Extrusion head

An extrusion head for producing flat profiles such as tread strips for automotive vehicles from three or more different rubber or plastics materials is disclosed. The head comprises a fixed central portion and upper and lower portions pivotally connected thereto, and is fed with the different mixtures by a plurality of screw or worm extrusion devices. Between the upper and central portion and the central and lower portions of the head, insert members are located. In the upper and/or lower surface of each insert member, flow channels for the mixtures are defined, the flow channels each being bounded upwardly or downwardly as appropriate, by a plane surface of one of the portions of the head. The insert members are axially divided and are made in one piece. The flow channels each have a longitudinal axis of symmetry and such axes lie in a common vertical plane. Such an arrangement permits the profile to be changed merely by replacing one or both insert members, permits the worms or screws to be readily removed for cleaning purposes and also ensures that the flow rates in each of the flow channels is substantially constant, thereby avoiding problems of pre-vulcanization.

BACKGROUND OF THE INVENTION 
The invention relates to an extrusion head for producing flat profiles from 
rubber or plastics material mixtures. 
A typical example of such a flat profile is a tread strip for automobile 
tires. In order to produce a tread strip for tires, it is necessary for 
three different types of mixtures to be combined because the strip 
comprises a tread surface made of a highly wear-resistant material, 
lateral portions made of highly compressible material and a so-called 
lower or base portion which forms the bottom layer of the tread surface 
and is usually formed from a softer mixture than the tread surface. 
These three mixtures have markedly different viscosities but must be 
brought together in a single extrusion head to form the tread strip. 
Moreover, the mixtures must flow in flow channels in the extrusion head at 
substantially identical flow rates. 
DISCUSSION OF PRIOR ART 
In German Offenlegungsschrift No. 2 622 011 there is disclosed an extrusion 
apparatus suitable for producing flat profiles from two different types of 
mixtures. The apparatus includes an extrusion head which is divided into 
two planes located one above the other. The central portion of such a head 
is fixedly connected to the extrusion devices, while the upper and lower 
portions of the head are pivotable. 
It is necessary for the head to be pivotable so that the flow channels can 
be cleaned if the mixture flowing therethrough is to be changed. Flow 
channel insert members can be inserted into the extrusion head if it is 
desired to alter the shape of the profile being produced. Such insert 
members are disposed in the head and each such member comprises an upper 
portion and a lower portion having a parting plane which extends along the 
length of the channel across the horizontal diameter. To define two flow 
channels, therefore, four insert members, each of which defines half a 
flow channel, are necessary. Each of these must be unscrewed and replaced 
if a tread strip of a different size is to be extruded. The head 
illustrated in this prior specification is thus only capable of processing 
two different types of mixtures. 
U.S. Pat. No. 3,099,359 discloses an extrusion apparatus wherein three 
extrusion devices extrude into one extrusion head to permit tread strips 
to be produced. However, despite the use of three extrusion devices, such 
apparatus can only be used to extrude two different types of mixtures. The 
tread surface is extruded by means of the central extrusion device and the 
lateral portions are extruded separately by laterally disposed extrusion 
devices. The lower or base layer used to form the tread strip, that is to 
say, the third mixture, is subsequently joined to the extruded tread 
surface and lateral portions on a doubling rolling mill. In consequence, a 
doubling calender is also required. Such calendering is relatively 
expensive and takes up additional space in the manufacturing area. The 
extrusion head illustrated in this prior document is not pivotable. If the 
mixture being used is changed and/or if the worms of the three extrusion 
devices need to be cleaned, the entire apparatus has to be dismantled. 
This is not economically viable. 
Since the extrusion head must be pivotable in order to permit a cleaning 
operation to be effected more quickly and because of the need for the 
insert members to be readily interchangeable to enable the production of 
different-sized profiles to be achieved, the extrusion heads disclosed in 
these prior art documents do not provide an economic solution. 
In order to permit the material utilised to form the lateral portions to be 
deflected to form the external surfaces, such material must traverse 
extremely long flow paths before it can emerge from the extrusion head. 
Howevere, if the mixture for forming the two lateral rubber strips or, if 
desired, the mixture for forming the base, is conveyed to the head by 
means of a fourth extrusion device, then this, according to the teaching 
of U.S. Pat. No. 3,099,359, would have to be disposed either to the left 
or right of the tread surface extrusion device. If the extrusion device is 
disposed, for example, on the left-hand side of the tread surface 
extrusion device, a very long flow channel would be required on the 
right-hand side. The mixture in such right-hand side channel would 
therefore flow more slowly, and the temperature thereof would differ from 
that of the mixture in the left-hand flow channel. As a consequence 
thereof, the different amounts of cooling of the materials would have a 
detrimental effect upon the combining process when the mixtures are 
brought together in the extrusion head. 
