Straight ply and angle ply comprising metallic monofilaments

Abstract

A ply (16, 18) comprises metallic monofilaments (46′, 46″). Each monofilament (46′) of a first group has a positive torsional elastic deformation in a first direction about its main axis (G). Each monofilament (46″) of a second group has a negative torsional elastic deformation in a second direction about its main axis (G). The absolute value of the torsional elastic deformation C of each monofilament (46′, 46″) is such that |C|≤6 turns per ten metres. The mean S of the torsional elastic deformations of the monofilaments (46′, 46″) of the ply (16, 18) is such that −0.25 turn per ten metres≤S≤+0.25 turn per ten metres. The monofilaments (46′, 46″) are arranged next to one another so as to alternate one or more monofilaments (46′) of the first group with one or more monofilaments (46″) of the second group.

Claims

1. A ply extending along a main direction P′ comprising: a polymer matrix; and metallic monofilaments embedded in the polymer matrix, the metallic monofilaments being straight and being substantially parallel relative to one another and to the main direction P′ of the ply, each metallic monofilament having a main axis G and a torsional elastic deformation C about its main axis G, wherein the ply comprises first and second groups of metallic monofilaments, each metallic monofilament of the first group having a torsional elastic deformation C in a first direction about its main axis G, each metallic monofilament of the second group having a torsional elastic deformation C in a second direction about its main axis G, the first direction being opposite to the second direction, and the torsional elastic deformation C being positive in the first direction and negative in the second direction, wherein the absolute value of the torsional elastic deformation C of each metallic monofilament is such that |C|≤6 turns per ten meters of metallic monofilament, wherein the mean S of the torsional elastic deformations of the metallic monofilaments of the ply is such that −0.25 turn per ten meters of metallic monofilaments≤S≤+0.25 turn per ten meters of metallic monofilaments, and wherein the metallic monofilaments are arranged next to one another so as to alternate one or more metallic monofilaments of the first group with one or more metallic monofilaments of the second group.

2. A tire comprising at least one ply according to claim 1.

3. A ply extending along a main direction P comprising: a polymer matrix; and metallic monofilaments embedded in the polymer matrix, the metallic monofilaments being straight and being substantially parallel relative to one another and making an angle A of between 10° and 40° with the main direction P of the ply, each metallic monofilament having a main axis G and a torsional elastic deformation C about its main axis G, wherein the ply comprises first and second groups of metallic monofilaments, each metallic monofilament of the first group having a torsional elastic deformation C in a first direction about its main axis G, each metallic monofilament of the second group having a torsional elastic deformation C in a second direction about its main axis G, the first direction being opposite to the second direction, and the torsional elastic deformation C being positive in the first direction and negative in the second direction, wherein the absolute value of the torsional elastic deformation C of each metallic monofilament is such that |C|≤6 turns per ten meters of metallic monofilament, wherein the mean S of the torsional elastic deformations of the metallic monofilaments of the ply is such that −0.25 turn per ten meters of metallic monofilaments≤S≤+0.25 turn per ten meters of metallic monofilaments, and wherein the metallic monofilaments are arranged next to one another so as to alternate one or more metallic monofilaments of the first group with one or more metallic monofilaments of the second group.

4. A tire comprising at least one ply according to claim 3.

5. A process for manufacturing a ply extending along a main direction P′ comprising: a polymer matrix; and metallic monofilaments embedded in the polymer matrix, the metallic monofilaments being straight and being substantially parallel relative to one another and to the main direction P′ of the ply, each metallic monofilament having a main axis G and a torsional elastic deformation C about its main axis G, wherein the ply comprises first and second groups of metallic monofilaments, each metallic monofilament of the first group having a torsional elastic deformation C in a first direction about its main axis G, each metallic monofilament of the second group having a torsional elastic deformation C in a second direction about its main axis G, the first direction being opposite to the second direction, and the torsional elastic deformation C being positive in the first direction and negative in the second direction, wherein the absolute value of the torsional elastic deformation C of each metallic monofilament is such that |C|≤6 turns per ten meters of metallic monofilament, and wherein the mean S of the torsional elastic deformations of the metallic monofilaments of the ply is such that −0.25 turn per ten meters of metallic monofilaments≤S≤+0.25 turn per ten meters of metallic monofilaments, said process comprising a calendering step during which the metallic monofilaments are arranged next to one another so as to alternate one or more metallic monofilaments of the first group with one or more metallic monofilaments of the second group.

