COEXTRUSION PLANT AND METHOD FOR PRODUCEING A RUNNING SURFACE WITH REINFORCEMENT INSERTS EMBEDDED DEEP IN THE RUNNING SURFACE PROFILE BLOCKS

Description

[0001] The present invention relates to the general field of coextrusion installations for producing profiles, in particular profiles based on elastomeric mixtures, which may, for example, be intended for the manufacture of pneumatic tires, and in particular be intended to form the tread of such tires.

[0002] In order for pneumatic tires to meet the required requirements in terms of road holding and low rolling resistance, it is known to produce treads which combine several functional elements, namely first of all a radially internal sub-layer which is made from a first elastomeric mixture and which is intended to come to bear on the crown reinforcement of the tire, a radially external layer which is formed by a second elastomeric mixture distinct from the first and which is intended to form the tread blocks of the tread, which will come into contact with the road when the tire is in service on a vehicle, and finally circumferential reinforcements, generally of triangular section, which are formed from an elastomeric mixture having a more rigid behavior than the second mixture constituting the tread blocks,so that said circumferential reinforcements can laterally support the tread blocks against drift deformations, that is to say against lateral shear deformations in a plane containing the central axis of rotation of the tire.,

[0003] To produce such profiles, the applicant has developed suitable coextrusion tools, as described in particular in applications WO-2019 / 002782, WO 2017 / 146734 A1 or WO-2019 / 081362, in which a channel of triangular section is provided which makes it possible to form the circumferential reinforcement in one piece with the underlayer and to delay the joining of the second elastomeric mixture forming the sculpture blocks with said reinforcement, so as not to destabilize or deform said reinforcement during extrusion.In the first of these applications, namely WO-2019 / 002782, the tooling makes it possible to form an underlayer which extends continuously over a significant width of the profile, in order to be common to several neighboring sculpture blocks, while in the second application WO-2019 / 081362, the underlayer is interrupted in width at each sculpture block, by means of scrapers which reserve free spaces in said underlayer, in order to form several portions of distinct underlayers, before the mixture constituting the sculpture blocks is introduced into said free spaces, and finally comes to bear against the reinforcements which form the limits of the portions of underlayer laterally bordering each sculpture block concerned.

[0004] However, it is now desired to produce even more complex treads, such as those illustrated in international application WO-2018 / 002487 filed by the applicant, in which, on the one hand, the circumferential reinforcement must be able to be produced in a third elastomeric mixture which is distinct both from the first elastomeric mixture constituting the underlayer and from the second elastomeric mixture constituting the tread blocks, and in which, on the other hand, the shapes, the implantation positions and the respective dimensions of the reinforcements, the underlayer and the tread blocks must be able to be decided very freely, both in the lateral direction corresponding to the width of the profile and in the vertical direction corresponding to the thickness of the profile.

[0005] The objects assigned to the invention therefore aim to remedy the aforementioned drawbacks and to propose a new coextrusion installation which, while exhibiting good reliability and relative simplicity of operation, makes it possible to produce such a profile of increased complexity.

[0006] The objects assigned to the invention are achieved by means of a coextrusion installation intended to generate a profile by jointly extruding a plurality of elastomeric mixtures in a common flow direction which corresponds to the longitudinal direction of said profile, said installation comprising an extrusion head bringing said elastomeric mixtures, as well as a receiving surface, such as a roller, which is placed opposite the extrusion head in order to define an air gap used to shape the section of the profile, in thickness in a direction called the "vertical direction" which is perpendicular to the longitudinal direction and to the receiving surface, and in width in a direction called the "lateral direction" which is perpendicular to the longitudinal direction and to the vertical direction, said installation being characterized in that the extrusion head comprises, from upstream to downstream in the flow direction: firstly a first head portion which is provided with one or more first intake channels opening into the air gap in order to bring into contact with the receiving surface a first elastomeric mixture intended to form a sub-layer of the profile, said first head portion also comprising at least one pre-scraper which projects vertically into the air gap while being delimited, in the lateral direction, by a first lateral face and a second lateral face, and, in the vertical direction, by a lower face which faces the receiving surface while being placed at a first predetermined, non-zero distance from said receiving surface, called "pre-scraping thickness", so that said pre-scraper can reserve, within the flow of the first elastomeric mixture,a trench called a "burial trench" which is bordered on the one hand laterally by a first lateral sub-flow of said first elastomeric mixture and by a second lateral sub-flow of said first elastomeric mixture, first and second lateral sub-flows which flow on either side of the pre-scraper, respectively along the first lateral face and along the second lateral face of said pre-scraper, and on the other hand vertically by a bottom sub-flow which flows between the receiving surface and the lower face of the pre-scraper, in the pre-scraping thickness, to form a residual layer of first elastomeric mixture, then a second head portion which is provided with one or more second inlet channels which open into the air gap to bring a second elastomeric mixture intended to cover the sub-layer of first elastomeric mixture coming from the first head portion,said second head portion comprising at least one scraper which extends in the longitudinal extension of the pre-scraper, and which projects vertically into the air gap so as to have a first lateral face, a second lateral face, as well as a lower face which faces the receiving surface, at a second vertical distance from said receiving surface called "scraping thickness" which is strictly less than the pre-scraping thickness, so that on the one hand said scraper can laterally preserve the burial trench by causing the flow of second elastomeric mixture to form a first lateral sub-flow of second elastomeric mixture and a second lateral sub-flow of second elastomeric mixture,which flow respectively along the first lateral face and along the second lateral face of said scraper and which come in excess of the thickness respectively of the first and second sub-flows of first elastomeric mixture which come from the first head portion, while on the other hand said scraper makes it possible to dig the burial trench vertically by reducing, in accordance with the scraping thickness, the thickness of the residual layer of first elastomeric mixture at the bottom of said burial trench, then a third head portion comprising at least one injector which projects into the air gap, in the longitudinal extension of the scraper, and which has an injection mouth intended to inject a third elastomeric mixture, distinct from the second elastomeric mixture, to form an insert in the burial trench, said third head portion further comprising,following the injector in the longitudinal direction, a cover wall which extends over a predetermined length called the “confluence length” along the longitudinal direction, from the injection mouth to the outlet of the air gap, so that the flow of the profile under said cover wall allows the first and second lateral sub-flows of second elastomeric mixture to close on the insert, thus filling the burial trench.

[0007] Advantageously, the extrusion head according to the invention therefore has a real burial device, which makes it possible to open a trench in the first elastomeric mixture constituting the underlayer, by means of the pre-scrapers, to preserve, thanks to the scrapers, this trench upon arrival of the second elastomeric mixture, which second elastomeric mixture is preferably intended to constitute tread sculpture blocks, then to deposit in said trench the third elastomeric mixture constituting the insert, here preferably intended to form a circumferential reinforcement, before finally allowing the second elastomeric mixture to fill said trench in order to coat the insert.

[0008] Such a burial device advantageously makes it possible to separate the management of the (at least) three different elastomeric mixtures which constitute the different functional members of the profile - here preferably: the underlayer, the sculpture blocks, and the circumferential reinforcements, which offers great freedom as to the choice of the respective compositions of said elastomeric mixtures, and as to the installation of the different corresponding functional members, both in the lateral direction and in the vertical direction.

[0009] Thus, in particular, the installation according to the invention makes it possible, in particular by means of an adapted configuration of the third head portion and of the injector, to bury the insert inside a block of the second elastomeric mixture both in the lateral direction, which makes it possible, for example, to position the insert substantially in the middle of said block of second elastomeric mixture, and in the vertical direction, which makes it possible, for example, for the second mixture to cover the insert, so that said insert is not exposed on the visible face of the profile.

