WO2020002835A1

WO2020002835A1 - Facility for extruding profile strips made of elastomer mixtures, and associated method

Info

Publication number: WO2020002835A1
Application number: PCT/FR2019/051577
Authority: WO
Inventors: Thomas Mosnier; Christophe Ougier; Arnaud Letocart; Henri Hinc
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-06-27
Filing date: 2019-06-26
Publication date: 2020-01-02
Also published as: FR3084844A1; FR3084844B1

Abstract

The invention relates to an extrusion facility (1) and method for producing a profile strip, such as a tyre tread, made from elastomer mixtures by coextrusion, comprising a plurality of extruders (10, 20, 30, 40) for supplying elastomer mixtures to an extrusion head (2), the extruders being supported by two subassemblies (I, II) arranged on either side of the extrusion head (2). Each extruder communicates directly with an inlet duct (15, 25, 35, 45) of the extrusion head and each subassembly (I, II) is mounted to move in translation by being driven by a driving device (70) between a closed position in which the subassemblies (I, II) are in contact with the extrusion head (2) and an open position in which the subassemblies (I, II) are spaced apart therefrom.

Description

EXTRUSION PLANT FOR MIXED PROFILE STRIP

ELASTOMERICS, AND ASSOCIATED METHOD

The invention relates to the field of extrusion of elastomeric mixtures intended for the manufacture of tires. More particularly, it relates to the manufacture of complex coextruded profiles based on elastomeric mixtures such as tire treads.

In known manner, during the manufacture of complex profiles by extrusion of at least two mixtures of elastomers of different compositions, or coextrusion, using several extruders connected to a common extrusion head. Each extruder is formed of a cylindrical body or fixed sheath inside which is a screw coaxial with the longitudinal axis of the sheath and which is rotated around the latter. Its function is to homogenize a rubbery mixture which is introduced therein in the form of a strip and to push it towards an outlet die. For a complex product, the output die receives several mixtures of elastomers of different compositions and determines the profile of the rubber band. This profile is defined by a fixed profiled blade cooperating with a rotary roller or with a fixed wall.

Nowadays, the use of complex products is increasingly used to reduce the number of successive poses of products in assembly, reduce costs and improve the quality of the final product. It is preferable to obtain these complex products by coextrusion because this process ensures better cohesion of the various components with one another. However, the number of components that form a complex profile tends to increase, which complicates the production of production equipment and makes it more bulky.

Document WO 2015/028166 is thus known, which describes a coextrusion installation using five extruders arranged in parallel and used for the manufacture of a tread for a tire. A complex profile is thus obtained by coextrusion of different mixtures arriving, via five different lanes, in a common extrusion head provided at the outlet with a profiling device. The extruders are all arranged on the side opposite that of the product outlet. When you want to change the profile of the extruded complex, the downstream part comprising the profiling die of the extrusion head is replaced, which is fixed. Thus, the upstream tool comprising the inlet passages for the mixtures is fixed to the extruders and can only be replaced by long dismantling operations. Furthermore, due to the convergence of the mixture flows on only one side, the size of the extrusion head is very large and the installation must include very robust extrusion head locking mechanisms to counter the extrusion pressure.

A solution to this problem is described in document JP 4053687 which proposes to have the various extruders on either side of the output die of the coextruded complex product. The coextrusion assembly according to this document comprises a fixed extrusion head provided with an outlet die in the lower central part and three extruders mounted fixed two to the right and one to the left of the die. According to this document, it is possible to change the type of profile by replacing the die with another which communicates with the three extruders as well as with a fourth removable extruder placed below. The forces collected by the extrusion head are certainly less than in the previous document due to the different arrangement of the extruders. However, the extrusion head of this document includes very deep preforming channels which connect the extruders to the die and which are difficult to clean. Therefore, the extrusion assembly of this document produces a lot of scraps when changing the mixtures of the different extruders. We also know from document US 7 311 505 another extrusion installation comprising a fixed extrusion head provided with an outlet die in the lower central part and four extruders mounted fixed two to the right and two to the left of the sector. The extrusion head also comprises three moving parts which are caused to move at the end of the operation to open the head and allow access to the deep channels which connect the extruders to the extrusion die. Being more judiciously carried out than that of the previous document, the structure of the extrusion head of this document turns out to be quite complex and must use several devices which ensure the opening and closing of all the parts which make up the head of 'extrusion. An object of the invention is to remedy the drawbacks of the aforementioned documents and to provide an original solution for designing an extrusion installation which is of compact construction while allowing a rapid change of extrusion head between two successive operations of coextrusion of strips of profiles having different geometries and / or compositions.