6. The process according to claim 5, further comprising, prior to the calendering step, a straightening step in which the residual stresses of each metallic monofilament are reduced by exerting forces substantially perpendicularly to the main axis G of the metallic monofilament.

7. The process according to claim 6, wherein the forces are exerted by means of a straightening device comprising: a succession of a first series of presser elements; and a succession of a second series of presser elements, wherein the presser elements of the first series exert forces on the metallic monofilament in the opposite direction to the presser elements of the second series.

8. The process according to claim 7, wherein each presser element comprises a pulley rotatably mounted about an axis R, the axes R of the presser elements of each first and second series being substantially aligned with one another along respectively first and second directions substantially parallel to the run direction F of the metallic monofilament.

9. The process according to claim 7, wherein the forces are exerted by means of first and second straightening devices, each first and second straightening device comprising: a succession of a first series of presser elements; and a succession of a second series of presser elements, wherein the presser elements of the first series of each first and second straightening device exert forces on the metallic monofilament in the opposite direction to the presser elements respectively of the second series of each first and second straightening device.

10. The process according to claim 9, wherein the presser elements of the first straightening device exert their forces along a direction D1 substantially perpendicular to the direction D2 along which the presser elements of the second straightening device exert their forces.

11. A process for manufacturing a ply extending along a main direction comprising the steps of: cutting several strips from a ply according to claim 1 so that each strip extends along a main direction P and so that the metallic monofilaments of each strip make an angle A of between 10° and 40° with the main direction P of the strip; and joining two ends of at least two strips so as to obtain the ply in which the metallic monofilaments make an angle A of between 10° and 40° with the main direction P of the ply.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from reading the following description, given solely by way of non-limiting example and with reference to the drawings in which:

(2) FIG. 1 illustrates a tyre according to the invention;

(3) FIG. 2 illustrates an angle ply of the tyre from FIG. 1 according to a first embodiment of the invention;

(4) FIG. 3 illustrates the angle ply from FIG. 2 along the cutting plane III-Ill′;

(5) FIGS. 4 to 6 illustrate angle plies respectively according to second, third and fourth embodiments;

(6) FIG. 7 is a diagram illustrating the steps of the process according to the invention;

(7) FIG. 8 illustrates first and second devices for straightening metallic monofilaments of a ply according to the invention;

(8) FIG. 9 illustrates the first straightening device from FIG. 8;

(9) FIG. 10 illustrates a device for manufacturing a straight ply according to the invention;

(10) FIG. 11 illustrates a step of cutting strips for manufacturing the angle ply according to the invention of FIGS. 1, 2 and 3 from the straight ply according to the invention manufactured in FIG. 10.

DETAILED DESCRIPTION

(11) In the following description, when the term “radial” is used, it is appropriate to make a distinction between several different uses of the word by a person skilled in the art. Firstly, the expression refers to a radius of the tyre. It is within this meaning that a point P1 is said to be “radially inside” a point P2 (or “radially on the inside” of the point P2) if it is closer to the rotation axis of the tyre than the point P2. Conversely, a point P3 is said to be “radially outside” a point P4 (or “radially on the outside” of the point P4) if it is further away from the rotation axis of the tyre than the point P4. Progress will be said to be “radially inwards (or outwards)” when it is in the direction of smaller (or larger) radii. It is this sense of the word that applies also when radial distances are being discussed.

(12) On the other hand, a reinforcing element or a reinforcement is said to be “radial” when the reinforcing element or the reinforcing elements of the reinforcement make an angle greater than or equal to 65° and less than or equal to 90° with the circumferential direction.

(13) An “axial” direction is a direction parallel to the axis of rotation of the tyre. A point P5 is said to be “axially inside” a point P6 (or “axially on the inside” of the point P6) if it is closer to the median plane M of the tyre than the point P6. Conversely, a point P7 is said to be “axially outside” a point P8 (or “axially on the outside” of the point P8) if it is further away from the median plane M of the tyre than the point P8.

