You're Too Tense!

Product Focus

When people outside the industry think "tension control," they tend to look for the nearest massage chair and hand over a checkbook. Even inside the industry, this kind of tension control may do wonders for operators, but a good rubdown won't do much for your machine.

When planning to purchase tension controls, there is a lot for the converter to consider. "There are an infinite number of parameters that will affect your tension," says Scott Durfee, district manager for Maxcess Intl., Camas, WA (maxcessintl.com). "It's not as easy as buying brand X controller and throwing it on your system and away you go."

Here are some important questions to consider, according to Durfee and other industry experts.

Is the machinery sound and in proper alignment? Excessive movement in mechanical parts will negate any benefit of tension control, says Mark Breen, marketing manager at Dover Flexo Electronics, Rochester, NH (dfe.com).

Durfee agrees, saying, "Some machines are just poorly built. You can put the world's best tension control system on a line, but if it's got a very poor brake, your tension will be no better than what it was."

Which zones in the process require tension control? Breen says placing controls at the unwind station will help compensate for out-of-round rolls. If you have perfect rolls to start with, however, he suggests skipping the unwind station and placing controls at the intermediate zone or the rewind.

What is the range of substrates being run? This will determine the acceptable level of tension variation and is becoming a greater factor with converters trying to appeal to broader audiences by branching into decorative foils and plastic packaging.

Certain films and foils will require greater levels of precision, says Doug Brockelbank, inside sales manager at Montalvo, Gorham, ME (montalvo.com). He also cites the process as a related factor, since coating and laminating applications will require more precise levels of control than just a paper slitter.

What devices on the machine need to be controlled? For Durfee, this is related to determining what is causing unacceptable tension. Out-of-round rolls, lack of operator adjustments, stick and slip of air brakes, or material issues all will require different adjustments. When controlling a brake, says Breen, the output may be pneumatic, which will require a special feature on the controller.

How fast is the machine running? Running speeds will affect the choice of transducer, says Breen. "The whole dynamics of a process can change with respect to resonate frequencies on the transducers if they start vibrating. Certain transducers might not be able to handle it as well as others." How do you want to read output? This will be a choice between analog and digital controls, which has marked a recent shift in the industry. "Everything seems to be going to digital display where the controller is microprocessor-based," says Breen.

Another option is graphical digital displays, a larger version of an LCD display that draws pictures instead of just numbers. Advancements in control technology make it easier to integrate with modern controls and communicate with the machine, notes Brocklebank.

And this leads to a greater ability to diagnose and remedy problems, Breen says. "By assessing a customer's problem over the Internet, we can tell them what's wrong and if they need to send it in for repair. This speeds up the process of getting help and eliminates downtime."

Integration reduces the need for operator intervention, says Chris Harper, district manager for Maxcess. "Features like automated control loop and load cell calibration can speed setup and changeover by standardizing routine processes. Additionally, these automated processes ensure consistency and reduce scrap."

Darrell Whiteside, product manager for Maxcess. reports, "Converters will see more access to automated features like weightless load cell calibration and gain compensation as control manufacturers work to simplify setup and increase consistency of tension from roll to roll. We are also working to reduce the physical size of components to conserve valuable machine space."

Ultimately this means smaller and smarter controllers, says Breen. "Just look at your MP3 players today. That's what will happen in industrial electronics as well."


For this and other related new products, see our June New Products section.



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