This objective is achieved by the invention which proposes an extrusion installation for manufacturing a profile strip, such as a tread, based on elastomeric mixtures by coextrusion, comprising several extruders for supplying elastomeric mixtures of an extrusion head, the extruders being supported by two subassemblies arranged on either side of the extrusion head characterized in that each extruder communicates directly with an inlet duct of the extrusion head and in that each sub-assembly is mounted movable in translation by being moved by a drive device between a closed position in which the sub-assemblies are in contact with the extrusion head and an open position in which the sub - sets are moved away from it.

Thus, the extruders of the installation which supply the various constituents of the extrusion head are distributed in two sub-assemblies arranged on two opposite faces of the extrusion head so as to communicate directly with the inlet ducts inside it. The two faces of the extrusion head are preferably mutually parallel or, in a variant, they are inclined relative to each other, the angle of inclination being less than 30 °. By two subassemblies is understood at least two subassemblies each supporting one or more extruders and being arranged each on one of the opposite faces of the extrusion head. However, several sub-assemblies can be arranged on the same face of the extrusion head and be connected to a moving drive device. The extrusion head is a monobloc assembly which contains the transfer channels between each extruder and the die, as well as the die. Such a one-piece assembly corresponds to a type of profile strip and is removably mounted in the installation. By the arrangement of the extruders on two opposite faces of the extrusion head, the installation has a reduced size. The opening movement of the sub-assemblies carrying the extruders makes it possible to free the extrusion head sufficiently so that it can be removed automatically and with less effort, without shearing of the rubber at the interface. This movement takes place in translation so that the plane of the interface on the installation side (plate which bears on the corresponding face of the head) always remains parallel to that of the corresponding face of the extrusion head.

Indeed, when the extruders are supported by a fixed frame and only the extrusion head is mobile, the extraction thereof is done with shearing of the rubber at the communicating orifices located at the interface between the head and the sub-assemblies. Aside from the significant effort that must be applied to the head to extract it, the gum residues stick to the walls of the installation, which means that they must be cleaned before introducing a new head. However, the translational movement of the parts of the installation supporting the extruders creates sufficient space between the entry holes in the head and those leaving the extruders to allow the gum to stretch and then break. This allows the extrusion head to be removed with less effort, while avoiding spreading the residue on the walls of the installation.

Advantageously, the sub-assemblies are arranged on two parallel faces of the extrusion head and the direction of movement in translation of the sub-assemblies is parallel to that of the longitudinal axis of the inlet conduits of the head d 'extrusion. Thus, the extruders are arranged with their longitudinal axes parallel to each other and parallel to the axes of the inlet conduits being perpendicular to the planes of the opposite faces of the extrusion head. The translational movement is in this case parallel to the axes of the inlet conduits and therefore to those of the longitudinal axes of the extruders.

Preferably, said drive device moves said subset in translation relative to the extrusion head by a distance d> 5 mm. It has been found, after laboratory tests with different elastomeric mixtures, that a displacement of at least 5 mm made it possible, by stressing the rubber in traction, to cause a necking thereof, then its rupture.

Advantageously, the distance d is at least equal to the diameter of the extruder screw having the largest diameter. This allows, when the extruders have different sizes, there is stretching, necking and rupture of the rubber even at the outlet of the extruder having the largest diameter.

Preferably, the extruder comprises a screw which rotates in a sheath whose outlet orifice communicates with the inlet orifice in the inlet duct of the extrusion head which is produced so that that its diameter is greater than that of the outlet opening of the sleeve.

Indeed, when the interface between the sub-assemblies and the extrusion head, is provided with slightly larger orifices on the side of the extrusion head than those on the side of the extruders, there is no risk of rubber residue being present at the interface. Any rubber residues which remain circumscribed in the diameter of the outlet orifice will thus be taken up by the conduit of the new extrusion head, which avoids any risk of sticking to the walls of the interface on the sub-assembly side of the installation, especially in the case of fairly fluid mixtures. Adding a simple chamfer locally to the entry port in the extrusion head is sufficient to achieve this.

In a first variant of a preferred embodiment of the invention, the inlet conduit in the extrusion head has an undercut shape over at least part of its circumference. This makes it possible to retain the rubber in the extrusion head, despite the traction forces, and thus avoid delamination. Thus, a rupture localized at the end of the extruders is controlled without the risk of having a residue of large volume which could compromise the closure of the installation during the installation of a new extrusion head.

