Multi-strand cable having two multi-strand layers

Abstract

The invention relates to a multi-strand cable (50) having two multi-strand layers, said cable (50) comprising:-a cable inner layer (CI) consisting of X = 3 or 4 multi-strands (M1), said multi-strands (M1) comprising K = 2, 3 or 4 strands (T1) wound helically about an axis (B), each strand (T1) being a strand having at least two layers (C1, C3), and-a cable outer layer (CE) consisting of X = 3 or 4 multi-strands (M1), each strand (T1) being a strand having at least two layers (C1, C3), the cable outer layer (CE) is made of Ygt wound around the cable inner layer (CI); the invention relates to a cable (50) comprising a plurality of strands (M2), each strand (M2) comprising L = 2, 3 or 4 strands (T2) helically wound about an axis (A '), each strand (T2) being a strand having at least two layers (C1', C3 '), in which the strands (M1) of the inner layer and the strands (M2) of the outer layer are helically wound about a main axis (A), said cable (50) having a structural elongation As satisfying As > = 1.0%.

Description

Technical Field

[0001] The present invention relates to cords and to tires comprising these cords. Background Art

[0002] Cords of structure (1+6)×(3+8) are known from the prior art (as described in document FR2969181B). These cords comprise 6 strands wound helically around a strand with a lay length of 60 mm. Each strand comprises an inner layer with 3 inner filaments wound helically with a lay length of 7.7 mm and an outer layer with 8 outer filaments wound helically around the inner layer with a lay length of 15.4 mm. The structural elongation of the cord is less than 2% and the breaking force is 19600 N.

[0003] These cords are rigid and have the advantage of relieving the tension on the working plies, but they considerably increase the circumferential stiffness of the structure and, when they are placed in additional reinforcements, lead to an increased sensitivity of the central crown block of the tread to attacks.

[0004] Nowadays, there is a growing need to develop new cords for use in the crown plies, especially those with a laying angle of less than 10°, such as additional reinforcements. The purpose of such reinforcements is to relieve the tension on the working plies and improve the durability properties of the tire, especially the crack resistance. Summary of the invention

[0005] The object of the present invention is a cord having a good compromise between stiffness and flexibility: flexible enough to reduce the stiffness of the crown blocks, but with sufficient breaking force to withstand tensile stress loads.

[0006] To this end, a subject of the invention is a multistrand cord having two layers of multistrand elements, wherein the cord comprises:

[0007] - an inner layer of cords, said inner layer of cords being composed of X=3 or 4 multi-strand elements, said multi-strand elements comprising K=2, 3 or 4 strands wound helically around an axis, each strand having at least two layers, said at least two layers comprising:

[0008] - an inner layer consisting of Q1 inner wires of diameter d1, and

[0009] - an outer layer consisting of Q3 outer metal wires of diameter d3 wound around the inner layer, and

[0010] - an outer layer of cords, said outer layer of cords being composed of Y>1 multi-strand elements wound around an inner layer of cords, each multi-strand element comprising L=2, 3 or 4 strands wound helically around an axis, each strand having at least two layers, said at least two layers comprising:

[0011] - an inner layer consisting of Q1' inner wires of diameter d1', and

[0012] - an outer layer consisting of Q3' outer metal wires of diameter d3' wound around the inner layer,

[0013] The inner layer of multi-strand elements and the outer layer of multi-strand elements are both helically wound around the main axis, and

[0014] The cord has a structural elongation As, satisfying As≥1.0%, and the structural elongation As is determined by applying the 2014 standard ASTM D2969-04 to the cord to obtain a force-elongation curve, and the structural elongation As is equal to the elongation corresponding to the intersection of the tangent to the elastic part of the force-elongation curve at a certain point along its elastic part and the elongation axis of the force-elongation curve, expressed in %.

[0015] Thanks to this multistrand cord construction with two layers of multistrand elements, the cord according to the invention makes it possible to obtain a cord with sufficient structural elongation (providing tensile flexibility) and sufficient metallic quality, while keeping the filaments thin to obtain bending flexibility, improving the compromise between shear in the polymer matrix, flexibility of the crown blocks and strength, and thus improving the compromise between cracking and attack performance.

