Apparatus and method for co-extrusion

Abstract

The present invention relates to an apparatus and a method for co-extrusion, in particular to a co-extrusion apparatus for producing co-extrusion molded elements for tyres made of rubber compounds of different compositions, the invention relates to a co-extrusion device comprising at least one first extruder (10) and at least one second extruder (20) and an extrusion head (2), the first extruder (10) having a screw (12) with a longitudinal axis (13); the second extruder (20) has a screw (22) with a longitudinal axis (23); the extrusion head (2) is connected to each of the extruders (10, 20) by a suitable conduit (11, 21). According to the invention, the feed inlet (16, 26) of each extruder (10, 20) is connected to the discharge opening (38, 48) of the gear pump (30, 40).

Description

[0001] This application is a divisional application of the Chinese patent application with application number 201880041088.8, application date June 21, 2018, and invention name “Device and method for co-extrusion”. Technical Field

[0002] The present invention relates to the field of extrusion of rubber compounds, more particularly for the manufacture of tires. More particularly, the present invention relates to the manufacture of extruded profiled elements made from rubber compounds of different composition, especially for the manufacture of treads or sidewalls of tires. Background Art

[0003] As is well known, the device for manufacturing composite molding elements by extruding the rubber compound (or coextrusion) of at least two different components comprises at least two extruders connected to an extrusion head. Each extruder is formed by a fixed cylindrical body or barrel, and has a screw coaxial with the longitudinal axis of the barrel and driven to rotate around the axis inside it. The purpose is to homogenize the rubber compound, and after receiving the rubber compound in the shape of the strip of the compound at the supply port, it is driven towards the outlet hole. For composite products, the outlet hole of each extruder leads to a common extrusion head, and the common extrusion head therefore receives the rubber compound of different components, and comprises an extrusion die at its outlet that limits the profile of the rubber strip. The profile is limited by a fixed molding blade or a fixed molding wall that cooperates with a rotating roller.

[0004] Tire manufacturing increasingly requires the use of composite products obtained in the form of composite semi-finished products in order to reduce the number of successive product laying operations during the tire manufacturing process, thereby reducing costs and increasing precision.

[0005] Today, the number of different rubber compounds used to make a single tire tends to increase in order to be able to improve the performance of the tire according to the areas in which these compounds are located. This is particularly true in the case of tire treads, which usually include two different rubbery compounds, to which other compounds are now added, such as conductive compounds and compounds for covering the sidewalls in the shoulder area.

[0006] During the manufacture of shaped elements by coextrusion, the different components of the compound are brought together towards the exit die, which means that they can be combined in a raw state before shaping, under the pressure and temperature of the compound, without contact with the outside air. This makes it possible to obtain good integrity of the coextruded product in the interface area between the compounds. However, since the rheological properties of one compound are different from those of another, it is difficult to perfectly control the geometry of the component, in particular because it is difficult to position the product made of one compound relative to another and to maintain this positioning for a long time.

[0007] The positioning of one product relative to another is determined by the forming device or the exit die, into which the different compounds from the different extruders arrive as unmixed extrudates to form a coextruded composite forming element at the exit. In practice, the geometry and dimensions of the forming device are determined by several successive iterative cycles. Once the device has been optimized, it can only produce the expected results when the extruder is running in a stable state and at a well-defined speed.

[0008] At present, unqualified coextruded elements account for a non-negligible proportion of the output produced by the machine. The shorter the production process is in order to achieve flexible production, the higher the scrap rate is (in practice, 5 to 20%). This leads to a reduction in the profitability of the machine. Moreover, since material waste is economically unacceptable, the waste, known as mixed (or multi-compound) waste, must be stored, re-homogenized and reintroduced into the subsequent production process in a controlled, precisely metered manner. In addition, the production costs thus incurred are accompanied by a reduction in the properties of the product finally obtained, which is partially contaminated with other compounds.

[0009] Furthermore, the coextruded product must be continuously checked by measuring the linear weight of the output product and comparing it with a predetermined weight. In addition, the shape and dimensions (width, thickness) of the composite product are evaluated using different sensors.