In a second variant of a preferred embodiment of the invention, the extruder comprises a screw which rotates in a sheath, the diameter of the screw being made so that it reaches its most high in an outlet section scabbard. Thus, the exit gap of the gum of the extruder is reduced, as well as the size of the gum residues, which makes it possible to reduce the value of the translational movement of the extruders.

In a third variant of a preferred embodiment of the invention, the extruder comprises a screw which rotates in a sheath and a ring provided with cutting blades arranged at the outlet of said sheath. This makes it possible to cut the rubber residues at the outlet of the extruder and therefore reduce the risk of rubber flowing at the opening, or even reduce the value of the distance d of displacement in translation.

Preferably, the screw is rotated synchronously with the translational drive of the sub-assemblies.

Before ordering the opening of the installation, the extruder screws are stopped. The translational displacement of the sub-assemblies creates a stretching of the rubber at the interface with the extrusion head, and if, at the same time as it opens (from the start of the opening or just after setting in motion sub-assemblies) the screw is slightly rotated, the tension in the rubber is maintained, which ensures better cutting efficiency. In a variant, the screw is rotated in the opposite direction to that of propulsion, which makes it possible to reduce the quantity of rubber sent at the outlet and, therefore, the distance "d" of opening, while maintaining the eraser in tension to promote cutting. In a fourth variant of a preferred embodiment of the invention the extruder comprises a screw which rotates in a sheath, the outlet of which communicates, in the closed position of the installation, with a conduit from the head extrusion via a communication orifice of diameter smaller than that of the sleeve, orifice which is crossed by a scraper rod which is integral with the subassembly or the extrusion head. This makes it possible to cut the rubber at the same time as the displacement in translation of the subassemblies is carried out relative to the extrusion head.

Advantageously, said scraper rod has a protruding end with a diameter close to that of the communication orifice. This solution allows to cut net any rubber residue during the translational movement of the extruders relative to the extrusion head.

Preferably, the surfaces of the walls which form the junction of each sub-assembly with the extrusion head are covered with a non-stick coating. This prevents gum residue from sticking to the walls of the installation, the residue remaining sticking rather to the extrusion head (which does not have a non-stick coating) and is removed with it.

The object of the invention is also achieved with an extrusion process for manufacturing a profile strip, such as a tread, based on elastomeric mixtures by coextrusion, using an extrusion installation comprising several extruders for supplying elastomeric mixtures to an extrusion head, the extruders being supported by two sub-assemblies arranged on either side of the extrusion head so that the outlet of each extruder communicates with an inlet duct for the extrusion head, characterized in that each sub-assembly is moved in translation between a closed position in which the sub-assemblies are in contact with the extrusion head and a position d opening in which the subassemblies are spaced therefrom relative to the extrusion head which remains stationary.

Advantageously, the extrusion head is extracted at the end of the movement of said subsets. The invention will be better understood from the following description, which is based on the following figures: Figure la is a schematic sectional view of an extrusion installation of the invention in the working position and Figure 1b is a view of the installation of Figure 1a illustrated in a rest position; - Figure 2 is a schematic sectional view of the extrusion installation of the invention in the open position according to a preferred embodiment of the invention; Figure 3 is a schematic sectional view of an extrusion installation of the invention in the open position according to a first embodiment of the invention; Figure 4 is a schematic sectional view of an extrusion installation of the invention in the open position according to a second embodiment of the invention; Figure 5 is a schematic sectional view of a detail of the installation according to a third embodiment of the invention; Figures 6a to 6c are schematic sectional views of a portion of the extrusion installation of the invention according to a first example of a fourth embodiment of the invention; Figures 7a to 7c are schematic sectional views of a part of the extrusion installation of the invention according to a second example of the fourth embodiment of the invention. In the various figures, identical or similar elements have the same reference. Their description is therefore not systematically repeated.

FIG. 1a illustrates an extrusion installation 1 for a strip of complex profile, such as a tire tread produced by coextrusion of different components of the strip, the components being elastomeric mixtures. The elastomeric mixtures which form the various components arrive from several extruders 10, 20, 30, 40, belonging to the extrusion installation 1, mixtures which converge together in a common extrusion head 2 and form at the outlet a strip of complex profiled product by coextrusion, for example a tire tread. In the exemplary embodiment of the invention, such a tread comprises a sub-layer made of an elastomeric mixture which arrives in the extrusion head 2 coming from the extruder 40 which is, for example, a material made from 100% natural rubber. This sub-layer is completed by an outer layer superimposed on it and which is produced in a mixture based on synthetic rubber with 100% comprising for example silica, a mixture which arrives in the head from the extruder 30. The outer layer comprises conductive inserts made from a mixture of natural rubber / synthetic rubber and carbon black from of the extruder 20. The assembly is finally completed by two lateral edges composed for example of a mixture of natural rubber / synthetic rubber (20% to 80% of natural rubber) coming from the extruder 10.

