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The Forming and Densification of Fibre Mats in Twin-Wire Formers

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The Forming and Densification  of Fibre Mats in Twin-Wire Formers Powered By Docstoc
					The Forming and Densification
 of Fibre Mats in Twin-Wire
     Formers: Modelling

 Vinicius Lobosco, Bo Norman & Sören
                Östlund
                    Outline
●   Background on forming
●   Model
●   Results
●   Conclusion
●   Future Work
Schematic Papermachine




                  A. Flaks
A Modern Forming Section
        ●   Blades improve formation
        ●   Mats start on the roll




                     Norman & Fellers
   Dewatering Mechanisms
Filtration                  Thickening




             Parker, 1972
                    Outline
●   Background on forming
●   Model
●   Results
●   Conclusion
●   Future Work
            Present Available Models
●   Incompressible
     –   Zhao & Kerekes
     –   Roshanzamir et al.
     –   Holmqvist

●   Elastic
    – Martinez
    – Zahrai et al.
Experimental Material Behaviour
                ●   Vomhoff & Schmidt
                    –   Permanent
                        deformation
                    –   Hysteresis
                Mathematical Model
●   Balance Equations:
    –   Mass;
    –   Momentum
●   Transfer Equations
●   Constitutive Equations
                   Assumptions
●   Continuum
●   Intertial effect neglected
●   Wire gives no resistance
●   Symmetry
●   Darcyan flow
●   No interface resistance
             Mathematical Model 2



Variation = Convection + Diffusion


●   Convective-diffusive time-dependent equation
●   Finite Element Method (FEM)
                    Outline
●   Background on forming
●   Model
●   Results
●   Conclusion
●   Future Work
Results 1
            ●   Filtration
            ●   Dryness
            ●   Unbeaten
                Kraft pulp
                – CSF 718
            ●   10 kPa –
                20 ms
Results 2
            ●   Dryness
            ●   Beaten kraft
                pulp CSF 598
            ●   10 kPa – 20 ms
Results 3
            ●   Thickning
            ●   Blade forming
            ●   Three
                haversinus
                pulses 15 kPa 2
                ms with 2 ms
                interval
Results 4
            ●   Contours of
                Structural stress
Results 5

       ●    Material response
            from the different
            elements and the
            experimental data
            (Vomhoff & Schmidt)
                               Results 6
                                      ●   Diminishing returns
Average final solids content




                                      ●   Average solids
                                          content vs. applied
                                          stress
                                      ●   No improvement
                                          after 15 kPa
                   Conclusions
●   Demonstrates considerable dryness gradient
    effects.
●   Demontrates dryness relaxation effects.
●   Needs more data on unloading of webs.
●   Available to the industry.
●   Will be of large interest in modelling of twin-wire
    roll and blade forming.
                       Future Work
●   Numerical
    –   Streamline diffusion
    –   Moving Finite Elements (Yi Liu – C4)
●   Physical Model
    –   Hysteresis operator
    –   Wire and interface resistance
●   Generalisation
    –   Couple with Holmqvist's blade pressure model
●   Validate
    –   Filtration and papermachine (e.g. Euro-FEX)
             Acknowledgements
●   CPDC for the funds that made this project
    possible
●   Hannes Vomhoff for making his experimental
    data available.
●   Raul Tempone (NADA – KTH) for the support
    regarding the numerical method

				
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posted:8/11/2012
language:English
pages:21