[0010] Thus, the known document WO 2015 / 028166 describes a method for manufacturing a tire tread by coextruding different compounds from a plurality of extruders arranged in parallel, in which the transverse profile is analyzed by a non-contact sensor. The profile of each part that makes up the tread is read by a sensor, and then the profile is analyzed by a central control unit that controls the operation of each extruder. The operation of the extruder is set to adjust the speed of the screw and the pressure at the end of the screw just before the outlet. However, its operation also depends on heating the compound to the correct temperature, heating the mold to the correct temperature, the extrusion rate, the rheological properties of the compound, the interruption of the strip supply, etc. All these factors interfere with the production capacity of the extruder, which means that a lot of settings need to be made before obtaining a qualified product.

[0011] Furthermore, the measurements carried out with optical sensors are not sufficient to guarantee that the different constituent parts of the composite product are correctly positioned relative to each other therein, nor to visualize their respective interfaces, especially when they overlap. As a result, the final inspection is carried out by taking samples. Since the components are composite, the samples taken in all this optimization work cannot be recovered, but rather they are discarded, wasting material and increasing the overall cost of the product obtained.

[0012] Document CN102173042 is also known, and this document describes the arrangement of two extruders, and each extruder has a gear pump at its outlet, for producing the coextruded product made of rubber.Such an arrangement makes it possible to adjust the flow rate of the material output by the extruder by adjusting the speed of the pump at the outlet.The major disadvantage of this solution is that the volume of the gear pump is very large, which directly affects the size of the forming tool, particularly when the number of paths and the number of extruders thus greater than two.Therefore, this tool is expensive and difficult to operate, and it takes longer time to reach the correct temperature.In addition, if with respect to volume, the diameter of the pump gear is reduced, then the latter will have to rotate at a higher speed, so as to discharge the material output by the extruder, which will have the consequence of heating the rubber, and there is the risk of premature vulcanization. Summary of the invention

[0013] The object of the present invention is to solve the drawbacks of the above-mentioned documents.

[0014] This object is achieved by the present invention, which proposes a co-extrusion device for producing co-extruded molding elements for tires, wherein the co-extruded molding elements for tires are made of rubber compounds of different components, and the co-extrusion device has at least one first extruder and at least one second extruder and an extrusion head, wherein the first extruder has a screw with a longitudinal axis; the second extruder has a screw with a longitudinal axis; the extrusion head is connected to each of the extruders by appropriate conduits, characterized in that the supply inlet of each extruder is connected to the delivery hole of a gear pump.

[0015] In other words, each extruder of the coextrusion device is supplied with the elastomeric compound directly from the gear pump. In this way, a positive displacement coextrusion device is obtained in which the outlets of the different extruders converge towards a common extrusion head, the gear pump being placed upstream of the latter. In this case, there is no compromise in terms of the diameter of the gears of the pump, which are dimensioned to ensure the supply required for the operation of the extruders without excessively heating the elastomeric compound.

[0016] Preferably, the axes of the extruders form an acute angle with each other.

[0017] The longitudinal axis of the extrusion screw of the extruder is arranged so that the compound they convey converges toward the extrusion head of the co-extrusion molding element. The longitudinal axis of the extruder is at an acute angle (less than 90 °) to the axis of the adjacent extruder. Therefore, the co-extruded molding element is obtained by co-extruding two separate compounding streams via the flow conduit connecting the outlet hole of the extruder to the extrusion head. The extrusion head is a flat head type, or has a molded fixed blade, which cooperates with a rotating roller, on which the co-extruded product is placed.

[0018] Advantageously, the gear pump comprises two pinions whose axes of rotation are parallel to the longitudinal axis of the extruder it feeds.This makes it possible to use a gear pump of simplified design and reduced volume.

[0019] Preferably, the pinion is of the herringbone type. This makes it possible to better direct the incoming compound to the central part of the pinion and limits the risk of leakage towards the bearings of the pinion.