[0016] The structural elongation As is a parameter well known to those skilled in the art and is determined, for example, by applying the standard ASTM D2969-04 of 2014 to the tested cord to obtain a force-elongation curve. As is derived from the curve obtained and is the elongation corresponding to the intersection between the tangent to the elastic part of the force-elongation curve and the elongation axis of the force-elongation curve, in %. It should be remembered that the force-elongation curve comprises a structural part, an elastic part and a plastic part in the direction of increasing elongation. The structural part corresponds to the structural elongation of the cord resulting from the movement together of the different strands and wires constituting the cord. The elastic part corresponds to the elastic elongation resulting from the construction of the cord (in particular the angles of the layers and the diameter of the wires). The plastic part corresponds to the plastic elongation resulting from the plasticity of the wires (irreversible deformation beyond the elastic limit).

[0017] In the present invention, the cord comprises two layers of multi-strand elements, which means that it comprises an assembly consisting of neither more nor less than a layer of Y>1 multi-strand elements wound around a single layer of multi-strand elements, which means that the assembly has two layers of multi-strand elements, not one layer, not three layers, but only two layers.

[0018] In the present invention, a multi-strand element has one strand layer, meaning that it comprises an assembly consisting of one (no more and no less) strand layer, meaning that the assembly consists of one strand layer, not zero layers, not two layers, but only one layer.

[0019] In one embodiment, the inner multi-strand element of the cord is surrounded by the polymer composition and then by the outer layer.

[0020] Advantageously, each strand has a cylindrical layer.

[0021] Advantageously, each strand of the multi-strand element has two layers, meaning that it comprises an assembly consisting of two (no more, no less) layers of metal wires, meaning that the assembly has two layers of metal wires, not one, not three, but only two. The outer layer of each strand is wound around the inner layer of the strand in contact with the inner layer of the strand.

[0022] Very advantageously, each strand of the inner layer and each strand of the outer layer has a cylindrical layer. It is recalled that such a cylindrical layer is obtained when the different layers of the strand are wound with different lay lengths and / or when the winding direction of the layers is different from one layer to another. The strands with cylindrical layers are very permeable, unlike strands with compact layers, in which the lay lengths of all the layers are the same and the winding direction of all the layers is the same, so that said strands exhibit a much lower permeability.

[0023] Advantageously, each strand of the inner layer and each strand of the outer layer is unsaturated, which means that there is sufficient space between the filaments of the outer layer to allow the elastomeric compound to impregnate each strand.

[0024] Preferably, the strands are not preformed.

[0025] Advantageously, the cord as defined above is bare, meaning that it does not have any polymer composition; in particular, the cord does not have any elastomeric composition.

[0026] Metallic wires are understood to be metal monofilaments whose core is mainly (i.e. more than 50% of its weight) or completely (100% of its weight) made of a metallic material, such as carbon steel. The metallic wires may advantageously comprise a layer of a metallic coating covering the core, the metallic coating being selected from zinc, copper, tin and alloys of these metals, such as brass. Each wire is preferably made of pearlitic or ferritic-pearlitic carbon steel.

[0027] The values ​​of the characteristics of the bare cord described in this application are measured or determined on the cord directly after it has been made, ie before any step of embedding in a polymer matrix, in particular an elastomeric matrix.

[0028] In the present application, any numerical range expressed by the expression "between a and b" represents a numerical range from greater than a to less than b (i.e., excluding the endpoints a and b), and any numerical range expressed by the expression "from a to b" means a numerical range from the endpoint "a" to the endpoint "b", i.e., including the strict endpoints "a" and "b".

[0029] Advantageously, As≥1.5%, and preferably, As≥2.0%.

[0030] Another subject of the invention is a cord extracted from a polymer matrix, wherein said extracted cord comprises:

[0031] - an inner layer of cords, said inner layer of cords being composed of X=3 or 4 multi-strand elements, said multi-strand elements comprising K=2, 3 or 4 strands wound helically around a main axis, each strand having at least two layers, said at least two layers comprising:

[0032] - an inner layer consisting of Q1 inner wires of diameter d1, and

[0033] - an outer layer consisting of Q3 outer metal wires of diameter d3 wound around the inner layer, and

[0034] - an outer layer of cords, said outer layer of cords being composed of Y>1 multi-strand elements wound around an inner layer of cords, each multi-strand element comprising L=2, 3 or 4 strands wound helically around an axis, each strand having at least two layers, said at least two layers comprising:

[0035] - an inner layer consisting of Q1' inner wires of diameter d1', and

[0036] - an outer layer consisting of Q3' outer metal wires of diameter d3' wound around the inner layer,

[0037] The inner layer of multi-strand elements and the outer layer of multi-strand elements are both helically wound around the main axis, and

[0038] The cord has a structural elongation As', satisfying As'≥0.3%, and the structural elongation As' is determined by applying the 2014 standard ASTM D2969-04 to the cord to obtain a force-elongation curve, and the structural elongation As' is equal to the elongation corresponding to the intersection of the tangent to the elastic part of the force-elongation curve at a certain point along its elastic part and the elongation axis of the force-elongation curve, expressed in %.