[0010] Applied to the manufacture of a tire tread, the fact of thus burying the circumferential reinforcement insert in third elastomeric mixture within the tread block made of second elastomeric mixture, so that the radially outermost apex of the insert is radially set back from the radially outer visible face of the tread block, under a predetermined thickness of said second elastomeric mixture, advantageously makes it possible to dissociate the load-bearing function, which is ensured by the tread block which works in elastic radial compression in contact with the roadway, without the insert coming into contact with the roadway or therefore interfering with this load-bearing function, from the drift resistance function, which is ensured by the insert which limits the axial shear of said tread block.

[0011] In addition, the use of a pre-scraper followed by a scraper in a row allows the first elastomeric mixture constituting the undercoat to be gradually shaped, which promotes regular and long-lasting operation of the installation. Indeed, first of all, the presence of the pre-scraper in the first head portion makes it possible to limit the residual thickness of the first elastomeric mixture which will then have to be dug further, or even completely removed, by the scraper in the second head portion, which avoids clogging (or "stuffing") of the first elastomeric mixture at the scraper.Furthermore, the fact of nevertheless maintaining an air gap of non-zero thickness between the pre-scraper and the receiving surface, by maintaining a separation distance between the pre-scraper and the receiving surface, avoids creating, in the first portion of the head, an early contact and therefore an early friction between the extrusion head and the receiving surface, that is to say a contact which would occur upstream of the scraper, which therefore makes it possible, when said receiving surface is driven in displacement relative to the extrusion head in the longitudinal direction in order to accompany the movement of the profile, to limit the wear of the pre-scrapers and the receiving surface, the quantity of energy necessary for driving said receiving surface, as well as the risks of untimely blocking of said receiving surface.

[0012] Advantageously, within a tread for a pneumatic tire, minimizing the thickness of the sub-layer in the first elastomeric mixture, or even eliminating said sub-layer, at the locations provided for the circumferential reinforcement inserts in the third elastomeric mixture, makes it possible to place said reinforcement inserts directly in contact with the underlying reinforcement of the crown of the tire, and consequently to avoid phenomena of energy dissipation by hysteresis in said sub-layer, which contributes to limiting the heating of the tire and to reducing the rolling resistance of said tire, and consequently to reducing the fuel consumption of the vehicle.

[0013] Other objects, characteristics and advantages of the invention will appear in more detail on reading the description which follows, as well as with the aid of the appended drawings, provided for purely illustrative and non-limiting purposes, among which: Therefigure 1 illustrates, according to a cross-sectional view in right section, normal to the longitudinal direction of the profile, an example of a profile obtained by a coextrusion installation in accordance with the invention, said profile being intended to form a tread. The figure 2 illustrates, in a perspective view from above, a coextrusion installation for manufacturing the profile of the figure 1 . There figure 3 illustrates the extrusion head of the installation of the figure 2 according to a perspective view from below. The figure 4 illustrates, in a perspective back view, with material cut away, the detail of the extrusion head of the figure 3 . There figure 5 illustrates, in a detailed perspective view, a blade equipping the third portion of the extrusion head of the figures 2 à 4 and carrying a plurality of injectors each intended to generate a reinforcement insert. The figure 6 illustrates the extrusion head of the figures 2 à 5 according to a front view. The figure 7 illustrates the extrusion head of the figure 6 according to a side sectional view. The figure 8 illustrates, according to a schematic view developed in side section accompanied by schematic views in corresponding extended sections, the principle of burying the insert according to the invention, according to which a burial trench is created by pre-scraping then scraping the first elastomeric mixture, the third elastomeric mixture forming the insert is then injected into said burial trench, then finally said insert is covered by filling the burial trench with the second material constituting the sculpture block, so that the insert is integrated into said sculpture block which it supports. figure 9A illustrates, according to a section view normal to the longitudinal direction of flow, the admission, within the first portion of the extrusion head of the figures 6 et 7 , of the first elastomeric mixture intended to form the underlayer, and the distribution of said first elastomeric mixture between several pre-scrapers. The figure 9B illustrates, according to a section view normal to the longitudinal direction of flow, at the downstream limit of the first head portion, the distribution and conformation of the sub-layer such that said distribution and said conformation result from the action of said first head portion and its pre-scrapers. figure 9C illustrates, according to a section view normal to the longitudinal direction of flow, in the second head portion, the action of the scrapers which each define a burial trench and distribute the first mixture forming the sub-layer and the second mixture intended to form the sculpture blocks in lateral sub-flows which laterally border the burial trench considered. figure 9D illustrates, according to a view in section normal to the longitudinal direction of flow, the injectors of the third head portion which are located in the continuity of the scrapers and which introduce into each burial trench concerned the third elastomeric mixture intended to form the inserts, and which shape said third elastomeric mixture according to the desired section for the insert, here a triangular section. figure 9E illustrates, according to a sectional view normal to the longitudinal direction of flow, in a part of the third head portion which is located downstream of the injectors, the reconstitution of a layer of second elastomeric mixture between the top of each insert concerned and the cover wall which overhangs said insert, said layer of second elastomeric mixture resulting from the confluence of the first and second lateral flows of second elastomeric mixture which meet at the trailing edge of each injector concerned and merge with each other above the insert. figure 10 illustrates, in a partial view, the section of a profile variant according to the invention including a wear indicator which has, relative to the receiving surface, an intermediate height between the upper height of the sculpture block and the lower height of the reinforcement insert.

[0014] The present invention relates to a coextrusion installation 1.

[0015] Said installation 1 is intended to generate a profile 2 by jointly extruding a plurality of elastomeric mixtures M1, M2, M3 in a common flow direction which corresponds to the longitudinal direction X of said profile 2.

[0016] For this purpose, said installation 1 comprises an extrusion head 4, which brings said elastomeric mixtures M1, M2, M3, as well as a receiving surface 5, such as a roller 6, which is placed opposite the extrusion head 4 in order to define an air gap 3 used to shape the section of the profile 2, in thickness H2 in a direction called the “vertical direction” Z which is perpendicular to the longitudinal direction X and to the receiving surface 5, and in width W2 in a direction called the “lateral direction” Y which is perpendicular to the longitudinal direction X and to the vertical direction Z.

[0017] An example of a section of such a profile 2 intended to form a tread for a wheel tire, for example for a pneumatic tire, or even for a non-pneumatic tire within which the tread is supported by a mechanical element of the solid hub or spoke network type, is illustrated in the figure 1 .

[0018] The receiving surface 5 is advantageously mounted to move relative to the extrusion head 4, so as to be able to be driven in movement in the longitudinal direction X, and thus accompany the longitudinal progression of the profile 2, or even pull the profile 2, as said profile 2 is generated by coextrusion.

[0019] In this respect, according to a possible implementation variant, the receiving surface 5 could be formed by a conveyor belt driven in translation in the longitudinal direction X relative to the extrusion head 4. According to this variant, the receiving surface 5 could form a flat surface.

[0020] Alternatively, according to another more preferred variant of implementation, the receiving surface 5 will be formed by a roller 6, and more particularly by the radially external surface of revolution of said roller 6, said roller 6 being driven in rotation relative to the extrusion head 4, around the central axis Y6 of said roller which is parallel to the lateral direction Y, and therefore perpendicular to the longitudinal direction X, as illustrated in the figure 2 . Said roller 6 will preferably form a straight cylinder, with a circular base.

