Improper Web
Tension
Excessive web tension can contribute to web marking by pulling
on the web and intensifying any flaw that may be in the roller's
surface. It can wrinkle, stretch, or break the web and cause unwanted
roll deflection. Excessive tension can come from too much drag on
idler rolls, bearing friction, roll weight, etc. or from too may
idler rolls between drive sections. Excessive tension is often identified
by stretched edges and slack centers on the web.
Lack of tension causes "bagging" meaning web edges are
loose while the center is slack or just the opposite. Baggy edges
and loose webs can result in folds, creases, and wrinkles. Lack
of sufficient tension can come from loosely wound parent rolls,
unsupported spans of web travel, drive sections out of sync, and/or
lack of nip or web pull through the line.
If you have a tension problem from rolls that are too heavy (drag),
be cautious about simply replacing them with smaller rolls. Smaller
rolls will have more deflection, which can cause just as many problems.
Lighter weight rolls may be the solution for tension problems experienced
during startup or speed changes. They can supply support without
excessive drag. If your problem occurs once you are up to speed,
an idler designed with special free-running bearings may be a good
solution.
If you suspect your tension problems come from too many rolls or
rolls that are too heavy, try some experiments. Spin individual
idlers by hand. Are they hard to turn? Can you selectively remove
or replace some rolls and see problems lessen? Rolls of the same
size but made of lighter material, such as aluminum or carbon fiber
with free running bearings could help. Webex provides rolls with
specially designed free-running bearings with optimal lubrication.
Converters running different web materials on the same line have
to find a balance among various solutions that will work best for
all runs. Often, you need to determine which material will be run
most and focus on maximizing production for that material. We need
to know this so that your rolls can be designed and balanced to
meet the most demanding specifications of your application.
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