Industry Q&A - Web tension developments answer converters' call for flexibility
Jim Berceau, engineering manager, Webex Inc.
Q: What are the most common web tension challenges in converting packaging film today?
A: The two most common web tension challenges for film converters today are running a range of films at a varying speeds and tensions, and making older machines operate faster with lighter films without a total revamp.
For older equipment, sometimes better use of current components is all that is needed. There are times when it is necessary to use diagnostic tools, such as vibration analysis equipment and high-speed video, to help locate an existing machine’s trouble spots and pinpoint the best solutions.
Q: How do tension control components help converters process different web materials-for example, increasingly thinner films-while remaining nimble enough to keep control of films that a converter has stocked for years?
A: Automating tension control with a “recipe” system and related components is one of the biggest aids to converters who run films of varying thicknesses. Automating changes in set-points creates quicker and easier changeover in products, eliminating the need for the operator’s attention at every change.
Another proven solution for a converter to expand the range of control needed when running a variety of films is using components such as load cells over a dancer system.
Q: What recent improvements to tension control components have made the greatest impact on flexible packaging converters?
A: New, state-of-the-art AC drive systems with greater velocity loop resolution and bandwidth have made a huge impact because of their ability to increase performance and their flexibility to integrate with existing control systems. The new drive systems allow tension systems to correct for smaller errors. With these, converters can run at lower tensions without risking web handling issues related to total tension loss. Closely electronically coupled drive systems, such as affordable servo drives, have made it possible to change speed quickly and smoothly with no compromise in tension control.
Tension load cells that routinely deliver tension ranges of 40:1 or better allow for more system flexibility with fewer parts and/or modifications. Systems that aid in fault-finding are also a huge benefit.
Q: How can tension control systems be optimized for handling of film and/or lighter webs at higher speeds?
A: Flexible packaging converters can optimize tension control systems for higher speeds by upgrading components, limiting vibration and controlling noise via controllers and amplifiers with more sophisticated noise filtering techniques. This allows for higher running speeds and lower tensions, as the tension system is not excited by electrical and/or mechanical system noise. Stiffer drive-trains with tighter tolerances allow for increased electronic drive system gains and generally faster error correction.
Vibration affects dancer and load cell systems but is especially critical in load cell systems, increasing the general “noise” in the tension signal. Appropriately tuned filtering can eliminate this noise. However, the best solution is to use quality rollers with excellent geometry from a quality supplier that are balanced to a tight tolerance and to use stiff machine frames and brackets to resist vibration. Stiffer components vibrate at higher frequencies, making it easier to filter the vibration from the tension signal. n