2)
Linear taper profile is still best for mitigating telescope in small rolls while advanced taper profile has the best overall performance.
Reference
- http://dx.doi.org/10.1016/j.ijmecsci.2012.03.005
- DOI: 10.1177/0040517514538697