[0039] Preferably, the polymer matrix is ​​an elastomeric matrix.

[0040] The polymer matrix, preferably an elastomeric matrix, is based on a polymer, preferably an elastomer, composition.

[0041] A polymer matrix is ​​understood to be a matrix comprising at least one polymer. The polymer matrix is ​​therefore based on a polymer composition.

[0042] An elastomeric matrix is ​​understood to mean a matrix containing at least one elastomer. Preferred elastomeric matrices are therefore based on elastomeric compositions.

[0043] The expression "based on" is understood to mean that the composition comprises a compound and / or in situ reaction product of the various components used, some of which are capable of reacting and / or are intended to react at least partially with one another during the various stages of manufacturing the composition; the composition can therefore be in a completely or partially crosslinked state or in a non-crosslinked state.

[0044] A polymer composition is understood to mean that the composition comprises at least one polymer. Preferably, this polymer may be a thermoplastic polymer (such as a polyester or a polyamide), a thermosetting polymer, an elastomer (such as natural rubber), a thermoplastic elastomer or a combination of these polymers.

[0045] An elastomeric composition is understood to mean a composition comprising at least one elastomer and at least one other component. Preferably, the composition comprising at least one elastomer and at least one other component comprises an elastomer, a crosslinking system and a filler. The compositions that can be used for these plies are conventional compositions for surface coatings of filamentary reinforcing elements and comprise 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 optionally a vulcanization accelerator and / or a retarder) and / or various additives. The bonding between the metal wires and the matrix in which they are embedded is achieved, for example, by a metal coating (for example a brass layer).

[0046] The values ​​of the characteristics of the extracted cords described in this application are measured or determined on cords extracted from a polymer matrix, in particular an elastomeric matrix, such as a tire. Thus, for example, on a tire, a strip of material radially located outside the cord to be extracted is removed so that the cord to be extracted can be seen radially flush with the polymer matrix. This removal can be accomplished by stripping using a cutter and a fixture or by planing. Next, the end of the cord to be extracted is uncovered using a knife. The cord is then pulled to extract it from the matrix, applying a relatively shallow angle so as not to plasticize the cord to be extracted. The extracted cord is then carefully cleaned, for example using a knife, so as to separate any polymer matrix residues that are locally bonded to the cord, while taking care not to damage the surface of the metal wire.

[0047] The advantages described below apply both to the cord as defined above and to the extracted cord.

[0048] Preferably, the cord has a cord diameter satisfying that the cord diameter D ranges from 4 mm to 10 mm, preferably from 5 mm to 8 mm.

[0049] By definition, the diameter of a strand is the diameter of the smallest circumscribed circle of the strand.

[0050] Preferably, the diameter of the metal wires independent of each other ranges from 0.15 mm to 0.50 mm, preferably from 0.18 mm to 0.35 mm, more preferably from 0.20 mm to 0.30 mm.

[0051] Preferably, the wires of the same layer of the predetermined strands all have substantially the same diameter. Advantageously, the outer strands all have substantially the same diameter. "Substantially the same diameter" means that the wires or strands have the same diameter within industrial tolerances.

[0052] Advantageously, Y is equal to 6, 7, 8, 9 or 10, preferably, Y=6, 7 or 8, and more preferably Y=6.

[0053] Advantageously, K=2, 3 or 4, preferably, K=3 or 4.

[0054] Advantageously, L=2, 3 or 4, and preferably, L=3 or 4.

[0055] In a first embodiment, each strand of the inner layer has two layers.

[0056] Advantageously, each strand of the outer layer has two layers.

[0057] Advantageously, in this first embodiment, in a preferred variant, each strand of the inner layer and each strand of the outer layer has two layers.

[0058] In a second embodiment, each strand of the inner layer has three layers and comprises:

[0059] an intermediate layer consisting of Q2 intermediate metal wires wound around the inner layer, and

[0060] The outer layer consists of Q3 outer metal wires wound around the middle layer.

[0061] Advantageously, each strand of the outer layer has three layers and comprises:

[0062] an intermediate layer consisting of Q2' intermediate metal wires wound around the inner layer, and

[0063] The outer layer consists of Q3' outer metal wires wound around the middle layer.

