Investigation of the pressure-throughput behavior of different spiral shearing sections on an analytical and simulative basis

Single-screw extruders have to take on ever-increasing mixing tasks in the course of more challenging demands on the products. Additives such as fillers, reinforcing materials or masterbatches are added. These additives often tend to form agglomerates. Within the extruder, the agglomerates must be broken down accordingly into smaller aggregates and particles. Conventional metering sections, however, usually do not cause sufficient shear forces at this point, so special shearing sections are used. Over the years, the spiral shearing section has proven to be the most commonly used shearing section. This shearing section is characterized by neighboring pairs of grooves as well as the pitch of the channels compared to the Maddock shearing section. Between the grooves is the shear gap, which is mainly responsible for the strain on the material due to its low height. In addition, the spiral shearing section also has a very positive effect on melting any remaining solid particles. Furthermore, it offers many geometric degrees of freedom so that the shearing section can be individually adapted to the process. However, due to the small gap, the shear section is usually a pressure consumer and accordingly has a direct effect on the throughput. The knowledge of the pressure loss is therefore of elementary interest for the design of a screw with a spiral shear section, since an incorrect design can lead to enormous reductions in throughput. Due to this fact, a large number of geometry variants will be analyzed simulatively on the basis of an extensive Central Composite Design (CCD) test plan and then compared with analytical models and experimental validation investigations.