MASCHINEN UND ANLAGEN
MACHINERY AND EQUIPMENT
QSM pin extruder Mixing zone Pin
Design Transfermix MCT MCTD Convert extruder Slab feeder Piggy back head designs (clamping
head, hammer head) Cassette
changing devices Roller head Single roll roller die
In recent years there were no revolutionary inventions in the field of
rubber compound plastification and
profile shaping (such as multi component heads, roller head and single
roll roller die units or pin extruders),
however, there are many most interesting developments and improvements of almost all line components, resulting in a better handling
and use of the line and first of all
better tire component quality. In the
article the most important subjects
will be demonstrated and summarized.
Neuste Entwicklungen auf dem
Gebiet der Extrusion von Reifen-Komponenten
QSM Stiftextruder Mischzone Stift-Form Transfermix MCT MCTD Convertextruder Fell-FuÈttervorrichtung HuckepackkopfKonstruktion (Klammerkopf, Hammerkopf) Kassettenwechselvorrichtung Roller head Einwalzkopf
(EWK)
In der juÈngsten Vergangenheit gab
es auf dem Gebiet der Gummi-Mischungs-Plastifizierung und ProfilAusformung kaum revolutionaÈre Erfindungen (wie z. B. Mehrkomponenten-KoÈpfe, Roller Head- und
EWK-Einheiten oder Stift-Extruder).
Allerdings kam es in fast allen Anlagenbereichen zu vielen, oft sehr interessanten Entwicklungen und Verbesserungen, die zu besserer
Handhabung und Verwendung der
Anlage fuÈhrten und vor allem zu
besserer Reifen-KomponentenQualitaÈt. In dem Artikel werden die
wichtigsten AÈnderungen vorgestellt
und erklaÈrt.
Recent Developments in
Extrusion of Tire Components1
H. J. Gohlisch, Hannover (Germany)
As is well known, tires comprise many
pre-fabricated extruded and calendered
products (Figure 1), plasticised as economically and homogeneously as possible and, above all, shaped with as much
precision and under as little stress as
possible, cooled, temporarily stored
and re-processed without further deformation.
Low maintenance machines with a
high level of automation and minimum
re-tooling and down-time are required
for this. Additionally, the entire process
and all line areas relevant to product quality must be controlled with maximum precision.
Figure 1. Main tire components
1
290
(presented at: ACS Rubber Division Meeting, Dallas, USA; April 3 ± 7, 2000)
For plastification and shaping of the
compound the most different extruders
have been developed; however, the pin
extruder meant the breakthrough for
cold feeding in the tire industry.
Pin extruders
The pin extruder represents the only wellknown system which is equally suitable
for practically all machine sizes and screw
flight depths (Figure 2). This machine has
therefore prevailed throughout the tire industry (except for some NR truck compounds where hot feed machines are
also used).
The operating principle of the QSM pin
extruder is to split and reverse the lamina
flow. At low shear rates the melt flow in
the screw flight is split into an increasing
number of new partial streams. Having
been split, reversed and slowed down locally, the streams merge again.
Figure 3 explains the effect the immersed pins have on the material flow.
The layers lying against the direction of
flow are reversed by the pins into the direction of flow and slowed down in comparison with the undisturbed layers in
neighbouring zones, and stretched in
this way and by the passage of the
pins through the slots in the screw flights.
The length of the pins and therefore the
depth of the screw channel clearly has no
effect on the function described. The surface area is expanded by reducing the
thickness of the layer and excellent plastification and homogenisation is achieved
if this process is repeated a sufficient
number of times (Figure 4).
