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Mechanics of paper webs in printing press applications
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).ORCID iD: 0000-0003-3611-2250
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The mechanics of paper is a difficult subject because paper is a unique material. It is very thin, flexible at bending, unstable in compression and stiff at tension. Dealing with paper we have to account for orthotropy and heterogeneities created during the manufacturing process.

This thesis addresses two topics in mechanics of paper webs in printing press applications. First is the dynamic behaviour of the travelling webs. Second is so-called “fluting” after heat-set web-fed offset printing.

There are a number of challenges in simulating the dynamics of the paper web. It is necessary to include the influence of the paper web transport velocity. Due to initial sag or vibrations, gyroscopic forces affect the dynamics of the webs. Furthermore, the transport velocity reduces the stress stiffening of the web. A good theoretical model should account for large displacements and should be capable of simulating wrinkles, which is essentially a post-buckling phenomenon. Finally, the paper web is surrounded with air which reduces the natural frequencies substantially by “adding" mass to the paper. A non-linear finite element formulation has been developed in this study for simulation of travelling webs. The results of the studies shows that for the tension magnitudes used in the printing industry the critical web speed lies far above those used today. Speed limitations are rather caused by ink setting and tension control problems. If the web tension profile is skew, however, edge vibrations are inevitable even at small external excitations.

Fluting is a permanent wavy distortion of the paper web after heat-set web offset printing. It is often seen in high quality printing products, especially in areas covered with ink. It is generally accepted that tension and heat are required to create fluting. However, there have been certain disputes as to the mechanism of fluting formation, retention and key factors affecting this phenomenon. Most of the existing studies related to fluting are based on linear buckling theories. A finite element model, capable of simulating a post-buckling behaviour has been developed and experimentally verified. Studies show that none of the existing theories can consistently explain fluting. A new basic mechanism of fluting formation has been proposed and numerically demonstrated. Fluting was explained as a post-buckling phenomenon due to small scale moisture variations developing during through-air drying. It was concluded that air permeability variation is the key factor affecting fluting tendency. Fluting is retained due to inelastic deformations promoted by high drying temperatures.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , v, 18 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0404
Keyword [en]
Travelling webs, skew tension profiles, mixed dynamic formulation, fluting
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3863OAI: oai:DiVA.org:kth-3863DiVA: diva2:9761
Public defence
2006-03-16, Fälldinsalen, Mittuniversitetet, Sundswall, 13:00
Opponent
Supervisors
Note

QC 20100906

Available from: 2006-03-03 Created: 2006-03-03 Last updated: 2013-01-14Bibliographically approved
List of papers
1. Modelling the dynamical behaviour of a paper web. Part I
Open this publication in new window or tab >>Modelling the dynamical behaviour of a paper web. Part I
2007 (English)In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, no 3-4, 131-147 p.Article in journal (Refereed) Published
Abstract [en]

A new shell element has been proposed for geometrically non-linear, finite element analyses of axially moving paper web. Web instability problems of paper travelling in a printing system, such as wrinkling and fluttering, pose special challenges in the numerical analyses. For examples, theme are finite bending stiffness (as opposed to membrane), orthotropy, and non-uniform distributions of mechanical and hygro-properties (in different length scales). The new formulation has accounted for paper transport velocity and paper bending stiffness based on a mixed -1-agrangian-Eulerian description of the motion. A natural coordinate system has been employed in the analytical and finite element formulations. Benchmarking with different finite elements in various tests showed that the proposed element is indeed more stable and reliable for the chosen application than existing elements. The usability of the shell element has been successfully demonstrated by two example p:,-oblems: wrinkling of stretched isotropic and orthotropic membranes, and the vibration of a web showing a speedtensioning effect above a critical web transport velocity.

Keyword
axially moving materials, Hamilton's principle, one-point quadrature element, physical hourglass control
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24376 (URN)10.1016/j.compstruc.2006.09.006 (DOI)000244511600002 ()
Note

Tidigare titel: A shell finite element for geometrically non-linear analyses of axially moving paper webs QC 20100906

Available from: 2010-09-06 Created: 2010-09-06 Last updated: 2017-06-08Bibliographically approved
2. Analysis of paper web tension profiles
Open this publication in new window or tab >>Analysis of paper web tension profiles
2005 (English)In: Journal of Graphic Technology, ISSN 1544-9599, E-ISSN 1544-9602, Vol. 2, 72-81 p.Article in journal (Refereed) Published
Abstract [en]

The tension profiles of paper webs are very important for determining the runnability in printing presses. Uneven tension profiles, with lower web tension toward the edges, develop in the paper machine due to many factors such as moisture content, residual strains related to drying and draw conditions, fibre orientation etc. This study presents some simple relations regarding the initial strain distribution, but also a method for adjusting the tension profile by choosing an appropriate moisture distribution. The method is verified on web tension and moisture measurements in a pressroom.

