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  • 1.
    Asplund, G
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Norman, Bo
    KTH, Superseded Departments, Pulp and Paper Technology.
    Fibre orientation anisotropy profile over the thickness of a headbox jet2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 8, p. 217-221Article in journal (Refereed)
    Abstract [en]

    The fibre orientation anisotropy at various levels of the jet from a model headbox has been investigated. Stiff nylon fibres, 3 mm long, were added at extremely low concentrations to make it possible to observe also the centre of the jet. This meant that fibre interactions, such as floc forming, could not take place. Transparent, parallel walls enclosed the jet where fibre orientation was measured. A thin laser sheet illuminated the jet from the side and a video camera captured the light reflected perpendicularly from the fibres. Using image analysis, the orientation of the fibres was evaluated. A central vane was mounted in the headbox nozzle so the effects of the vane wake could be studied. The results show that the effect a the boundary layers, at the walls of a headbox and at the surface of a vane, was to locally reduce fibre orientation anisotropy. Depending on the vane tip shape, fibre orientation anisotropy could be additionally decreased. Overall, the fibre orientation anisotropy was weakly affected by changes inflow rate and strongly dependent on the contraction ratio in the nozzle; low speed and large contractions produced more anisotropic orientations.

  • 2.
    Bergström, Roger
    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.
    Floc behaviour during roll formingManuscript (Other academic)
  • 3.
    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.

  • 4.
    Holm, Richard
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Paper Technology.
    Experimental studies on dewatering during roll forming of paper2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 205-211Article in journal (Refereed)
    Abstract [en]

    Pressure and wire position measurements have been performed in an experimental facility, the KTH-Former, which intends to model the roll-forming zone of a paper machine. The measured pressure distributions in the forming zone are shown to have more complex patterns than the simple model p=T/R, which normally is referred to as the nominal pressure. It is also shown that an increase in wire tension has a similar effect as a decrease in flow-rate on the shape of the pressure distribution. This is a consequence of that the flow to a large extent is governed by the relation between the dynamic pressure and the nominal pressure. For the case of partial dewatering the suction peak that appears at the roll-wire separation point has a strong influence on the pressure distribution upstream. Finally, it is shown that the drainage has a stabilizing effect on the dewatering pressure.

  • 5.
    Holmqvist, Claes
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dahlkild, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Norman, Bo
    STFI-Packforsk.
    A flexible approach for modelling flow in multi-component blade formers2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 73-81Article in journal (Refereed)
    Abstract [en]

    The internal structure of the fibre network constituting a paper is to a dominating extent determined in the forming zone of the paper machine. In this article we present a method for modelling the pressure distributions in blade forming sections, which is commonly considered to be a key quantity of the process. The ambition is to obtain a tool by which the interaction between the different components of blade sections can be studied. It is achieved by defining modules out of which arbitrary sections can be constructed. The modules are solved independently and matched to each other iteratively Keeping the interface between the modules simple provides great flexibility in the modelling. By virtue of a slenderness assumption, the equations governing each module can be reduced to one-dimensional form, hence limiting the computational work and permitting systems of many components to be studied. Dimensionless numbers defining the problem are identified, and the magnitude of the nonlinear effects are estimated. Simulations are presented that illustrate the potential of the method.

  • 6. Kemper, M
    et al.
    Norman, Bo
    Sandberg, C
    Bergström, Jonas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ko, J
    Vomhoff, Hannes
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mannes, W
    Paul, T
    Method for fractionating an aqueous paper fibre suspension and hydrocyclone for carrying out said method2008Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention relates to a method and to a device which is used to fraction aqueous paper fibre suspensions (S). Relatively large centrifugal forces are used, also in suspension components having essentially the same densities, in order to achieve good results. This is achieved by virtue of the fact that the paper fibre suspension (S) entering via the inlet (10) is guided initially in a first annular chamber (4) which narrows in an axial direction (4) and subsequently in a second annular chamber (5) which widens in an axial direction. As a result, good fractionating results can be obtained, in particular, when the fibre material consistency in the inlet area is approximately 0.5 - 2 % and also the necessary mass fluxes are maintained at a relatively low level. Said method can be used, for example, for fractionating fresh cellulose and/or wood pulp. It can also be used in the preparation of used paper, wherein said method is particularly economical.

