AU2020218926A1

AU2020218926A1 - High energy to breakage multi-strand cable with 1xN structure

Info

Publication number: AU2020218926A1
Application number: AU2020218926A
Authority: AU
Inventors: Romain BARBAT; Marianna CHEVALLEY; Stéphane LAURENT; Rémi PINAUT
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2019-02-05
Filing date: 2020-01-14
Publication date: 2021-07-29
Also published as: FR3092343A1; EP3921466A1; WO2020161404A1; CA3124460A1; JP2022519863A; BR112021015434A2; EP3921466B1; CN113396255B; CN113396255A

Abstract

The extracted cable (60') has a 1xN structure comprising a single layer (61) of N strands (62) wound in a helix. Each strand (62) has two layers of metal wires (F1, F2) with diameters D1 and D2. The extracted cable (60') has a structural elongation As' ≥1.00 % and a modulus of elasticity MC' ≤ 80 GPa. The mechanical resistance of at least 50% of the metal wires (F1, F2) with diameters D1 and D2, measured in accordance with standard ASTM D2969-04, is greater than or equal to 3,500-2,000 x D1 for a metal wire with diameter D1 and greater than or equal to 3,500-2,000 x D2 for a metal wire with diameter D2.

Description

W O 2 02 0/16 140 11||||||||||||||||||||||||||i|||||||||||||||||||| 4 A1 Hi| | | | | | | | Hi| | I| | | | | |I| | li| Fl, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, KM, ML, MR, NE, SN, TD, TG).

Publi6e: - avec rapportde recherche internationale(Art. 21(3))

Multi-strand cord of xN structure exhibiting high energy at break

[001] The invention relates to cords and to a tyre comprising these cords.

[002] A tyre for a construction plant vehicle, having a radial carcass reinforcement comprising a tread, two inextensible beads, two sidewalls connecting the beads to the tread and a crown reinforcement, disposed circumferentially between the carcass reinforcement and the tread, is known from the prior art, in particular from the document W02016/131862. This crown reinforcement comprises a plurality of plies reinforced by reinforcing elements such as metal cords, the cords of one ply being embedded in an elastomer matrix of the ply.

[003] The crown reinforcement comprises a working reinforcement, a protective reinforcement and possibly further reinforcements, for example a hoop reinforcement.

[004] The protective reinforcement comprises one or more protective plies comprising a plurality of protective filamentary reinforcing elements. Each protective filamentary reinforcing element is a cord exhibiting a 1xN structure. The cord comprises a single layer of N=4 strands wound in a helix at a pitch p3=20 mm. Each strand comprises, for the one part, an internal layer of M=3 internal threads wound in a helix at a pitch P1=6.7 mm and an external layer of P=8 external threads wound in a helix around the internal layer at a pitch p2=10 mm. Each of the internal and external threads has a diameter equal to 0.35 mm and a mechanical strength equal to 2765 MPa.

[005] On the one hand, as the tyre passes over obstacles, for example in the form of rocks, these obstacles risk perforating the tyre as far as the crown reinforcement. These perforations allow corrosive agents to enter the crown reinforcement of the tyre and reduce the life thereof.

[006] On the other hand, it has been found that the cords of the protective plies may exhibit breakages resulting from relatively significant deformations and loads applied to the cord, in particular as the tyre passes over obstacles.

[007] An aim of the invention is a cord that makes it possible to reduce, or even eliminate, the number of breakages and the number of perforations.

[008] To this end, a subject of the invention is a cord exhibiting a 1xN structure comprising a single layer of N strands wound in a helix, each strand having two layers of metal threads and comprising: - an internal layer made up of M1 internal metal thread(s) of diameter D1, - an external layer made up of P>1 external metal threads of diameter D2 wound around the internal layer. The cord according to the invention exhibits a structural elongation As determined by applying the standard ASTM D2969-04 of 2014 such that As 3.00%.

The cord according to the invention satisfies MC<5 127, where MC= 200 x cos(a) x [M x (D1 / 2)2 x cos4 (p) + P x (D2 / 2)2 x cos4 (y)] / [M x (D1 / 2)2 + P x (D2 / 2)2], where: - D1 and D2 are expressed in mm, - a is the helix angle of each strand in the cord, - P is the helix angle of each internal metal thread in the internal layer, and - y is the helix angle of each external metal thread in the external layer.

[009] The indicator MC represents the elastic modulus of the cord. In this formula, the factor 200 represents the elastic modulus of steel, which is around 200 GPa. In the cord according to the invention, the mechanical strength of at least 50% of the metal threads of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 for a metal thread of diameter D2.