The extruders 10, 20, 30, 40 have been illustrated schematically by representing only their respective screws, but it is understood that, in a generally known manner, the screw of each extruder rotates inside a cylindrical sheath provided with an inlet for supplying an elastomeric mixture, in the form of a mixing strip, and with an outlet which opens into the extrusion head 2 when the latter is in place. The screw of each extruder is driven in rotation about its longitudinal axis by a motor, located at the end of the screw opposite to that which arrives in the extrusion head, so that it rotates inside of its respective sheath in order to provide the extrusion head with a homogenized elastomeric mixture and ready to be shaped by it.

The extruders 10, 20, 30, 40 are grouped into two sub-assemblies I and II, arranged on either side of the extrusion head 2 and in such a way that the output of each extruder communicates directly with an inlet duct 15, 25, 35, 45 for mixing in the extrusion head 2. In other words the extrusion head 2 is connected directly to the extruders 10, 20, 30, 40 without there being any elastomeric mixture transfer channel between the two. The extrusion head 2 groups together all of the dimensional tools (transfer channels connecting it to the outputs of the extruders and the extrusion die) specific to a given profile in a single monobloc assembly mounted removable. In the event of a change of profiled product, such a monobloc assembly is quickly removed and replaced by another adapted to the new product.

The inlet conduits 15, 25, 35, 45 of the mixture extend in the direction of an outlet die 3 via distribution channels 2a, 2b, 2c, 2d of the mixtures. The longitudinal axis 16, 26, 36, 46 of each of the inlet conduits 15, 25, 35, 45 is located in the extension of the respective longitudinal axis 11, 21, 31, 41 of the corresponding extruder 10, 20, 30, 40 opposite. The distribution channels 2a, 2b, 2c and 2d extend in a direction substantially perpendicular to that of the longitudinal axes of the mixture inlet conduits in the extrusion head. By sub-assemblies I and II located on either side of the extrusion head, it is understood that the two sub-assemblies face each other by being arranged on either side with respect to a vertical plane median which passes through the center of the extrusion head 2. The subassembly I groups the extruders 10 and 30 on a common rigid support and the subassembly II groups the extruders 20 and 40 on a common rigid support. Such an arrangement with facing extruders makes it possible to use more compact extrusion heads with shorter channels.

In a preferred embodiment, the extruders 10, 20, 30, 40 are arranged with their longitudinal axes 11, 21, 31, 41 parallel to each other and parallel to the longitudinal axes 16, 26, 36, 46 of the conduits 'inlet 15, 25, 35, 45 being perpendicular to the planes of the opposite faces of the extrusion head which form interface planes. The translational movement is in this case parallel to the axes of the inlet conduits and therefore to those of the longitudinal axes of the extruders.

When the size of the gearmotor requires it, the extruders can be inclined, being installed so as to form an angle with respect to each other (angle of about 10 ° to 30 ° between their axes respective longitudinal) and this is symmetrically with respect to a median plane passing between two adjacent extruders, or asymmetrical, one of them remaining for example perpendicular to the interface plane, and the other being inclined.

In operation, when each extruder is supplied with an elastomeric mixture, the various mixtures coming from the extruders 10, 20, 30, 40 pass through the distribution channels 2a, 2b, 2c, 2d provided for this purpose in the extrusion head 2 and converge towards the die 3 which gives the final shape of the product, in this case to the tread. At the end of the extrusion operation, when we want to change the mixture and / or tread profile we remove the extrusion head 2 already used, the extrusion head which is mounted removable in the installation, and we replace it with a new one. Figure lb illustrates such an operation in which the extrusion head 2 is withdrawn in the direction of arrow E. In this case, the extruders 10, 20, 30, 40 are supported by a fixed frame. However, in order to be able to extract the extrusion head at the end of the operation and to ensure the sealing of the assembly in operation, a sealing clearance “j” is provided between the extrusion head 2 and the walls 50, 60 of the installation. In the open position, the clearance “j” is obtained by the displacement of the side walls 50, 60. In order to limit the displacement of the side walls 50, 60, the values of the clearance “j” of sealing are chosen the lowest possible, for example in a range from a few tenths of a mm to 1 mm. Thus, a small displacement of value equal to the sealing clearance “j” of each wall makes it possible to extract the extrusion head by shearing the rubber at the level of the existing interface between the walls of the extrusion head and those opposite the installation. However, apart from the efforts exerted by the head extraction device to shear the gum, it has been found that after extraction of the extrusion head, the gum is driven by the displacement of the latter in its vertical movement and remains glued to the side walls 50, 60. Cleaning operations on the walls of the installation must then be undertaken before the introduction of a new extrusion head. The object of the invention is to allow an automatic change of the extrusion head 2 without prior manual operation of cleaning the surfaces of the walls of the installation located at the interface with those of the extrusion head.

