Extrusion International 2-2024

49 Extrusion International 2/2024 The impact of these two variables was tested and the results are shown in diagram2. It shows that a longer EVI section increases the throughput by 10 to 20%, while a larger EVI diameter massively increases the throughput by 50%. The overall increase in the throughput com- pared to the reference is approx. 60 %. Besides the intake section, an optimized process sec- tion was evaluated through adjusted designs of the transition and mixing zones. The designs of configura - tions of the COMPEO process section using 3-flight- or 4-flight-technology or a combination of both were com - pared in their impact on temperature rise and specific energy input. The unequaled flexibility of the combination of these various technologies is a particular advantage of the COMPEO series. This flexibility also includes the possibility of using two flight elements that operate like dynamic restric - tion rings cleaned by pins. Due to this principle, the risk of burning is significantly lower compared to using real restriction rings. The target was to define the optimal transition and mixing zones regarding specific energy input and prod - uct conveying. Firstly, different transition zone screw configurations were tested. The findings from these tests are shown in diagram 3. The use of 4-flight elements (configuration 1) results in very good feeding behavior, and reduced shear in- put at the end of the feeding zone. Conversely, using 3-flight elements (configuration 2) shows reduced con - veying capacity and increased shear input. The third configuration was a combination of 3- and 4-flight ele - ments that achieved a very good intake behavior, com- bined with increased specific energy input in the tran - sition zone. The flexible configuration offers superior processing performance. To optimize the mixing zone performance, differ- ent screw configurations were tested. The results are displayed in diagram 4 and the findings are as follows: the use of 3-flight elements with long shearing flanks (configuration 1) results in very high energy input and long residence time. This is not favorable for PVC com- pounding. In configuration 2 (3-flight elements with short shearing flanks), still a long residence time was observed with a reduction of shear input compared to configuration 1. In contrast to these previous configurations, the use of 4-flight elements with long shearing flanks (configu - ration 3) performed optimally in terms of a short resi- dence time together with very high conveying stiffness. The use of 4-flight elements with short shearing flanks (configuration 4) also showed a short residence time; on the other hand, the conveying stiffness was reduced. These results reveal the huge potential of this concept to adjust the configuration depending on the product/ customer requirements. Diagram 1: Throughput as a function of the inlet length Diagram 2: Influence of the EVI diameter and length on the machine throughput Diagram 3: Temperature trends of different screw configurations Diagram 4: Impact of different flight geometries on the temperature trend