SAMPE Journal - November/December 2021 - 21

a)
Figure 1. a) Schematic and b) photograph of standard fixed rollers double belt press installed in the KIT
Innovative Composite Center (ICC).
INTRODUCTION
Fiber reinforced thermoplastics are gaining
importance for a wide range of light-weight
applications. It offers higher toughness and
recyclability than thermoset composites. Complex
parts can be manufactured by automated
high-speed stamp forming process from flat
laminates, so called organo-sheet1-3
. The key
process for manufacturing these intermediates
is the impregnation of fiber reinforcement with
high viscosity thermoplastics4-5
. Because the
impregnation quality of laminates will affect the
mechanical property of stamp-formed composites,
low void content is desirable. Normally,
impregnation in thermoplastic laminates is
achieved by heat and cool process using a hot
press. This process involves heating up and cooling
down the mold, which consume high energy and
long time. Thus, the utilization of continuously
running a double belt press is an efficient and costeffective
way for high volume production6-8
.
Standard fixed rollers double belt press is
schematically shown in Figure 1a. The machine
manufactured by IPCO was installed into
Innovative Composite Center (ICC), as shown in
Figure 1b. In this system, the material is pulled into
the press by steel belts. Inside the press, sufficient
pressure produced by fixed rollers behind the belt
is consistently imposed on the laminate. The gap
between the belts are fixed to desired distance and
thus the material thickness is controlled well during
impregnation process. At the same time, the belt
temperature is elevated by hot air blow behind the
belt to ensure impregnation of fiber reinforcement
with melted resin. Subsequent consolidation and
cooling of the laminate is provided by a hydrostatic
pressure using cooling fluid.
Key Issue is Heating Capability of Double Belt
Press Process
One of the intrinsic problems in double belt
press lies in an inferior ability for raising material
temperature during continuous process. Figure
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2 shows typical temperature profiles that were
recorded with thermocouples on the belt surface at
the process velocity of 0.2 m/min and 1 m/min, and
at the center of 6 mm thick CF/PA6 laminate stack at
a process velocity of 0.2 m/min. It can be observed
that the non-thermal history of temperature versus
positions in double belt press changes depending
on process velocity, and the build-up of temperature
is delayed at a higher process velocity. Also, similar
delay appears in temperature at the center of
laminate stack. These phenomena are governed by
heat transfer and conduction between steel belts
and materials through thickness direction9-10
. The
residence time in high temperature regions will
inevitably make a great influence on impregnation
progress. Consequently, standard double belt
press system is not effective for manufacturing
thick organo-sheet at a high process velocity, with
involving impregnation of many layers of fiber
reinforcements.
The objective of this study is to develop high rate
manufacturing of thick organo-sheet using double
belt press, ensuring good impregnation quality
Figure 2. Recorded temperature profiles during double belt press process
at the belt surface with different process velocity, and at the center of 6 mm
thick CF/PA6 laminate stack.

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SAMPE Journal - November/December 2021

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