More particularly according to the invention and as best seen in FIG. 2, each sub-assembly I, II is arranged so as to be movable in translation on a rail (symbolized by the slide 71) supported by a frame (symbolized by the support 72). Each sub-assembly I, II is moved in a rectilinear movement of horizontal translation in the direction of the arrows A, B while being moved by a hydraulic cylinder 73 which is part of a drive device 70 in movement of each sub-assembly . Alternatively, an electric cylinder is used. In another variant, a common drive device ensures the movement of the two subsets I and II. The drive device 70 also comprises a command and control unit for the movement of each sub-assembly (not shown).

Thus, according to the invention, the subsets I and II of the installation are moved in translation in a direction A, B parallel to that of the axes 16, 26, 36, 46 of the inlet conduits in the extrusion head over a distance “d” so as to separate them enough to stress the rubber in traction until a necking is obtained, then the rupture of the rubber bridges which form between the outlet orifice of each extruder and that entry correspondent in the extrusion head.

Preferably according to the invention, before removing the extrusion head 2, each subset I, II is moved in horizontal translation, moving it away from the extrusion head 2 which remains in place , from a distance "d" equal to at least 5 mm. Even more preferably, the distance "d" has a value which is at least equal to the diameter of the screw of the extruder of the installation having the largest diameter.

Such displacement of the two sub-assemblies I, II to open the installation 1 before removing the extrusion head 2 allows the rubber, which is present in conduits of sub-assemblies which communicate with those of the head when the installation is closed, to stretch forming gum gi, gt bridges. The rubber stretches with the displacement of the subassemblies, so that the cross section of the rubber bridges decreases until the bridges are finally broken, as shown in FIG. 2 to 4. When the rubber bridges are broken, the extrusion head is removed and replaced with a new one. Thus, it has been observed during tests carried out with different mixtures that, during the stretching of the rubber and the rupture of the rubber bridges, the residues generally remain circumscribed within the diameter of the orifice. This also applies to the part gi of the rubber bridge which remains attached, if necessary, to the material contained in the outlet duct of the sheath, and which remains circumscribed inside a fictitious envelope whose diameter coincides with the diameter of the corresponding outlet orifice 14, 24, 34, 44 of the barrel of the extruder, that, respectively, for the part gt of the rubber bridge which remains if necessary attached to the material contained in the inlet conduit 15, 25 , 35, 45 of the extrusion head, and which remains circumscribed inside a fictitious envelope whose diameter coincides with the diameter of the corresponding inlet orifice of said inlet duct of said extrusion head. Thus, when a new head is put in place and the side walls 50, 60 are brought together, the rubber residues are again engaged in the orifices of the new extrusion head, without forming burrs which would spread beyond the diameter of the aforementioned orifices and which would be pinched between said side walls 50, 60 and the mating faces of the extrusion head, and therefore without the need to clean the installation beforehand. Thus a new extrusion head can be set up automatically, without any manual intervention of cleaning the installation. The extrusion head which has already been used is then cleaned in masked time. Preferably, the inlet conduit 15, 25, 35, 45 of the extrusion head 2 has a diameter equal to that of the outlet orifice of the sleeve 14, 24, 34, 44 of the extruder , but a chamfer 18, 28, 38, 48, for example 2 mm at 45 °, is provided at the interface of the two, on the side of the inlet orifice of the extrusion head. This chamfer ensures that the rubber residues remain circumscribed in the diameter of the outlet orifice on the extruder side, which is smaller, and they are taken up by the inlet pipe opposite the new extrusion head, the l he inlet is of larger diameter thanks to the chamfer.

In a preferred embodiment of the invention, the surfaces la, Ib, le and Ha, Ilb, Ile of the walls which form the junction of each sub-assembly I, II with the extrusion head 2 are covered non-stick coating. Such a non-stick coating is for example polytetrafluoroethylene (PTFE). Thus, when very fluid mixtures are sent into the extrusion head at high pressures, leaks may appear at the junctions between the sub-assemblies I, II and the extrusion head 2. Such a non-stick coating allows residues to be detached from the walls of the subassemblies, while remaining bonded to the walls of the head which are themselves devoid of non-stick coating, so that said residues are finally removed with said head.