[0064] Advantageously, in this second embodiment, in a preferred variant, each strand of the inner layer and each strand of the outer layer has three layers.

[0065] Advantageously, each strand is of the non-in-situ rubberized type.Non-in-situ rubberized means that each strand is constituted by the filaments of individual layers and does not have any polymer composition, in particular any elastomeric composition, before assembling the strands to each other.

[0066] Strands of the inner multi-strand element of the cord according to the invention

[0067] Advantageously, Q1=1, 2, 3 or 4, preferably, Q1=1, 2 or 3, and more preferably, Q1=1 or 3.

[0068] Advantageously, Q3=5, 6, 7, 8, 9 or 10, preferably, Q3=6, 7, 8 or 9, and more preferably, Q3=6 or 9.

[0069] In one embodiment, Q1=1.

[0070] Advantageously, Q3=5, 6 or 7, and preferably, Q3=6.

[0071] In another preferred embodiment, Q1>1, and preferably, Q1=2, 3 or 4.

[0072] Advantageously, Q3=7, 8, 9 or 10, and preferably, Q3=7, 8 or 9.

[0073] In a first variant, Q1=2 and Q3=7 or 8, and preferably, Q1=2, Q3=7.

[0074] In a second variant, Q1=3 and Q3=7, 8 or 9, and preferably Q1=3, Q3=8.

[0075] In a third variant, Q1=4 and Q3=7, 8, 9 or 10, and preferably Q1=4, Q3=9.

[0076] Strands of the outer multi-strand element of the cord according to the invention

[0077] Advantageously, Q1′=1, 2, 3 or 4, preferably, Q1′=1, 2 or 3, and more preferably, Q1′=1 or 3.

[0078] Advantageously, Q3′=5, 6, 7, 8, 9 or 10, preferably, Q3′=6, 7, 8 or 9, and more preferably, Q3′=6 or 9.

[0079] In one embodiment, Q1'=1.

[0080] Advantageously, Q3'=5, 6 or 7, and preferably, Q3'=6.

[0081] In another preferred embodiment, Q1′>1, and preferably, Q1′=2, 3 or 4.

[0082] Advantageously, Q3′=7, 8, 9 or 10, and preferably, Q3′=7, 8 or 9.

[0083] In a first variant, Q1 ′=2 and Q3 ′=7 or 8, and preferably, Q1 ′=2, Q3 ′=7.

[0084] In a second variant, Q1′=3 and Q3′=7, 8 or 9, and preferably, Q1′=3, Q3′=8.

[0085] In a third variant, Q1′=4 and Q3′=7, 8, 9 or 10, and preferably, Q1′=4, Q3′=9.

[0086] Advantageously, Q1=1 and Q3=6, Q1′=1 and Q3′=6.

[0087] Enhanced product according to the invention

[0088] Another subject of the invention is a reinforced product comprising a polymer matrix and at least one cord or extracted cord as defined above.

[0089] Advantageously, the reinforced product comprises one or several cords according to the invention embedded in a polymer matrix and, in the case of several cords, said cords are arranged side by side in a main direction.

[0090] Tire according to the invention

[0091] Another subject of the invention is a tyre comprising at least one extracted cord or reinforcement product as defined above.

[0092] A tire comprising an extracted cord means a tire comprising a cord whose properties measured before extraction from the tire are the properties of the extracted cord, such as the cords described above, before incorporation into the tire.

[0093] Preferably, the tire has a carcass reinforcement anchored in two beads and radially covered by a crown reinforcement, itself covered by a tread, joined to the beads by two sidewalls and comprising at least one cord as defined above.

[0094] In a preferred embodiment, the crown reinforcement comprises a protective reinforcement, a working reinforcement and an additional reinforcement, wherein the additional reinforcement comprises at least one cord as defined above, the additional reinforcement forms an angle with the circumferential direction Z of the tire of at most 10°, preferably in the range of 5° to 10°, and is radially inserted between the working reinforcement and the carcass reinforcement.

[0095] The cords are most particularly intended for industrial vehicles chosen from heavy vehicles such as "heavy load vehicles" - ie metros, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles - agricultural vehicles or construction site vehicles, or other transport or handling vehicles.

[0096] Preferably, the tyre is intended for vehicles of the construction site type.The tyre is therefore of such dimensions that the diameter of the base of the rim on which it is intended to be mounted is greater than or equal to 40 inches in inches.