However, an even greater danger resides in the fact that the mixture in the 
long right-hand flow channel may easily become partially pre-vulcanized. 
Consequently, during subsequent vulcanization in a tyre heating press, the 
tread strip would be double vulcanized in places and would therefore 
contain weakened portions. 
OBJECTS OF THE INVENTION 
The invention seeks to provide an extrusion head which is of the pivotal 
type disclosed in German Patentschrift No. 2 201 631, but which permits 
three or more different mixtures to be extruded simultaneously. In a 
subsidiary aspect, the present invention seeks to provide an extrusion 
head which permits the shape and constitution of the profile being 
produced to be changed rapidly. 
Particular care must be taken to ensure that, despite the fact that three 
or more very different types of mixtures are being processed, the flow 
rates of the mixtures must be kept as constant as possible in all of the 
flow channels. This applies particularly to flow channels which may be 
used for forming the lateral portions of a tread strip since these emerge 
from the outer edges of the extrusion head and are considerably spaced 
apart from one another. The head must be capable of being rapidly cleaned 
and insert members provided therein to form flow channels must be readily 
changeable when it is desired to produce a differently shaped profile. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided an extrusion head for 
producing flat profiles from different rubber or plastics material 
mixtures, the head including flow channels communicatable with worm or 
screw extrusion devices, the head comprising a central portion is fixedly 
connected to a worm or screw extrusion device and upper and lower portions 
which are pivotably connected thereto, the flow channels being defined by 
interchangeable insert members which are centrally and axially divided in 
a longitudinal direction, wherein insert members defining the flow 
channels are integrally formed, the upper and/or lower surfaces of such 
inserts defining flow channels, the flow channels being bounded in an 
upward or downward direction along their length by plane surfaces of the 
pivotable upper or lower portion or of the stationary central portion, the 
longitudinally extending axes of symmetry of the flow channels being 
disposed one above the other in a common, vertical plane. 
Because the insert members used in such an arrangement are detachably 
retained in locking means, and complete flow channels (with the exception 
of the upper or lower boundaries thereof) are formed in such insert 
members, one or two new flow channels can be produced simply by replacing 
one insert member. The replacement operation, necessary when a differently 
shaped profile is to be produced, is therefore considerably facilitated 
and can be performed more rapidly. 
Because the upper or lower boundaries of the flow channels, which extend 
longitudinally through the insert members, are covered by the respective 
sealing faces of either the pivotable upper or lower portions of the 
extrusion head or by the stationary central portion of the head, the 
construction of the head itself is simplified. The pivotable upper and 
lower portions, as well as the stationary central portion, additionally 
fulfil a sealing and covering effect for the flow channels. 
However, it must be particularly emphasized that symmetrical flow path 
lengths are achived in the channels because all of the flow channels in 
the extrusion head are disposed one above the other so that their 
respective longitudinal axes of symmetry are disposed in a common vertical 
plane. This is achieved despite the fact that three or more flow channels 
are provided in the head. 
To permit an extrusion head for producing tread strips to operate 
satisfactorily, it is vitally important for all of the flow channels to 
have virtually the same length. Only when this is ensured, as is the case 
in the arrangement of the present invention, can a tread strip extrusion 
head cope in fact with three or more different mixtures.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1, there is shown an extrusion head 1 which comprises extrusion 
devices 14, 15 and 16. The devices 14, 15 and 16 are disposed generally 
above one another and are flange-mounted on the extrusion head 1. 
The head 1 comprises an upper portion 2, a lower portion 3 and a stationary 
central portion 4. The portions 2 and 3 are pivotable away from the 
stationary portion 4 by means of hydraulic cylinders. When the head is in 
its closed position, as is shown in FIG. 1, the upper portion 2 and lower 
portion 3 are held together by means of a hydraulic locking device (not 
shown). 
FIG. 2 illustrates a second embodiment of an extrusion head in accordance 
with the present invention. There are many similarities between the heads 
shown in FIGS. 1 and 2 but two major points of difference are that the 
head shown in FIG. 2 is in its open position and that four extrusion 
devices 14, 15, 16 and 17 are provided rather than three as in FIG. 1. 
Insert members 8 and 9 are provided in the extrusion devices in both 
embodiments but are only visible in FIG. 2. These insert members 8 and 9 
are shown in greater detail in FIGS. 5 to 8. 
