Sunday, October 14, 2007

Holes in Paper (Troubleshooting Guide)

Holes in Paper (Troubleshooting Guide): "Holes (Pick-outs, Slime) Some detective work may be required to determine the cause of holes in a web of paper coming from a paper machine.

Even more detective work may be needed if the holes are causing breaks, so that the web doesn't make it to the reel.

Besides causing web breaks on the paper machine, holes also cause breaks during subsequent coating.
Customers usually will reject product that has more than a very rare incidence of holes, and papermakers spend a lot of time and effort splicing paper in order to remove and holes that have been automatically detected during production.
One of the first things that you will want to determine is the general category of the hole problem.

Three primary causes of holes in paper are
  1. tacky materials on rolls or other rotating elements within forming, pressing, or drying equipment on paper machines,
  2. slime, and
  3. equipment defects.
Tacky materials on a roll can cause holes by 'picking out' the fibers from the part of the paper that comes into contact with them.

Consequences of this effect can range from a mild roughening of the paper surface, to the accumulation of dust or 'crumbs' of fibers in the system, to partial delamination, to the development of holes in the paper by a pick-out mechanism, and ultimately to web-breaks.

Bacterial slime can cause holes in quite a different way. "

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