FR2879956A1 - Pneumatic tyre tread manufacturing procedure includes injection of raw insertion mixture at predetermined points prior to moulding - Google Patents

Abstract

The procedure for making a tyre tread (7) from a base mixture (MB) with at least one insert of an insertion mixture (MI) consists of preparing the tread from the base mixture and injecting it at predetermined points (P) with a given quantity of an injection mixture prior to moulding. The mixture is injected into the raw tread through a nozzle (12) that has been forced into it and then withdrawn after the injection has been completed, and the injection mixture is delivered to the nozzle by an extruder (10) through a series of parallel ducts. During the final moulding of the tread a series of grooves is made, and at least one wall of each groove contains a layer of the insertion mixture.

Description

The present invention relates to the manufacture of tires. More

  specifically, it relates to the manufacture of tires whose tread comprises one or more inserts of an elastomeric material different from the elastomeric material which constitutes the bulk of said tread.

  It is known to design tires whose tread comprises different rubber compounds. The application WO 03/089257 describes examples of such treads.

  The industrial manufacture of such treads poses difficulties. Some desired effects can be obtained only insofar as the position of the inserts of elastomeric material in the final tread (ie after molding) is sufficiently precise and reproducible. Similarly, it may be desirable that the dimensions of these inserts are also accurate and reproducible. Such industrial manufacture must also be economical.

  The object of the invention is a method and a device for manufacturing tires whose tread comprises inserts of different elastomeric material that overcomes at least some of the aforementioned difficulties.

  For this, the invention proposes a method of manufacturing a tire, said tire comprising a tread essentially consisting of a base mixture, the tread further comprising at least one insert of an insertion mixture. said method comprising the steps of: preparing a raw base mixture tread, injecting into the green tread a predetermined amount of the green insert mixture at a predetermined position with respect to the tread Molding said tread.

  Preferably, the insertion mixture is injected into the green tread via a nozzle after the end of the nozzle has been driven into the green tread. Preferably, the end of the nozzle is extracted from the green tread at the latest during the injection of the insertion mixture.

  Preferably, the insertion mixture is conveyed to the end of the nozzle by an extruder and more preferably by a plurality of substantially parallel conduits.

  Preferably, the final molding step of the tread is made to form cutouts, at least one wall of said cutouts having an insertion mixture layer.

  P 10-1695-EN-CL According to a preferred embodiment of the invention, the tire is manufactured on a core whose shape is close to the final shape of the inner cavity of the tire. Preferably, the tread comprising a molded tread, the position of said insert being determined relative to the molded tread, said method comprises the steps of: forming the green tire around the core; Injecting at least one insert into the raw tread in a determined position relative to said core; Positioning said core carrying said green tire and said at least one insert in an outside mold according to a predetermined azimuth; Molding said tire.

  The invention also relates to a device for manufacturing a tire according to the above method, said tire comprising a tread consisting essentially of a base mixture, the tread further comprising at least one insert of an insertion mixture, said device comprising a rotary core adapted to support the green tire, means for supplying raw insertion mixture of a nozzle and means for positioning the nozzle relative to the core.

  Preferably, the outer shape of the end of the nozzle corresponds substantially to the shape of the insert.

  Preferably, the raw insertion mixture feed means comprises an extruder.

  Preferably, the device further comprises means for indexing the position of the insert or inserts 25 with respect to the tread of the molded tire.

  Preferably, the indexing means comprise a first index linked to the core and adapted to cooperate with a first complementary index linked to a motor member of the core during the assembly of the green tire and comprising a second index linked to the core and adapted to cooperate during molding with a second complementary index linked to the outer mold.

  Preferably, the first and second indexes constitute a unique means.

  Preferably, the nozzle comprises a plurality of substantially parallel conduits.

  Other advantages of the invention will also be deduced from the description of the following figures: FIG. 1 is a diagrammatic sectional view along a plane perpendicular to the axis of a tire comprising an insert according to the invention.

  Figure 2 is a detailed view of the portion of the tire contained in the circle B of Figure 1. Figures 3 to 11 schematically shows the principle of the method of the invention.