(14) The “median plane” M of the tyre is the plane which is normal to the axis of rotation of the tyre and which is situated equidistantly from the annular reinforcing structures of each bead.

(15) A “circumferential” direction is a direction which is perpendicular both to a radius of the tyre and to the axial direction.

(16) Furthermore, any range of values denoted by the expression “from a to b” means the range of values ranging from the end point “a” to the end point “b”, i.e. including the strict end points “a” and “b”.

(17) Tyre and Angle Plies According to the Invention

(18) A frame of reference X, Y, Z corresponding to the usual respectively axial (X), radial (Y) and circumferential (Z) directions of a tyre has been depicted in the figures.

(19) FIG. 1 depicts a tyre, in this case a pneumatic tyre, in accordance with a first embodiment of the invention and denoted by the general reference 10. The tyre 10 substantially exhibits revolution about an axis substantially parallel to the axial direction X. The tyre 10 here is intended for a passenger vehicle.

(20) The tyre 10 comprises a crown 12 comprising a crown reinforcement 14 comprising a working reinforcement 15 comprising two working plies 16, 18 of reinforcing elements according to the invention and a hoop reinforcement 17 comprising a hooping ply 19. The crown reinforcement 14 is surmounted by a tread 20. In this case, the hoop reinforcement 17, in this case the hooping ply 19, is radially interposed between the working reinforcement 15 and the tread 20.

(21) Two sidewalls 22 extend the crown 12 radially inwards. The tyre 10 further comprises two beads 24 radially on the inside of the sidewalls 22 and each comprising an annular reinforcing structure 26, in this instance a bead wire 28, surmounted by a mass of filling rubber 30, and also a radial carcass reinforcement 32. The crown reinforcement 14 is radially interposed between the carcass reinforcement 32 and the tread 20. Each sidewall 22 connects each bead 24 to the crown 14.

(22) The carcass reinforcement 32 preferably comprises a single carcass ply 34 of radial textile reinforcing elements. The carcass reinforcement 32 is anchored to each of the beads 24 by being turned up around the bead wire 28, so as to form, within each bead 24, a main strand 38 extending from the beads 24 through the sidewalls 22 as far as into the crown 12, and a turn-up strand 40, the radially outer end 42 of the turn-up strand 40 being radially on the outside of the annular reinforcing structure 26. The carcass reinforcement 32 thus extends from the beads 24 through the sidewalls 22 as far as into the crown 12. In this embodiment, the carcass reinforcement 32 also extends axially through the crown 12.

(23) Each working ply 16, 18, hooping ply 19 and carcass ply 34 comprises a polymer matrix in which the reinforcing elements of the corresponding ply are embedded. Each polymer matrix, here an elastomer matrix, of the working plies 16, 18, hooping ply 19 and carcass ply 34 is made from a conventional composition for the calendering of reinforcing elements conventionally comprising a diene elastomer, for example natural rubber, a reinforcing filler, for example carbon black and/or silica, a crosslinking system, for example a vulcanization system, preferably comprising sulfur, stearic acid and zinc oxide, and possibly a vulcanization accelerator and/or retarder and/or various additives.

(24) The hooping ply 19 comprises hooping textile reinforcing elements that form an angle at most equal to 10°, preferably ranging from 5° to 10°, with the circumferential direction Z of the tyre 10. In this case, each hooping textile reinforcing element is made from a heat-shrinkable material, here made of polyamide 66. Each hooping textile reinforcing element comprises two multifilament strands made from a heat-shrinkable material, here made of polyamide 66, which are individually overtwisted at 250 turns.Math.m.sup.−1 in one direction then twisted together at 250 turns.Math.m.sup.−1 in the opposite direction. The two multifilament strands are helically wound around one another. Each multifilament strand has a titer equal to 140 tex. The thermal contraction TC of each hooping textile reinforcing element is approximately equal to 7%.

