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Clamp Force
The calculation of clamp force is similar to that of the injection pressure. The isothermal
clamp force is determined from [19]
where F1(T2) = isothermal clamp force (N).
F1(T2) for the example above is with Equation 5.80
(5.80)
The actual clamp force can be obtained from the following empirical relation, which was
developed from the results published in [19].
Hence the actual clamp force F from Equation 5.81
(5.81)
The above relationships are valid for disc-shaped cavities. Other geometries of the mold
cavity can be taken into account on this basis in the manner described by STEVENSON
[19].
5.3.3 Flowability of Injection Molding Resins
The flowability of injection molding materials can be determined on the basis of melt
flow in a spiral channel. In practice, a spiral-shaped mold of rectangular crosssection
with the height and width in the order of a few millimeters is often used to classify the
resins according to their flowability. The length L of the solidified plastic in the spiral is
taken as a measure of the viscosity of the polymer concerned.
Figure 5.39 shows the experimentally determined flow length L as a function of the height
H of the spiral for polypropylene. A quantitative relation between L and the parameters
influencing L such as type of resin, melt temperature, mold temperature, and injection
pressure can be developed by using the dimensionless numbers as defined by THORNE
[23] in the following manner:
The Reynolds number Re is given by [23]
where
(5.82)
(5.83)