Efforts must be made, however, to ensure that, whenever possible, only compounds with a similar degree of plastifica-
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
Recent Developments in Extrusion of Tire Components
Figure 5. Screw mixing zone (feed area)
Figure 2. Cross
section of a QSM pin
extruder1
Figure 3. Material
flow in a pin extruder
Figure 4. Homogenization in a pin
extruder
tion reach the row of pins. Where viscosity differs widely, the more highly viscous
parts can evade the flow splitting elements. This means that plastification errors must already be eliminated in the
feed zone. This consideration led to the
development of the mixing zone. Here,
several superimposed flight geometries
with differing pitches and depths ensure
that the compound is thoroughly
kneaded, broken down and mixed in
the feed area itself (Figure 5).
This type of extruder is essential if high
output rates under conditions of perfect
plastification, acceptable extrudate temperatures and good product tolerances
have to be achieved.
With extruders, as with all technology,
the general aim is to achieve optimum
output by the simplest means. The typical
pin extruder therefore has a screw with a
1
Querstrom-Misch-Extruder (approx. ªcross flow
mixing extruderº)
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
mixing area in the feed zone, and is otherwise of a relatively simple design. The
pins are designed to ensure optimum
strength and flow, and remain immersed
at a constant depth. A spiral undercut is
part of the hopper section liner while the
barrel is totally smooth except for the
holes for the pins.
As already stated at the beginning, the
standard pin extruder is able to plasticise
and extrude the most widely diverse
compounds with great precision and in
a homogeneous way almost always without the need for any mechanical modifications (e. g. pin adjustments or the introduction of flow restrictors).
Some special designs have not become widely used because they are unnecessarily complex or because they
have several disadvantages. They include:
a) Pin extruders with adjustable pin
depths,
b) Multi Cut Transfermix (MCT),
c) A Transfermix zone combined with flow
restricting adjustable pins (Convert-Extruder or MCTD1).
For pin extruders with adjustable pin
depth radially adjustable cylindrical pins
are required, and these are prone to fatigue failure due to the notch effect in the
area where they protrude through the
barrel. This design is therefore less suitable for problem free production. In addition, bent pins (for instance caused by
contact with foreign bodies) are extremely
difficult to be removed (Figure 6).
The MCT is a modification of the Transfermix extruder, introduced several decades ago, i. e. a special extruder with
flights in the screw as well as the barrel
(Figure 7).
The flight depths in both screw and
barrel change, alternating from a maximum to a minimum value in a way that
1
MCTD ˆ MCT with Drossel ˆ with throttle
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Recent Developments in Extrusion of Tire Components
Figure 6. Pin designs
Figure 7. Sketch of
a Transfermix extruder princible
Figure 8. Principle
and view on a MCT
rotor and stator
for instance the screw is at its maximum
depth while the barrel is shallow. The
compound is thus forced between screw
and barrel, and the compound is carried
in layers from flights that reduce in size to
292
the opposite flights, which increase in
size. In comparison to the cold feed extruders known before the transfermix
made a clear quality improvement possible. An improved plastification and mixing
is achieved by flow division at low shear
rates.
To increase the dispersion effect, the
number of flights was steadily increased
over the years, and finally produced the
MCT (Figure 8).
Transfermix extruders are more complex than other extruders because they
also have flights in the barrel. They also
have the disadvantage of poor self-cleaning and the problem of removing the
screw after longer (unplanned) stoppages
due to scorch of the compound.
The ªConvert Extruderº combines an
MC Transfermix zone with radially adjustable pins functioning mainly as variable
flow restrictors. The MCTD achieves its
goal with the aid of flat-topped, rotatable
pins (Figure 9).
The L/D ratio is normally lower than for
other extruders so the machine is of a
more compact construction, but also
has the disadvantages common to all
shorter extruders: a high head pressure-output dependency and, with respect to product tolerances, a strong reaction to feed irregularities.
Compounds that are easy to plasticise
require processing with as little flow restriction as possible. If the level of plastification difficulty increases, also the resistance has to be increased, and with it the
compound dwell time. This also leads often to a substantially reduced output and
increased extrudate temperature.
As a general rule, an extruder should
be designed to be as simple as possible,
i. e. it should achieve high output rates at
acceptable extrudate temperatures and
good tolerances by the most simple
method possible.
