Many shades of black: A new die plate

Issue
1-2/2014
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Many shades of black: A new die plate design allows Hubron
to produce polyamide compounds in an underwater pelletizer
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Hubron operates five extruder lines with underwater pelletizers
for the production of about 35,000 t/a of carbon black compounds
for technical applications.
Photo: Hubron
Special Print Issue 1-2/2014
Photo: Hubron
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One benefit of the Gala- underwater pelletizer is the
automated process, which allows a more efficient deployment
of personnel.
Many shades of black
A new die plate design allows Hubron to produce polyamide compounds
in an underwater pelletizer
Hubron International Ltd. of Manchester/UK has equipped its
underwater pelletizer with a new die plate to produce spherical
pellets made of polyamide carbon compounds. The second-largest European manufacturer of black plastic masterbatch is
now perfectly prepared to accommodate the rising demand for
high-quality PA compounds. Craig A. Hodgkinson, Technical
Director at Hubron, and Michael Eloo, Managing Director of Gala
Kunststoff- und Kautschukmaschinen GmbH with headquarters
in Xanten/Germany explain the benefits of the new die plate.
Written by Dipl.-Ing. (FH) Karin Regel, Editor K-PROFI
Carbon black polymer compounds have become indispensible additives not only for automotive applications, but also for many other plastic products. Added as masterbatches they ensure that the
final product has a black colouring but also provide it with a high
UV stability and /or electrical conductivity. At its production facility in Manchester/UK, Hubron operates five extrusion lines for the
production of more than 100 different grades of carbon black compounds. The company’s products are based on polyamide as well as
on polyolefin and polystyrene.
“We know exactly which grade of carbon black is suitable for which
polymer. Extensive experience is paramount for the production of
high-quality products, as carbon black has a substantial effect on
the polymer’s viscosity. There are many shades of black”, Hodgkinson explains. As Hubron specializes in the production of black pellets for technical applications, not only carbon black, but additives
such as stabilizers, processing aids or fillers are mixed with the compounds. The plastics processor has an output of about 35,000 t/a of
TECHNOLOGY ‹
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As a rule, the carbon black specialist manufactures its products in
fully automated processes using continuous mixers made by Farrel Corporation, Ansonia/USA and Buss AG, Pratteln/Switzerland
for material compounding as well as a range of Gala underwater
pelletizers for pellet production. Up until now, PA compound production required the use of a strand pelletizer due to process fluctuations and pulsations in the short screws used for processing
high-temperature polymers – which allows a more efficient deployment of operating personnel. “Thanks to our cooperation with Gala
and the investment in a HeatFlux die plate, we can now process PA
with an underwater pelletizer”, says Hodgkinson. Michael Eloo explains: “The die plate ensures that the polymer melt emerges from
the compounding unit and can be cut directly downstream from it
in the cutting chamber. Released into the cold water, the material forms spherical pellets. Conventional systems require a relatively
high and constant pressure level in the compounding unit for pressing the polymer material through the die plate. The new design and
surface insulation of our HeatFlux die plate significantly reduces
the pressure drop across the entire bore. This allows processors to
run the same machine with a higher output or to make the process
gentler, thus preventing any material damage.”
Gala’s Managing Director also points out that the new die plate minimizes bore clogging and therefore reduces start-up scrap. Less waste
is a general feature that distinguishes Gala underwater pelletizers:
they are outstandingly eco-friendly and cost-efficient. Another aspect of their environmentally-friendly and economic operation is
the fact that underwater pelletizers with a HeatFlux die plate consume up to 70 % less energy than conventional die plates; they often render melt pumps for balancing out imminent pressure and pulsation fluctuations superfluous. “The special insulation design and
low heat conductivity of the die plate allows the polymer to be cut in
its plasticized, elastic state, which reduces the finest-particle content. It is significantly lower than that produced by competing systems.” With their minimized finest-particle content and low amount
of dust particles compared to strand pellets, spherical pellets are
very popular with processors. It is because of these benefits that the
demand for spherical pellets is on the increase. Thanks to their geometry, they are easier to meter, particularly when it comes to processing small batches. A low dust particle content is paramount for
clean production conditions. Hodgkinson sums up: “Compared with
conventional strand pelletizing, HeatFlux technology reduces production start-up times and start-up scrap while allowing automated processing and improving the pellet quality. Investment costs for
this new technology will have paid off within only one year.”
Not only Hubron benefits significantly from the new HeatFlux technology. In response to the rising demand, Gala went one step further
and launched an exchanger package for underwater die plates at the
K trade show last autumn. “For customers running high-quality as
well as standard applications, we now offer a con ventional die plate
called NHF (Non HeatFlux) which is compatible with the HeatFlux die
plate chassis. Both die plates have a straightforward geometry and
can be exchanged without silicone as a sealant. When asked about
the usefulness of HeatFlux technology for every-day processes, Eloo
Photo: K-PROFI
carbon black compounds, with about 50 % readily available from
storage and 50 % customized upon request in batch sizes of between
5 and 600 tons. “Our customers told us that we are the “cleanest”
black company they know”, Hodgkinson confides with a grin.
Michael Eloo (left) and Craig Hodgkinson are delighted with their successful
project. Thanks to the HeatFlux die plate, Hubron can now produce PA carbon
black compounds with an underwater pelletizer.
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Special Print Issue 1-2/2014
responded: “Due to their complex design,
HeatFlux die plates are slightly more expensive than conventional die plates. In order to
ensure that the new die plate has a long service life, it is economically sensible to use it
according to the material being processed.“ ‹
Strand pelletizing vs. underwater pelletizing
Every pellet production requires a compounding unit for plasticizing and homogenizing, whether the process is carried out with a strand pelletizer or an underwater pelletizer.
www.gala-europe.de, www.hubron.com
Photo: Gala
During strand pelletizing, the polymer melt emerges in several strands from the
strand die head flanged to the extruder and is cooled in a water bath. The residual water is removed by suction or blowing nozzles. In the pelletizer, strands are
cut between a rotor and a bed knife into roughly cylindrical pellets. Often, the
dried and solidified strands are manually transported to the pelletizer, a procedure
that has to be repeated when the strands tear. Alternatively, the strands can be
transported to the pelletizer by means of a cooling water slide, allowing an automated process. Downstream from the pelletizer, a filter screen removes oversized
and undersized particles from the cylindrical pellets.
The design and surface insulation of the
HeatFlux die plate minimize pressure loss
across the entire bore diameter
In contrast to strand pelletizing, the underwater pelletizing cutting process takes
place when the melt is still in its plasticized state, and it produces spherical pellets. The melt emerges horizontally from the extruder and is pressed through the
underwater pelletizer’s die plate with its radial bores. As they are discharged
from the pelletizer die plate, the strands are directly cut in the cutting chamber,
which is flooded with process water, and conveyed by the water flow. The slurry
that emerges from the pelletizer’s cutting chamber is conveyed to the agglomerate
catcher and from there to the centrifugal dryer. Once they are separated from water, the pellets are moved on to a blower which removes surface moisture from the
still-warm pellets.
Photo: Hubron
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The company’s range of 100 grades of carbon black ensures that the final product has a black colouring but also provide it with a high UV stability and/
or electrical onductivity.