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  • 1.
    Bergström, Roger
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Åkesson, Krister
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A twin-wire model gap former: design and evaluation methods2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 54-58Article in journal (Refereed)
    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.

  • 2.
    Åkesson, Krister
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Floc behaviour in a twin-wire blade pressure pulse2004Licentiate thesis, comprehensive summary (Other scientific)
  • 3.
    Åkesson, Krister
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Flow mechanism in twin-wire blade forming. Part I2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 59-66Article in journal (Refereed)
    Abstract [en]

    In a one-sided twin-wire model gap former, the KTH-former, the effects of blade load and wire permeability upon a blade forming pressure pulse, flow velocity and roll-to-wire gap has been studied. A forming blade was applied against the Outer wire of the forming roll and the blade pressure was measured with a pressure sensor mounted in the roll surface. A camcorder was used to evaluate the roll-to-wire gap. Increased blade load gave higher pressure peaks upstream of the blade tip. Tracer particles (fibre floc fragments, confetti) were injected into the headbox and recorded with a high speed video camera when passing the blade in the forming zone. Velocity measurements of the tracer particles showed how the velocity was slowed down upstream of the blade, and then was accelerated when the blade was approached. Tracer particles were pinned to the permeable forming wire and their velocity eventually reached the wire velocity. Increased blade load generated a higher pressure peak and was accompanied by a lower velocity and larger gap upstream of the blade tip.

  • 4.
    Åkesson, Krister
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Flow mechanism in twin-wire blade forming. Part II2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 67-72Article in journal (Refereed)
    Abstract [en]

    In a one-sided twin-wire model gap former, the KTH-former, the behaviour of pulp fibre floes in the presence of blade forming pressure pulses has been studied at different blade loads and wire permeabilities. Pulp fibre floes were injected into the headbox and recorded with a high speed video camera when passing a forming blade ill the forming zone. With a visual evaluation method the fibre floes were found to be elongated and some of them ruptured during the acceleration when the floes passed the forming blade. Floc strain and floc breaking ratio increased with blade load because of a higher acceleration. Floes partially pinned to the permeable wire will elongate and tend to rupture more due to the mix-to-wire speed difference upstream of the forming blade. Sonic differences for rupture using different pulp qualities are quantified.

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