[0021] For convenience of description, with reference to such a roller 6, and / or with reference to the arrangement of the finished bandage within which the profile 2 forming a tread is integrated, the longitudinal direction X can be likened to the “circumferential” direction, the lateral direction Y to the “axial” direction, and the vertical direction Z to the “radial” direction.

[0022] Whatever the shape of the receiving surface 5, the extrusion head 4 will preferably have a substantially conjugate shape, so as to cover the receiving surface 5 over a common overlapping zone defining the air gap 3. Thus, in particular, when the extrusion head 4 cooperates with a roller 6, said extrusion head 4 will generally have a conjugate cylindrical shape, in an arc of a circle, preferably centered on the central axis Y6 of the roller 6.

[0023] The profile 2 is advantageously generated continuously in the direction of its length, in the longitudinal direction X.

[0024] The concepts of "upstream" and "downstream" will be understood here in consideration of the overall direction of flow of profile 2, which progresses from upstream to downstream in the longitudinal direction X.

[0025] According to the invention, the extrusion head 4 comprises a first head portion 10 which is provided with one or more first intake channels 11 opening into the air gap 3 in order to bring into contact with the receiving surface 5 a first elastomeric mixture M1 intended to form a sub-layer 12 of the profile 2.

[0026] In the case where the profile 2 is intended to form a wheel tread, said underlayer 12 is intended to come to bear on and around the crown reinforcement of the tire into which said tread will be integrated.

[0027] Preferably, the underlayer 12 extends, in the lateral direction Y, over a cumulative width which represents more than 80% of the width W2 of the profile 2, preferably more than 90% of the width W2 of the profile 2. Within the profile 2 leaving the installation 1, said underlayer 12 may extend continuously over said cumulative width, or, in a preferred variant, be interrupted punctually at the locations receiving inserts 33, as will be explained below.

[0028] Preferably, the first elastomeric mixture M1 is a mixture based on unvulcanized rubber.

[0029] The first head portion 10 also comprises, as is clearly visible in the figures 3 , 4 , 6 , 8 And 9A, at least one pre-scraper 13 which projects vertically into the air gap 3 while being delimited, in the lateral direction Y, by a first lateral face 13L and a second lateral face 13R, and, in the vertical direction Z, by a lower face 13B which faces the receiving surface 5 while being placed at a first predetermined, non-zero distance H13 from said receiving surface 5, called “pre-scraping thickness” H13, so that said pre-scraper 13 can reserve, within the flow of the first elastomeric mixture M1, a trench 14 called “burial trench” 14.

[0030] As seen on the figures 8 And 9A, said burial trench 14 is bordered on the one hand laterally by a first lateral sub-flow F1_M1 of said first elastomeric mixture and by a second lateral sub-flow F2_M1 of said first elastomeric mixture, first and second lateral sub-flows which flow on either side of the pre-scraper 13, respectively the first sub-flow F1_M1 along the first lateral face 13L and the second sub-flow F2_M1 along the second lateral face 13R of said pre-scraper 13, and on the other hand vertically by a bottom sub-flow F3_M1 which flows between the receiving surface 5 and the lower face 13B of the pre-scraper 13, in the pre-scraping thickness H13, to form a residual layer 15 of first elastomeric mixture M1.

[0031] Thus, the pre-scraper 13 acts as a separator which splits the flow of first elastomeric mixture M1 into several sub-flows F1_M1, F2_M1, F3_M1 which bypass said pre-scraper 13 while the latter occupies the volume of the desired burial trench 14.

[0032] As a guide, the pre-scraping distance H13 will be less than or equal to 0.8 mm, and for example between 0.6 mm and 2 mm.

[0033] Following the first head portion 10 in the flow direction, the extrusion head 4 comprises a second head portion 20 which is provided with one or more second inlet channels 21 which open into the air gap 3 to bring a second elastomeric mixture M2 intended, as can be seen in the figures 1 , 8 And 9C , to cover the sub-layer 12 with first elastomeric mixture M1 from the first head portion 10.

[0034] Preferably, the second elastomeric mixture M2 is a mixture based on unvulcanized rubber.

[0035] Within a profile 2 intended to form a tread, like that illustrated on the figure 1 , said second elastomeric mixture M2 will be intended to form sculpture blocks 22, which will come into contact with the roadway.

[0036] The second head portion 20 comprises at least one scraper 23 which extends in the longitudinal extension of the pre-scraper 13, and which projects vertically into the air gap 3 so as to have a first lateral face 23L, a second lateral face 23R, as well as a lower face 23B which faces the receiving surface 5, at a second vertical distance H23 from said receiving surface, called “scraping thickness” H23, scraping thickness H23 which is strictly less than the pre-scraping thickness H13. We therefore have: H23 < H13.

[0037] In this way, on the one hand, said scraper 23 can laterally preserve the burial trench 14 by causing the flow of second elastomeric mixture M2 to form a first lateral sub-flow of second elastomeric mixture F1_M2 and a second lateral sub-flow of second elastomeric mixture F2_M2, which flow respectively along the first lateral face 23L of the scraper 23 for the first sub-flow F1_M2 and along the second lateral face 23R of said scraper 23 for the second sub-flow F2_M2, and which come in excess of the first lateral sub-flow of first elastomeric mixture F1_M1 and the second lateral sub-flow of first elastomeric mixture F2_M1 which come from the first head portion 10, while on the other hand, said scraper 23 makes it possible to dig the trench vertically. burial 14 by reducing, in accordance with the scraping thickness H23,the thickness of the residual layer 15 of first elastomeric mixture M1 at the bottom of said burial trench 14.,

[0038] Thus, the scraper 23 makes it possible to keep the burial trench 14 which was previously initiated by the pre-scraper 13 open, by maintaining, throughout the second head portion 20 in the flow direction X, a lateral gap on the one hand between the first lateral sub-flow of first elastomeric mixture F1_M1 and the second lateral sub-flow of first elastomeric mixture F2_M1 initially separated by the pre-scraper 13, and on the other hand a similar lateral gap between the first lateral sub-flow of second elastomeric mixture F1_M2 and the second lateral sub-flow of first elastomeric mixture F2_M2 which, in the second head portion 20, are superimposed on the lateral sub-flows of first elastomeric mixture F1_M1, F2_M1 to form an overlayer covering at least in part the underlayer 12.

[0039] At the same time, the scraper 23 further digs the burial trench 14 deep.

[0040] In this respect, it will be noted that, preferably, the scraping distance H23 is chosen to be zero, so that, in the second head portion 20, the scraper 23, and more particularly the lower face 23B of said scraper 23, rubs against the receiving surface 5, so as to eliminate the residual layer of first elastomeric mixture M1 at the bottom of the burial trench 14.

[0041] Advantageously, the progressiveness of the scraping ensured successively by a pre-scraper 13 then by a scraper 23 allows a distribution and a gentle conformation of the sub-layer 12 of first elastomeric mixture M1, without excessive friction, which limits the energy consumption necessary for driving the receiving surface 5 and avoids any phenomenon of chattering or blocking of said receiving surface 5, and more particularly of the roller 6, and any phenomenon of jamming of the first elastomeric mixture M1 in the air gap 3, or any phenomenon of premature wear of the pre-scraper 13, of the scraper 23 or of the receiving surface 5.

[0042] The scraper 23 may preferably have a friction pad intended to come into sliding contact against the receiving surface 5, said friction pad being made of a material which has a low coefficient of friction with respect to the material constituting the receiving surface 5. For example, said friction pad may be made of a polymer of the PTFE (PolyTetraFluorEthylene), POM (PolyOxyMethylene) or PEEK (PolyEtherEtherKetone) type, or even of a copper-based metal alloy.