When a high degree of plastification is
required, it is therefore better to design
the extruder with a sufficient number of
pin planes and a number and geometry
of mixing zones to meet requirements
early on, avoiding the need for additional
devices.
Simple, but very effective, is the combination of a mixing zone on the screw
with a pin area. The different flight pitches
and depths and the varied flow speeds in
the mixing zone assist the function of the
pins (Figure 10).
Feed unit
The substantial influence this device has
on a consistently even extruder output
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
Recent Developments in Extrusion of Tire Components
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
293
Recent Developments in Extrusion of Tire Components
Figure 9. Schematic representation of
the convert extruder
and the MCTD extruder (bottom)
of capacity by feeding more than one
slab to the extruder, the present aim is
to balance out any differences of the
compound in the extruder by additional
blending, i. e. to some degree the final
mixing of the compound has been transferred from the mixing room to the extruder.
Metal detecting devices detect metallic
contamination in the slabs, and trigger an
alarm. The contaminated area is then
marked by additional devices, for instance chalk markers, so that the contaminated section can be removed. If
this section is not removed promptly, an
emergency stop is triggered automatically (Figure 11).
Multi-component piggy-back
units for the manufacture of
tread and sidewall profiles
Figure 10. Mixing
zone with pins
Figure 11. Modern
triplex extruder unit
with slab feeder
was not given sufficient recognition in the
past. Until 15 ± 20 years ago, it simply
comprised a hopper with guide rolls enabling 1 or 2 slabs to be fed automatically
to the extruder.
Today, these have in some cases, become very complex pieces of equipment
294
which allow several sheets to be drawn
automatically and simultaneously from
pallets, to be checked for metal inclusions, and fed to the extruder over dancer
rollers or via loop control systems.
Whereas earlier developments were directed solely towards making better use
In modern tire manufacture the various
components for treads and sidewalls
are formed simultaneously either as single or twin profiles in multi-component
heads with a high level of precision, without any displacement of the individual
components, and with no air pockets between the individual parts.
While the tread cap, base and wings
are generally combined in one unit, there
are however different opinions about the
production of the cushion. Both 4-component piggy-back units and downstream calenders, used to apply the cushion, have advantages and disadvantages.
Use of a 4-component piggy-back extrusion unit has the advantage of saving
the space needed for a downstream machine and eliminating any handling problems, but it also has the disadvantage
of being an even more complex extruder
unit with poor on-line control of the cushion thickness.
Most sidewall units comprise 2 extruders if no additional whitewall component
is needed.
Both tread and sidewalls are extruded
as single and dual profiles.
The widest range of designs have been
developed for clamping the head sections together, all with the purpose of producing short compound change over
times and the minimum amount of scrap.
All movements of the piggy-back head,
including clamping, are hydraulic in the
more common designs. The most usual
versions are:
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
Recent Developments in Extrusion of Tire Components
Figure 12. Piggy
back head types
a) The clamping head
b) The hammer head (Figure 12).
The clamping head is held together by
two integral, hydraulically activated
clamps. These very powerful wedge
shaped clamping devices press the
head sections together. The forces produced in the flow channels by melt pressure are thus self-contained (Figure 13).
The advantage of this design lies in the
powerful locking force produced with low
hydraulic pressure.
However, this design does not allow a
single channel to be opened separately.
For example: if only the cap compound
is to be changed the complete head
has to be opened and the compounds removed from all flow channels.
The hammer head design (Figure 14)
allows the upper and lower head section
to be closed and opened separately. Instead of clamps, pairs of hydraulic cylinders apply pressure to lock the head sections together. The cylinders are flanged
onto the fixed middle section and have
hammer-like extensions at the end of
the piston rods, which are hingemounted in fork-like recesses above
the hydraulic rotary cylinder.
