Maximilian Prechtl,
"Axial Torque Measurement in Single-Screw Extrusion"
, 10-2022
Original Titel:
Axial Torque Measurement in Single-Screw Extrusion
Sprache des Titels:
Englisch
Original Kurzfassung:
In single-screw extrusion approx. \SI{80}{\percent} of the energy needed to plasticize the material during processing is transferred mechanically and only approx. \SI{20}{\percent} is transferred via heat conduction. Despite this great fraction, there is a striking information gap regarding the mechanical energy input into the polymer. For a precise investigation, a measurement method is needed to determine the mechanical energy input at any axial position of the extruder. With the ongoing digitalization trend and rise of data-based modeling approaches, data generation is an additional key in the polymer processing industry. These must have a certain quality, quantity and information content. However, for many cases, data with essential information is either unavailable, of low quality, or in small quantity. Here, online or inline measurement systems are the most suitable solution, as they can meet these requirements. In this thesis a novel online measuring system is presented, for measuring the torque distribution along the screw and thus the distribution of the mechanical energy input.
In the first part of this thesis, the object to be measured, the measurand and measurement unit are defined. Furthermore, the physical principles of the measurement are presented, commonly known as the measurement principle. This is followed by the description of the measurement method, which is the generic description of a logical organization of operations used in the measurement to gain the solution. The physical realization is defined as the measurement system and contains the measurement instruments, supply, software, or other devices regarding the measurement. In addition, the theory and the procedure of the measurement system analysis is introduced, which contains the investigation of repeatability, bias, linearity, stability and the theoretical measurement resolution.
The second part of this work deals with the practical investigation of the measuring system. For this purpose, experiments were carried out with 3 materials, 3 screws, 6 screw speed settings and 2 back-pressure settings. The evaluation of these experiments focused on the comparison of the axial torque profiles and the profiles of the specific mechanical energy input. Here, the influence of material, screw design, screw speed and dynamic pressure was investigated. Furthermore, the analysis of the measuring system was carried out by repeated measurements and the comparison of the maximum measured screw-torques with those from the extruder drive. Finally, a failure analysis was performed, giving an overview of the known failures and highlighting those parts of the measuring system with the greatest potential for improvement.
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