[0097] The invention also relates to a rubber product comprising the component according to the invention or comprising the impregnated component according to the invention. A rubber product is understood to mean any type of product made of rubber, such as a ball, a non-pneumatic object (such as a non-pneumatic tire casing), a conveyor belt or a crawler track. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] The invention will be better understood by reading the following embodiments given by way of non-limiting example only and with reference to the accompanying drawings, in which:

[0099] - Figure 1 is a cross-sectional view perpendicular to the circumferential direction of the tire according to the invention;

[0100] - Figure 2 for Figure 1 Detail of Area II;

[0101] - Figure 3 is a cross-sectional view of a reinforced product according to the present invention;

[0102] - Figure 4 is a schematic diagram of a cross section perpendicular to the cord axis (assuming that the cord is straight and stationary) of a cord (50) according to a first embodiment of the present invention;

[0103] - Figure 5 is a schematic diagram of a cross section perpendicular to the cord axis (assuming that the cord is straight and stationary) of an extracted cord (50') according to a first embodiment of the invention; and - Figure 6 For Figure 4 A similar diagram of a cord (60) according to a second embodiment of the invention. DETAILED DESCRIPTION

[0104] Embodiments of the tire according to the invention

[0105] Figure 1 and Figure 2 Reference frames X, Y, Z are depicted corresponding to the general axial direction (X), radial direction (Y) and circumferential direction (Z) of the tire, respectively.

[0106] The "median circumferential plane" M of the tyre is the plane perpendicular to the axis of rotation of the tyre and equidistant from the annular reinforcing structures of each bead.

[0107] Figure 1 and Figure 2 A tyre according to the invention is shown, indicated overall by 10 .

[0108] The tyre 10 is intended for heavy vehicles of the construction site type, for example of the "dump truck" type. The tyre 10 therefore has a size of the 53 / 80R63 type.

[0109] The tire 10 has a crown 12, reinforced by a crown reinforcement 14, two sidewalls 16 and two beads 18, each of these beads 18 being reinforced with an annular structure, in this example a bead wire 20. The crown reinforcement 14 is radially covered by a tread 22 and connected to the beads 18 by the sidewalls 16. A carcass reinforcement 24 is anchored in the two beads 18, in this example wound around the two bead wires 20, and comprises a turn-up 26 arranged towards the outside of the tire 20, which is shown here mounted on a wheel rim 28. The carcass reinforcement 24 is radially covered by the crown reinforcement 14.

[0110] The carcass reinforcement 24 comprises at least one carcass ply 30 reinforced by radial carcass cords (not shown). The carcass cords are arranged substantially parallel to one another and extend from one bead 18 to the other, making an angle of between 80° and 90° with the median circumferential plane M (a plane perpendicular to the axis of rotation of the tire, midway between the two beads 18 and passing through the center of the crown reinforcement 14).

[0111] The tire 10 also comprises an airtight ply 32 made of elastomer, generally called “inner liner”, which defines a radially inner surface 34 of the tire 10 and is intended to protect the carcass ply 30 from air diffusion from the interior space of the tire 10 .

[0112] The crown reinforcement 14 includes, radially from the outside to the inside of the tire 10, a protection reinforcement 36, which is radially arranged on the inside of the tread 22; a working reinforcement 38, which is radially arranged on the inside of the protection reinforcement 36; and an accessory reinforcement 40, which is radially arranged on the inside of the working reinforcement 38. Therefore, the protection reinforcement 36 is radially inserted between the tread 22 and the working reinforcement 38. The working reinforcement 38 is radially interposed between the protection reinforcement 36 and the accessory reinforcement 40.

[0113] The protective reinforcement 36 comprises a first protective ply 42 and a second protective ply 44 comprising protective metal cords, the first ply 42 being arranged radially on the inside of the second ply 44. Optionally, the protective metal cords form an angle at least equal to 10°, preferably ranging from 10° to 35°, more preferably from 15° to 30° with the circumferential direction Z of the tire.

[0114] The working reinforcement 38 comprises a first working ply 46 and a second working ply 48 , the first ply 46 being arranged radially on the inside of the second ply 48 .

[0115] The additional reinforcement 40 , also called limiting unit, one of the purposes of which is to partially absorb the mechanical stresses of inflation, comprises at least one cord 50 and forms an angle with the circumferential direction Z of the tire 10 of at most 10°, preferably ranging from 5° to 10°.

[0116] Embodiments of the enhanced product according to the invention

[0117] Figure 3 A reinforced product according to the invention is depicted, indicated overall with 100. The reinforced product 100 comprises at least one cord 50 (in this example a plurality of cords 50) embedded in a polymer matrix 102.