[0020] Advantageously, the gear pump has a body provided with an inlet opening for the elastomeric compound and with a delivery opening for the compound.

[0021] Preferably, the inlet opening of the gear pump is fed with the elastomeric compound strip. The feeding is a direct feeding of the elastomeric strip without heating, in order to simplify the construction of the assembly.

[0022] Advantageously, the inlet orifice of the gear pump is directly connected to the outlet orifice of the feed extruder for feeding the elastomeric compound. In this way, each gear pump is fed with a fluidized or homogenized hot compound, making it possible to use an extruder at the outlet, the screw of which has only the function of conveying the compound towards the extrusion head. This allows the design of the gear pump to become more compact and cheaper, while extending its service life.

[0023] Preferably, the device of the present invention has a control unit which synchronizes the rotation speed of the screw with the rotation speed of the gear of the gear pump.

[0024] This makes it possible to adjust the amount of work applied to the compound, the flow rate of which is determined by the gear pump. Thus, the speed of the extruder screw is selected to be proportional to the speed of the pump's gears, depending on the amount of shear that is desired to be applied to the compound. For example, a lower speed of the screw applies more shear and heat to the compound, while a gear-like speed of the screw ensures faster transport of the compound to the extruder outlet.

[0025] The object of the present invention is also achieved by a coextrusion method for producing coextruded molding elements for tires, wherein the coextruded molding elements for tires are made of rubber compounds of different components, the coextrusion method having at least one first extruder and at least one second extruder and an extrusion head, the first extruder having a screw with a longitudinal axis; the second extruder having a screw with a longitudinal axis; the extrusion head is connected to each of the extruders by appropriate conduits, characterized in that each extruder is supplied with an elastomer compound from a gear pump.

[0026] Advantageously, the rotation speed of the screw is synchronized with the rotation speed of the pinion of the gear pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will be better understood from the remainder of the description based on the following drawings:

[0028] - Figure 1 is an axial cross-sectional view of a device according to a first embodiment of the present invention;

[0029] - Figure 2 yes Figure 1 A perspective view of a partial cross section of the device in FIG.

[0030] - Figure 3a and Figure 3b A sectional view and a perspective view showing a preferred embodiment variant of a gear pump used in the device of the invention;

[0031] - Figure 4 is an axial cross-sectional view of a device according to a second embodiment of the present invention;

[0032] - Figure 5 yes Figure 4 A perspective view of a partial cross section of the device in FIG.

[0033] - Figures 6a to 6c An example of a coextrusion apparatus of the present invention is shown.

[0034] In different figures, identical or similar elements are provided with the same reference signs, so that their description is not systematically repeated. DETAILED DESCRIPTION

[0035] Figure 1 and Figure 2 A coextrusion device 1 according to a first embodiment of the invention is shown. The cross-section is in a plane parallel to the plane of symmetry of the extrusion head 2. The device comprises two extruders 10 and 20 each outputting into a duct 11 and 21 of the extrusion head 2, respectively.

[0036] The extruder 10 comprises an extrusion screw 12 or Archimedean screw and a barrel 14 for holding the screw, and a gear motor 15 for driving the screw 12 in rotation about its longitudinal axis 13. The barrel 14 has a supply inlet 16 for supplying an elastomeric compound and an outlet 17 leading to the conduit 11. The extruder 20 comprises an extrusion screw 22 or Archimedean screw and a barrel 24 for holding the screw, and a gear motor 25 for driving the screw 22 in rotation about its longitudinal axis 23. The barrel 24 has a supply inlet 26 for supplying an elastomeric compound and an outlet 27 leading to the conduit 21. The longitudinal axes 13 and 23 converge toward the extrusion head 2 and are symmetrical relative to the axis of symmetry of the extrusion head 2.