In a preferred embodiment of the invention, the installation comprises a device which modifies the flow of rubber at the opening making it possible to orient and / or reduce the length of bridge of rubber which is formed during from the opening of the installation. FIG. 3 illustrates a first variant of this device which consists in arranging an undercut shape in the inlet conduits 15, 25, 35 and 45 of the extrusion head 2. To do this, each of the inlet ducts have a conical wall 15 ′, 25 ′, 35 ′, 45 ′ inclined in the direction of the axis 16, 26, 36, 46 of the orifice from a bottom wall 17, 27, 37 , 47 of the duct and over at least one sector in an arc of about 30 °, preferably 180 ° of the inlet duct. Alternatively, the orifices 15, 25, 35, 45 have a conical shape over their entire circumference. It will therefore be closed without the risk of sandwiching a residue of gum.

FIG. 4 illustrates a second variant of the device for limiting the flow of rubber on opening. According to this variant and as visible in the drawings, the screw 12, 22, 32, 42 of the extruder 10, 20, 30, 40 has an increasing diameter in the direction of an outlet section 13, 23, 33, 43 of the sleeve 14, 24, 34, 44 of the extruder. In an exemplary embodiment of this variant, the diameter of the screw is constant over the entire length of the screw and it has a larger diameter only in the outlet section 13, 23, 33, 43 of the sleeve. This makes it possible to reduce the exit section of the mixture from the extruder and therefore the amount of rubber residue when the installation is opened.

FIG. 5 illustrates a third variant of the device for limiting the flow of rubber on opening. The solution consists in adding a ring 5 provided with cutting blades 6 on its internal surface 7. The ring 5 has a cylindrical tubular shape with an outside diameter less than the outside diameter of the sheath 24 and an inside diameter equal to the inside diameter of the sheath 24. Such a ring 5 is fixedly mounted at the outlet of the sheath 24, in an end section 23 thereof. One or more fixed cutting blades 6 (for example up to twelve cutting blades) are provided on the internal surface 7 of the ring 5. Their role is to shear the rubber by cooperating with the end of the threads of the screw 22, upon rotation thereof, which results in a finer gum residue upon opening the installation. Preferably, the number of threads at the end of the screw is equal to or close to the number of fixed knives. FIG. 5 illustrates in a simplified manner a ring 5 mounted at the end of the sheath 24 and of the screw 22 of the extruder 20, but each of the other extruders 10, 30 and 40 can be provided with such a ring 5 with blades cutting 6. To improve the efficiency of the device, a slight rotation of the screw to obtain an angular displacement thereof (for example less than 1 turn and this depending on the number of cutting blades) in synchronization with the movement of movement during opening, or just after the start of opening to benefit of the tensioning of the rubber which is favorable for cutting. The direction of rotation may be that corresponding to the normal direction of propulsion of the rubber, or in the opposite direction to minimize the stroke d in the case where this does not disturb the supply of the extruder upstream.

Figures 6a to 6c and 7a to 7c illustrate two embodiments of a fourth variant of the device for restricting the flow of rubber on opening. The installation 1 is represented in a simplified manner in these figures by a part of the subassembly I, in particular the sheath 14 of the extruder 10 and the corresponding conduit provided with an inlet conduit 15 in the extrusion head 2 .

