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 (μp–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 μp–b is increased, three regimes with distinct behavior were identified. For up to μp–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 μp–b > 2.00 a plug-type behavior is anticipated.