[0118] Figure 3 The polymer matrix 102 and the cord 50 are depicted in a reference system X, Y, Z, wherein direction Y is a radial direction and directions X and Z are axial and circumferential directions. Figure 3 In the embodiment of the invention, the reinforced product 100 comprises a plurality of cords 50 which are arranged side by side in a main direction X, extend parallel to each other within the reinforced product 100 and are embedded together in a polymer matrix 102 .

[0119] Here, the polymer matrix 102 is an elastomeric matrix based on an elastomeric composition.

[0120] Cord according to the first embodiment of the present invention

[0121] Figure 4A cord 50 according to a first embodiment of the invention is depicted.

[0122] Reference Figure 5 , each reinforcing element of the additional reinforcement is formed by an extracted cord 50' as described below, after extraction from the tire 10. The cord 50' is obtained by embedding in a polymer matrix, in this example, in each polymer matrix respectively forming each working ply.

[0123] Both the cord 50 and the extracted cord 50' are made of metal and are of the multi-strand type having two multi-strand cylindrical layers. It will therefore be understood that the cord 50 or 50' consists of two (no more, no less) layers of multi-strand elements.

[0124] At least 50% of the metal wires of the cord, preferably at least 60%, more preferably at least 70% of the metal wires, highly preferably the steel core of each metal wire has a composition according to standard NF EN 10020 of September 2000, with a carbon content C>0.80%, preferably C≥0.82%, and at least 50% of the metal wires of the cord, preferably at least 60%, more preferably at least 70% of the metal wires, highly preferably the steel core of each metal wire has a composition according to standard NF EN 10020 of September 2000, with a carbon content C≤1.20%, preferably C≤1.10%. Here, the steel core of each metal wire has a composition according to standard NF EN 10020 of September 2000, with a carbon content C=0.86%.

[0125] Each wire has a breaking strength, denoted as Rm, satisfying 2500≤Rm≤3100 MPa. The steel of these wires is referred to as SHT ("Super High Tensile") grade. Other wires may be used, such as lower grade wires, such as NT ("Normal Tensile") or HT ("High Tensile") grade wires, and higher grade wires, such as UT ("Ultra Tensile") or MT ("Mega Tensile") grade wires.

[0126] Method for manufacturing a cord according to the invention

[0127] One embodiment of a method for manufacturing the multi-strand cord 50 will now be described.

[0128] Each of the aforementioned internal strands T1 is manufactured according to a known method comprising the following steps, preferably carried out in sequence and continuously:

[0129] - First, a first step is the assembly, by cabling or twisting six external threads F3 around the internal thread F1 of the internal layer C1 in the S direction with a lay pitch p3, so as to form the external layer C3 at a first assembly point;

[0130] - Preferably, a final twist balancing step.

[0131] Each of the aforementioned external strands T2 is manufactured according to a known method comprising the following steps, preferably carried out in sequence and continuously:

[0132] - firstly, a first step of assembly, by cabling or twisting six external threads F3' in the S direction with a lay pitch p3' around the internal thread F1' of the inner layer C1', so as to form the outer layer C3' at a first assembly point;

[0133] - Preferably, a final twist balancing step.

[0134] As is known to those skilled in the art, "twist balance" here means the elimination of the residual torque applied to each filament of the strand in the outer layer (or the elastic recovery of the twist).

[0135] After this final twist balancing step, the manufacture of the strands is complete.Before the subsequent operation of assembling the elementary strands by cabling to obtain a multistrand cord, each strand is wound on one or more take-up drums for storage.

[0136] To manufacture the multistrand cord of the invention, the method consists in cabling together the strands previously obtained using a cabling machine of a size matching that of the assembled strands, as is well known to those skilled in the art.

[0137] In the step of manufacturing the multi-strand element M1 , K=3 internal strands T1 are assembled by cabling in the S direction with a lay pitch P1 , thereby forming the multi-strand element M1 of the inner layer CI at a first assembly point.

[0138] In the step of manufacturing the inner layer CI, X=3 multi-strand elements M1 are assembled by cabling in the Z direction with a lay pitch pi, so that the inner layer CI is formed at a first assembly point.

[0139] In the step of manufacturing the multistrand element M2 of the outer layer CE, the multistrand element M2 of the outer layer CE is formed at a first assembly point by assembling L=3 outer strands T2 with a lay length P2 in the S direction.

