Modeling of the dissipation in the solid conveying section in single screw extruders

In addition to the task of supplying the melt dominated sections with sufficient material, the solids conveying section also is important for the drive dimensioning, since a considerable part of the drive power is converted in the form of dissipated friction power. The dissipation energy is caused between the granules and screw or barrel and by the internal friction of the material caused by relative movements in the solid block. The latter is not taken into account in current power models due to the complex kinematic movements of the granules. For simplification, it is assumed that there is a block flow of the granule bed in which the energy is passed purely by heat conduction to the granules in the interior of the block. However, this assumption is inadequate for many applications and the studies presented in this paper show that internal dissipation accounts for a significant proportion of temperature generation in the solids conveying section. Due to the current achievable resolution in the area of DEM simulations, the description of the granules in the solid block is now made tangible. In this way, investigations can be done regarding the granular shape influence on the development of heat by dissipation. In the case of cylindrical particles, for example, there is the possibility that the particles regularly align themselves in the screw channel and unroll beneath each other. This is of great importance for practical applications, as it is well known that a poor melting behavior of cylindrical polyamide on universal screws is observed. The influence of the granulate form and the material parameters as well as other process parameters has been investigated and mathematically recorded. Numerous simulations based on the Discrete Element Method (DEM) have been performed and validated by experimental data. The results are summarized in this paper.