Figures 6a to 6c illustrate the different positions taken by the device between that of closing the installation (6a), an intermediate opening position (6b) and the final opening position (6c) of the installation. The sheath 14 has an internal diameter D substantially equal to that of the inlet conduit 15. The passage of the elastomeric mixture m from the extruder 10 takes place through a baffle 105 in the closed position of the installation. The baffle 105 is obtained by reducing the internal diameter D of the facing pipes to a value dl <D, in particular by making a communication orifice 130 with a diameter less than the internal diameter through the end wall of the extruder 114 and that of the conduit 115 at the junction of the two conduits. The protruding end 120 of a scraper rod 110 passes through the communication orifice. The end 120 is cylindrical with a circular section and a diameter slightly less than the diameter dl of the passage orifice so that it can pass through it. with a clearance of about 0.5 to 1mm. The end 120 is extended by a neck 121 of diameter less than that of the end 120 and of length greater than the thickness of the bottom walls 114, 115 of the conduits. The neck extends in the direction of the extruder 10 by a core 122 of the same diameter as that of the end 120 of the rod. The scraping rod 110 is fixed at the end of the screw of the extruder 10. Thus, as visible in FIG. 6a, in the closed position of the installation, the mixture m coming from the sleeve 14 passes through the baffle 105 thus formed between the scraper rod 110 and the communication orifice between the two conduits to arrive in the inlet conduit 15 of the extrusion head. When opening (fig. 6b), the subassembly I is moved relative to the extrusion head 2 to the left in the direction of arrow A and the end 120 of the scraper rod 110 closes l communication port 130 between the two. This results in cutting off the flow of gum and any gum residue that may appear at the interface of the two organs. FIG. 6c illustrates the position of complete opening of the installation when the scraper rod 110 is completely extracted from the duct 15 of the extrusion head 2, the distance d being equal to the stroke of the scraper rod 110 at which a spacing is added allowing the extraction movement of the extrusion head. Of course, this solution also applies to the extruder 30 of the sub-assembly I, as well as to the extruders 20, 40 of the sub-assembly IL

Figures 7a to 7c illustrate another example of this embodiment which operates similarly to that of the example of Figures 6a to 6c, but in which the scraper rod 110 is arranged inside the duct 15 of the extrusion head 2. The baffle 105 is obtained by making a communication orifice 130 of diameter dl <D as in the previous example, with the difference that the end 120 of the scraper rod 110 is extended in this case with a core 122 of constant diameter and that the diameter of the conduit 15 also has a diameter equal to approximately dl. The scraper rod 110 is integral with the extrusion head 2. The rubber passes from the sheath 14 of the extruder 10 into the duct 15 of the extrusion head via the baffle 105 (FIG. 7a). At the end of the operation, the installation is ordered to open, the subassembly I moves to the left in the direction of arrow A, the extrusion head remaining in place, which means that the end 120 of the scraper rod 110 closes the communication orifice 130 between the two and cuts off the flow of rubber and any residue of rubber between the two (FIG. 7b). FIG. 7c illustrates the position of complete opening of the installation when the scraper rod 110 is completely extracted from the sheath 14 of the extruder 10, the distance d being equal to the stroke of the scraper rod 110 to which we add a spacing allowing the extraction movement of the extrusion head, as in the previous example. Of course, this solution also applies to the extruder 30 of the sub-assembly I, as well as to the extruders 20, 40 of the sub-assembly assembly II, the extrusion head comprising for this purpose several rods 110 whose protruding ends 120 protrude from each orifice 15, 25, 35, 45 in the direction of an opposite extruder.

In a variant of the invention, all the extruders 10, 20, 30, 40 of the installation 1 are Archimedes screw extruders. In another variant of the invention, at least one of the extruders of installation 1 is a volumetric extruder, for example of the twin-screw, counter-rotating volumetric extruder type with interpenetrated threads and conjugate profiles of the type described in the patent application W02017 / 109419 in the name of the plaintiff. In addition, other types of volumetric extruders can be used, for example of the gear pump or piston pump type.

In operation, the extrusion installation 1 is in the closed position, the sub-assemblies sealingly communicating with the extrusion head 2. Each extruder is supplied with an elastomeric mixture and the various mixtures extruded by the extruders 10, 20, 30 and 40 pass through the distribution channels provided for this purpose in the extrusion head 2 and converge towards a die 3 which gives the final shape of the product, in this case to the tread. At the end of the operation, each of the subassemblies I, II is moved in translation, in opposite directions and in directions A, B parallel to that of the conduits 15, 25, 35, 45 of the extrusion head , while keeping the latter stationary. When the preset value "d" of the spacing is reached, the movement of the subassemblies is stopped and the extrusion head 2 is removed in a direction perpendicular to those A, B of displacement of the subassemblies I, II. Preferably, a gripping and translational displacement device is used on a rail provided for this purpose in order to hold the extrusion head in place during the translational displacement of the subassemblies and to move it at the end of the stroke of the sub -sets. When it is desired to change mixtures or profiles, a new extrusion head is introduced into the installation and the latter is closed in a sealed manner with respect to the head by performing the same movements as at opening but In the opposite way. Other variants and embodiments of the invention can be envisaged without departing from the scope of its claims.

Thus, more than four extruders can be arranged on either side of the extrusion head, or even on the other faces of the extrusion head which are not dedicated to one at the outlet of the mixtures. in the direction of the extrusion die and the other to grip the head for its displacement at least two of them working with different mixtures and some others with the same mixture of elastomers.