[0140] Then, in a subsequent manufacturing step, Y=9 external multifilar elements M2 are assembled by cabling around the inner layer CI with a lay pe in the Z direction, thus forming the assembly of layers CI and CE. Possibly, in a final assembly step, an external winding F is wound around the previously obtained assembly with a lay pf in the S direction.

[0141] The cords 50 are then incorporated by calendering into a composite fabric formed from a known composition based on natural rubber and carbon black as reinforcing filler and commonly used in the manufacture of crown reinforcements for radial tires. In addition to the elastomer and the reinforcing filler (carbon black), this composition essentially contains antioxidants, stearic acid, extender oil, cobalt naphthenate as adhesion promoter and finally a vulcanization system (sulphur, accelerators and ZnO).

[0142] The composite fabrics reinforced by these cords have an elastomeric composition matrix formed by two thin skins of elastomeric composition superimposed on both sides of the cords and each having a thickness ranging between 1 mm and 4 mm. The calendering pitch (the distance at which the cords are laid in the elastomeric composition fabric) ranges from 4 mm to 8 mm.

[0143] These composite fabrics are then used as working plies in the crown reinforcement during a method for manufacturing a tire, the steps of which are known to those skilled in the art.

[0144] Cord according to the second embodiment of the present invention

[0145] Figure 6 A cord 60 according to a second embodiment of the invention is shown.

[0146] Unlike the first embodiment described above, the cord 60 according to the second embodiment satisfies Q1=Q1′=1; Q2=Q2′=5 and Q3=Q3′=10.

[0147] Table 1 below summarizes the characteristics of the various cords 50 , 50 ′ and 60 .

[0148] To determine the breaking force of the cord, extract the cord and then the multi-strand elements M1 and M2 and perform a tensile test on each multi-strand element individually. The breaking forces of all multi-strand elements are added together and then multiplied by a correction factor of 90% to take into account the performance losses during assembly.

[0149] [Table 1]

[0150]

[0151]

[0152] Table 2 below summarizes the characteristics of the prior art cords described in FR2969181B.

[0153] [Table 2]

[0154] Cord PA (1+6) / cord direction (1+6) / S Direction of strands S Q1 3 Q3 8 p1(mm) 7.7 p2(mm) 15.4 Pi(mm) inf Pe(mm) 60 At% 2 As% 0.1 Breaking force (daN) 19 600

[0155] It was found that the cords 50, 50' and 60 according to the invention make it possible to obtain cords with sufficient elongation, sufficient metal mass and sufficient breaking force compared to the cords of the prior art, with the aim of obtaining cords with a good compromise between stiffness and flexibility; flexibility sufficient to reduce the stiffness of the crown blocks, but with a breaking force sufficient to withstand tensile stress loads.

[0156] The present invention is not limited to the embodiments described above.

Claims

1. A multi-strand cord (50) having two multi-strand layers, characterized in that The cord (50) comprises: - an inner layer (CI) of cords, said inner layer (CI) being composed of X=3 or 4 multi-strand elements (M1), said multi-strand elements (M1) comprising K=2, 3 or 4 strands (T1) wound helically around an axis (B), each strand (T1) having at least two layers (C1, C3), said at least two layers (C1, C3) comprising: - an inner layer (C1) consisting of Q1 inner metal wires (F1) of diameter d1, and - an outer layer (C3) consisting of Q3 outer metal wires (F3) of diameter d3 wound around the inner layer (C1), and - a cord outer layer (CE), said cord outer layer (CE) being composed of Y>1 multi-strand elements (M2) wound around a cord inner layer (CI), each multi-strand element (M2) comprising L=2, 3 or 4 strands (T2) wound helically around an axis (A'), each strand (T2) having at least two layers (C1', C3'), said at least two layers (C1', C3') comprising: - an inner layer (C1') consisting of Q1' inner metal wires (F1') of diameter d1', and - an outer layer (C3') consisting of Q3' outer metal wires (F3') of diameter d3' wound around the inner layer (C1'), The inner multi-strand element (M1) and the outer multi-strand element (M2) are both helically wound around the main axis (A), and The cord (50) has a structural elongation As, satisfying As≥1.0%, and the structural elongation As is determined by applying the 2014 standard ASTM D2969-04 to the cord (50) to obtain a force-elongation curve, and the structural elongation As is equal to the elongation corresponding to the intersection of the tangent line of the elastic part of the force-elongation curve at a certain point along its elastic part and the elongation axis of the force-elongation curve, expressed in %.