  • 7.
    Yan, Huawei
    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.
    Fibre floc behaviour of softwood kraft pulp in flowing suspensions2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 24-29Article in journal (Refereed)
    Abstract [en]

    Deformation of floes in flowing suspensions was studied in a flow loop system. A fibre suspension jet from a model headbox was further accelerated by a secondary contraction with a width reduction of 50%. The fibre suspension flocculation was studied using an optical detection method. For the suspension of bleached softwood kraft Pulp at a fibre concentration of 5 g/l, fibre floes were followed manually along the secondary contraction. About 115 of the floes were stretched to breakage in the contraction. The floes were stretched in MD whereas they were even more compressed in CD, so that the total floe area in the MD-CD plane decreased, indicating an increase of fibre concentration in the individual floes. This was confirmed by an increase of gray value of the floes in the light transmission images. Fibre floe orientation in MD increased when passing along the contraction. The manual evaluation confirmed the validity of the power spectrum analysis results. Increasing fibre concentration gave larger fibre floes. The floe area reduction in MD-CD plane during contraction passage increased when increasing fibre concentration, which might be due to an increase of mechanical forces in CD generated by the contracting walls, since less free water existed between the fibre floes at a higher fibre concentration. Increased absolute flow velocity had an insignificant effect on the fibre floes within the investigated range.

  • 8.
    Yan, Huawei
    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.
    Lindström, T.
    A flow loop system for study of fibre suspension flocculation2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 19-23Article in journal (Refereed)
    Abstract [en]

    A flow loop system for study of fibre flocculation in Suspensions has been developed. The system is designed to simulate the flow conditions in a paper machine headbox. It is equipped with a radial distributor feeding a step diffuser pipe package, after which the flow is contracted in a 2-D nozzle. The flow system is also equipped with a secondary flow contraction, which is aimed for studies of fibre floc rheology. The conditions of the secondary contraction can be changed in order to generate different acceleration rates. The flow system is also equipped for dosage of retention/formation aids to Study the chemical effects oil fibre flocculation. The maximum flow velocity in the system is 16 m/s. Fibre Suspension flows were Studied using a high speed video camera and transmitted infra-red laser light pulse illumination. Images were taken either separately before and after or along the secondary contraction. Images of-fibre flocculation were evaluated by using power spectrum and wavelet transform analysis. By comparing the fibre flocculation before and after the secondary contraction, or by following the fibre floes during the secondary contraction, rheology information oil the fibre flocs call be obtained. By comparing the fibre flocculation information with and Without chemical additions, the effects of chemicals on fibre flocculation can also be studied.

  • 9.
    Yan, Huawei
    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.
    Lindström, T.
    Ankerfors, M.
    Fibre length effect on fibre suspension flocculation and sheet formation2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 30-35Article in journal (Refereed)
    Abstract [en]

    Fibre suspension flocculation was studied in a flow loop system, simulating the flow conditions in a modern paper machine headbox. The fibre suspensions after the headbox were accelerated by a secondary contraction, mimicking flow accelerations that may take place during forming. Fibre suspensions were studied using an optical detection method. Images were taken by a high speed video camera with transmitted infrared laser light pulse illumination separately before and after the secondary contraction. The mean fibre floc size was evaluated by power spectrum analysis in MID and CID respectively. A series of twelve pulp samples, four different commercial bleached softwood kraft pulps refined to three different levels, were used in the experiments. The fibre physical properties and formation number for paper sheets produced on a pilot paper machine with these pulp samples were characterised. Refining shortened the fibre length, thus decreased the fibre floc size in flowing suspensions and improved the formation in paper sheets. A series of mixtures at different ratios of bleached softwood and hardwood kraft pulps were also used in the experiments. The fibre physical properties of the mixtures were also characterised. The fibre length increases when increasing the ratio of softwood pulp in the mixture, thus fibre floc size in the suspension increases.

  • 10.
    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.

  • 11.
    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.

1 - 11 of 11
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