[010] By virtue of the relatively high structural elongation and of the indicator MC that represents the relatively low elastic modulus of the cord, the cord according to the invention makes it possible to reduce perforations and therefore lengthen the life of the tyre. Specifically, the inventors behind the invention have discovered that a cord less stiff than that of the prior art performs better with respect to obstacles. The inventors have found that it was more effective to hug the obstacle by using a cord with a lower stiffness than to attempt to stiffen and reinforce the cords as far as possible in order to oppose the deformations imposed by obstacles as is taught in a general manner in the prior art. By hugging the obstacles, the load set against the obstacles is reduced, and therefore so is the risk of the tyre being perforated.

[011] By virtue of the relatively high structural elongation, of the indicator MC that represents the relatively low elastic modulus of the cord and of the relatively high mechanical strength of the majority of the metal threads of the cord, the cord according to the invention also makes it possible to reduce the number of breakages. Specifically, the inventors behind the invention have discovered that the determining criterion for reducing cord breakages was not only the force at break, as is widely taught in the prior art, but the energy at break, which is represented in the present application by an indicator equal to the product of the force at break and the elongation at break. Specifically, the cords of the prior art either have a relatively high force at break but a relatively low elongation at break, or a relatively high elongation at break but a relatively low force at break. In both cases, the cords of the prior art break with a relatively low energy. On account of its relatively high structural elongation, the cord according to the invention exhibits an elongation at break that is necessarily relatively high. Synergistically, the relatively low modulus makes it possible to push back the elongation at break on account of a relatively low gradient of the force-elongation curve in the elastic domain. Finally, and above all, the inventors have discovered that the increase in the mechanical strength of the majority of the metal threads made it possible, as demonstrated by the comparative tests below, both to increase the structural elongation, making it possible, as explained below, to push back the elongation at break, and therefore the energy-at-break indicator, and also to increase the force at break, making it possible to increase the energy-at-break indicator.

[012] The structural elongation As, which is a parameter well known to a person skilled in the art, is determined for example by applying the standard ASTM D2969-04 of 2014 to a cord tested so as to obtain a force-elongation curve. As is derived from the curve obtained as the elongation, in %, corresponding to the projection onto the elongation axis of the intersection between the tangent to the structural portion of the force elongation curve and the tangent to the elastic portion of the force-elongation curve. It will be recalled that a force-elongation curve comprises, in the direction of increasing elongations, a structural portion, an elastic portion and a plastic portion. The structural portion corresponds to a structural elongation of the cord that results from the moving together of the different strands and metal threads that make up the cord. The elastic portion corresponds to an elastic elongation that results from the construction of the cord, in particular of the angles of the various layers and of the diameters of the threads. The plastic portion corresponds to the plastic elongation that results from the plasticity (irreversible deformation beyond the elastic limit) of the metal threads. The helix angles are defined by the following formulas: a = arctan (2 x Tr x R3 / p3), in which R3 is the radius of winding of the strands and p3 is the pitch at which the strands are wound. P = arctan (2 x Tr x R1 / p1), in which R1 is the radius of winding of the M internal metal thread(s) and p1 is the pitch at which the M internal metal thread(s) is or are assembled in the cord. The pitch p1 is such that 1/p1 = 1/p1O + 1/p3 where p10 is the pitch of the M internal metal thread(s) in the strand before the strands are assembled to form the cord. When M=1, R1=0 and therefore P=0. y = arctan (2 x Tr x R2 / p2), in which R2 is the radius of winding of the N external metal threads and p2 is the pitch at which the N external metal threads are assembled in the cord. The pitch p2 is such that 1/p2 = 1/p20 + 1/p3 where p20 is the pitch of the M external metal threads in the strand before the strands are assembled to form the cord.

[013] The radius of winding R3 is measured on a transverse cross section perpendicular to the main axis of the cord and corresponds to the distance between the centre of the helix described by each strand and the centre of the cord. Analogously, the radii of winding R1 and R2 are measured on a transverse cross section perpendicular to the main axis of each strand considered individually and correspond to the distance between the centre of the helix described by each internal and external thread and the centre of the strand, respectively.

[014] In the invention, the cord comprises a single layer of N strands, meaning that it comprises an assembly made up of one layer of strands, neither more nor less, meaning that the assembly has one layer of strands, not zero, not two, only one.

[015] Each strand has two layers, meaning that it comprises an assembly made up of two layers of metal threads, neither more nor less, meaning that the assembly has two layers of metal threads, not one, not three, only two. The external layer of each strand is wound around the internal layer of this strand in contact with the internal layer of this strand.

[016] The cord as defined above and according to the invention is bare, meaning it does not have any polymer composition; in particular the cord does not have any elastomer composition.

