The influence of pellet-barrel friction on the granular transport in a single screw extruder

The flow of individual polymer pellets along the solids conveying zone of a single screw extruder is studied by means of a numerical model based on the discrete element method (DEM). The effect of the pellet-barrel friction coefficient (mu(p-b)) is discussed in terms of mass output, volume fraction, residence time distribution and velocity profiles. Model predictions are compared with experimental data, showing a good match, and with calculations using traditional analyses by assuming the movement of an elastic solid plug. As mu(p-b) is increased, three regimes with distinct behavior were identified. For up to mu(p-b) = 0.25 (this value coinciding with that of the pellet screw friction coefficient), particle collisions drive the granular transport. For higher values, friction determines the conveying efficiency, but when mu(p-b) > 2.00 a plug-type behavior is anticipated. (C) 2014 Elsevier B.V. All rights reserved.