[0043] Following the second head portion 20 in the flow direction, the extrusion head 4 comprises a third head portion 30 comprising at least one injector 31 which projects into the air gap 3, in the longitudinal extension of the scraper 23, and which has an injection mouthpiece 32 intended to inject a third elastomeric mixture M3, distinct from the second elastomeric mixture M2, to form an insert 33 in the burial trench 14.

[0044] When the profile 2 is intended to form a tread, said insert 33 preferably constitutes a circumferential reinforcement, called a “corner”, which makes it possible to support the sculpture block 22 against lateral shear deformations, in order to improve the drift behavior of the bandage.

[0045] Preferably, the third elastomeric mixture M3 is a mixture based on unvulcanized rubber.

[0046] Advantageously, the injector 31 being in the continuity of the scraper 23, said injector 31 makes it possible to deposit the third elastomeric mixture M3 inside, and more particularly on the bottom, of the burial trench 14, the volume of which has been cleared and shaped successively by the pre-scraper 13 then by the scraper 23 which precede said injector 31.

[0047] In other words, the progressive digging and shaping of the burial trench 14 carried out by the pre-scraper 13 then the scraper 23 makes it possible to prepare in a precise, reproducible and clean manner the location intended for the installation of the insert 33.

[0048] Preferably, the injection mouth 32, and consequently the resulting section of the insert 33, has a triangular shape whose base 32B, 33B is oriented towards the receiving surface 5, and preferably rests on said receiving surface 5, and whose apex 32A, 33A is oriented towards the extrusion head 4.

[0049] Such a triangular section in fact provides particularly rigid and stable support for the insert 33, which prevents the said insert 33 from tilting in the lateral direction Y and which therefore allows the said insert 33 to firmly support the tread block 22 against the shear forces in lateral drift, while allowing the said insert 33 to withstand well, without undergoing excessive deformation, the compressive stresses exerted by the roadway, via the tread block 22, in the vertical direction Z.

[0050] It will also be noted that, when the scraper 23 rubs in contact with the receiving surface 5 and therefore locally interrupts the sub-layer 12 in the lateral direction Y, at the location of the burial trench 14, by eliminating the residual layer of first elastomeric mixture M1 at the bottom of the burial trench 14 as stated above, then this advantageously allows the injector 31 of the third head portion 30 to place the insert 33 in third elastomeric mixture M3 in contact with the receiving surface 5.

[0051] Such a preferred arrangement advantageously provides a good, stable and rigid base for the insert 33, which can thus, in particular, in the case where the profile 2 constitutes a tread, rest directly on the crown reinforcement of the bandage, underlying said tread.

[0052] It will be noted that if the scraper 23 does not rub against the receiving surface 5 and leaves a thin film of first elastomeric mixture M1 under the insert 33, this can allow the sub-layer 12 to preserve its continuity, and if necessary to preserve its continuity over the entire cumulative width that said sub-layer 12 occupies, in the lateral direction Y, within the profile. Conversely, if the scraper 23 rubs against the receiving surface 5, as is preferred to ensure better seating of the insert 33, then the sub-layer 12 will be interrupted locally, at the location of each insert 33 concerned. Preferably, the sub-layer 12 will then nevertheless extend continuously, in the lateral direction, outside of said locations where said sub-layer 12 is interrupted to accommodate an insert 33.

[0053] Furthermore, the third head portion 30 further comprises, following the injector 31 in the longitudinal direction X, a cover wall 34 which extends over a predetermined length L34 called the “confluence length” L34 along the longitudinal direction X, from the injection mouth 32 to the outlet of the air gap 3, so that the flow of the profile 2 under said cover wall 34 allows the first lateral sub-flow of second elastomeric mixture F1_M2 and the second lateral sub-flow of second elastomeric mixture F2_M2 to close on the insert 33, thus filling the burial trench 14.

[0054] Thus, because the burial trench 14 is filled in using the second elastomeric mixture M2, the insert 33 is perfectly integrated within the sculpture block 22 formed by said second elastomeric mixture M2, in a position which can be freely chosen, along the lateral direction Y, by determining the appropriate location of the injector 31 in said lateral direction Y.

[0055] For information purposes, the shortest distance which separates, in the lateral direction Y, the insert 33 integrated into a sculpture block 22 from the lateral edge 22L, 22R of said sculpture block 22 which is closest to said insert 33, may be between 3 mm and 12 mm, and / or equal to or greater than 20%, or even 30% of the overall width of said sculpture block 22.

[0056] Advantageously, the burial of the insert 33 substantially at mid-width of the tread block 22 allows the same insert 33 to laterally support said tread block 22 effectively in both directions, by limiting the shearing and tilting of the tread block 22 both to the left and to the right, which gives said tread block 22 better drift behavior. When the tread block 22 extends, in the lateral direction Y, from a first lateral edge 22L to a second lateral edge 22R, the base 33B of the insert 33 may thus preferably be located at a non-zero distance, and preferably substantially at the same non-zero distance, from each of said lateral edges 22L, 22R, as is notably visible on the figure 1 .

[0057] In absolute terms, the invention could be applied to the production of a profile 2 in which the top 33A of the insert 33 is flush with the upper surface 22U of the tread block 22 formed by the second elastomeric mixture M2. To this end, it would be sufficient to make the height of the cover wall 34, considered relative to the receiving surface 5 in the vertical direction Z, coincide with the top 32A of the injection mouth 32, and therefore with the top 33A of the insert 33, so that the first lateral sub-flow of second elastomeric mixture F1_M2 would come into contact with one of the side walls of the insert 33 while the second lateral sub-flow of second elastomeric mixture F2_M2 would come into contact with the opposite side wall of said insert 33, and that the top 33A of the insert would mark the boundary between the first lateral sub-flow of second elastomeric mixture F1_M2 and the second lateral sub-flow of second elastomeric mixture F2_M2.

[0058] However, in a particularly preferential manner, and as illustrated in the figures 1 , 5 , 7 , 8 , 9D et 9E , the injector 31 is arranged so as to position the point 32A of the injection mouth 32, called “top 32A of the injection mouth”, which is the furthest from the receiving surface 5, in the vertical direction Z, and which thus corresponds to the top 33A of the insert 33, at a non-zero vertical distance P31 from the cover wall 34, called “burial depth” P31, so that the first lateral flow of second elastomeric mixture F1_M2 and the second lateral flow of second elastomeric mixture F2_M2 can join and merge in the space which is vertically between the top of the insert 33A and the cover wall 34, in order to bury said insert 33 in the second elastomeric mixture M2, at said predetermined burial depth P31.

[0059] Thus, when filling the burial trench 14, a junction of the first and second lateral sub-flows of second elastomeric mixture F1_M2, F2_M2 will preferably be carried out with each other, over the top 33A of the insert, so that this confluence of the first and second lateral sub-flows of second elastomeric mixture F1_M2, F2_M2 will have the effect not only of placing the second elastomeric mixture M2 in joint with the side walls of the insert 33 but also and above all, more generally, of covering the insert 33 under a layer of second elastomeric mixture M2 whose thickness, non-zero, corresponds to the burial depth P31.

[0060] According to such an arrangement, the distance which vertically separates the top 33A of the insert from the receiving surface 5 is therefore strictly less, here by a value equal to the burial depth P31, than the distance, corresponding here to the overall thickness H2 of the profile 2, which vertically separates the upper face 22U of the sculpture block 22 from said receiving surface 5 directly above said top 33A of the insert.