[0037] Rubber or elastomer should be understood to mean preferably any type of diene or non-diene elastomer, such as thermoplastic elastomers or mixtures of elastomers: natural rubber and synthetic rubber; reinforcing fillers: carbon black and silica; plasticizers: oils, resins and other chemical elements, such as sulfur. The extrusion device of the invention seeks to produce coextruded shaped elements made of different compounds. By way of example, such different elastomeric compounds are elastomeric compounds or rubber compounds used to form a tread component, such as: a first material made of 100% natural rubber is used to form an elastomeric compound or rubber compound of the base layer, and then a second material made of 100% synthetic rubber forms the tread. A third or even a fourth material may be added to form the sidewalls, this other material being made of a natural rubber / synthetic rubber compound containing from 20% to 80% of natural rubber.

[0038] According to the invention, each extruder 10, 20 is fed by a gear pump 30 and 40, respectively. The gear pump 30 comprises a supply inlet 37 for supplying a first elastomeric compound and a delivery outlet 38, the supply inlet 37 being connected in a sealed manner to the supply inlet 16 of the extruder 10. The gear pump 40 comprises a supply inlet 47 for supplying a second elastomeric compound and a delivery outlet 48, the supply inlet 47 being connected in a sealed manner to the supply inlet 26 of the extruder 20.

[0039] exist Figure 1 and Figure 2 In the example shown, the pump 30 is fed with a strip 4 and the pump 40 is fed with a strip 5 of elastomeric compound, the strips 4 and 5 being at ambient temperature. In a variant not shown in the figures, the gear pumps 30, 40 are provided with drive pinions for driving the compound strips 4, 5 into the pumps, these drive pinions being placed in front of the inlet orifice 37, 47 of each pump in a manner known to those skilled in the art.

[0040] Each gear pump 30 and 40 comprises two cylindrical pinions 31, 32 and 41, 42 with axes 33, 34 and 43, 44, respectively, which are parallel to each other and to the longitudinal axes 13 and 23 of the extrusion screws 12 and 22, respectively. Pinion 31 is driven to rotate about its axis 33 by a gear motor 35, and pinion 32 is driven to rotate about its axis 34 by pinion 31. Similarly, pinion 41 is driven to rotate about its axis 43 by a gear motor 45, and pinion 42 is driven to rotate about its axis 44 by pinion 41. Pinions 31 and 32 are housed in a housing 36 of the pump. Pinions 41 and 42 are housed in a housing 46 of the pump.

[0041] In one embodiment variant of the invention, the pinions 31, 32 and 41, 42 have straight teeth. In another embodiment variant, as in Figure 3b As can be seen more clearly in FIG. 1 , all pinions 31 , 32 and 41 , 42 are of the herringbone type.

[0042] Reference Figure 3a and Figure 3b The operation of the gear pump 30 of the present invention is explained. The elastomeric compound enters the pump 30 through the inlet opening 37 having a funnel-shaped cross section in the direction of arrow I so that the teeth of the pinion 31 can be properly filled with the compound. The compound is transmitted by the teeth of the pinion 31 to the compression area, in which the teeth of the pinion 31 mesh with the teeth of the pinion 32. Under the effect of the pressure exerted by the teeth of the gears, the compressed compound is sent into the chamber 39 and leaves the pump in the direction indicated by the arrow II.

[0043] exist Figure 3a In a variant of the embodiment of the present invention, the pump is mounted on the barrel 14 of the extruder 10 by means of a flange 70 so that the delivery outlet 38 of the pump 30 corresponds to the supply inlet 16 of the extruder 10 .

[0044] In another variation ( Figure 1 and Figure 2 ), the screws 12, 22 of the extruders 10, 20 pass through the housings 36, 46 of the gear pumps 30, 40, and the upstream ends of the barrels 14, 24 are fastened to the sides of the same housings.

[0045] In an advantageous embodiment, if Figure 3b As shown, it is preferred to provide the pump 30 with pinions 31 and 32 of the herringbone type. The orientation of the herringbone pattern is such that it directs the flow of the elastomeric material to the center 31 ′, 32 ′ of each pinion 31, 32, so that the pressure on the edges of the pinions can be reduced. This makes it possible to ensure a sealing structure at the lateral bearings of the pump body to support the pinion shaft with a simple seal, thereby ensuring a simple and inexpensive mechanical structure of the gear pump. In this variant, the gear pump 40 has a pinion of the herringbone type and a structure similar to that of the pump 30.