(25) The carcass ply 34 comprises radial carcass textile reinforcing elements that form an angle ranging from 65° to 90° with the circumferential direction Z of the tyre 10. In this case, each carcass textile reinforcing element comprises two multifilament strands made of polyester, here made of PET, which are individually overtwisted at 420 turns.Math.m.sup.−1 in one direction then twisted together at 420 turns.Math.m.sup.−1 in the opposite direction. The two multifilament carcass strands are helically wound around one another. Each multifilament carcass strand has a titer equal to 144 tex.

(26) The working ply 16 according to the invention has been represented in FIG. 2. The working ply 16 extends along a main direction P. Once the working ply 16 is incorporated into the tyre 10, the main direction P of the working ply 16 is substantially parallel to the circumferential direction Z of the tyre 10. The working ply 16 comprises metallic reinforcing elements 44. Each reinforcing element 44 comprises, here consists of, a metallic monofilament 46 embedded in a polymer matrix 23 as described above.

(27) The metallic monofilaments 46 of the working ply 16 are substantially parallel to one another and make an angle A ranging from 10° to 40°, preferably ranging from 20° to 30° and here equal to 26° with the circumferential direction Z of the tyre 10. Each metallic monofilament 46 is here made of steel coated with a protective coating comprising for example brass or zinc. Each metallic monofilament 46 has a diameter ranging from 0.10 mm to 0.50 mm, preferably from 0.20 mm to 0.40 mm and more preferentially from 0.25 mm to 0.35 mm, and here equal to 0.30 mm.

(28) The working ply 18 according to the invention has features identical to those of the working ply 16 except for the orientation of the metallic monofilaments 46 that form an angle B ranging from 10° to 40°, preferably ranging from 20° to 30° and here equal to 26°, the angle B being opposite to the angle A. In other words, the reinforcing elements of the working plies 16 and 18 are crossed.

(29) Owing to the angle A or B that each metallic monofilament 46 makes with the circumferential direction Z of the tyre 10, each working ply 16, 18 is said to be an angle ply.

(30) As represented in FIG. 3, each working angle ply 16, 18 comprises first and second groups of metallic monofilaments 46′ and 46″. Each metallic monofilament 46′, 46″ has a main axis G that is coincident with its axis of revolution. Each metallic monofilament 46′ of the first group has a positive torsional elastic deformation C in a first direction about its main axis, for example in the clockwise direction in FIG. 3. Each metallic monofilament 46″ of the second group has a negative torsional elastic deformation C in a second direction about its main axis, for example the anticlockwise direction in FIG. 3. The first direction is therefore opposite to the second direction.

(31) In each working angle ply 16, 18, the metallic monofilaments 46′, 46″ are arranged next to one another so as to alternate one or more metallic monofilaments 46′ of the first group with one or more metallic monofilaments 46″ of the second group.

(32) Each ply comprises m successions of Ni≥1 metallic monofilaments 46′ of the first group, i ranging from 1 to m, and n successions of Mj≥1 metallic monofilaments 46″ of the second group, j ranging from 1 to n. Each succession Ni is adjacent to at least one succession Mj and, with the exception of the successions located at the edges of the ply, each succession Ni, Mj is adjacent to two successions, respectively Mj, Ni.

(33) In the embodiment illustrated in FIG. 3, the ply comprises m=3 successions of metallic monofilaments 46′ of the first group and n=3 successions of metallic monofilaments 46″ of the second group. For each succession of Ni≥1 metallic monofilaments 46′ of the first group, N1=N2=N3=1. For each succession of Mj≥1 metallic monofilaments 46″ of the second group, M1=M2=M3=1. Thus, the metallic monofilaments 46′, 46″ are arranged next to one another so as to alternate one metallic monofilament 46′ of the first group with one metallic monofilament 46″ of the second group.

(34) The absolute value of the torsional elastic deformation C of each metallic monofilament 46′, 46″ is such that |C|≤6 turns per ten metres of metallic monofilament 46′, 46″.

(35) The mean S of the torsional elastic deformations of the monofilaments of the ply is such that −0.25 turn per ten metres of metallic monofilament≤S≤+0.25 turn per ten metres of metallic monofilament.