[0061] Advantageously, by burying the insert 33 vertically set back from the visible, radially external upper face 22U of the tread block 22, at a predetermined non-zero burying depth P31 which in practice separates the top 33A of the insert from the roadway, the insert 33 is prevented from coming directly into contact with the roadway and thus interfering with the function assigned to the tread block 22.

[0062] Advantageously, the burial depth P31, and therefore the vertical positioning of the insert 33 within the sculpture block 22, can be freely chosen by adapting the dimensions of the injector 31, and more generally by adapting the dimensions of the third head portion 30, so as to position the top 32A of the injection mouth 32 in vertical projection from the cover wall 34, by a value corresponding to the desired burial depth P31, so that the top 32A of the injection mouth 32 is at a distance from the receiving surface 5 which is less, in the vertical direction Z, than the distance which separates said receiving surface 5 from the cover wall 34.

[0063] As an indication, the burial depth P31 will preferably be between 3 mm and 8 mm, more preferably between 5 mm and 7 mm.

[0064] For information purposes, and in particular when the profile 2 is intended to form a tread for a tire intended for a passenger vehicle whose dimensions correspond to rims of 15 inches to 20 inches, the thickness H2 of said profile will preferably be between 6 mm and 12 mm.

[0065] Similarly, the width W2 of profile 2 will preferably be between 150 mm and 350 mm.

[0066] Preferably, the height H33 of the top of the insert 33A relative to the receiving surface 5 represents between 30% and 60%, or even between 40% and 50%, of the height of the upper face 22U of the corresponding sculpture block 22, and more generally of the overall thickness H2 of the profile 2.

[0067] Preferably, the injection mouth 32 is located on the downstream face of the injector 31, that is to say on the trailing edge of said injector 31, which marks the point of confluence from which the lateral sub-flows of second elastomeric mixture F1_M2, F2_M2 and the flow of third elastomeric mixture M3 forming the insert 33 join.

[0068] Preferably, the base 32B of the injection mouth 32 is located slightly set back from the receiving surface 5 in the vertical direction Z, for example at a distance of between 0.5 mm and 0.8 mm from said receiving surface 5, in order to prevent the injector 31 from rubbing against the receiving surface 5. The base 32B of the injection mouth 32 will then preferably be completely open, so that the third elastomeric mixture M3 which emerges therefrom can come to rest directly against the bottom of the burial trench 14, and more particularly directly in contact with the receiving surface 5.

[0069] With regard to the cover wall 34, and more particularly the confluence length L34 that said cover wall defines, in the longitudinal direction X, between the injection mouth 32 and the outlet of the air gap 3 where the extrusion head 4, and more precisely where the cover wall 34, ends or at least moves away sufficiently from the receiving surface 5 to release the profile 2 and release the compressive stress that said cover wall 34 exerted on said profile in the vertical direction Z, the inventors have found that it is appropriate for said confluence length L34 to be on the one hand sufficiently long so that the first and second lateral sub-flows of second elastomeric mixture F1_M2, F2_M2 operate a satisfactory junction with the insert 33, and more particularly, when said lateral sub-flows of second elastomeric mixture come into contact with each other above insert 33,so that said lateral sub-flows of second elastomeric mixture F1_M2, F2_M2 adhere perfectly to each other without leaving any zone of fragility or even crack (crack) at the level of their joint plane, directly above the top 33A of the insert, and on the other hand sufficiently short nevertheless to prevent the second elastomeric mixture M2, and more particularly the layer of second elastomeric mixture M2 which is reconstituted above the insert 33, from causing vertical settling, and therefore undesirable deformation, of said insert 33, in particular excessively marked crushing of the tip of the top 33A of said insert 33.,

[0070] Therefore, preferably, the confluence length L34 covered by the cover wall 34 is between 10 mm and 14 mm.

[0071] This range of values ​​is in particular applicable for a profile 2 whose overall thickness H2 is between 6 mm and 12 mm as indicated above, and whose height H33 of the top 33A of the insert 33, considered in relation to the receiving surface 5, is equal to or preferably strictly less than said thickness H2, for example less than or equal to 60%, or less than 50%, of the thickness H2. By way of example, the invention may in particular be applied to a profile whose thickness H2 is between 10 mm and 12 mm and whose insert(s) 33 will have a height H33 of between 5 mm and 7 mm.

[0072] The inventors have also found that it would appear that the greater the height H33 of the insert 33, and therefore the thinner the thickness of the layer of second elastomeric mixture M2 which covers the top of the insert 33A, i.e. the lower the burial depth P31 (although not zero), the more necessary it is to provide a high confluence length L34 (which, here, tends towards, or even equals, 14 mm), whereas when the height H33 of the insert 33 is lower, and therefore when the burial depth P31 is greater, it is possible to reduce the confluence length L34 (here to make it tend towards, or even equal, 10 mm).

[0073] Once the confluence length L34 has been traveled under the covering wall 34, the profile 2 leaves the air gap 3, and is thus released at ambient atmospheric pressure. The profile 2 can then cool and stabilize dimensionally on the continuation of the receiving surface 5, then on a conveyor (not shown), such as a roller or belt conveyor, which takes charge of said profile following the receiving surface 5.

[0074] It will also be noted that, for convenience of description and to avoid any confusion, reference is preferably made to a pre-scraper 13, a scraper 23, a burial trench 14, an injector 31 and a corresponding insert 33. This being so, of course, it will be possible to preferably provide, as illustrated in the various figures, several assemblies each associating in series a pre-scraper 13 and a scraper 23, said assemblies being distributed at a distance from each other over the width of the air gap 3 so as to dig as many burial trenches 14 distributed over the width W2 of the profile and which will make it possible to install as many inserts 33 by means of as many injectors 31 within a plurality of tread blocks 22. The characteristics of the different elements of the same nature will preferably be deduced identically from what has been described above.

[0075] For ease of construction, the extrusion head 4 will preferably have a modular structure, and will preferably comprise, for example: a first module 4_1 forming the first head portion 10, a second module 4_2 forming the second head portion 20, a first blade 41 called “transition blade” 41 which is interposed between the first module 4_1 and the second module 4_2 to ensure a transition between the first portion 10 and the second portion 20, and more particularly to ensure, before the flow of first elastomeric mixture M1 enters the second portion 20 of the extrusion head, a pre-conformation of the sub-layer 12 in first elastomeric mixture M1, a second blade 42, which forms the upstream part of the third portion 30 of the extrusion head 4, and which carries the injector(s) 31, as can be seen in the figures 5 And 9D, and a third blade 43, attached to the second blade 42, and which forms the downstream part of the third head portion 30 and comprises for this purpose the cover wall 34 which overhangs the insert 33, as can be seen in the figures 3 , 7 And 9E .

[0076] Said modules 4_1, 4_2 and blades 41, 42, 43 will be assembled and fixed to each other, preferably by screwing, and contiguously to each other in order to ensure the continuity of the extrusion head 4 in the longitudinal direction X.

[0077] It should be noted that, as is particularly visible on the figure 9B , the first blade 41 preferably comprises teeth 44 which form terminal longitudinal extensions of the pre-scrapers 13, and can therefore be functionally assimilated to said pre-scrapers 13, teeth 44 which make it possible on the one hand to force the bottom sub-flow F3_M1, which forms the residual sub-layer 15 constituting the bottom of the burial trench 14, to substantially retain the pre-scraping thickness value H13 which was given to it by the pre-scraper 13 which precedes the tooth 44 considered, and on the other hand to distribute and refine the first and second lateral sub-flows of first elastomeric mixture F1_M1, F2_M1 on each side of said burial trench 14 so as to define a sub-layer bottom 40 which is intended to receive the second elastomeric mixture M2 and thus to offer a fixing base to the sculpture blocks 22.

