(708f) Simulations of an Unwound Paste Extruder Flight

Simulations of an Unwound Paste Extruder Flight

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, 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 [2].  In this and related work
[1,3], 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 [4]. 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 using
finite element methods. 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.  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]
A.S. Burbidge, J. Bridgwater.? The single screw extrusion of pastes?. Chem.
Eng. Sci. Pg 2531?2543. 1995.

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

Oxford. Clarendon Press. 1993.

[3] 
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.

 [4]
Darnell, W.H. and Mol, E.A.J. ?Solids Conveying in
Extruders.? SPE Journal. April 1956.