  Figure 12 is a schematic view of the molding of a coverslip according to the method of the invention.

  Figure 13 is a schematic view of the molding of a sculpture block comprising a coverslip according to the method of the invention.

  FIGS. 14 to 16 show an example of a nozzle that can be used in the manufacturing device according to the invention.

  Figures 17 and 18 illustrate the principle of a preferred embodiment of the invention.

  In Figure 1, there is shown a green tire 3, that is to say as it is before its final molding (we also use the term "rough"). The green tire comprises a radially outer portion (5), generally called "vertex" which appears here in section.

  Figure 2 is a more detailed but also schematic view of the area delimited by the circle B in Figure 1. The top 5 mainly comprises the tread 7 and reinforcements structure. Diagrammatically represented by a dotted line the reinforcing structure 9 (reinforcements carcass, crown or protection, these reinforcements may be radial, bias or circumferential). The tread 7 consists mainly of a basic elastomeric material (or mixture) and comprises at least one insert 6 of an elastomeric material different from the elastomeric base material. This insert is disposed in the green tread in a determined position P.

  For the convenience of the following description, the base elastomeric material will be referred to as the base mix (MB) and the different elastomeric material constituting the insert (s) will be referred to as the insertion mix (MI).

  One embodiment of the method according to the invention is schematically described by the series of FIGS. 3 to 8 which show a complete cycle of mixing insertion in a green tread.

  In FIG. 3, a mixture insertion device 10 capable of conveying a determined quantity of insertion mixture (MI) is positioned facing the surface 8 of the tread 7. The tread consists of a raw base mixture (MB). The insertion device 10 comprises a nozzle 12 whose outlet 14 faces the green tread.

  In Figure 4, the nozzle 12 sinks into the green tread 7 in a substantially radial direction and preferably a depth substantially equal to the depth of the proposed insert. A P 10-1695-EN-CL cavity 15 whose shape is complementary to the shape of the end of the nozzle 12 is formed in the green tread. Means for positioning the nozzle (not shown) make it possible to move the nozzle at least radially with respect to the tread.

  In FIG. 5, the insertion mixture MI is deposited in the cavity 15. The nozzle 12 of the insertion device is extracted from the green tread at the latest during the injection of the insertion mixture. Preferably, the nozzle is progressively extracted from the cavity 15 at a speed corresponding to the insertion mixture flow MI. This precaution ensures that the cavity created by the nozzle does not close (due to the reflux of the displaced base mixture) before being filled by the insertion mixture.

  In FIG. 6, the insertion mixture intake continues until substantially filling the cavity 15. The nozzle is then completely extracted from the cavity.

  In FIG. 7, the supply of insertion mixture is interrupted and the recoil of the nozzle continues so that the insertion mixture breaks at the outlet 14 of the nozzle.

  In FIG. 8, the tread provided with a first insert 6 is moved relative to the insertion device 10 (or vice versa) and a new mixing insertion cycle can begin. In this figure, the rotary movement of the tread 7 is shown. However, the displacement can of course be axial or both rotary and axial. The steps described above can then be repeated the number of times necessary to insert the desired number of inserts, these inserts can also be identical or different.

  As has been seen above, the invention makes it possible to insert a determined quantity of a different mixture into a green tread for subsequent molding and thus for cooking. The method according to the invention may therefore further comprise a particular molding step. Figures 9 to 11 illustrates a preferred embodiment of the method according to the invention wherein the insert 6 is shaped in a particular way during the final molding of the tire.

  In FIG. 9, the tread 7 carrying the insert 6 is placed in a mold 16 in a relative position such that the insert 6 is opposite a projection 18 of the mold, this projection being intended to mold a mold. corresponding relief (hollow) in the tread. In this example the stop 19 of the projection is substantially centered with respect to the insert 6.

  Figure 10 shows the situation created by the depression of the projection 18 in the green tread 7 during molding. The raw insertion mixture was partially carried away by the stop 19. On the 0-1695-FR-CL it is understood that according to the characteristics of the two mixtures, the shape of the projection 18 and its stop 19 and especially depending on the relative positioning of the mold and the raw tread, it will be possible to obtain different results.