[0078] Preferably, in the first head portion 10, the width of the pre-scraper 13, considered in the lateral direction Y, increases in the upstream-downstream direction of the flow direction, as is clearly visible in the figure 3 .

[0079] Thus, the pre-scraper 13 generally forms a divergent bow with respect to the flow direction, which makes it possible to progressively distribute the first elastomeric mixture M1 into the first lateral sub-flow F1_M1 and the second lateral sub-flow F2_M1.

[0080] Advantageously, the free space which separates two neighboring pre-scrapers 13 in the lateral direction Y thus forms a funnel which causes the first elastomeric mixture M1 to converge towards the corresponding tooth 44 of the first blade 41, in order to promote a smooth conformation of the underlayer base 40 which will then be brought to support the sculpture blocks 22 in second elastomeric mixture M2.

[0081] Preferably, in the second head portion 20, the scraper 23 has a convergent portion 23C which connects to the injector 31 and the width of which, considered in the lateral direction Y, narrows in the upstream-downstream direction of the flow direction.

[0082] Thus, the section of the scraper 23, and therefore of the burial trench 14, gradually narrows to gradually approach a width equal to, or close to, the width of the base 33B of the insert 33. This allows in particular the first and second lateral sub-flows of second elastomer mixture F1_M2, F2_M2 to operate, in the third head portion 30, a smooth and laminar junction with the flow of third elastomer mixture M3 forming the insert 33, without said first and second lateral sub-flows F1_M2, F2_M2 having to operate a sudden lateral detachment which could disturb the good flow of the flows or disturb the conformation of the insert 33.

[0083] For information purposes, the maximum width of the scraper 23, and therefore of the burial trench 14, in the second head portion 20, at the upstream limit of the converging portion 23C of the scraper 23, may be chosen between two times and three times the width of the base 33B of the desired insert 33, for example equal to 2.6 times the width of the base 33B. Such proportions in fact make it possible to optimize the efficiency of the scraping.

[0084] Likewise, from the material point of view of the dimensioning of the tooling, the maximum width of the scraper 23 may be substantially between two times and three times the width of the base 32B of the injection mouthpiece 32.

[0085] Advantageously, the invention will make it possible to use a first, a second and a third elastomeric mixture M1, M2, M3 which will have different compositions from each other, and therefore distinct mechanical properties, even if, preferably, all these elastomeric mixtures M1, M2, M3 will be based on unvulcanized rubber.

[0086] More particularly, it will be possible to use a third elastomeric mixture M3, intended to form the reinforcement inserts 33, which intrinsically has a stiffness greater than that of the second elastomeric mixture M2 which is intended to form the sculpture blocks 22, which second elastomeric mixture M2 is therefore intentionally softer.

[0087] The parameter used to characterize and select the elastomeric mixtures M1, M2, M3 will preferably be the complex dynamic shear modulus, noted G*.

[0088] Thus, a third elastomeric material M3 will preferably be chosen, used for the inserts 33, whose complex dynamic shear modulus G*_M3 is strictly greater than that G*_M2 of the second elastomeric mixture M2, used here for the sculpture blocks 22. Similarly, the complex dynamic shear modulus G*_M3 of the third elastomeric mixture M3 constituting the inserts 33 will preferably be strictly greater than that G*_M1 of the first elastomeric mixture M1 used for the underlayer 12.

[0089] Said complex dynamic shear modulus G* is in fact representative of the rigidity of the elastomeric mixture considered, and characterizes the behavior of the elastomeric mixture considered when the latter is subjected to an alternating shear stress. Said complex dynamic shear modulus G* has, in representation in the complex plane, a real part, also called "elastic part" and noted G', which characterizes the elastic behavior of the mixture, and an imaginary part, also called "viscous part" and noted G'', which characterizes the dissipation of energy linked to the viscous behavior of the mixture.

[0090] The term "dynamic loss" or "viscoelastic loss", denoted Tgδ, refers to the ratio of the viscous part G" to the elastic part G', i.e. the tangent of the argument δ of said complex dynamic shear modulus G*: Tgδ = Tan(δ) = Tan(Arg(G*)) = G'' / G'.

[0091] The viscoelastic loss Tgδ and the complex dynamic shear modulus G* can be determined according to the ASTM D 5992-96 standard, by measuring the dynamic properties of the elastomeric mixture on a viscoanalyzer (here a Metravib VA4000 model). The measurement of the dynamic properties is carried out on a sample of vulcanized elastomeric mixture, here more particularly vulcanized under the curing conditions applicable to the bandage in the constitution of which the profile 2 enters, the sample having the shape of a cylindrical test piece having a thickness equal to 2 mm and a section equal to 78.5 mm 2< . The response of the sample of elastomeric mixture to a sinusoidal stress in alternating simple shear, having a peak-peak amplitude equal to 0.7 MPa and a frequency equal to 10 Hz, is recorded.

[0092] In addition, during this measurement campaign, a temperature scan is carried out at a constant temperature rise rate of +1.5°C / min. The glass transition temperature Tglass of the sample is in fact the temperature at which the dynamic loss Tgδ reaches a maximum during the temperature scan.

[0093] The value of G* measured at 23°C, or where appropriate at 60°C, is representative of the rigidity of the elastomeric mixture considered, i.e. its resistance to deformation, in particular its elastic deformation.

[0094] It will be noted that, beyond the parameters actually retained to measure the complex dynamic shear modulus G* of each elastomeric mixture, it is, with identical measurement parameters, the order of magnitude and the relative value of said modulus G* from one elastomeric mixture to another which are important for quantifying the stiffness of said elastomeric mixture compared to the other elastomeric mixtures, and consequently the behavior of said elastomeric mixture within the vulcanized bandage.

[0095] For information purposes, the elastomeric mixtures M1, M2, M3 may be chosen such that they have, in the vulcanized state, complex dynamic shear moduli respectively between 0.5 MPa and 5 MPa for the first elastomeric mixture M1, between 0.9 MPa and 5 MPa for the second elastomeric mixture M2, and between 40 MPa and 60 MPa for the third elastomeric mixture M3, said complex dynamic shear moduli G* being measured here at 60°C according to the standard mentioned above.

[0096] The invention of course relates as such to a method of manufacturing a profile 2, and more particularly a profile 2 intended to form a tire tread for a vehicle wheel.

[0097] Thus, the invention relates in particular to a method for manufacturing a profile 2 during which a burial trench 14 is opened, by means of a pre-scraper 13, in a first elastomeric mixture M1 constituting a sub-layer 12 of the profile 2, then a second elastomeric mixture M2 is brought in to cover said sub-layer 12 while preserving, by means of a scraper 23, the burial trench 14 within the first and second elastomeric mixtures M1, M2, then a third elastomeric mixture M3 constituting an insert 33 is deposited in said burial trench 14, then the second elastomeric mixture M2 is allowed to fill said burial trench 14 in order to coat the insert 33.

[0098] Preferably, as described above, the second elastomeric mixture M2 comes, during this method, to cover the burial trench 14 and the insert 33 so as to bury the top of said insert 33 to a non-zero burial depth P31, preferably between 3 mm and 8 mm.

[0099] Preferably, the method is implemented to manufacture a profile 2 intended to form a tire tread for a vehicle wheel, profile 2 within which the first elastomeric mixture M1 forms a sub-layer 12 intended to be fixed to a crown reinforcement of the tire, the second elastomeric mixture M2 is intended to form tread blocks 22 coming into contact with the road, and the insert in third elastomeric mixture M3 is intended to form a circumferential reinforcement within the tread.

