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A twin-wire model gap former: design and evaluation methods
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, 54-58 p.Article in journal (Refereed) Published
Abstract [en]

A one-sided model twin wire gap former, the KTH-former has been developed. The former consists of headbox with transparent gables, forming unit, including a forming roll with a transparent surface and outer forming wire and a reservoir system for water/fibre suspension handling. To allow the study of blade forming, a blade can be introduced against the outer wire to generate a pressure pulse.

Two measurement techniques have been utilized to study the flow mechanisms of fibre suspension flow in the forming zone;

A pressure sensor has been used to study the dewatering pressure along the forming zone.

A high speed video system was used to visually study the suspension flow.

The study was made with pulp fibres. Fibre floes were introduced in the center of the headbox at the beginning of the linear nozzle contraction, by an introduction tube with an inner diameter of 10 mm. The acceleration in the nozzle contraction was used to separate the fibre floes in the Suspension making them move individually, thus making the visualisations easier. To avoid the problem of floc break-down at nozzle exit when using a conventional linear nozzle with parrot's beak outlet, two Curved contraction blocs were inserted, giving a more constant acceleration profile, letting the floes keep their integrity in the emerging jet.

The high speed video system had two main arrangements, for the Study of floc behaviour in the forming zone. A mirror installed on the machine structure visualised a certain area of the forming zone. Alternatively, a mirror fastened to the back plate of the forming roll followed a specific area of the wire (and roll), making it possible to follow the floes through the entire forming zone. It is then possible to detect any relative motion between floes and wire.

Place, publisher, year, edition, pages
2006. Vol. 21, no 1, 54-58 p.
Keyword [en]
Blade forming, Experimental studies, Fibre flocs, Roll forming, Twin-wire forming, Dewatering, Flocculation, Reservoirs (water), Video cameras, Blade forming, Experimental studies, Fibre flocs, Twin-wire forming, Fibers, Blade, Drainage, Fibers, Flocculation, Forming Rolls, Gap Formers, Twin Wire Machines
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-5218ISI: 000236358800009Scopus ID: 2-s2.0-33645656027OAI: oai:DiVA.org:kth-5218DiVA: diva2:8036
Note
QC 20100901. Tidigare titel: The KTH-Former, a model gap former: design and evaluation methods. Titel ändrad samt uppdaterad från Manuskript till Artikel i tidskrift 20100901.Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Fibre flow mechanisms
Open this publication in new window or tab >>Fibre flow mechanisms
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The flow behaviour, and primarily the floc-floc interaction, of pulp paper suspensions have been studied visually. Analogy models based on these observations have been developed as well as the identification of important parameters of floc break-up in low shear rate flow fields. Floc compressions and the locations of voids (areas of lower fibre concentration) where found to influence the floc splitting mechanism. Based on this investigation an equipment for measuring the load carrying ability of fibre flocs and networks was designed, and the effect of measurement geometry, network structure and fibre suspension concentration was investigated. The load carrying ability with concentration increases rapidly when going from 1% to 2% in initial suspension concentration.

A model handling the fibre floc behaviour during extension and compression has been developed, and some basic flocculated flow mechanisms are discussed on an analogy basis. A modified Voigt element is use, describing mainly the compressional behaviour and plastic behaviour of loose fibre network structures. Further the pos- sibility of stress chain formation is discussed on a fibre level as well as on a floc level.

The effect of fibre flow (shear field) occurring in the forming zone of a roll former has been studied in detail. Basic forming mechanisms on floc scale has been investi- gated, and the effect of running parameters like dewatering pressure and jet-to-wire speed difference as well as the fibre type and concentration of the pulp suspension has been evaluated. It is evident that floc elongation increases with shear rate (jet-to-wire speed difference) and lower dewatering rate. The latter is because the fibre floc is subjected to the shear field longer due to slower immobilisation. Shorter fibre tends to create weaker networks, which promotes a higher elongation of the flocs.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 15 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:17
Keyword
Fibre flow, floc, shear, compression, fibre network, stress chain
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-240 (URN)
Public defence
2005-06-17, Hörsal D2, Kungliga Tekniska Högskolan, Lindstedtsvägen 5, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100901Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2010-09-01Bibliographically approved

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