HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
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where<br />
HF = feed depth<br />
H = metering depth<br />
D = screw diameter<br />
N" = screw speed<br />
Indices: 1 = screw of known geometry and 2 = screw to be determined.<br />
The exponent s is given by<br />
where nR is the reciprocal of the power law exponent n. The shear rate required to<br />
determine n is obtained from<br />
Example<br />
Following conditions are given:<br />
The resin is LDPE with the same constants of viscosity as in Example 1 of Section 5.1.1.4.<br />
The stock temperature is 200 0 C. The data pertaining to screw 1 are:<br />
D1 = 90 mm; HF = 12 mm; H1 = 4 mm<br />
feed length = 9 D1<br />
transition length =2 D1<br />
metering length =9 D1<br />
output Ih1 = 130kg/h<br />
screw speed N1 = 80 rpm<br />
The diameter of screw 2 is D2 = 120 mm. The geometry of screw 2 is to be determined.<br />
Solution<br />
The geometry is computed from the equations given above [3]. It follows that<br />
D2 =120 mm<br />
Hp2 = 14.41mm<br />
H2 = 4.8 mm<br />
m2 = 192.5 kg/h<br />
N1 = 55.5 rpm<br />
Other methods of scaling up have been treated by SCHENKEL [29], FENNER [30], FISCHER<br />
[31],andPoTENTE [32].<br />
Examples for calculating the dimensions of extrusion screws and dies are illustrated in<br />
the following figures: