Q&A: Collecting Process Tension Data Over Time

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The manual web tension control system that was being used produced readings in percentages rather than absolute web tension in pounds. The fact that the tension of the polypropylene web was not accurately reproducible created productivity losses and material waste. The operator's inability to make adjustments of consistent magnitude with respect to changes in the monitored web tension was causing stretch in various locations on the web which ultimately caused the web to be thrown out of register in many locations.

This laminating process required a closed-loop tension control system which could measure actual tension in pounds and maintain substrate tension precisely and accurately within each batch and between batches. Maintenance of a set tension to within a few ounces throughout each production run was required to control the amount of polypropylene stretch to within 1/32". The problem was solved quickly, and affordably by installing a pneumatic tension control system including tension transducers and an automatic controller with a soft start feature to the unwind stand of the plant's extrusion laminating equipment.

This application illustrates the importance of using accurate tension control to reduce process deviations which have a negative effect on productivity or product quality. By reducing web scrap and allowing a process to run at higher speeds with defect-free output, a good web tension control system will not only improve a machines bottom line performance but can pay for itself in as little as a few weeks.

- DFE Case History from 5/96