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we get
The dimensionless parameter is the ratio between the amount of melted polymer per
unit down channel distance to the extruder output per unit channel feed depth.
5.23.4 Melting Profile
The melting profile provides the amount of unmelted polymer as a function of screw
length (Figure 5.25) and is the basis for calculating the stock temperature and pressure.
It thus shows whether the polymer at the end of the screw is fully melted. The plasticating
and mixing capacity of a screw can be improved by mixing devices. Knowledge of the
melting profile enables to find the suitable positioning of mixing and shearing devices in
the screw [21].
The following equation applies to a screw zone of constant depth [6]
and for a tapered channel [6]
where
X
W
Screw
t
X
W
Axial distance along the screw
Cross-section of screw channel
Figure 5.25 Solid bed or melting profiles X/W and Gs/G [21 ]
G: total mass flow rate, G5: mass flow rate of solids
X/WA/G
Melt Solid bed Melt film
Barrel
(5.57)
(5.58)
(5.59)