The clamping mechanism is purely hydraulic without the assistance of any extra devices so that considerably higher
Figure 14. Triplex hammer head (above:
closed, below: upper part opened)
Figure 13. Quadruplex clamp head (left: closed, right: opened)
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
hydraulic pressures are necessary. All
hinge and bolt elements are situated on
the head to give excellent front and
side access.
As already stated, with the hammer
head design the cap compound can be
changed without the need to open the
lower head section. However, if the wings
are to be applied from above ± as is
usually the case ± the wing extruder
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Recent Developments in Extrusion of Tire Components
must be placed underneath and the
compound fed through openings in the
base flow channel (Figure 15).
The tool design of this extruder arrangement is also substantially more
complicated.
By clamping both hinged head parts
with each other (Figure 18) they can be
opened together for cleaning. By this,
the wing extruder can remain in the top
position that is logical in respect to profile
design and the drilled connecting holes
through the base flow channel, which
are unfavourable for material flow and
cleaning, are avoided. The cassette design is also essentially simpler.
For optimum material flow in the head,
the flow channels must be easily interchangeable so that, depending on the
product, the best conditions for conveying the material to the die cassette are established, and impact surfaces (ªdead
spotsº) in front of the cassette are kept
to a minimum. To facilitate change-over,
the flow channels are always positioned
in the lower parting sections.
If only the final die is to be changed, this
can be done quickly by partially releasing
the die clamping mechanism. If the complete cassette has to be changed, it is
hinged so that it swings outwards when
the clamping mechanism has been released, and a new one can be swung
in from the other side. There are also 2
automatic options for this operation:
a) The changing device, which allows the
cassette to be exchanged by moving it
hydraulically across the extrusion direction (Figure 19). This device requires
a lot of space on either side of the head
because the cassette take-up unit is
mounted on both sides. Also, the exchanged cassette cannot be removed
on the operator's side.
Figure 15. Typical
extruder arrangements
Figure 17. Flow channels for above tread
profile in a triplex hammer head
b) The better alternative is a multi-level
changing device that removes the cassette, then transfers the new cassette
vertically (hydraulically) to the level of
the head-die-mounting. The cassette
can then be swung into position (Figure 20).
The advantage of this device is that it
requires little space, and operates on
one side only. It can also accept up to
4 cassettes, which can be pre-heated
by internal rod heaters while in the
stand-by position.
It is also possible to pre-heat the final
dies and/or complete cassettes in a
pre-heating oven.
Machines for forming innerliners
Today, two types of machine are in common use:
a) the Roller Head system (RH), and
b) the Single Roll Roller Die unit (SRRD)
Both designs are used in lines singly or
in combination so that, in one line, two
component innerliners can be produced
by doubling, even with additional gum
strips if required.
Features of modern Roller Head
units:
Figure 16. Schematic representation of material flow
in a clamp head and
a hammer head
296
a) Cold feed pin-type extruder
b) Roller head
c) Head locking frame (independent of
the calender frame)
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
Recent Developments in Extrusion of Tire Components
Figure 18. Internal
locking of head
parts
Figure 19. Cassette
changer
Figure 20. Multi level cassette changing device
d) Two roll calibrating calender (for contoured innerliners with quick-change
profile sleeves)
When the head clamp has been released,
the head and extruder, mounted on a
base plate, can be moved backwards
away from the head frame and the calender area. To be able to remove the extruder screws, the base frame must either
be moved backwards a sufficient dis-
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
tance, or if space is limited, swung to
the side out of the way and the head
must be opened (Figure 21).
The head distributes the compound as
evenly as possible to the required width,
and conveys it to the calender nip as e.g.
5 ± 20 mm thick sheet (for innerliners: approx. 7,5 mm).
By inserting adapters, the width of the
material leaving the head can be changed
so that small product widths can be produced with reduced compound dwell
times and / or edge trimming (Figure 22).
