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| en:berechnungen:wandgleitende_materialien [2024/10/17 20:24] – [Wall-slipping materials] neelest | en:berechnungen:wandgleitende_materialien [2026/09/17 09:23] (aktuell) – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1 | ||
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| - | ======Wall-slipping materials====== | ||
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| - | The content is currently being processed and will be made available shortly. Please be patient. | ||
| - | When considering the flow processes in rheometers but also in practical modules | ||
| - | such as dies, plasticating units and between gaps, the flowing melt is presumed to be | ||
| - | wall adhering. In polymer melting this is true for the majority of the materials. | ||
| - | However, there are some materials, among which the ultrahigh molecular | ||
| - | polyethylene of high density (HDPE) and the economically important polyvinylchloride | ||
| - | (PVC, frequently provided with outward lubricants for a gentle processing), | ||
| - | wall slipping under certain conditions. | ||
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| - | In order to calculate the plastisicating process with the simulation programs **REX** and | ||
| - | **PSI**, the option “wall slipping” has been added in the software. For this, critical shear stress values must be entered in the rheological material data as explained in the | ||
| - | Chapter Rheological Material Data. | ||
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| - | When choosing the menu item Wall slipping, **REX/PSI** considers that wall slipping | ||
| - | occurs above the critical wall shear stress. For this, the shear stresses at the barrel | ||
| - | wall and the root surface are evaluated and limited to a value whose maximum is | ||
| - | equal to the critical shear stress at the wall. | ||
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| - | $$τ_ {WH,S} > τ_{krit} ⇒ τ_S = τ_{krit}$$ | ||
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| - | This limitation affects the flow profile in the screw channel and decreases the local | ||
| - | pressure gradient. Thus, the pressure build-up capacity decreases but also the | ||
| - | pressure consumption of overridden screw sections. | ||
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| - | **Platzhalter Abb. 9.36: Druckverlauf mit und ohne Wandgleiten** | ||
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| - | ===Further topics=== | ||
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