Extrusion International 1-2016

33 / 46

Extrusion International 1/2016 33
Pultrusion for LFT pellet production
The production of long fiber reinforced thermo-
plastics takes place within the pultrusion process.
Here glass, carbon, metal or natural fibers are
mixed into a polymer matrix. Through the pultru-
sion process, the individual fibers of the strands are
impregnated. A homogenous bond of carrier polymer and
individual fiber results. Melting of the polymers and mixing
of additives takes place within the extruder. Coperion uses
the ZSK Mc18 twin screw extruder or the STS Mc11. The
ZSK Mc18 series is used in particular for products with a high
torque demand, such as Engineering Plastics or high-tem-
perature applications; the STS Mc11 series is used for stan-
dard plastics such as polypropylene and polyethylene.
Coperion K-Tron equipment is used for feeding, as it is par-
ticularly suited for raw materials in powder form, such as
polymer powder, additive powder, or filler materials such as
talc and chalk. Following impregnation, the fiber-polymer
strands are cooled in a water bath and subsequently pel-
letized to rod shaped pellets. Coperion Pelletizing Technol-
ogy GmbH’s pelletizer is equipped with a special chopping
rotor for this task. The final pellet length is usually between
,
5 and 12 mm. Whereas in the past, primarily polypropylene
was used as the base polymer, there is now a clear trend to-
ward other polymers such as PA, PEEK or PLA, and others
can be used as well according to need. Line speeds are up
to 50 meters per minute, depending upon the used poly-
mer.
Collaboration offers many advantages
The collaboration between Coperion and ProTec Polymer
Processing offers numerous advantages. The complete line
is offered with optimized components to enable the highest
quality LFT pellet manufacturing. Among these, along with
the ZSK Mc18 or STS Mc11 twin screw extruder series, is a
specially designed impregnation die head, developed by Pro-
Tec, which cannot clog with filler material. Moreover, roving
unwinding with rotating coils, as well as roving pre-warming
with individual fiber spreading, enable the best possible fiber
impregnation. The complete installation offers one further
advantage: different polymers in combination with special
additives can be used in the same production line. Support
and development of customer-specific formulations can take
place in ProTec’s Testing Center in Bensheim. This produc-
tion of product samples allows to validate components man-
ufactured with LFT pellets. Using twin screw technology and
the special impregnation die head, it is also possible to use
additional fillers and even regrind material. As a result, the
customer receives a fully automated production line, set and
optimized to the customer’s formulation.
The automotive industry is one typical area of use for LFT;
however, this technology offers advantages for further ap-
plication fields in which products are exposed to higher de-
mands and stresses, and would thus benefit from higher
quality. At this time, Coperion and ProTec are working on
their first joint client project in Europe.
Roving pre-warming with spreading of the individual fibers enables the best
individual fiber wetting (Photo: ProTec Polymer Processing)