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5.3.4.2 Amorphous Polymers
Amorphous polymers do not exhibit the sharp enthalpy change as crystalline plastics
when passing from liquid to solid. Consequently, when applying the numerical method
of SCHMIDT [24], the correction for the latent heat can be left out in the calculation.
A sample plot calculated with the computer program given in [3] is shown in Figure 5.44
for amorphous polymers.
It is to be mentioned here that the analytical solutions for non-steady heat conduction
given in Section 3.2.1 serve as good approximations for crystalline as well as for
amorphous polymers.
5.3.5 Design of Cooling Channels
5.3.5.1 Thermal Design
In practice, the temperature of the mold wall is not constant, because it is influenced by
the heat transfer between the melt and the cooling water. Therefore, the geometry of the
cooling channel lay out, the thermal conductivity of the mold material, and the velocity
of the cooling water affect the cooling time significantly.
The heat transferred from the melt to the cooling medium can be expressed as (Figure
5.45)
The heat received by the cooling water in the time tK amounts to
(5.89)
(5.90)
The cooling time tK in this equation can be obtained from Equation 3.41. The influence
of the cooling channel lay out on heat conduction can be taken into account by the shape
factor Se according to [23, 26].
Figure 5.45 Geometry for the thermal design of cooling channels