Feed Screws, Designs

The Conical Concept of the Future

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Extrusionstechnik
Extrusion Technology
The Conical Concept of the Future
SMS Plastics Technology
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The author of this article:
Manfred Jäcker, born in 1945, is head of
the construction department and product
manager for twin-screw extruders and
profile extrusion at Battenfeld Extrusion
Technology of Bad Oeynhausen/Germany.
Copyright:
Battenfeld Extrusionstechnik GmbH
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The Conical Co
Contents
The Conical Extruder
The feed zone/
Advantages
The compression zone/
Advantages
The metering zone/
Advantages
The processing unit
The future
2/3
4/5
6/7
8/9
10
11
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ncept of the Future
Active conical
(new)
Double conical
(standard)
Single conical
(standard)
uniform flight depth
decreasing flight depth
increasing flight depth
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The Conical Concept of the Future
The Conical Extruder
Conical twin-screw extruders are usually used in the low to medium output
range of the machine spectrum.
At the moment single conical and double conical, so-called super
conical extruders are available on the market.
Despite many attempts, the output capacity of single conical extruders
could not be improved, a fact that compelled machine manufacturers to
increase output figures by enlarging the screw flight depth in the feed
section.
This measure caused problems in the metering zone of the screw since the
available volume in this section could not be extended any further.
The only remedy left was to increase the screw speed which had the well-
known drawbacks of inhomogeneous extrudate and higher wear.
In order to avoid these drawbacks, the US company American Maplan came
up with the idea of reducing the flight depth in the feed zone while increasing
it in the metering zone instead.
This was the birth of the active conical flight depth, a concept which will
be explained in more detail in the following:
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The Conical Concept of the Future
The feed zone
The flight depth in the screw’s feed zone can be reduced without any
problems.
In this area, the screw diameter is almost twice as wide as in the metering
section which ensures that a sufficient transport volume can be made
available at all times.
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The Conical Concept of the Future
Advantages
Hopper feeding
In many cases, the combination of an excessive theoretical feed volume in
the feed zone together with a low drive torque results in the extruder
requiring a supplementary metering device to avoid an excessive torque
absorption during hopper feeding.
A slightly reduced feeding volume in connection with a sufficiently high
torque ensures a safe feeding procedure from the full hopper.
Certainly, customers may add a metering device if they wish to do so.
Good pre-heating of the material
The negative screw flank angle used in the metering zone widens the screw
surface available in the screw root surface.
This measure improves the transport of heat from the screw to the material
being processed and improves the pre-heating process.
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The Conical Concept of the Future
The compression zone
The screw flight widths of conventional conical screws are often very low.
The new screw design allows flight widths ranging from 10 mm up to 15 mm.
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The Conical Concept of the Future
Advantages
Wide screw flights
The new screw design accommodates flight widths from 10 mm up to
15 mm in this area of the screw which is particularly vulnerable to wear
even for machine sizes with outlet diameters of 54 mm for example.
This measure considerably increases the service life of the screws.
Active screw flank angles
Moreover, the screws have a slightly active screw flank angle in this section.
The advantages of an active screw flank angle are outlined in the following:
Flight width
Standard
New
The flight land adjacent to the
barrel has the same root width of
the tooth at the reference diameter
but is increased by 30 per cent.
The increase in this supporting
surface reduces wear.
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The Conical Concept of the Future
The metering zone
The most critical area of conical screws is the metering zone since the
available screw volume becomes increasingly smaller.
Hence, the deeper screw flight depth in this particular area has the major
advantages.
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The Conical Concept of the Future
Advantages
Low screw speed
The deeper screw flight depth leads to an increased transport volume per
revolution at unchanged screw pitch.
This particular design reduces the screw speed but maintains the same
output rate which increases the service life of the screws.
Less friction
The increasing screw flight depth counterbalances most of the compression
conventionally created in the screw’s metering zone which in turn reduces
the friction created during the extrusion process.
Easy control of the melt temperatures
Reducing the screw speed while maintaining the same output rate and
allaying the friction due to the elimination of unnecessary compression leads
to an easily controllable temperature of the extrudate.
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The Conical Concept of the Future
The Processing unit
In addition to the introduction of the active conical flight depth, the
processing unit has also been lengthened by approximately 15 per cent.
The advantages are obvious:
l Longer dwelling times
l Higher energy input through thermal conductivity
l More gentle plastification
Standard
+15%
New
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The Conical Concept of the Future
The future
The volume gradient of the active conical screw flight depth shows a certain
approximation to that of the volume gradient of a parallel twin screw
extruder.
The advantage of the new concept becomes obvious in the critical metering
zone but also along the progression of the screw.
This new generation of conical extruders offers the benefits of parallel
processing technology and the constructional advantages of drive units for
conical extruders.
These are the prospects for the future.
Metering zone
Degassing zone
Feed zone
Comp.
zone
Screw length
Vo
lume thr
oughput
Volume gradient
Active conical
Standard
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Extrusion Technology
Battenfeld Extrusionstechnik GmbH
Königstraße 53 · D-32547 Bad Oeynhausen
Tel. ++49 5731/242-0 · Fax ++49 5731/27124
American Maplan Corporation
823 S.By-Pass · P.O. Box 832 · McPherson, KS 67460 · USA
Tel. ++1 316 241 6843 · Fax ++1 316 241 0207
Battenfeld Chen Extrusion Systems Limited
Fengxiang Road, Hexi District
Daliang Shunde, Guangdong – PR. China
Tel. ++86 765 22 37 803 · Fax ++86 765 22 37 801
E-Mail: info@bex.battenfeld.com · www.battenfeld.com
The Conical Concept of the Futur
e, Bad Oeynhausen, 03/
2002, FSW
SMS Plastics Technology

Battenfeld Extrusion Technology