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The shear rate required for determining the viscosity ?]a at the given melt temperature T
is obtained from
Symbols and units used in the formulas above:
(5.36)
Db: Barrel diameter mm
H: Channel depth mm
e: Flight width mm
s: Screw lead mm
& Flight clearance mm
L: Length of melt zone mm
v: Number of flights -
Ap: Pressure difference across the melt zone bar
Yi: Shear rate s" 1
Qp > Qd : Volume flow rate of pressure flow and drag flow, respectively m 3 /s
thp,md: Mass flow rate of pressure and drag flow, respectively kg/s
th: Extruder output kg/h
Tja: Melt viscosity Pa • s
ad: Ratio of pressure flow to drag flow -
T: Melt temperature 0 C
N: Screw speed min" 1
Example
For the following conditions the extruder output is to be determined:
Resin: LDPE with the same constants of viscosity as in Example 1 in Section 4.1.1.
Process parameters:
Screw speed N - 80 min" 1 (rpm)
Melt temperature T =200 0 C
Melt pressure Ap = 300 bar
Geometry of the metering zone:
Dh = 60 mm; H= 3 mm; e = 6 mm; s = 60 mm;