the forming and densification of fibre mats in twin-wire formers: modelling vinicius lobosco, bo...
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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
A. Flaks
Schematic Papermachine
● Blades improve formation● Mats start on the roll
A Modern Forming Section
Norman & Fellers
Dewatering Mechanisms
ThickeningFiltration
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
● Convective-diffusive time-dependent equation● Finite Element Method (FEM)
Variation = Convection + Diffusion
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 solids
content vs. applied stress
● No improvement after 15 kPa
Ave
rage
fin
al s
olid
s co
nten
t
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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