[0046] In operation, the continuous supply of the gear pumps 30, 40 makes it possible to fill the teeth of the drive pinion and provide a constant and measurable material flow rate at the outlet. The speed of rotation of the screw 12, 22 of each extruder 10, 20 is controlled synchronously with the speed of rotation of the gears of the dedicated pump and depends on the rheological properties of the compound it conveys. In this way, positive displacement extrusion is obtained at the outlet of each extruder, the flow rate of the material is constant, and the material has been more or less sheared between the feed inlet 16, 26 and the outlet 17, 27 of each extruder 10, 20. The extrudate reaching the outlet of each extruder is fed under pressure into the ducts 11, 12 of the die without mixing, so as to obtain in this way a coextruded shaped element.

[0047] The elastomer compound passing through the extruder 10 is different from the elastomer compound in the extruder 20 (different is understood to mean that it has different physical and chemical properties). When the screws 12 and 22 are set to rotate, the two compounds are brought together through the ducts 11 and 21 towards the outlet die 3 of the extrusion head 2, which means that they are combined in the original state under the pressure and temperature of the two compounds, without contact with the outside world and before molding. This makes it possible to obtain a good integrity of the coextruded product at the interface between the compounds, as well as a constant geometry of the components forming the coextruded molded product.

[0048] Figure 4 and Figure 5 A coextrusion device 1 according to a second embodiment of the invention is shown. The cross-section is in a plane parallel to the plane of symmetry of the extrusion head 2 . Figure 4 and Figure 5 The device 1 in the embodiment comprises a first extruder 10 and a second extruder 20, which are respectively fed by gear pumps 30 and 40, and the structure and operation of the gear pumps 30 and 40 are similar to the gear pumps described above. According to this embodiment, each gear pump 30, 40 is fed by a feed extruder 50 and 60, respectively.

[0049] The feed extruder 50 comprises an extrusion screw 52 or Archimedean screw and a barrel 54 for holding the screw, and a gear motor 55 for driving the screw 52 in rotation about its longitudinal axis 53. The barrel 54 has a feed inlet 56 for feeding the elastomeric compound in the form of a strip 4 and an outlet 57 leading to the inlet orifice 37 of the gear pump 30 in a sealed manner.

[0050] The feed extruder 60 comprises an extrusion screw 62 or Archimedean screw and a barrel 64 for holding the screw, and a gear motor 65 for driving the screw 62 in rotation about its longitudinal axis 63. The barrel 64 has a feed inlet 66 for feeding the elastomeric compound in the form of a strip 5 and an outlet 67 leading in a sealed manner to the inlet orifice 47 of the gear pump 40.

[0051] In an advantageous embodiment, the longitudinal axis 53 is parallel to the axes 33, 34 of the pinions 31, 32, and the longitudinal axis 53 is parallel to the axes 43, 44 of the pinions 41, 42, to achieve an optimal volume of the device 1. In another embodiment, the feed extruders 50, 60 are arranged tangentially to the inlet of the gear pump (their axes 53, 63 are perpendicular or inclined relative to the axes of the pinions of the gear pumps 30, 40).

[0052] According to this embodiment, each pump 30, 40 receives a supply of an elastomeric compound that has been processed, fluidized and set to a temperature. In this way, the gear pumps 30, 40 are supplied with more fluid compound, so that the load on the bearings and the wear of the gear teeth can be limited, and the service life of the pump is increased. In addition, the supply of the fluidized compound requires less torque, so the power set in the gear pump is less, and therefore, a more compact structure and lower cost can be achieved. In this case, the structure of the extruders 10 and 20 can be simplified, and the screw thereof is mainly used to constantly convey the elastomeric compound to the extrusion head 2, and the flow rate of the elastomeric compound is appropriately metered by the pump.

