What is Web Tension Control?
Web tension control can be defined as the maintenance of a set amount of web tension (pull or force) for the material being processed, often measured in oz, lbs, grams, kg, or newtons. Proper tension must be maintained to prevent stretching, wrinkling, breaking, or inconsistent print registration of the material during its process.
Web tension control also improves uniformity in coating applications and material lamination while decreasing the incidence of rewind defects such as crushed cores, starring and telescoping. When web tension is under control it can enable processes to run at higher speeds while reducing scrap, delivering a rapid return on investment that boosts users' long term profitability.
Web tension control is most commonly used in three zones: unwind (infeed), intermediate (process), and rewind (take up). The web tension is controlled during the rewind and unwind zones where the material has to be kept at specific tensions in each zone to go through its process correctly. The material travels over rolls or through nips often controlled by motors and brakes.
The most reliable means of calculating web tension is by measuring force on an idler roll paired with load cells (also called transducers). The resulting load cell strain gage output provides a proportionate signal that is used to monitor feedback and adjust output in a closed-loop control system.
Typical tension control solutions incorporate:
- A closed-loop tension controller such as the SteadyWeb 6 digital controller
- A load cell roller such as the Tension Roll transducer
- A Pneumatic Brake (unwind zone) OR
- A Magnetic Particle Brake (unwind zone) OR
- A pneumatic or electric output to a clutch (intermediate or rewind zone) OR
- An electric output to a motor drive system (intermediate or rewind zone)
Customers integrating tension control with their PLC most often utilize: