Unterschiede

Hier werden die Unterschiede zwischen zwei Versionen angezeigt.

--- en:grafische_darstellung_der_ergebnisse:schlepp-druckstroemung [2024/11/17 19:21] – neelest
+++ en:grafische_darstellung_der_ergebnisse:schlepp-druckstroemung [2025/09/05 10:27] (aktuell) – [Analysing the drag pressure flow] neelest
@@ Zeile 1: / Zeile 1: @@
 ======Drag-pressure flow ======
-The drag pressure flow is an important mechanism in the plasticising process of a screw extruder. It describes the interaction between the drag flow caused by the screw rotation and the pressure flow generated by the pressure difference along the screw. Both types of flow affect the material flow and influence the throughput and quality of the extruded material. In the technical analysis, the dimensionless throughput (πm˙πm˙) and the dimensionless pressure gradient (πpπp) are graphically represented as key parameters.
+-> [[en:berechnungen:schlepp-druckstroemung|To the calculation bases]]
-**Aufrufen des Diagramms**
+===== Visualisation of the drag pressure flow =====
-=====Description of the parameters=====
+{{ :grafische_darstellung_der_ergebnisse:rex171_grafisch_en_010.png?nolink&1000 |}}
-  *     **Dimensionless throughput ($\pi_{\dot{m}}$):** The dimensionless throughput describes the conveying capacity of the extruder as a function of the flow conditions and the screw geometry. This value is represented by the ratio of the actual mass flow rate to a standardised reference value. A high dimensionless throughput indicates efficient material conveying, while a low value may indicate potential blockages, high friction or insufficient conveying. In the diagram, the course of the dimensionless throughput is shown as a curve that runs along the length of the screw. This curve provides information on how the throughput varies in the different zones of the screw - from the feed zone to the plasticising zone to the discharge zone.
+===== Interpretation of the curves =====
-  *     **Dimensionless pressure gradient ($\pi_p$):** The dimensionless pressure gradient describes the change in pressure along the screw. This gradient is a measure of how much the pressure increases or decreases in the various sections of the extruder. It is crucial for understanding the pressure flow, which is driven by the pressure difference along the screw. A positive pressure gradient means that the pressure along the screw is increasing, while a negative pressure gradient indicates a pressure release. These pressure changes significantly influence the shear stress of the material and therefore also the homogeneity and quality of the melt. The course of the pressure gradient is also shown as a separate curve over the length of the screw and provides an insight into the pressure distribution along the screw.
-=====Interpretation of the diagram=====
+  * **Blue curve**: The blue curve represents the dimensionless mass flow rate $\pi_\dot m$ and, together with the dimensionless pressure gradient, is a measure of the flow profile and the local conveying effect in the extruder.
-  *     **Interaction of drag and pressure flow**: In an ideal extrusion process, drag flow (due to screw rotation) and pressure flow (due to pressure gradient) work together in equilibrium. The drag flow conveys the material along the screw, while the pressure gradient provides additional forces to support or regulate the material flow.
+  * **Red curve**: The red curve represents the dimensionless pressure gradient $\pi_p$. If the value is 0, there is a pure drag flow. If the value is greater than 0, there is an increase in pressure and the pressurised flow flows against the drag flow (the dimensionless mass flow rate decreases); if the value is less than 0, there is a drop in pressure and the pressurised flow supports the drag flow (the dimensionless mass flow rate increases).
-  *     **Progression of the dimensionless flow rate**: Typically, the dimensionless throughput shows a slow increase in the feed zone as the material is initially compacted here. In the plasticising zone, where the material begins to melt, the throughput can increase sharply as the material becomes more flowable. In the discharge zone, the flow rate should remain constant to ensure that the molten material is conveyed evenly.
-  *     **Progression of the dimensionless pressure gradient**: The pressure gradient varies depending on the screw geometry and material properties. The pressure gradient can increase in areas with high compression or narrower screw flights. In degassing zones or at the end of the screw, the pressure often drops to allow the material to be relieved before it exits.
+The parameters cannot be calculated in shear and mixing parts.
+=====Analysing the drag pressure flow=====
+A dimensionless pressure gradient greater than 0 means that the pressurised flow flows against the drag flow. Although this reduces the mass throughput, at the same time the flow in the opposite direction ensures good mixing of the melt. Continuous ‘overrunning’ of the screw with a negative dimensionless pressure gradient and thus a high dimensionless throughput (as is usual with grooved barrel extruders) is therefore bad for the mixing effect in the extruder. \\
+The influence of the different screw zones can be analysed based on the progression of the parameters.
-{{ :grafische_darstellung_der_ergebnisse:rex171_grafisch_en_010.png?nolink |}}
 ===Further topics===
@@ Zeile 31: / Zeile 34: @@
   * [[en:grafische_darstellung_der_ergebnisse:scherdeformationsgradient_und_schergeschwindigkeit]]
   * [[en:grafische_darstellung_der_ergebnisse:schlepp-druckstroemung]]
+  * [[faserlaengenabbau|]]
+  * [[faserlaengenverteilung|]]
+  * [[spannungsanalyse|]]
+  * [[kennlinienfeld|]]
+  * [[entgasung|]]
+  * [[zykluszeit|]]
   * [[en:grafische_darstellung_der_ergebnisse:kurzbericht]]
   * [[en:grafische_darstellung_der_ergebnisse:langbericht]]