Flexible Packaging recently caught up with Mark Breen, marketing manager at Dover Flexo Electronics, to get an update on what’s new in tension control.
Q: Is there anything new or emerging in the field of tension control that converters should be aware of?
A: Most of the advancements in tension control are coming in the form of electronic features added to digital control software and firmware. For instance, specific to controller tuning for improved tension control and web process consistency, the SteadyWeb5 Tension Controller includes a P.I.D. tuning feature, TuneView, which allows the machine operator to view a time-lapse line graph of fluctuations in tension on the unit’s graphic user display. The operator may change P.I.D. values and see a graphic of the real-time output response. This allows fine tuning of the process to achieve a flatter system response.
Another emerging trend that has mirrored the increased use of smart user interfaces in consumer electronic devices is the incorporation of touch screens into devices. Touch screens provide a more intuitive user experience and replace the need for separate navigation buttons and switches on controller overlays and front panels. Many more next generation products will have touch screens.
On the pneumatic brake side of the tension control industry, brake squeal has been a problem for some flexible packaging printers and converters for decades. Dover Flexo Electronics has spent years solving this problem for brake customers. Last year, we got the patent on the Silencer friction pad technology, which has proven 100 percent successful in eliminating brake squeal since the introduction of the technology in 2011.
Q: One thing we hear often is how there’s a lack of understanding when it comes to tension control. Do you agree with this sentiment? If so, what can be done to give proper attention to tension control?
A: Yes. While we see a continued increase in general understanding of the need for tension control, and in basic tension control application, there are still many misconceptions about this process variable. One of the most misunderstood aspects of tension control is the term “tension” itself. Some film converters are under the misconception that a dancer controller can provide the same level of tension control as a transducer-based tension control system. This isn’t true because a dancer controller is reacting to a change in web position versus a true change in web tension.
Whether a novice or a control expert, production personnel experiencing tension-related web problems in their process should be prepared to provide metrics about their machinery to an application engineer at their chosen vendor. These metrics include web wrap angles, estimated running tensions, idler roll weight(s), zone(s) to be controlled and the device(s) to be used for tensioning the web.
Q: Can you explain the relationship between the size of roll build and tension control when it comes to selecting the right tension control platform?
A: As a rule of thumb, on a rewind on a piece of converting machinery, any roll build in excess of about 20 inches will require a tapered-tension signal output. Taper tension is a tension controller feature that will slightly reduce the applied web tension as a rewind roll builds. If a converter is experiencing crushed cores, telescoping or stared rolls, or deformed material at the center of rolls, these defects could be the result of a web that was wound too tightly as the roll was building. In most cases, paper rewinds will require taper.
Q: What – if any – special considerations do thin web films require when it comes to tension control?
A: It really depends on the type of film substrate we’re discussing, whether there are special considerations or not. The most obvious issues occur with extensible thin films that could be permanently deformed and ruined if they’re pulled too hard. These films would need to be wound at a precise light tension, but not so light that they droop or wrinkle. Some film substrates tear easily, so again, they would need to be wound under a lighter tension load.
Q: Is there anything else you’d care to share about tension control?
A: Although tension measurement and control equipment plays a vital role in the production quality aspect of flexible packaging, converting and web printing, it’s a process variable that our customers want to work invisibly, without them having to worry about how or why it’s working. The greatest compliment we can hear from customers is that they’re not even aware that their tension control equipment is doing anything. They mount it to the machine, and it sits there and it works. That’s how it should be.