  In a manner known per se, the molding can be caused by a radial movement of closure of the mold or by a radial expansion movement of the green tire or by a combination of these two radial movements.

  Figure 11 shows the demolding of the tread after cooking. The projection-molded cutout 18 has a wall F covered with an insertion mixture layer MI. The other walls of the cutout 20 here consist of the base mixture MB. In this example, the cutout 20 has a depth approximately 2 times greater than that of the starting insert.

  In Figure 12, there is shown another example of cutting. This is an incision 22 which has been molded using a slat 24 whose end is thickened. The two walls of the incision 22 are covered with an insertion mixture layer MI. It is understood that to obtain such a result, the different mixing insert must be substantially centered with respect to the blade 24 during molding. The fact that the end of the lamella is thickened promotes the displacement of the insertion mixture. A thin flat slat will tend to slice the mixture while minimizing its movement. In either case, the walls of the incision are covered in whole or in part with a layer of insertion mixture.

  In Figure 13, there is shown another example of molding. In this view, the mold 16 forms both two wide grooves 20 and an incision 22 in the block 21 located between the grooves. Here, all the substantially radial faces of the cutouts are covered with the insertion mixture MI. It is understood that such a result can be obtained according to the method described above after having placed five inserts in the raw tread, four inserts being positioned each facing a stop 19 of the mold 16, the fifth facing the slat 24.

  According to the principles of the invention, it is also possible to produce insertion mixture layers at the bottom of the grooves or in the center of the contact area of a sculpting element. The method according to the invention allows in fact innumerable variants around the principle of a molding of a raw tread containing different mixing inserts. Examples of treads containing different mixing inserts are described in particular in international application WO 03/089257. Most of these examples can be achieved using the present method by injecting a suitable number of inserts at suitable circumferential positions of the raw tread.

  In FIG. 14, there is shown an example of a nozzle 12 of the mixture insertion device 10. The nozzle here has a flattened shape and a rectangular outer section. Such a nozzle when it is introduced radially into the green tread (as described in FIG. 4) will have the effect of forming a substantially parallelepipedic cavity. The outlet 14 of the nozzle is fed by a plurality of parallel ducts 26.

  FIG. 15 shows the end of the nozzle in section along the plane C of FIG. 14. It is clearly seen on this section that the outlet 14 has a relatively large mouth with respect to the duct 26.

  This feature can promote reproducible breaking of the insertion mixture at the shoulder 30 when removing the nozzle (see Figure 7). For the same purpose, for a given feed section, a large number of small ducts may be preferred to a smaller number of larger ducts. The appropriate number of ducts also depends on the profile of the nozzle considered.

  Figure 16 shows a variant of the nozzle of Figure 14 wherein the conduit 26 further has a reduction of its final section to further facilitate the separation of the insert.

  The thickness of the nozzle may, for example, vary from 2 to 10 mm to achieve the examples illustrated here, the width of the nozzle then being preferably comparable to the width of the tread rolls envisaged on the tread.

  In the more general context of the invention, several nozzles may be fed by a single feed means. It is also possible to implement parallel, on the same tire blank, several mixing insertion devices 10, each of these devices opening onto one or more nozzles.

  The feeding means of the (or) nozzle (s) insertion mixture may be an extruder. The flow rate of the extruder can be controlled by the rotational speed of its screw or by any other flow control device.

  In order to guarantee the precision of the molding with respect to the position of the insert or inserts, the method of the invention is preferably implemented in the context of a manufacture of tires on a core and indexing means are preferably used. whose principle is illustrated in Figures 17 and 18.

  For the sake of clarity of the drawing, these figures show a single insert 6 but as described above, the method according to the invention allows the installation of inserts in unlimited number.