(36) In the embodiment illustrated in FIG. 3, (which illustrates an angle ply comprising a reduced number of metallic monofilaments for the purposes of clarity and conciseness of the disclosure of the invention), each metallic monofilament 46′ of the first group has a torsional elastic deformation such that C<+6 turns per ten metres of metallic monofilament 46′, preferably C<+5 turns per ten metres of metallic monofilament 46′, in this case C=+3.5 turns per ten metres of metallic monofilament 46′. Each metallic monofilament 46″ of the second group has a torsional elastic deformation such that C>−6 turns per ten metres of metallic monofilament 46″, preferably C>−5 turns per ten metres of metallic monofilament 46″ (|C|<6 turns per ten metres of metallic monofilament 46″, |C|<5 turns per ten metres of metallic monofilament 46″), in this case C=−3.1 turns per ten metres of metallic monofilament 46″ (|C|=3.1 turns per ten metres of metallic monofilament 46″). Thus, the mean S is equal to S=3×(+3.5−3.1)/6=+0.20 turns per ten metres of metallic monofilament 46′, 46″.

(37) FIGS. 4, 5 and 6 respectively depict second, third and fourth embodiments of angle plies according to the invention. Elements similar to those of the first embodiment are denoted by identical references.

(38) With reference to FIG. 4, unlike the first embodiment, the angle ply of the second embodiment comprises m=2 successions of metallic monofilaments 46′ of the first group and n=1 succession of metallic monofilaments 46″ of the second group. For each succession of Ni≥1 metallic monofilaments 46′ of the first group, N1=N2=2. For the succession of Mj≥1 metallic monofilaments 46″ of the second group, M1=2. Thus, the metallic monofilaments 46′, 46″ are arranged next to one another so as to alternate two metallic monofilaments 46′ of the first group with two metallic monofilaments 46″ of the second group.

(39) With reference to FIG. 5, unlike the first embodiment, the angle ply of the third embodiment comprises m=2 successions of metallic monofilaments 46′ of the first group and n=2 successions of metallic monofilaments 46″ of the second group. For each succession of Ni≥1 metallic monofilaments 46′ of the first group, N1=N2=1. For each succession of Mj≥1 metallic monofilaments 46″ of the second group, M1=M2=2. Thus, the metallic monofilaments 46′, 46″ are arranged next to one another so as to alternate one metallic monofilament 46′ of the first group with two metallic monofilaments 46″ of the second group.

(40) With reference to FIG. 6, unlike the first embodiment, the angle ply of the third embodiment comprises m=3 successions of metallic monofilaments 46′ of the first group and n=2 successions of metallic monofilaments 46″ of the second group. Unlike the preceding embodiments in which, for each succession, Ni=N and Mj=M, there are, in the embodiment from FIG. 6, at least two values k and k′ between 1 and m, such that Nk≠Nk′ and/or there are at least two values I and I′ between 1 and n, such that MI≠MI′. In this case, for each succession of Ni≥1 metallic monofilaments 46′ of the first group, N1=N2=N3=1 and there are at least two values I and I′ between 1 and n, such that MI≠MI′. Here, M1=1 and M2=2. A variant could also be envisaged in which instead of having Ni=N for i ranging from 1 to m, there would be at least two values k and k′ between 1 and m, such that Nk≠Nk′.

(41) Straight Ply According to the Invention, Process for Manufacturing a Straight Ply and an Angle Ply According to the Invention

(42) A process for manufacturing straight and angled plies according to the invention will now be described with reference to FIGS. 7 to 11.

(43) With reference to FIG. 7, during a step 100, a monofilament 46 with a diameter d of between 0.10 mm and 0.50 mm is manufactured from a metallic monofilament with a diameter D of between 0.75 mm and 2.5 mm. In order to do this, the first step 100 comprises an uninterrupted series of steps 100.sub.1-100.sub.p of drawing the metallic monofilament from a diameter D to a diameter d. Each step 100.sub.1-100.sub.p consists in passing the monofilament through a die of diameter d′.sub.i, being between 1 and p, d′.sub.i, being between d and D, the diameter d′.sub.i, of each die decreasing in the run direction of the metallic monofilament. Such a step 100 is well known to a person skilled in the art.

