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May 13, 2006
Crossweb Tension/Bagginess Measurement?
How do you measure a baggy web?
A common, practical, but tough question. I suggest several options, some off-line, others on-line.
1. Measure skew from a straight line in sweeping out a web (measure asymmetry only).
2. Measure crossweb droop variations in a lightly tensioned horizontal span.
3. Qualitatively judge a sheet of film as you pull it from a roll, grading it a 1, 2,..5 as you pull a web to tautness with finger, wrist, elbow, shoulder, or full body strength.
4. Combine 2 and 3 above, measuring tension to pull horizontal span up to less than X (say 1") droop.
5. Mark crossweb lines in a wide web, then cut it into machine direction strips and measure the length differential of the strips.
6. Lay flat test, place sheet on flat plate and measure ripple or curl deviations from planar.
On-line tests (measuring the moving web):
1. Droop test with scanning distance measurement, such as laser triangulation micrometer or ultrasonic sensor.
2. Low angle laser - Visualize droop with a low-angle linear laser or combine this with a camera and vision system to quantify bagginess (I don't know of any commercially available system to do this.)
3. Multi-segment tension roller - Dover flexo makes this. Segmented tension roller.
4. Multi-segment tension bar - Same idea, but for scratch-insensitive webs, using a segmented bar instead of rolling elements. (I don't know of a commercially available design, but Paprican will talk about this at the AWEB next week.)
5. Air turn back pressure - Float the web over an air bar and measure the back pressure in discrete positions across the web width. (I haven't seen this commercially available in the US, but I expect any air turn manufacturer could put one together, such as MEGTEC. I have seen this marketed in Japan by Bellmatic Ltd.
6. Speed of sound - Measure the speed of a sound wave in the web. First demonstrated by Dr. Richard Lowery at the OSU WHRC. Limited marketing of this device by Ron Markum of Advanced Web Systems.
More. I don't think any of these have completely satisfied the need. Let me know if you want to add to the list.
tjw
Posted by Tim Walker at May 13, 2006 08:26 AM