  FIG. 17 shows the tire of FIG. 1 during its manufacture according to a preferred embodiment of the invention. The green tire is here made on a rotating core 1 by winding materials of great length and / or successive deposition (s) of reduced length elements. The core 1 is driven by a motor member such as a spindle or hub 2. The position of the core 1 relative to the hub 2 is fixed by first indexing means (symbolized here by first indexes 42 and 43 of shapes complementary to each other). The angular position of the core 1 during its rotation can therefore be controlled in connection with the control of the various laying tools, including the mixing insertion tool described above. There are many known indexing means such as a groove and key system or a fitting with a flat or any form of assembly allowing only one relative angular position. The angular position of the spindle or hub 2 is controlled directly or indirectly in a manner known per se, for example by means of an incremental encoder.

  Thus when an insert 6 is placed in the green tread, the position P of this insert relative to the core 1 is not random, it is instead quite reproducible. This position P can be broken down into three elements which we will now detail: The radial position of the insert (in the direction of the thickness of the tread) is given by the insertion method, for example according to the depth of introduction of the nozzle into the tread, É The transverse position of the insert (in the axial direction of the tire) is also given by the insertion method and in particular by the axial position of the nozzle Finally, the circumferential position of the insert (for example the azimuth a) with respect to the core is controlled according to the invention by means of the indexing system, for example as described above. .

  When the assembly of the raw tire is completed, that is to say that all its constituent elements (including the inserts) are in place on the core, this assembly (core + raw tire) is placed in an outer mold which gives its final shape to the tire and particularly to its tread.

  FIG. 18 shows the stage of the manufacturing process during which the raw tire assembled on its core is placed in an external mold (here symbolized by molding sectors 35). The sectors 35 comprise projections 18 intended to form negative reliefs on the surface of the tire (see FIGS. 9 to 13). So that the position of the insert 6 with respect to the grooves or incisions of the molded tread is reproducible from one tire to another, the core carrying the green tire is positioned reproducibly relative to the outer mold (c is here in relation to sectors 35). This can be done through second indexing means P 10- 1695-FR-CL comparable to the first indexing means described above for the insertion of the inserts. The second indexing means comprise a second index linked to the core and a second complementary index linked to the outer mold. It is of course possible to use second indexes (44, 45) independent of the first indexes (42, 43). One can also use the first index (43) linked to the core, said first index cooperating this time with the second complementary index (44) linked to the mold provided that the angular positioning of the tire in the mold is reproducible during manufacturing cycles. Indeed, it is well understood in this figure that any point of the core is fixed relative to the position P of the insert 6. We can therefore associate any point (but only) of the nucleus to any point (but only ) of the outer mold so that the angular position of the insert in the mold is reproduced from one manufacturing cycle to another. If one takes the example described in FIG. 18 where the indexes 44 and 43 have been used as second indexing means, the insert 6 considered here will be at each manufacturing cycle, ie in each tire manufactured, positioned with respect to the mold (considered fixed) at azimuth a + 13 relative to the horizontal. On the other hand, if the indexing during the molding uses as the second indexing means the association of the indexes 44 and 45, the insert 6 will be at each manufacturing cycle positioned with respect to the mold at the azimuth a + R + y relative to the horizontal since the index 45 is offset relative to the index 43 by an angle y.

  The second indexing means can also operate at the level of the tools (not shown) which are used to manipulate the core for molding after making the green tire.

  Indeed, a hub identical or similar to the hub 2 of Figure 17 can be used to transport and / or angularly position the core within the mold. The second indexing takes place in this case by the center and not by the periphery of the core as shown in FIG. 18.

  The reproducible positioning can also be obtained in the following way: the core carrying the green tire being placed in the same angular position at the end of each insertion of the inserts cycle, the core is transported and placed in the mold avoiding any rotation (or allowing rotation of a constant angle). This can be implemented in a simple manner, for example by a translation on rails or by rotation by carousel of the insertion station at the molding station.

  When the sculpture of the tire (or the part of sculpture concerned) has a pattern that repeats itself two or more times along the circumference, that is to say that the inserts can take several positions for an identical effect during molding, one can naturally use indexing means comprising a corresponding number of possible positions (or a sub-multiple of this number).

  P 10-1695-EN-CL The core (1) can take different forms, it can be rigid, for example according to the teaching of document EP0242840, or more or less deformable (inflatable) according to documents FR2005116 or EP822047, provided that it allows both making and molding.

