Web Lines | Unwritten Rules, Part 2
- Published: June 09, 2015, By Tim Walker
Here are a couple more web handling rules Tim Walker keeps forgetting to tell you.
There are a few things that I almost always forget to include in web handling training. In Part 1 of this Web Lines column, I gave you three rules:
- Keep tension.
- Avoid rapid speed changes.
- The web should be narrower than the rollers.
Here are two more:
4. Overly narrow web vs. roller width is trouble, too.
Don't run overly narrow web on wide rollers. You can get away with this, but overly wide rollers have overly high inertial drag as mass to accelerate goes up directly with width. Running centered on overly wide rollers may not pose much of a problem, but:
- Run narrow webs down the middle of the wide rollers.
I sometime hear or see people who want to justify their web to one side. This may be due to the location of fixed web guide edge detectors, or it may be a process constraint of a coating or other process. Laterally offset web will see roller deflection as roller misalignment, leading to lateral shifting and potential web wrinkling.
5. Try to avoid discontinuity in winding.
The best winding occurs when forming the roll runs from core to final diameter in a smooth, uninterrupted process.
- Don't change settings in the middle of a roll.
- Don't stop and start.
- Don't have nips open and close.
- Avoid excessive out-of-roundness and eccentricity.
- Don't change the product thickness, stiffness, friction, or other major winding process variable.
Wound rolls know what you've done to them. Like the rings of a tree will remember the seasons of their life, a wound roll will remember the upsets in tension, nipping, speed, and slippage that occurred during its short life (winding time).
Often, upsets or discontinuities in winding are where defects form or rolls telescope in handling or unwinding. I guess this is the winding version of “don't change horses mid-stream.”
Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; This email address is being protected from spambots. You need JavaScript enabled to view it.; www.webhandling.com.
