EXTRUSION
Benefits of
Greater Length
Pipe Production. 36D single-venting twin-screw extruders
lend themselves to a broad range of applications and are
highly adept at processing all standard PVC pipe formulations.
In addition, throughput has been further increased.
Twin-screw extruder KMD 75-36 E/R with gravimetric metering (figs.: KraussMaffei)
HANS-PETER SCHNEIDER
he requirements in the highly competitive PVC pipe market have risen
steadily in recent years. Producers
expect an efficient pipe extrusion line to
offer high performance, versatility, and
not least, excellent value for money.
On the basis of these requirements,
KraussMaffei Berstorff, Munich, Germany, together with its customer and
partner Wavin NV, Netherlands, has developed the concept of the 36D singleventing twin-screw extruder series that
fully satisfies these high expectations.
Wavin N.V., one of the largest European
manufacturer of innovative piping systems, has many years of experience in pipe
production and is well positioned by
virtue of its global sales network .
The versatility of the 36D twin-screw
extruder with single venting is manifested by its ability to process all kinds of pipe
formulations. The extruders in this machine series are usually equipped with a
T
Translated from Kunststoffe 5/2011, pp. 81–83
Article as PDF-File at www.kunststoffeinternational.com; Document Number: PE110751
Kunststoffe international 5/2011
basic geometry and can be used worldwide for the production of all kinds of
PVC pipes, e.g. for smooth or corrugated
tubes and foam-core pipes made of rigid
PVC (PVC-U), for pipes made of PVC-M
(modified PVC), PVC-U pipes with high
filler loading (more than 30 parts by
weight) and bi-oriented pipes (PVC-O)
(Title photo).
Screw Concept Ensures Wide
Field of Application
The specially designed screw concept
known as HPG (High-Performance
Geometry) combines an extended preheating zone and an extended metering
zone with a new, dynamic mixing head
(Fig. 1).
The HPG screws are fitted with internal temperature control as standard. This
self-regulating system is based on extremely efficient cooling of the screw tips
and uniform preheating of material by
means of the screw root. Finally, the
processor can produce more efficiently,
despite the higher output. In addition to
energy savings of around 15 % relative to
screws with external temperature control,
internal screw-temperature control contributes significantly to a uniform material processing and therefore to optimum
melt homogeneity.
Several series of experiments on the
prototype trial involving finely ground
post-consumer material (mixture of pipe
and profile regrind in varying proportions) as well as recipes for standard, compact and foam-core pipes provided lasting proof that this approach is suitable for
a diverse range of material.
The processing unit based on 36D
technology offers processors a number of
advantages over competitive machines on
the market:
A preheating zone which is 30 % longer
than in the 26D series increases the versatility for processing all kinds of formulations. At the same time it meets all the
requirements for advanced material processing, better mixing in of color batch
and efficient preheating of highly filled
formulations. Finally, better material processing leads to a more homogeneous
melt.
Extending the preheating length in the
36D series significantly reduces the specific drive energy relative to the 26D se- >
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47
EXTRUSION
ries. Due to the associated reduction in
shear energy, the heat energy content increases to the same degree and, with it,
the machine’s versatility across its entire
output range (Fig. 2).
Having the metering zone twice as long
as in the 26D series ensures higher pressure build-up capacity, greater process
stability and reliable control over the melt
temperature across the entire output
range. Finally, the mixing zone, which is
70 % longer than in the 26D series, in
conjunction with optimized mixer geometry, ensures excellent melt homogeneity.
There are also positive effects on the dispersion of additives and blowing agents.
The resultant improvement in melt homogeneity reduces degree of rippling in
the extruded pipes and thus ensures excellent product quality. Not least, the additional 10 % increase in output and, consequently, the excellent price/performance ratio are key criteria in any product
comparison.
The screw concept also bestows advantages in the processing of highly filled
mixtures. Thus, formulations with a high
chalk content require significantly higher energy input. The long effective preheating length takes this into account.
Specific drive energy
Fig. 1. Design of a 36D
single-venting twinscrew extruder
90
kWh/kg
80
70
Fig. 2. Comparison of
the specific drive
energy of the 36D and
the 26D series
60
50
40
26D-machine series
36D-machine series
30
ns min.
ns mean
ns max.
Screw speed
© Kunststoffe
Furthermore, the interplay of gravimetry,
vertical metering and screw configuration
minimizes entrainment of air via controlled screw filling. Finally, process variability in the processing of highly filled
PVC pipe mixtures can be reduced to an
absolute minimum (Fig. 3).
Range of Applications
In the central and eastern European regions, the machines are primarily used for
the production of foam-core pipes (both
dry blends and up to 100 % recycled ma-
terial for the middle layers); further applications are cable protection, drainage
and corrugated pipes (Fig. 4).
In northern and southern Europe and
in Turkey, the chief application areas are
the manufacture of sewage pipes (both of
compact PVC and with PVC foam core)
as well as pressure pipes.
In the CIS and the GCC states, the installations find application in pressure
pipe, well-pipe and sewage pipe production.
In South Africa, the machines are increasingly used for the production of
Fig. 4. Extrusion installation
consisting of 36D twin-screw
extruders and pipe head for
producing PVC foam-core pipes
48
© Carl Hanser Verlag, Munich
Kunststoffe international 5/2011
EXTRUSION
pressure and well pipes, and for biaxially-oriented and M-PVC pipes, while in
South and Central America they produce
all kinds of pipes for domestic applications, as well as M-PVC pipes.
In Asia, the 36D twin-screw extrusion
lines mainly produce cable protection
pipes, pressure pipes and sewage pipes.
KraussMaffei Berstorff is meeting the
trend emanating from Europe across more
and more of the world markets, namely
higher filler loading, through the further
development of direct additions of chalk.
Retrofitting of existing installations
with a direct addition unit is possible at
any time and available on request.
Fig. 3. Twin-screw extruder KMD 90-36 E/R
fitted out for processing highly filled PVC
compounds
Conclusion
In summary, it can be stated that the versatility of the 36D twin-screw, single-venting extruder lends itself to the production
of PVC-U compact and foam-core pipes,
PVC-M pipes and the production of PVCU pipes with a high chalk content. In addition, the output of the machine series
has been increased by 10 %. THE AUTHOR
DIPL.-ING. (FH) HANS-PETER SCHNEIDER, born in
1955, is Project Manager for Process Engineering
Development Twin-Screw Extruders at KraussMaffei
Technologies GmbH, Munich, Germany.