Furthermore, one can envisage combinations between different embodiments of the invention, for example one can equip the conduits of the extrusion head with conduits undercut and provide screws with diameter increased to l end of the extruder and / or a ring fitted with sharp blades.

Claims

1. Extrusion installation (1) for manufacturing a profile strip, such as a tread, based on elastomeric mixtures by coextrusion, comprising several extruders (10, 20, 30, 40) for supplying elastomeric mixtures of an extrusion head (2), the extruders being supported by two subassemblies (I, II) arranged on either side of the extrusion head (2) characterized in that each extruder communicates directly with a conduit inlet (15, 25, 35, 45) of the extrusion head and in that each sub-assembly (I, II) is mounted movable in translation by being moved by a drive device (70) between a closed position in which the sub-assemblies (I, II) are in contact with the extrusion head (2) and an open position in which the sub-assemblies (I, II) are spaced therefrom.

2. Installation according to claim 1, characterized in that the sub-assemblies are arranged on two parallel faces of the extrusion head and the direction of movement in translation of the sub-assemblies is parallel to that of the longitudinal axis of the conduits inlet (16, 26, 46, 36) of the extrusion head (2).

3. Installation according to one of claims 1 or 2, characterized in that said drive device displaces said subassembly (I, II) in translation relative to the extrusion head (2) by a distance d > 5 mm.

4. Installation according to claim 3, characterized in that the distance d is at least equal to the diameter of the screw of the extruder (10, 20, 30, 40) having the largest diameter.

5. Installation according to one of the preceding claims, characterized in that the extruder (10, 20, 30, 40) comprises a screw (12, 22, 32, 42) which rotates in a sleeve (14, 24, 34 , 44) whose outlet orifice communicates with the inlet orifice in the inlet duct (15, 25, 35, 45) which is made so that its diameter is greater than that of the orifice out of the sheath.

6. Installation according to one of the preceding claims, characterized in that the inlet duct (15, 25, 35, 45) in the extrusion head (2) has an undercut shape on at least part of its circumference.

7. Installation according to one of the preceding claims, characterized in that the extruder (10, 20, 30, 40) comprises a screw (12, 22, 32, 42) which rotates in a sleeve (14, 24, 34 , 44), the diameter of the screw being made so that it reaches its highest values in an outlet section (13, 23, 33, 43) of the sleeve.

Installation according to one of the preceding claims, characterized in that the extruder (10, 20, 30, 40) comprises a screw (12, 22, 32, 42) which rotates in a sleeve (14, 24, 34, 44 ) and a ring (5) provided with cutting blades (7) arranged at the outlet of said sheath.

9. Installation according to claim 8, characterized in that the screw (12, 22, 32, 42) is rotated synchronously with the translational drive of the subassemblies (I, II).

10. Installation according to one of claims 1 to 5, characterized in that the extruder (10, 20, 30, 40) comprises a screw (12, 22, 32, 42) which rotates in a sleeve (14, 24 , 34, 44) whose outlet communicates, in the closed position of the installation, with a conduit (15, 25, 35, 45) of the extrusion head (2) via a communication orifice of diameter smaller than that sheath, orifice which is crossed by a scraper rod

(110), rod which is integral with the subassembly (I, II) or with the extrusion head (2).

11. Installation according to claim 10, characterized in that said scraper rod (110) has a protruding end (120) of diameter close to that of the communication orifice.

12. Installation according to one of the preceding claims, characterized in that the surfaces (la, Ib, le; Ha, Ilb, Ile) of the walls which form the junction of each sub-assembly (I, II) with the head d extrusion (2) are covered with a non-stick coating.

13. Extrusion process for manufacturing a profile strip, such as a tread, based on elastomeric mixtures by coextrusion, using an extrusion installation comprising several extruders (10, 20, 30, 40) supplying elastomeric mixtures to an extrusion head (2), the extruders being supported by two sub-assemblies (I, II) arranged on either side of the extrusion head (2) so as to that the outlet of each extruder communicates directly with an inlet duct (15, 25, 35, 45) of the extrusion head, characterized in that each sub-assembly (I, II) is displaced in translation in a direction parallel to that of the longitudinal axis (16, 26, 46, 36) of the inlet duct between a closed position in which the sub-assemblies (I, II) are in contact with the extrusion head ( 2) and an open position in which the sub-assemblies (I, II) are separated from cell this in relation to the extrusion head which remains stationary.

14. Method according to claim 13, characterized in that the extrusion head is extracted at the end of the movement of said subsets (I, II).