National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5399 (URN)
Note

QC 20100906

Available from: 2006-03-03 Created: 2006-03-03 Last updated: 2017-11-21Bibliographically approved
3. Tension Wrinkling and Fluting in Heatset Web Offset Printing process. Post buckling analyses
Open this publication in new window or tab >>Tension Wrinkling and Fluting in Heatset Web Offset Printing process. Post buckling analyses
2005 (English)In: ADVANCES IN PAPER SCIENCE AND TECHNOLOGY: TRANSACTIONS OF THE 13TH FUNDAMENTAL RESEARCH SYMPOSIUM, VOLS 1-3 / [ed] IAnson, SJ, The Pulp and Paper Fundamental Research Society , 2005, 1075-1099 p.Conference paper, Published paper (Refereed)
Abstract [en]

Geometrically non-linear, large scale post-buckling analyses were carried out to investigate the influence of different parameters on residual waviness (fluting) after printing in a heat set web offset printing press. Mixed implicit-explicit finite element techniques were used in the analyses. The numerical procedure was verified by experimentally acquired data. Results show that when the paper web is perfectly flat before printing, fluting patterns after drying and moisture recovery generally have higher wavelength than those typically observed in fluted samples. Initial cockles of imprinted sheets were found to have impacts on the fluting patterns and amplitudes. Among the factors investigated, ink thickness and hygroexpansivity had significant influences on fluting: increasing these factors increased fluting amplitudes.

Place, publisher, year, edition, pages
The Pulp and Paper Fundamental Research Society, 2005
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5401 (URN)000283529400031 ()978-0-9545272-3-5 (ISBN)
Conference
13th Fundamental Research Symposium on Advances in Paper Science and Technology Location: Univ Cambridge, Cambridge, ENGLAND Date: SEP, 2005
Note

QC 20100906

Available from: 2006-03-03 Created: 2006-03-03 Last updated: 2016-05-11Bibliographically approved
4. Modelling the dynamical behaviour of a paper web. Part II
Open this publication in new window or tab >>Modelling the dynamical behaviour of a paper web. Part II
2007 (English)In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, no 3-4, 148-157 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a finite element procedure is used to study the dynamic behaviour of a paper web in a free span between two rollers, including effects of transport velocity and surrounding air. The paper web is modelled as a three-dimensional orthotropic structure. The influence of air is accounted for by utilizing fluid-solid interaction analyses based on acoustic theory. The contribution of transport velocity is included through gyroscopic matrices and forces. The structural response on harmonic excitations has been studied using linear and non-linear models. Results show that air significantly reduces eigenfrequencies of the web. So called "edge-flutter" is nothing but the result of skew tension profile. Excessive web vibration can be eliminated by adjusting the web tension.

Keyword
axially moving materials, edge flutter, skew tension profile
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24377 (URN)10.1016/j.compstruc.2006.09.007 (DOI)000244511600003 ()2-s2.0-33846235916 (Scopus ID)
Note

Tidigare titel: Modelling the dynamical behaviour of a paper web QC 20100906

Available from: 2010-09-06 Created: 2010-09-06 Last updated: 2017-12-12Bibliographically approved
5. Basic Mechanisms of Fluting
Open this publication in new window or tab >>Basic Mechanisms of Fluting
2006 (English)In: Annual Meeting of the Pulp and Paper Technical Association of Canada (PAPTAC), 2006, A161-A173 p.Conference paper, Published paper (Refereed)
Abstract [en]

Out-of-plane deformations of paper, such as fluting, significantly deteriorate the quality of a printed product. There are several explanations of fluting presented in the literature but there is no unanimously accepted theory regarding fluting formation consistent with all field observations. The present paper reviews the existing theories and proposes a mechanism that might give an answer to most of the questions regarding the fluting. The fluting formation has been considered as a post-buckling phenomenon which is analysed with the help of the finite element method. Fluting retention has been modelled by introducing an ink layer over the paper surface with ink stiffness estimated from experimental results. The impact of fast drying on fluting has been assessed numerically and experimentally. The result of the study suggests that fluting occurs due to small-scale strain variations, which in turn are caused by the moisture variations created during fast convection drying. The result also showed that ink stiffening alone cannot explain the fluting amplitudes observed in practice, suggesting the presence of other mechanisms of fluting retention.

Keyword
Curing, Dewatering, Drying, Ink, Mechanisms, Paper and pulp industry
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5402 (URN)2-s2.0-52749092563 (Scopus ID)
Conference
92nd Annual Meeting of the Pulp and Paper Technical Association of Canada (PAPTAC); 7 February 2006 through 7 February 2006
Note

QC 20100906

Available from: 2006-03-03 Created: 2006-03-03 Last updated: 2016-05-11Bibliographically approved

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Kulachenko, Artem

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