2. The cord (50) according to the preceding claim, wherein As ≥ 1.5%, and preferably, As ≥ 2.0%.

3. A multistrand cord (50') having two multistrand layers, extracted from a polymer matrix (102), characterized in that The extracted cord (50') comprises: - an inner layer (CI) of cords, said inner layer (CI) being composed of X=3 or 4 multi-strand elements (M1), said multi-strand elements (M1) comprising K=2, 3 or 4 strands (T1) wound helically around a main axis (B), each strand (T1) having at least two layers (C1, C3), said at least two layers (C1, C3) comprising: - an inner layer (C1) consisting of Q1 inner metal wires (F1) of diameter d1, and - an outer layer (C3) consisting of Q3 outer metal wires (F3) of diameter d3 wound around the inner layer (C1), and - a cord outer layer (CE), said cord outer layer (CE) being composed of Y>1 multi-strand elements (M2) wound around a cord inner layer (CI), each multi-strand element (M2) comprising L=2, 3 or 4 strands (T2) wound helically around an axis (A'), each strand (T2) having at least two layers (C1', C3'), said at least two layers (C1', C3') comprising: - an inner layer (C1') consisting of Q1' inner metal wires (F1') of diameter d1', and - an outer layer (C3') consisting of Q3' outer metal wires (F3') of diameter d3' wound around the inner layer (C1'), The inner multi-strand element (M1) and the outer multi-strand element (M2) are both helically wound around the main axis (A), and The cord (50') has a structural elongation As', satisfying As'≥0.3%, and the structural elongation As' is determined by applying the 2014 standard ASTM D2969-04 to the cord (50') to obtain a force-elongation curve, and the structural elongation As' is equal to the elongation corresponding to the intersection of the tangent line of the elastic part of the force-elongation curve at a certain point along its elastic part and the elongation axis of the force-elongation curve, expressed in %.

4. The cord (50; 50') according to any one of the preceding claims, wherein The diameter D of the cords ranges from 4 mm to 10 mm, preferably from 5 mm to 8 mm.

5. The cord (50; 50') according to any one of the preceding claims, wherein The diameter of the metal wires ( F1 ; F3 ; F1 ′; F3 ′) which are independent of each other ranges from 0.15 mm to 0.50 mm, preferably from 0.18 mm to 0.35 mm, more preferably from 0.20 mm to 0.30 mm.

6. The cord (50, 50') according to any one of the preceding claims, wherein Y is equal to 5, 6, 7, 8, 9 or 10, preferably, Y=6, 7 or 8, and more preferably, Y=6.

7. The cord (50, 50') according to any one of the preceding claims, wherein K=2, 3 or 4, preferably, K=3 or 4.

8. The cord (50, 50') according to any one of the preceding claims, wherein L=2, 3 or 4, preferably L=3 or 4.

9. The cord (50; 50') according to any one of claims 1 to 8, wherein Each strand (T1) of the inner layer (CI) has two layers (C1, C3).

10. The cord (50; 50') according to any one of claims 1 to 8, wherein Each strand (T2) of the outer layer (CE) has two layers (C1', C3').

11. The cord (60) according to any one of claims 1 to 8, wherein Each strand (T1) of the inner layer (CI) has three layers (C1, C2, C3) and comprises: an intermediate layer (C2) consisting of Q2 intermediate metal wires (F2) wound around the inner layer (C1), and An outer layer (C3) consisting of Q3 outer metal wires (F3) wound around the middle layer (C2).

12. The cord (60) according to any one of claims 1 to 8, wherein Each strand (T2) of the outer layer (CE) has three layers (C1', C2', C3') and comprises: an intermediate layer (C2') consisting of Q2' intermediate metal wires (F2') wound around the inner layer (C1'), and An outer layer (C3') consisting of Q3' outer metal wires (F3') wound around the middle layer (C2').

13. The cord (50; 50') according to any one of claims 1 to 10, wherein each strand (T1; T2) of the inner and outer layers (CI; CE) has two layers (C1, C3, C1', C3').

14. An enhanced product (100), characterized in that The reinforced product (100) comprises a polymer matrix (Ma) and at least one cord (50'), the properties of which, after extraction, are measured, are the properties of the extracted cord (50') according to any one of claims 3 to 13.

15. A tire (10), characterized in that The tyre (10) comprises at least one cord (50') the properties of which, after extraction, are measured, are the properties of an extracted cord (50') according to any one of claims 3 to 13, or are the properties of a reinforced product according to claim 14.

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