What creates tension variations in a draw zone?

Asking this question may be missing the point, since draw control usually is intended to control strain, not tension. But since draw control is used in tension control, it’s worth talking about how strain becomes tension.

All the variables reviewed so far (speeds, initial strains, time) will lead you to the draw zone’s web strain. To find tension, multiply the strain by the web’s modulus. Is the modulus constant? It would be nice to say “yes,” but material properties change from moisture, temperature, cross-linking, strain rates, and the big wildcard—viscoelasticity. In many processes, the web’s response to strain will be predictably elastic, but be on the lookout for unusual mechanical properties and the resulting drawing confusion.