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Processing of Plastics 259

output,

Q"

0 P,, Pressure, P
Fig. 4.12 Extruder and die characteristics

4.2.5 Other Die Geometries
For other die geometries it is necessary to use the appropriate form of equation
(4.12). The equations for a capillary and a slit die are derived in Chapter 5.
For other geometries it is possible to use the empirical equation which was
developed by Boussinesq. This has the form

Fbd3
Q=- (4.14)
12qLdeP
where b is the greatest dimension of the cross-section
d is the least dimension of the cross-section
F is a non-dimensional factor as given in Fig. 4.13.

Using equation (4.14) it is possible to modify the expression for the operating
pressure to the more general form
21rqpNH sin 4 cos 4
(4.15)
+ (OH3 sin2 4/3L)