The experimental results suggested that the effects
of various fins on the tensile properties were very
limited. On the other hand, the experimental data in
Fig. 10 suggested that increasing the mold’s rotational
speed increases somewhat the thickness
uniformity of molded parts. Nevertheless, the effect
of fins on the thickness distribution of molded parts
was negligible.
The global shrinkage [7] of parts molded by
various fins was examined and the measured results
are shown in Fig. 11. Parts cooled by still air
exhibited a larger shrinkage rate than those cooled
by forced air circulation . This is due to the fact that
the parts cooled by still air cool down slower, which
in turn results in a higher degree of crystallization
and larger shrinkage in the polymer.
Furthermore the experimental results suggested that triangular
fins molded parts with the least shrinkage under still
air cooling conditions, while the pin fin molded
parts with the least shrinkage when the parts were
cooled by forced circulation. This is not surprising
since both the pin and triangular fins have the
highest heat transfer rates and therefore cool parts
relatively rapidly. Molded materials thus exhibit low
crystallinity and part shrinkage.