[0053] Figures 6a to 6c An example of a coextrusion apparatus according to the present invention is shown, which uses a plurality of extruders output in an extrusion head to extrude a coextruded composite product.

[0054] Figure 6a The device 1a in Figure 1 shows an arrangement of several extruders all arranged in the plane of symmetry of the extrusion head 2. As mentioned above, each extruder 10, 20, m, n is a positive displacement extruder fed with the compound by a dedicated gear pump.

[0055] Figure 6b The device 1b in Figure 1 shows an arrangement of several extruders arranged on both sides of the plane of symmetry of the extrusion head 2. As mentioned above, each extruder 10, 20, m, n is a positive displacement extruder fed with the compound by a dedicated gear pump.

[0056] Figure 6c The device 1c in Figure 1 shows an arrangement of multiple extruders arranged side by side on both sides of the symmetry plane of the extrusion head 2. As mentioned above, each extruder 10, 20, m, n is a positive displacement extruder fed with compound by a dedicated gear pump.

[0057] In another variant, not shown in the figures, at least two additional extruders 10′, 20′ are arranged, the longitudinal axes 13′, 23′ of the two additional extruders 10′, 20′ being arranged in a single plane intersecting the plane of symmetry of the extrusion head 2. The two extruders 10′, 20′ are arranged to output into a flow duct lying in the plane defined by the axes 13′, 23′ in order to obtain an optimal volume of the extruders. Figure 6b The variant shown can also be used with Figure 6a and Figure 6c The arrangement shown is combined with application.

[0058] In a variant, at least two of the extruders 10, 20, m, n output the same elastomeric compound (having the same composition).

[0059] The device comprises a control unit capable of regulating the rotational speed of the screws 12 , 22 of the extruders 10 , 20 and of the drive pinions 31 , 41 of the gear pumps 30 , 40 , in particular depending on the dimensions of the coextruded profiled elements and the rheological properties of the conveyed material.

[0060] The control unit drives the speed of the gear motors 15, 25, 35, 45 according to the required size of the coextruded molding element or according to the operating conditions (speed change, stop-start conditions). The rotation speed of the drive pinions 31, 41 of the pumps 30, 40 is proportional to the change in flow rate. This allows the control unit to adjust the flow rate of each extruder 10, 20 according to the size of the coextruded product, and also to keep it constant during operation.

[0061] In a variant, an optical sensor located at the outlet of the extrusion head 2 is used to pre-establish and measure the dimensions of the coextruded shaped element, in particular its width and thickness. The sensor is linked to a control unit, which checks the dimensions of the coextruded shaped element and its conformity with the preset dimensions. In a variant, a weight sensor measures the weight of the coextruded shaped element and is linked to a control unit, which thus allows an even finer adjustment of the tolerances of the coextruded product.

[0062] In another variant, the control unit is also connected to a drawing device which draws off the strip of coextruded profiled elements in order to adjust its speed.

[0063] Other variants and embodiments of the invention can be envisaged without departing from the scope of its claims.

[0064] Therefore, in a more economical variant, a single gear motor assembly is used to simultaneously drive the screw and the shaft of the pinion of the gear pump located upstream thereof. In a more economical variant, a single gear motor drives the screw feeding the extruder, the pinion of the gear pump and the extrusion screw of the extruder that transfers the compound into the extrusion head.

[0065] In another variation, pumps 30 and 40 have different structures from each other, or have the same structure but with different sizes of their respective components (eg, the diameter of the pinion gear is different in one pump than in the other).