[0100] Preferably, the complex dynamic shear modulus G*_M3 of the third elastomeric mixture M3 is strictly greater than the complex dynamic shear modulus G*_M2 of the second elastomeric mixture M2.

[0101] As indicated above, this will make it possible to confer greater rigidity to the reinforcement insert 33, and greater flexibility to the sculpture block 22.

[0102] Preferably, the elastomeric mixtures M1, M2, M3 may be chosen so that they have complex dynamic shear moduli in the ranges of values ​​indicated above.

[0103] Of course, the method for manufacturing profile 2 described above preferably uses an installation 1 as described above for manufacturing said profile 2.

[0104] According to a preferred application possibility, the invention relates to a method for manufacturing a tire for a vehicle wheel during which a profile 2 is manufactured according to the above profile manufacturing method, and said profile 2 is used to form the tread of said tire.

[0105] According to a preferred possibility of implementing said method for manufacturing a tire for a vehicle wheel, provision may be made to shape in at least one of the tread blocks 22 formed in the second elastomeric mixture M2 at least one wear indicator 50 making it possible to monitor the state of wear of the tire, and to ensure that the top 33A of the insert 33 formed from the third elastomeric mixture M3 has a height H33, relative to the receiving surface 5 and in the vertical direction Z, or, more particularly within the finished tire, a radial distance from the axis of said tire, which is strictly less than the height H50 (respectively strictly less than the radial distance from the axis) of said wear indicator 50 so that, when the tire is in service, the wear indicator 50 is reached before uncovering the top 33A of the insert buried in the at least one of the tread blocks 22.

[0106] Advantageously, this will allow the reinforcement insert 33 to fully fulfill, throughout the life of the bandage, its function of controlling drift, without being exposed on the visible face of the tread and therefore without interfering with the road.

[0107] The wear indicator 50 may preferably be obtained during the molding of the tire in a vulcanization press, at the junction between the visible lateral edge 22L of a sculpture block 22 and the bottom of the circumferential groove 51 bordered by said sculpture block 22, as can be seen in the figure. figure 10 , by shaping said side edge 22L in said vulcanization press.

[0108] Furthermore, it will be possible, after the coextrusion of the profile 2, to complete said profile by laterally attaching auxiliary reinforcements 52, for example of triangular section, to certain sculpture blocks 22, as indicated in dotted lines on the figure 1 .

[0109] Thus, preferably, during the tire manufacturing process according to the invention, the profile 2 may be produced in such a way that said profile 2 comprises at least one tread block 22 which is delimited in the lateral direction Y by at least one lateral edge 22L, 22R and which comprises an insert 33 buried in said tread block 22 at a distance from said at least one lateral edge 22L, 22R, and an auxiliary reinforcement 52, preferably of triangular section, will be added against said at least one lateral edge 22L, 22R of the tread block 22.

[0110] Preferably, the height of the top of the auxiliary reinforcement 52 will be strictly greater than the height H33 of the top of the buried insert 33, and more preferably, the top of the auxiliary reinforcement 52 will be flush with the upper face 22U of the sculpture block 22.

[0111] Preferably, the base of the auxiliary reinforcement 52 will rest directly on the sub-layer 12 made of the first elastomeric mixture M1. More preferably, the base of the auxiliary reinforcement 52 will preferably rest on a so-called “intermediate” portion of the sub-layer 12 made of the first elastomeric mixture M1, an intermediate portion of sub-layer which ensures, in the lateral direction Y, the continuity of the sub-layer 12 with the sub-layer bases 40 serving as bases for the tread blocks 22, and in particular the continuity of the sub-layer 12 under the grooves 51. It will also be noted that the thickness of the sub-layer 12 may be less, in the intermediate portion(s) located under the auxiliary reinforcement(s) 52 and / or at the bottom of the groove(s) 51, than the thickness that said sub-layer 12 has in the sub-layer bases 40 which carry the tread blocks 22.

[0112] Preferably, the auxiliary reinforcement 52 will be formed in an elastomeric mixture, preferably based on raw rubber, which has, once vulcanized, a complex dynamic shear modulus G* strictly greater than that G*_M2 of the second elastomeric mixture M2 constituting the sculpture block 22, in order to present greater stiffness, and thus to be able to contribute to supporting and stiffening the sculpture block 22 against lateral drift.

[0113] Likewise, preferably, the complex dynamic shear modulus G* of the auxiliary reinforcement 52 will be strictly greater than that G*_M1 of the first elastomeric mixture M1 constituting the sub-layer 12.

[0114] The auxiliary reinforcement 52 may be added to the raw profile 2, after said profile 2 has been produced by coextrusion, by integrating, for example by rolling, said auxiliary reinforcement 52 in the location reserved for this purpose in the profile 2, against the lateral edge 22L, 22R of the sculpture block 22 concerned. The assembly will then be vulcanized, during the curing of the bandage.

[0115] Advantageously, the combination of an insert 33 buried in the sculpture block 22 and a lateral auxiliary reinforcement 52 placed at the interface between said sculpture block 22 and the circumferential groove 51 makes it possible to optimize the drift behavior of the sculpture block 22 concerned.

[0116] Of course, the invention as such also relates to a profile 2 obtained as indicated above, and to a bandage, in particular a pneumatic bandage, provided with such a profile 2.

[0117] In particular, the invention may relate to a profile 2 comprising one or more inserts 33 each buried in a sculpture block 22, to a profile 2 called an “improved profile” combining one or more inserts 33 each buried in a sculpture block 22 with one or more auxiliary reinforcements 52 as described above, as well as, finally, to a tire for a vehicle wheel comprising a tread formed by such an improved profile 2.

