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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======
-The content is currently being processed and will be made available shortly. Please be patient.
-===== Wall-slipping materials =====
-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), which are
-wall slipping under certain conditions.
-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.
-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.
-$$τ_ {WH,S} > τ_{krit} ⇒ τ_S = τ_{krit}$$
-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.
-**Platzhalter Abb. 9.36: Druckverlauf mit und ohne Wandgleiten**