Claims

1. A coextrusion device for producing coextruded elements for tires, the coextruded elements for tires being made of rubber compounds of different compositions, the coextrusion device comprising at least one first extruder (10) having a screw (12) with a longitudinal axis (13) and at least one second extruder (20) having a screw (22) with a longitudinal axis (23), wherein the outlets (17, 27) of at least the first extruder (10) and the second extruder (20) converge towards a common extrusion head (2), the extrusion head (2) being connected to each of the first extruder (10) and the second extruder (20) by suitable conduits (11, 21), characterised in that Each of the first extruder (10) and the second extruder (20) is fed by a respective gear pump (30, 40), the respective gear pump (30, 40) being located upstream of the respective first extruder and the second extruder, the feed inlet (16, 26) of each of the first extruder (10) and the second extruder (20) being connected to a delivery orifice (38, 48) of one of the gear pumps (30, 40), so that the gear pump (30, 40) determines the flow rate of the rubber compound conveyed through the respective extruder (10, 20) through the screw (12, 22) of the respective extruder (10, 20) towards the extrusion head (2), Such that positive displacement extrusion of the rubber compound under consideration is obtained at the outlet (17, 27) of each of the first extruder (10) and the second extruder (20), the respective flow rate of the rubber compound being metered by means of a gear pump (30, 40) connected to the extruder (10, 20) under consideration.

2. The coextrusion device for producing coextruded elements for tires according to claim 1, characterized in that The longitudinal axes (13, 23) of the first extruder (10) and the second extruder (20) form an acute angle with each other.

3. Coextrusion device for producing coextruded profiled elements for tires according to any one of the preceding claims, characterized in that The gear pump (30; 40) comprises two pinions (31, 32; 41, 42) whose rotation axes (33, 34; 43, 44) are parallel to the longitudinal axes (13; 23) of the first extruder (10) and the second extruder (20) it supplies.

4. The coextrusion device for producing coextruded elements for tires according to claim 3, characterized in that The pinions (31, 32; 41, 42) are herringbone type pinions.

5. The coextrusion device for producing coextruded molding elements for tires according to claim 1, characterized in that The gear pump (30, 40) has a body (36, 46) provided with an inlet opening (37, 47) for the elastomeric compound and with a delivery opening (38, 48) for the compound.

6. A coextrusion device for producing coextruded elements for tires according to claim 5, characterized in that The inlet opening (37, 47) of the gear pump (30, 40) is fed with a strip (4, 5) of elastomeric compound.

7. The coextrusion device for producing coextruded profiled elements for tires according to claim 5, characterized in that The inlet port (37, 47) of the gear pump is directly connected to the outlet port (57, 67) of the feed extruder (50, 60) for feeding the elastomeric compound.

8. The coextrusion device for producing coextruded molding elements for tires according to claim 1, characterized in that The device has a control unit which synchronizes the rotation speed of the screw (12, 22) with the rotation speed of the gear of the gear pump (30, 40).

9. The coextrusion device for producing a coextruded profiled element for a tire according to claim 1, characterized in that The delivery orifice (38, 48) of each gear pump (30, 40) is connected in a sealing manner to the supply inlet (16, 26) of the corresponding extruder (10, 20).

10. A coextrusion method for producing coextruded elements for tires, said coextruded elements for tires being made of rubber compounds of different compositions, said coextrusion method comprising at least one first extruder (10) having a screw (12) with a longitudinal axis (13) and at least one second extruder (20) having a screw (22) with a longitudinal axis (23), wherein the outlets (17, 27) of at least the first extruder (10) and the second extruder (20) which are different converge towards a common extrusion head (2), said extrusion head (2) being connected to each of the first extruder (10) and the second extruder (20) by suitable conduits (11, 21), characterised in that Each of the first extruder (10) and the second extruder (20) is fed with an elastomeric compound from a respective gear pump (30, 40) located upstream of the respective first extruder and the second extruder such that positive displacement extrusion is obtained at the outlet (17, 27) of each of the first extruder and the second extruder, wherein the flow rate of the rubber compound conveyed by the respective extruder (10, 20) through the screw (12, 22) towards the extrusion head (2) is determined by the respective gear pump (30, 40).

11. A coextrusion method for producing a coextruded profiled element for a tire according to claim 10, characterised in that The rotation speed of the screw (12, 22) is synchronized with the rotation speed of the pinion of the gear pump (30, 40).

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