(442y) Finite Element Simulations of Granular Compaction Part 2: Paste Extruder

Finite Element Simulations of Granular Compaction

Part 2: Paste Extruder

Matthew
Pruitt, Matthew Brown, Brandon Ennis, Bryan J. Ennis*

Department
of Chemical Engineering, The University of Tennessee at Chattanooga

*Corresponding author, bryan-j-ennis@utc.edu

Paste extrusion is widely used in processing (food,
pharmaceuticals, and catalysts).  As a
matter of design, pressure is developed within the screw (screw
characteristic), which then allows extrusion of the paste at the die (die
characteristic).  There have been few
advances, either analytically or modelling since Benbow & Bridgwater [1].  In this and related work [2], analytical
expressions for the rise in flight pressure with axial position, based on an
unwound flight model have been developed, as a variant of the Janssen equation
and originally based on the work of Darnell and Mol [3]. Here, feed pressure is
amplified by sliding friction of barrel conveying pastes through a flight
channel forward to the die face, leading the extrusion of
strings of compacted paste, or extrudate. 

This work revisits unwound flight models for screw characteristic
analysis using finite element methods. A full representative model of screw
could also be attempted, but the results should be identical [3]. In
particular, arbitrary Lagrangian/Eulerian methods are employed through LS-DYNA.
The impact of various material models (both plastic and geotechnical: Mohr-Coulombic,
Federal Highway Administration (FHWA) Soil Model, and Drucker-Prager) on the
development of flight pressure is explored, as well as the impact of both
flight and barrel friction.  These are
compared to experimental data to confirm the simulation maintains physical
sense throughout each step.  Model
validation also occurs through approximate analytical solution of the unwound
flight, modified Janssen equations.

Keywords: Paste
Extrusion, Screw Extrusion, Material Modeling, Finite Element

References:

 [1] Benbow,
John and Bridgwater, John. ?Paste Flow and Extrusion.? University of
Birmingham,

Oxford. Clarendon Press. 1993.

[2]  Botten,
A.J., Burbride, A.S., and Blackburn, S. ?A model to predict the pressure
development in single screw extrusion.? University of Birmingham. Journal of
Materials Processing Technology 135. 2002.

 [3]
Darnell, W.H. and Mol, E.A.J. ?Solids Conveying in Extruders.? SPE Journal.
April 1956.