(44) Next, the process comprises first and second steps 200 and 300 of straightening the metallic monofilament 46 of diameter d in order to reduce the residual stresses present at the surface of the metallic monofilament 46. During these steps 200 and 300, the residual stresses of each metallic monofilament 46 are reduced by exerting forces substantially perpendicularly to the main axis G of the metallic monofilament 46 by means of first and second straightening devices 50, 50′ illustrated in FIG. 8. The first straightening device is illustrated in detail in FIG. 9.

(45) Each first and second straightening device 50, 50′ comprises a succession of a first series of presser elements 52, 52′ and a succession of a second series of presser elements 54, 54′.

(46) The presser elements 52, 52′ of the first series of each first and second straightening device 50, 50′ exert forces on the metallic monofilament 46 in the opposite direction to the presser elements 54, 54′ respectively of the second series of each first and second straightening device 50, 50′. These forces have been represented by arrows in FIG. 9.

(47) The presser elements 52, 54 of the first straightening device 50 exert their forces along a direction D1 substantially perpendicular to the direction D2 along which the presser elements 52′, 54′ of the second straightening device 50′ exert their forces.

(48) In this case, each presser element 52, 52′, 54, 54′ comprises a pulley rotatably mounted about an axis R. The axes R of the presser elements 52, 54 of the first and second series of the first straightening device 50 are substantially aligned with one another along respectively first and second directions F1, F2 substantially parallel to the run direction F of the metallic monofilament 46. Similarly, the axes of the presser elements 52′, 54′ of the first and second series of the second straightening device 50′ are substantially aligned with one another along respectively first and second directions F1′, F2′ substantially parallel to the run direction F of the metallic monofilament 46.

(49) Next, in a subsequent storage step (not illustrated), after the straightening steps 200, 300, each metallic monofilament 46 is stored on a storage reel. Each storage reel comprises an indicator as to whether the metallic monofilament belongs to the first or second group and also the value of the torsional elastic deformation of the metallic monofilament. In this case, when the metallic monofilament 46′ has a torsional elastic deformation in the first direction, here the clockwise direction, a green sticker is affixed to the storage reel and the value of the torsional elastic deformation is written thereon, +3 for the first embodiment from FIG. 3. Similarly, when the metallic monofilament 46″ has a torsional elastic deformation in the second direction, here the anticlockwise direction, a red sticker is affixed to the storage reel and the value of the torsional elastic deformation is written thereon, −2 for the first embodiment from FIG. 3.

(50) Next, in a step 400, the metallic monofilaments 46′, 46″ are arranged next to one another so as to alternate one or more metallic monofilaments 46′ of the first group with one or more metallic monofilaments 46″ of the second group and so as to meet the requirement regarding the mean S of the torsional elastic deformations, namely the mean S of the torsional elastic deformations of the metallic monofilaments 46 being such that −0.25 turn per ten metres of metallic monofilaments≤S≤+0.25 turn per ten metres of metallic monofilaments.

(51) The metallic monofilaments 46′, 46″ are embedded in the polymer matrix 23 by means of a calender 56 as is represented in FIG. 10. Such a calendering step and also a suitable calender are in particular described in EP2047962. A straight ply 58 according to the invention is then obtained, in which the metallic monofilaments 46′, 46″ are substantially parallel to one another and to a main direction P′ of the straight ply 58.

(52) Next, in a step 500 depicted in FIG. 11, the angle ply 16, 18 from FIGS. 2 and 3 is manufactured as described previously from the straight ply 58.

(53) For this, several strips Bi are cut from the straight ply 58 so that each strip Bi extends along the main direction P and so that the metallic monofilaments 46 of each strip Bi make the angle A (or B for the ply 18) of between 10° and 40° with the main direction of the strip Bi, here an angle equal to 26°. Each strip Bi thus obtained has two longitudinal edges Bli and also two ends Bei.

(54) Next, the ends Bei of several strips Bi obtained previously are joined in twos so as to obtain the angle ply 16, 18 in which the metallic monofilaments 46 make an angle of between 10° and 40° with the main direction P of the angle ply.

(55) The invention is not limited to the embodiments described above.

(56) The various embodiments described above may be combined provided that these embodiments are compatible with one another.