Tension Control and the Price of Energy

As a result of recent and on-going price volatility in petroleum and other forms of energy, materials, especially plastic film, are becoming an increasingly expensive asset. In a time of thin profit margins and after multiple rounds of adding value such as printing, coating, laminating and slitting, the one thing the converter must try to do is to make the best use of available resources and, where possible, avoid producing too much waste.

With substrates such as film becoming thinner and more extensible, the risk of damaging the film or producing a product that quality wise is unacceptable becomes more of an issue. Controlling tension to avoid wrinkling or stretching the film is one way to minimize wasted material.

Web tension controls, applied properly, will decrease waste due to web defects and will also allow an operator to concentrate on other critical areas of production. The latter has become increasingly important given the undeniable trend towards shorter production runs and innumerable product changeovers, which can overwhelm an operator, experienced or otherwise. Following on-site consultation and process evaluation, one of the options that Montalvo may propose is a closed-loop tension sensing load cell (transducer) control system, which monitors and adjusts web tension according to set point, correctly and continuously on an automatic basis with minimal operator intervention.

The name of the game in all industries is to go faster, to derive maximum product yield from the machine while maintaining the highest levels of accuracy. Accurate tension control enables converters to move in the direction of meeting these goals. Accurate tension control can even allow the converter to run different webs and processes through a machine. This contributes to profits, enabling the converter to bid for jobs that otherwise would have been out of reach.

Films can create tension control and registration problems. The extensible nature of films necessitates lower tension levels, if the material elongates registration can be affected. Low tension and wide tension ranges can be problematic, especially for some dancer control systems because of friction and inertia of their components. Dancers typically oscillate or ‘hunt,’ resulting in tension variations, web length variations and shifting from side-to-side. If the ‘hunting’ is excessive the dancer may reach the end of its travel, resulting in web breaks and other quality related problems. A solution to these problems for those companies’ using a dancer is the Montalvo D-3400ce dancer roll controller. This module functions in such a manner that it keeps the dancer position constant by adjusting input or output of web speeds.

Another dancer control alternative, one developed to provide a higher standard of tension control by simultaneously processing the signals from a dancer roller and a pair of load cells (transducers) is the DTI-3400ce dancer controller with tension indication. It combines the storage and shock capabilities of a dancer with the accurate, repeatable results of the load cell (transducer). Control is provided by ‘progressive PID circuitry,’ which regulates the output to an unwind brake and maintains the position of the dancer arm. The signal provided by the load cells (transducers) is displayed on the analog meter. ‘Actual’ web tension is used by the operator to adjust the load on the dancer arm and thereby maintain desired tension.

Montalvo load cells (transducers), used in conjunction with an X-3400ce tension controller, provide the ultimate in closed loop control. By closed loop we mean that the output of the system (tension) is fed back to the input forming a continuous path through the regulator and back to the input (controller), circulating in an endless unbroken loop.

The X-3400 is Montalvo’s top range controller with an optimised combination of analog and digital features. Using feedback from load cells (transducers), this controller may be used on unwind and rewind positions, and, with feedback from load cells (transducers) and a tachometer input, the X-3400 may also be used as an intermediate controller. Control modules including, the X-3400, D-3400 and DTI-3400 share a degree of commonality in that they offer web break detection, inertia compensation, fieldbus connectivity, transferable memory card and much more.

Load cells (transducers), specially designed force transducers are normally mounted in pairs with one installed on either end of an idler roll. Load cells (transducers) also offer an additional advantage in that these compact devices can be installed on any tension zone of a machine, from unwind to intermediate to rewind. Montalvo load cells (transducers), used in conjunction with the appropriate Montalvo controller provide the measurement and instantaneous adjustment necessary in a high-speed production environment.

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