Claims

1. Coextrusion installation (1) intended for generating a profiled element (2) by conjointly extruding a plurality of elastomeric compounds (M1, M2, M3) along a shared flow direction which corresponds to the longitudinal direction (X) of the said profiled element (2), the said installation comprising an extrusion head (4) which feeds the said elastomeric compounds (M1, M2, M3), and a receiving surface (5), such as a roller (6), which is positioned facing the extrusion head (4) in order to define a gap (3) serving to shape the cross section of the profiled element (2), in terms of thickness (H2) along a direction referred to as "vertical direction" (Z), which is perpendicular to the longitudinal direction (X) and to the receiving surface (5), and in terms of width (W2) along a direction referred to as "lateral direction" (Y), which is perpendicular to the longitudinal direction (X) and to the vertical direction (Z), the said installation (1) being characterized in that the extrusion head (4) comprises, from upstream to downstream along the flow direction: - first of all a first head portion (10), which is provided with one or more first intake channels (11) leading into the gap (3) in order to bring a first elastomeric compound (M1), intended to form a sublayer (12) of the profiled element (2), into contact with the receiving surface (5), the said first head portion (10) also comprising at least one pre-scraper (13) which projects vertically into the gap (3) with delimitation, along the lateral direction (Y), by a first lateral face (13L) and a second lateral face (13R), and, along the vertical direction (Z), by a lower face (13B) which faces towards the receiving surface (5) with positioning at a first predetermined, non-zero distance (H13) from the said receiving surface, referred to as "pre-scraping thickness" (H13), such that the said pre-scraper (13) can reserve, within the stream of the first elastomeric compound (M1), a trench referred to as "embedding trench" (14) which is bordered for the one part laterally by a first lateral substream (F1_M1) of the said first elastomeric compound (M1) and by a second lateral substream (F2_M1) of the said first elastomeric compound (M1), which first and second lateral substreams (F1_M1, F2_M1) flow on either side of the pre-scraper (13), along the first lateral face (13L) and along the second lateral face (13R) of the said pre-scraper respectively, and for the other part vertically by a bottom substream (F3_M1) which flows between the receiving surface (5) and the lower face (13B) of the pre-scraper (13), in the pre-scraping thickness (H13), to form a residual layer (15) of first elastomeric compound (M1), - then a second head portion (20) which is provided with one or more second intake channels (21) which lead into the gap (3) in order to feed a second elastomeric compound (M2) intended to cover the sublayer (12) of first elastomeric compound (M1) coming from the first head portion (10), the said second head portion comprising at least one scraper (23) which extends in the longitudinal continuation of the pre-scraper (13), and which projects vertically into the gap (3) so as to have a first lateral face (23L), a second lateral face (23R), and a lower face (23B) which faces towards the receiving surface (5), at a second vertical distance (H23) from the said receiving surface (5) referred to as "scraping thickness" (H23) which is strictly less than the pre-scraping thickness (H13), such that, for the one part, the said scraper (23) can laterally preserve the embedding trench (14) by making the stream of second elastomeric compound (M2) form a first lateral substream (F1_M2) of second elastomeric compound and a second lateral substream (F2_M2) of second elastomeric compound, which flow along the first lateral face (23L) and along the second lateral face (23R) respectively of the said scraper and which form an added thickness of the first and the second lateral substream (F1_M1, F2_M2) of first elastomeric compound respectively, which come from the first head portion (10), whereas, for the other part, the said scraper (23) makes it possible to vertically deepen the embedding trench (14) with a reduction, in accordance with the scraping thickness (H23), in the thickness of the residual layer of first elastomeric compound (M1) at the bottom of the said embedding trench (14), - and then a third head portion (30) comprising at least one injector (31) which projects into the gap (3), in the longitudinal continuation of the scraper (23), and which has an injection opening (32) intended to inject a third elastomeric compound (M3), distinct from the second elastomeric compound (M2), so as to form an insert (33) in the embedding trench (14), the said third head portion (30) further comprising, following the injector (31) in the longitudinal direction (X), a covering wall (34) which extends over a predetermined length referred to as "confluence length" (L34) along the longitudinal direction (X), from the injection opening (32) to the outlet of the gap (3), in order that the flow of the profiled element (2) below the said covering wall (34) allows the first and second lateral substreams (F1_M2, F2_M2) of second elastomeric compound to close up over the insert (33), thus filling the embedding trench (14).

2. Installation according to Claim 1, characterized in that the scraping distance (H23) is zero, such that, in the second head portion (20), the scraper (23) rubs against the receiving surface (5) so as to eliminate the residual layer of first elastomeric compound (M1) at the bottom of the embedding trench (14), in order to allow the injector (31) of the third head portion (30) to place the insert (33) made of third elastomeric compound (M3) in contact with the receiving surface (5).

3. Installation according to Claim 1 or 2, characterized in that the injector (31) is arranged so as to position the point of the injection opening (32) that is furthest away from the receiving surface (5), along the vertical direction (Z), and that thus corresponds to the apex (33A) of the insert, at a non-zero vertical distance from the covering wall (34), referred to as "embedding depth" (P31), such that the first lateral stream (F1_M2) of second elastomeric compound and the second lateral stream (F2_M2) of second elastomeric compound can meet and fuse in the space which is vertically comprised between the apex (33A) of the insert and the covering wall (34), in order to embed the said insert (33) in the second elastomeric compound (M2) at the said embedding depth (P31).

4. Installation according to Claim 3, characterized in that the embedding depth (P31) is comprised between 3 mm and 8 mm, preferably between 5 mm and 7 mm.

5. Installation according to one of the preceding claims, characterized in that the confluence length (L34) covered by the covering wall (34) is comprised between 10 mm and 14 mm.

6. Installation according to one of the preceding claims, characterized in that, in the first head portion (10), the width of the pre-scraper (13), considered along the lateral direction (Y), increases from upstream to downstream in the flow direction.

7. Installation according to one of the preceding claims, characterized in that, in the second head portion (20), the scraper (23) has a convergent portion (23C) which connects to the injector (31) and the width of which, considered along the lateral direction (Y), narrows from upstream to downstream in the flow direction.

8. Installation according to one of the preceding claims, characterized in that the injection opening (32), and consequently the resultant cross section of the insert (33), has a triangular shape, of which the base (33B) is oriented towards the receiving surface (5) and the apex (33A) is oriented towards the extrusion head (4).

9. Installation according to one of the preceding claims, characterized in that the receiving surface (5) is formed by a conveyor belt driven in a translational movement along the longitudinal direction (X) in relation to the extrusion head (4) or, more preferably, by a roller (6) which is driven in rotation in relation to the extrusion head (4), about its central axis (Y6) which is parallel to the lateral direction (Y).

10. Method for manufacturing a profiled element (2), characterized in that a pre-scraper (13) is used to open an embedding trench (14) in a first elastomeric compound (M1) making up a sublayer (12) of the profiled element (2), then a second elastomeric compound (M2) is fed so as to cover the said sublayer (12), whilst still preserving the embedding trench (14) within the first and second elastomeric compounds (M1, M2) by virtue of a scraper (23), then a third elastomeric compound (M3) making up an insert (33) is deposited in the said embedding trench (14), and then the second elastomeric compound (M2) is allowed to fill the said embedding trench (14) in order to coat the insert (33).

11. Method according to Claim 10, characterized in that the second elastomeric compound (M2) covers the embedding trench (14) and the insert (33) so as to embed the apex of the said insert (33) to a non-zero embedding depth (P31) preferably comprised between 3 mm and 8 mm.

12. Method according to Claim 10 or 11, characterized in that the profiled element (2) is intended to form a tread of a tyre for a vehicle wheel, in that, within the said profiled element (2), the first elastomeric compound (M1) forms a sublayer (12) intended to be secured to a crown reinforcement of the tyre, the second elastomeric compound (M2) is intended to form tread pattern blocks (22) that come into contact with the road, and the insert (33) made of third elastomeric compound (M3) is intended to form a circumferential reinforcer within the tread, and in that the complex dynamic shear modulus (G*_M3) of the third elastomeric compound (M3) is strictly greater than the complex dynamic shear modulus (G*_M2) of the second elastomeric compound (M2).

13. Method for manufacturing a tyre for a vehicle wheel, in the course of which method a profiled element (2) is manufactured according to the method of Claim 12 and the said profiled element (2) is used to form the tread of the said tyre.

14. Method for manufacturing a tyre for a vehicle wheel according to Claim 13, characterized in that at least one wear indicator (50) for monitoring the state of wear of the tyre is shaped in at least one of the tread pattern blocks (22) formed in the second elastomeric compound (M2), and in that the apex (33A) of the insert (33) formed from the third elastomeric compound (M3) has a height (H33), in relation to the receiving surface (5) and along the vertical direction (Z), which is strictly less than the height (H50) of the said wear indicator (50) such that, when the tyre is in use, the wear indicator (50) is reached before the apex (33A) of the insert embedded in the at least one of the tread pattern blocks (22) is uncovered.

15. Method for manufacturing a tyre for a vehicle wheel according to Claim 13 or 14, characterized in that the profiled element (2) produced comprises at least one tread pattern block (22) which is delimited along the lateral direction (Y) by at least one lateral edge (22L, 22R) and which comprises an insert (33) embedded in the said tread pattern block (22) at a distance from the said at least one lateral edge (22L, 22R), and in that an auxiliary reinforcer (52), preferably of triangular cross section, is added against the said at least one lateral edge (22L, 22R) of the tread pattern block (22).