Gear pumps
Everything clean?
The requirements on the compound quality, especially in profile and hose manufacturing, increase from year to year. Owing to
weight and functional reasons, the crosssections of rubber components are becoming smaller. The slightest compound impurities become visible on the surface immediately. In the production process, impurities
can lead to clogged tool openings, so that
production must be interrupted. Moreover,
it is a fact that due to rising raw material
prices, the trend is increasing towards using
cost-effective raw materials that contain impurities to an increasing extent.
To remove such impurities or compound
particles which are not adequately mixed
prior to extrusion, the compound is cleaned
through a straining process – by pressing the
compound through a fine-mesh screen. The
straining process can take place at different
process stages:
• Directly after the mixing process with an
extruder-gear pump combination.
• Prior to the extrusion process through a
separate gear extruder.
• During the extrusion in front of the profile
head.
D. Eberhard*
speed rolling mill. A short extruder in connection with compound-friendly processing
in a gear pump are the best prerequisites for
pressing the compound through even fine
screens, at compound temperatures as low
as possible.
A special feature is the self-sealing strainer
plate developed by Troester. The screen can
be changed quickly and easily via a manual
or a hydraulic quick-change clamp without
additional tools. To minimise exchange time,
a second strainer head is also mounted laterally on the extruder barrel. The installation
of an automatic screen changer therefore
offers hardly any advantages. Extrusion tools
are installed at the outlet of the strainer
head. Through the exchange of these extrusion tools, the required strip dimensions can
be produced. At the same time, several strips
can also be produced in parallel.
The output of this machine combination is
based on screen fineness and maximum possible temperature stress of the compound.
In a normal straining process this machine
combination attains an output of approx.
4,800 kg/h.
Cold-feed gear extruder
Hot-feed extruder-gear pump
combination
For several years now, Troester has combined its extruders with its own gear pumps
to form an extruder gear pump unit for centralised straining in the mixing chamber. Hot
feeding of the extruder allows direct integration of this combination of machines in a
mixing line. This strainer is installed upstream
of the batch-off plant behind a controlled-
Alternatively, a cold-feed gear extruder
can be used in a decentralised manner upIllustration of an
extruder-gear pump combination for an
output of approx. 4,800 kg/h
stream of the process-extruder in a production line. The gear extruder works according
to the principle of a gear pump, whereby
in the feed zone two feed gears are connected upstream. With this proven technology, all common rubber compounds are
drawn-in in cold condition. In contrast to an
extruder-gear pump combination, the rubber is strained at significantly lower temperatures. In particular, for highly accelerated compounds, this concept offers a high
degree of process reliability.
Depending on the compound, the screen
fineness and the compound pressure, outputs of up to 800 kg/h can be reached in
production.
Cold-feed extruder-gear pump
combination
As a further possibility, the compound can
also be strained with a screen pack directly
upstream of the extrusion head. To avoid an
excessive temperature increase through the
larger extrusion resistance, the installation
of a gear pump is recommended in this case.
The combination of an extruder and a gear
pump in a production line also has the advantage that output fluctuations are minimised and product tolerances are improved.
When a vacuum extruder is used, the process
reliability against flooding the vacuum area
is increased.
The output of the extruder-gear pump
combination depends on the compound,
the output of the vacuum extruder and the
max. output of the gear pump. In standard
applications, outputs of up to 1,500 kg/h can
be achieved.
Which system is finally used depends on
the local conditions and requirements on the
process. Through different strainer design
forms, Troester offers the customer attractive alternatives and possibilities for cleaning a rubber compound, in order to produce
high quality components.
* Dr. Dieter Eberhard
Sales Manager
Rubber Machines Non-Tire Market,
Troester GmbH & Co. KG, Hannover, Germany
RFP 4/2008 – Volume 3
205
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