  It has been found that the method of the invention allows great consistency in the final positioning of the inserts within the finished tires. The method of the invention can make it possible to obtain a dispersion of less than or equal to 1 mm on the circumference of a passenger or motorcycle tire.

  The choice of the MI insertion elastomeric material is of course related to the function it must provide in the finished tire. Preferably, however, an elastomeric material is used whose uncured mechanical properties promote tensile failure in order to obtain a sufficiently reproducible separation (see the description of FIGS. 7 and 14 to 16).

  When it is said that an elastomeric material is raw, it means that it is not cooked with reference to the crosslinking which is generally carried out during the final molding of the tires. In practice, the crosslinking can be started before molding, for example due to the temperature increase caused by the extrusion. Thus, it should be understood that the elastomeric material is said to be raw as long as it is not yet completely crosslinked.

  The invention is particularly applicable to obtaining multi-material treads. Naturally, the invention can be applied to other areas of the tire with the necessary adaptations.

  In general, the term "pneumatic" used herein naturally covers any type of elastic tire, pneumatic or non-pneumatic, the invention essentially concerning the molding of this "tire" and not its operation.

P 10-1695-EN-CL - 10 -

Claims (15)

  A method of manufacturing a tire, said tire comprising a tread (7) consisting essentially of a base mixture (MB), the tread further comprising at least one insert (6) of a mixture insertion method (MI), said method comprising steps of: a. prepare a tread mixture of raw base, b. injecting into the green tread a predetermined quantity of the raw insertion mixture in a position (P) determined with respect to the tread, c. molding said tread.   The method of claim 1 wherein the insertion mixture is injected into the green tread via a nozzle (12) after the end of the nozzle has been driven into the raw tread. .   3. Method according to claim 2 wherein the end of the nozzle (12) is extracted from the green tread at the latest during the injection of the insertion mixture.   4. Method according to one of claims 2 or 3 wherein the insertion mixture is conveyed to the end (14) of the nozzle (12) by an extruder (10).   5. Method according to one of claims 2 to 4 wherein the insertion mixture is fed to the end of the nozzle by a plurality of conduits (26) substantially parallel.   6. Method according to one of the preceding claims wherein the final molding step of the tread is formed to form cutouts (20, 22), at least one wall (F) of said cutouts having a layer of insertion mixture (MI).   7. Method according to one of the preceding claims wherein the tire is manufactured on a core (1) whose shape is close to the final shape of the inner cavity of the tire.   The method of claim 7, the tread comprising a molded tread, the position (P) of said insert being determined relative to the molded tread, said method comprising the steps of: forming the green tire (3) around the core (1); P10-1695-EN-CL E inject at least one insert (6) within the green tread (7) in a position (P, a) determined with respect to said core; Positioning said core carrying said green tire (3) and said at least one insert in an outer mold (35) according to a predetermined azimuth (13); Molding said tire.   9. Device for manufacturing a tire according to the method of the preceding claims, said tire comprising a tread (7) consisting essentially of a base mixture, the tread further comprising at least one insert (6) of an insertion mixture, said device comprising a rotary core (1) adapted to support the green tire (3), feed means (10) in raw insertion mixture of a nozzle (12) and means for positioning the nozzle relative to the core.   10. Device according to claim 9 wherein the outer shape of the end of the nozzle substantially corresponds to the shape of the insert.   11. Device according to one of claims 9 or 10 wherein the raw insertion mixture feed means comprises an extruder.   12. Device according to one of claims 9 to 11 further comprising means for indexing the position of the insert or inserts relative to the tread of the molded tire.   13. Device according to claim 12 wherein the indexing means comprises a first index (43) connected to the core (1) and adapted to cooperate with a first complementary index (42) linked to a motor member (2) of the core when the assembly of the green tire and comprising a second index (43; 45) connected to the core and adapted to cooperate during molding with a second complementary index (44) connected to the outer mold (35).   14. Device according to claim 13 wherein the first and the second index constitute a single means (43).   15. Device according to one of claims 9 to 14 wherein the nozzle comprises a plurality of conduits (26) substantially parallel. P 10-1695-EN-CL