Calibration of a Contact Model for DEM Simulations of Grooved Feed Sections of Single Screw Extruders

For the design of feed sections in single-screw extruders, the simulation of solids conveying processes using the discrete element method (DEM) is increasingly being used, as this method does not require any a priori knowledge of the complex behaviour of the pellet movement. The output of such simulations strongly depends on the material parameters and the used contact model. In this work the accuracy of solids conveying simulations with a pressure gradient in a grooved feed section is examined for different material and contact model settings. First, the contact model parameters for the Hertz-Mindlin and the Hysteretic contact model have to be found for the investigated polymers PP, LLDPE and PA6. Therefore, the pellet geometries and coefficients of friction are determined experimentally. The accuracy of the settings is checked by compression tests and throughput measurements with a grooved barrel extruder. The compression tests are conducted to evaluate the pressure-deformation behaviour, while the throughput tests determine the accuracy of the simulated throughput values. Overall, the selected material and contact model settings show good accuracies for the solids conveying simulations. The Hysteretic contact model shows slightly better accordance to the compression tests. Regardless of the contact model chosen, there is very good agreement in the throughput experiments for the materials PP and LLDPE, but a little more deviation for PA6. Hence, both models can be used for the calculation of the throughput, although the Hertz-Mindlin model has advantages in terms of simulation duration and stability.