As illustrated in FIG. 1 but more clearly in FIG. 5, a flow channel 13 
without a parting plane is provided in one face of the insert member 8, 
which flow channel 13 is supplied with material by the device 16. The 
lower surface 19 of the upper portion 2 of the head 1 defines the upper 
surface of the channel 13 when the head 1 is in its closed position. 
As can also be seen in FIG. 4a and 5, both the upper and lower surfaces of 
the insert member 9 are provided with flow channels 10 and 11. The insert 
members 8 and 9 are both retained or held in the extrusion head 1 by 
locking devices (not shown). 
The insert member 9, shown in FIGS. 5 to 8 is provided with a lower flow 
channel 10 which is supplied with material by the extrusion device 14 
through a connecting channel 7. 
The channel 7, visible in FIG. 1, extends from the outlet aperture 12 of 
the extrusion device 14 and widens out to the width of the flow channel 
10, as can be seen in FIG. 6. The lower boundary of the flow channel 10 is 
defined by the plane surface 21 of the lower portion 3 of the head 1 in 
the arrangement shown in FIG. 5. In the arrangement shown in FIG. 4a, the 
upper boundary of the flow channel 10 is defined by the plane surface 20 
of the central portion 4. 
The flow channel 11, as can best be seen in FIG. 8, is bifurcated to form 
two separate channels and is used for the extrusion of the lateral rubber 
portions. The upper boundary of the flow channel 11 is limited by the 
plane surface 20 of the central portion 4 in the FIG. 5 embodiment and the 
lower boundary of such channel is defined by the plane surface 21 of the 
lower portion 3 in the FIG. 4a embodiment. 
It may, on occasions, be desired to replace the insert members 8 and/or 9 
if, for example, a differently shaped profile is to be produced. 
Alternatively, it may be desired to remove and clean the members 8 and/or 
9 if, for example, the mixture supplied to the head 1 is being changed. 
This is effected in a simple manner by pivoting the portions 2 and 3 of 
the head 1 away from the central portion 4 utilising the hydraulic 
cylinders. The insert members 8 and/or 9 are detached from their locking 
devices (not shown) and simply removed. Thereafter, the screw or worms can 
also be simply extracted from the extrusion devices 14, 15, 16 and, if 
provided, 17, cleaned and replaced. 
The device shown in FIG. 1 can be used to produce a tread strip from three 
different mixtures. As aforementioned, a tread strip comprises a tread 
surface made of a highly wear-resistant material, lateral portions made of 
highly compressible material and a so-called lower or base portion which 
forms the bottom layer of the tread surface and is usually formed from a 
softer mixture than the tread surface. Each of the extrusion devices 14, 
15 and 16 illustrated in FIG. 1 is supplied with one of the mixtures. Each 
mixture is then plasticized and homogenized and extruded through a nozzle 
(not shown). 
Since the longitudinal axes of symmetry of the flow channels 10, 11 and 13 
in the head 1 are disposed in a common vertical plane 18, all three 
mixtures have substantially identical flow rates and hence remain in the 
extrusion head for substantially identical periods of time. 
In the arrangement illustrated in FIG. 2, four extrusion devices are shown, 
the extrusion devices 15, 16 and 17 being disposed one above the other, 
whilst the extrusion device 14 is disposed at an angle to the vertical 
plane containing the other three devices. The extrusion head 4 in the FIG. 
1 embodiment may also be angularly off-set in a similar manner and such an 
arrangement is illustrated in FIG. 3. Despite the fact that, in the FIG. 2 
embodiment, four extrusion devices discharge into a single extrusion head, 
it is still possible for symmetrical flow paths to be maintained in the 
head and for the flow channels to be disposed in a common vertical plane. 
Since the insert members 8 and 9 are formed in one piece and may be 
provided with flow channels in both their upper and lower surfaces, only 
two insert members are required, even if four extrusion devices are being 
used. In consequence, it is never necessary to remove or replace more than 
two insert members. 
Moreover, the use of the arrangement illustrated in FIG. 2 permits two 
tread strips formed from four different mixtures to be produced 
simultaneously. In such a case, it is necessary for inserts to be used 
which are formed in such a manner and which permit the tread strips to be 
extruded alongside one another. 
The arrangements illustrated in FIGS. 1 and FIGS. 2 also permit all of the 
screws or worms to be extracted and cleaned once the head has been 
pivoted-open and the insert members 8 and 9 have been removed. To achieve 
this, it is not necessary for the head itself to be dismantled. This is, 
however, essential in the prior art arrangement such as the arrangement 
disclosed in U.S. Pat. No. 3,099,359.