The flow channels are designed basically like those in a tread head, and are
chrome plated to prevent the compound
from sticking to the surface. So that the
compound can be easily removed, both
halves of the die head should be hydraulically hinged. After cleaning, the head is
closed again and re-positioned with the
extruder in the locking frame.
At the front of the head a pair of dies
span the entire width. By changing one
or both die plates the thickness of the extruded sheet can be altered to the specified range (Figure 22).
A pressure transducer is fitted to the
extruder head to automatically adjust
the screw speed, thus ensuring a constant head pressure, which is one of
the conditions for accurate tolerances.
The measuring point is usually positioned
directly following the screw tip.
The frame of the locking mechanism
comprises a top and bottom crossbeam and lateral connecting columns
which ensure that the head locking forces
are contained, i.e. the calender frame
only has to take the weight of the equipment. While the lower section of the head
rests on the lower cross-beam, hydraulic
cylinders (mounted on the upper crossbeam) press the upper section downwards (Figure 23).
Other designs have the disadvantage,
particularly with large widths and/or high
pressures, that the head bends open in
the middle, having a negative effect on
the product thickness.
As normally the two roll calibrating
calender is used for the manufacture of
contoured innerliners, the top roller of
the calender comprises a core and a profile
sleeve which can be changed in just 5 minutes using a sleeve changing device. The
sleeve change, i. e. replacement by a preheated new sleeve, takes place through
the front calender frame (Figure 24).
297
Recent Developments in Extrusion of Tire Components
Figure 21. Roller
Head unit with open
head
Single roll roller dies (SRRD)
The single roll roller die comprises an
upper section with material flow channels
and a die retained by a wedge shaped
Figure 22. Exchangeable dies and/or inserts
for thickness and width alteration
gib, and a lower section with a driven cylindrical roller. Hydraulic cylinders operate
the locking mechanism of both main
head sections, the hinge mechanism of
the upper section, and the movement
of the wedge shaped gib. For precision
adjustment of product thickness the
gap between the roller and the die can
be changed. This is done by moving
the roller vertically by means of motor dri-
Figure 23. Calender
with head locking
frame
Figure 24. Calender equipped with C-frame during sleeve change
298
ven spindles. The main advantage of this
head is that, owing to the drag-effect of
the roller, the pressure required to overcome the die resistance is supplied
only partially from the extruder and so
pressure and melt temperature can be
substantially reduced (Figure 25).
Due to adhesion to the roller, even products with large differences in thickness
leave the head without tension in a
straight line, which simplifies the design
of the die.
However, for thin sheets or those with
thin areas, compounds free from contaminations must be ensured, or a screen
changing device must be used to prevent
the sheet from tearing or the roller from
becoming damaged as a result of impurities trapped between the die and the
roller.
Although single roll roller dies were originally developed for much narrower
widths, machines are in use today for a
trimmed product width of approx.
1200 mm (approx. 47 1/4 00 ).
Figure 25. SRRD unit with hydraulic screen changer
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
Recent Developments in Extrusion of Tire Components
Conclusions
To meet the expectations of tire manufacturers requiring solutions to processing
problems, reduction of man power, improvements to personnel-dependent
processes, and increased efficiency, machine manufacturers have been compelled to make continuous developments
and detailed improvements to what are,
by and large, already familiar machines
and equipment.
Today's goal is a ªperfectº low maintenance production line, which is easy to
operate and control.
Figure 26. SRRD
(max. width ˆ 47.5 00 )
Trimming devices are required for both
roller head and single roll roller dies. The
knives can be operated either manually or
automatically. The complete cutter bar
can be swung in and out of position
pneumatically ensuring the smooth passage of the product sheet. The edge trims
are returned to the extruder feed hopper
via conveyer belts.
KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr. 6/2001
The Author
Hans J. Gohlisch, Executive Vice President of Paul
Troester Maschinenfabrik.
Corresponding author
Hans J. Gohlisch
Paul Troester Maschinenfabrik
Postfach 890 180
D-30514 Hannover
299