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Modeling of bagginess due to storage of paper reels with ridges
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. (Paper Technology)
Karlstad University, Faculty of Technology and Science.
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
2009 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 8, no 9, 18-22 p.Article in journal (Refereed) Published
Abstract [en]

Paper is subjected to stress relaxation during storage in reels. Ridges in the paper reel subject the paper in the ridge to a higher strain than the paper adjacent to the ridge. The strain difference can become a permanent strain difference, resulting in a baggy web after unwinding. Researchers used a geometrical model based on stress relaxation test results to determine when the bagginess is substantial enough to cause problems. The results showed that runnability problems will appear if the ridge is about 1–2 mm high. This applies for a reel with a diameter of 1.2–1.8 m stored for 1 week.

Place, publisher, year, edition, pages
2009. Vol. 8, no 9, 18-22 p.
Keyword [en]
paper, baggy web, relaxation, reels, ridges
National Category
Paper, Pulp and Fiber Technology
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-6430OAI: oai:DiVA.org:kau-6430DiVA: diva2:353870
Available from: 2010-09-29 Created: 2010-09-29 Last updated: 2011-10-27Bibliographically approved
In thesis
1. Baggy paper webs: Effect of uneven moisture and grammage profiles in different process steps
Open this publication in new window or tab >>Baggy paper webs: Effect of uneven moisture and grammage profiles in different process steps
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the problems encountered in paper converting is caused by the occurrence of "baggy webs", which essentially is when the tension profile of the paper web is uneven. In an area with low tension the paper is longer, which results in bagginess. The baggy parts can not usually be stretched to even out the tension of the paper web in a converting machine, with the result that runnability problems are likely to occur.

The aim of the work described in this thesis was to investigate three particular stages in papermaking, namely drying, calendering and storage, and rank them according to their propensity for inducing baggy webs. The focus was placed on investigating the effects of uneven moisture and grammage profiles on the machine-direction strain difference profile.

The largest strain difference occurred when there were systematic thick streaks throughout a reel that formed ridges. Stress relaxation during storage then gave rise to a difference in strain of 0.14% when the ridge height was around 2-3 mm. Thickness variations due to variations in grammage is also a source of moisture variation.

A difference in moisture of 5% in the calendering stage resulted in strain differences of about 0.05-0.08%. These strain differences resulted in creases being formed as early on as in the calender nip when differences in both grammage and moisture content were present. Most creases appeared when the moisture difference was 2-8%. The difference in grammage could be large without creases being formed when no differences in moisture content were present.

A moisture difference of about 5-6% during drying resulted in a strain difference of 0.1% measured on isotropic samples. The moist area turned into a tight streak when the moisture difference appeared at moisture contents higher than 25%. At moisture contents lower than 20%, on the contrary, the moist area turned into a slack streak.

The conclusion drawn is that papermakers should concentrate first and foremost on eliminating variations in grammage, especially if these are systematic. This would also eliminate some variations in moisture content, which would solve more problems.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2010. 49 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2010:29
Keyword
bagginess, drying, calendering, grammage, moisture content, paper, profile, reels, softwood kraft pulp, storage, strain, tension, web
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-6421 (URN)978-91-7063-320-1 (ISBN)
Public defence
2010-12-03, Rejmersalen, 9C 204, Karlstads universitet, 09:15 (English)
Opponent
Supervisors
Available from: 2010-11-08 Created: 2010-09-28 Last updated: 2011-10-27Bibliographically approved

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