SAMPE Journal - September/October 2016 - 50

Feature Article

Figure 4. The pultrusion process
and its characteristics.

It is the aim of the paper to depict the development and
characteristics of the integrated process. That includes
the analysis of the two single processes pultrusion and
extrusion, the assessment of the key challenges and the
features of the integrated process technology. Finally, a
proof of concept is given.
Characteristic of Pultrusion and Extrusion
The Pultrusion Process
Process Characteristics
In the pultrusion process (Figure 4), rovings are
continuously pulled from a creel into a fiber guidance
unit, which leads the rovings into the impregnation
unit. In thermoset pultrusion, the impregnation unit is
responsible for wetting the roving with the liquid, lowviscous (usually less than 3 Pas) reactive thermoset
resin system5. It can either be designed as an open bath
(for resin systems with long pot life and low sensitivity
to ambient conditions) or as a closed injection box
(for highly-reactive resin systems or high sensitivity
to ambient conditions). For the matrix systems used
for the integrative process, it is reasonable to use a
closed injection box. The resin system is mixed and
dosed online and injected into the injection box. After
impregnation, the system containing of rovings and
liquid resin is pulled into a heated pultrusion die, which
is usually 700 mm to 1000 mm long. Here, the chemical
curing reaction is started and catalyzed by the applied
heat. When the profile leaves the pultrusion die, it is
cured and dimensionally stable. It cools down below
the glass transition temperature of the thermoset matrix
system and is subsequently pulled off and cut.5,9,10
The pultrusion process depends mainly on the
viscosity development, the temperature and pressure
trajectories (Figure 4). The temperature is low in the
injection box (room temperature or slightly higher) and
is quickly raised in the pultrusion die. Here, the surface
of the profile quickly reaches die temperature, whereas
the middle of the profile reaches the temperature later.
50

However, an overshooting of the inner temperature might
occur due to exothermal effects during curing5,10. The
temperature profile and the absolute figures depend on
various factors such as profile geometry, matrix system
and die design5,10. Generally, the temperatures peak at
around 80°C to 180°C.
The pressure during the whole process is usually
comparably low. There is no additional pressure needed
to run the process as the haul-off unit constantly pulls
the profile out of the die which in turn, by drag forces,
drags the liquid matrix into the process. Besides a little
pressure development within the conical injection box,
the whole process runs at ambient pressure.
Common Matrix Systems and Applicability in the InPulSE
Process
Commonly, pultruded profiles are manufactured with
unsaturated polyester resins (UP), vinyl ester (VE) or
epoxy (EP). Recently polyurethanes (PU) have also been
in the focus as a composite matrix system, because they
offer advantages concerning both the process and the
product characteristics:
- Good impregnation qualities within low impregnation
times thanks to the low start viscosity (e.g. below 0.3
Pas ast room temperature)18
- High process speed of up to 2.0 m/min thanks to
high reactivity combined with a low enthalpy of reaction
and a corresponding low exothermal10,12,14
- Low to no volatile organic compounds (VOC) which
results in a high degree of working safety
- High adjustability of the matrix material properties,
ranging from thermoplastic to thermoset and from rigid
to elastic
- Good fatigue behavior under cyclic load11,13
The good mechanical properties of composites with
PU matrix are mostly thought to be caused by the good
adhesion of PU, which enables a well bonded fibermatrix interface and an efficient load transfer. On the
other hand, the good adhesion of PU is responsible for a
SAMPE Journal, Volume 52, No. 5, September/October 2016



Table of Contents for the Digital Edition of SAMPE Journal - September/October 2016

Contents
SAMPE Journal - September/October 2016 - Cover1
SAMPE Journal - September/October 2016 - Cover2
SAMPE Journal - September/October 2016 - Contents
SAMPE Journal - September/October 2016 - 2
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SAMPE Journal - September/October 2016 - Cover3
SAMPE Journal - September/October 2016 - Cover4
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