- August 14, 2012, Timothy J. Walker
If I had to pick three recommendations to blindly give out to help any process, they would be:
- Avoid nips
- Use bigger cores
- Measure tension
The first two are about avoiding defects. The last one is about diagnosing your process.
Direct measurement of web tension is the best diagnostic sensor for web conveyance performance. I strongly recommend this as the top improvement project to reduce all web handling related waste.
Improved tension sensing and control will reduce waste from scratching, wrinkling, web bagginess and camber, curl, web shifting, and most winding defects. Many on-line web quality measurements are difficult, expensive, or impossible. Tension measurement is easy, reasonably price, and proven. I believe there is no greater measurement of web and web process quality than on-line tension measurement in all tension zones.
In addition to a single tension-sensing roller in each zone, for tension zones where there are many, many rollers (e.g., long roller ovens or web accumulators) there is added value in installing two tension rollers, one before and one after the elevator. The dynamics of accumulators require many rollers to rapidly accelerate or decelerate, adding or subtracting inertial loads on the web.
Tension measurement at the input and output of an accumulator will help monitor the tension change between input and output during the web accumulator’s steady-state, accelerating, and decelerating conditions. In a zone with many rollers, the tension differential of upstream and downstream tension rollers will show changes in roller and bearing drag. In either case, this information can be used in a preventive maintenance program diagnosing significant change in roller bearing over time.
Of course, like any measurement, a tension-measuring roller requires calibration. When you use tension rollers, include them in your maintenance schedule to verify they are holding calibration.
Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; firstname.lastname@example.org; www.webhandling.com.