Page 270 - Plastics Engineering

Processing of Plastics 253

- plate
vd
Moving

Y

Stationary plate
(a) Drag Flow

High Pressure Low Pressure

F3

(b) Pressure Flow
In both cases, AB = dz, element width = dx and channel width = T
Fig. 4.7 Melt Flow between parallel plates

where N is the screw speed (in revolutions per unit time).
T = (IrDtan4 - e)cos4
so Qd = 4 (XD tan 4 - e)(XDN cos2 4)H
In most cases the term, e, is small in comparison with (nDtan4) so this
expression is reduced to
Qd = ~I~~DZNH cos 4 (4.3)
4
sin
Note that the shear rate in the metering zone will be given by Vd/H.