[017] A metal thread is understood to be a metal monofilament comprising a core made up predominantly (that is to say more than 50% of its weight) or entirely (100% of its weight) of a metal material, for example carbon steel. The metal thread may advantageously comprise a layer of a metal coating covering the core, the metal coating being chosen from zinc, copper, tin and alloys of these metals, for example brass. Each thread is preferably made of pearlitic or ferritic-pearlitic carbon steel.

[018] The values of the features described in the present application for the bare cord are measured on or determined from cords directly after they have been manufactured, that is to say before any step of embedding in a polymer matrix, in particular an elastomer matrix.

[019] In the present application, any range of values denoted by the expression "between a and b" represents the range of values from more than a to less than b (that is to say excluding the end points a and b), whereas any range of values denoted by the expression "from a to b" means the range of values from the end point "a" as far as the end point "b", namely including the strict end points "a" and "b".

[020] In one preferred embodiment, As 3.10%. Thus, the energy-at-break indicator of the cord is increased even further and therefore the risk of breakage is reduced.

[021] Optionally, As5 4.00%, preferably As5 3.75% and more preferably As 5 3.50%. By limiting the structural elongation, it is ensured that the cord can nevertheless absorb sufficient loads for relatively low deformations.

[022] In advantageous embodiments that make it possible to achieve the above- described properties, a ranges from 130 to 39, preferably from 16 to 270 and more preferably from 210 to 27.

[023] In advantageous embodiments that make it possible to achieve the above described properties, P ranges from 60 to 22, preferably from 8 to 15°.

[024] In advantageous embodiments that make it possible to achieve the above described properties, y ranges from 130 to 30, preferably from 160 to 23.

[025] In one preferred embodiment, MC 5 125. By further limiting the modulus indicator MC, the elastic portion is extended even further and therefore the energy-at-break indicator is increased.

[026] Advantageously, MC 100, preferably MC - 110 and more preferably MC 115. With a relatively high modulus indicator MC, it is ensured that the cord can nevertheless absorb sufficient loads for relatively low deformations.

[027] Advantageously, the cord exhibits a force at break Fr such that Fr 8500 N, preferably Fr - 9000 N, more preferably Fr 9350 N and even more preferably Fr 9600 N. The force at break is measured according to the standard ASTM D2969-04.

[028] Advantageously, the cord exhibits an elongation at break Ar such that Ar 6.50%, preferably Ar 6.75% and more preferably Ar - 6.90%. The elongation at break is measured according to the standard ASTM D2969-04.

[029] Very preferably, the cord exhibits an energy-at-break indicator Er equal to the product of the force at break Fr, expressed in N, and the elongation at break Ar, expressed in %, such that Er 60 000 N.%, preferably Er 63 000 N.% and more preferably Er - 64 000 N.%.

[030] Very advantageously, the cord exhibits an energy-at-break indicator Er equal to the product of the force at break Fr, expressed in N, and the elongation at break Ar, expressed in %, and a diameter D expressed in mm such that Er/D 15 000, preferably Er/D 15 800, more preferably Er/D 16 000 and very preferably Er/D 16 500. Thus, the cord exhibits an advantageous compromise between energy at break and bulk, in particular in order to reduce the thickness of the ply in which the cord will be located and therefore the weight of the tyre.

[031] A further subject of the invention is a cord extracted from a polymer matrix, the cord exhibiting a xN structure comprising a single layer of N strands wound in a helix, each strand having two layers of metal threads and comprising: - an internal layer made up of M 1 internal metal thread(s) of diameter D1, - an external layer made up of P>1 external metal threads of diameter D2 wound around the internal layer. The extracted cord according to the invention exhibits a structural elongation As' determined by applying the standard ASTM D2969-04 of 2014 such that As' 1.00%. The extracted cord according to the invention exhibits an elastic modulus MC' s80 GPa. In the extracted cord according to the invention, the mechanical strength of at least 50% of the metal threads of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 for a metal thread of diameter D2.

[032] The extracted cord according to the invention comes from the embedding of a bare cord in the polymer matrix, in contrast to the bare cord described above, which does not exhibit any polymer matrix.

[033] The structural elongation As' of the extracted cord is measured in a similar way to the structural elongation As of the bare cord defined above.

[034] The elastic modulus MC' of the extracted cord is calculated by measuring the gradient of the elastic portion of a force-elongation curve obtained by applying the standard ASTM D2969-04 of 2014 to the extracted cord tested, and then by apportioning this gradient to the metal cross section of the cord, that is to say to the sum of the cross sections of the threads that make up the extracted cord. Alternatively, the metal cross section can be determined by measuring the metal linear density of the extracted cord in accordance with the standard ASTM D2969-04 of 2014 and by dividing this metal linear density by the density of the steel used.

[035] Preferably, the polymer matrix is an elastomer matrix.

[036] The extracted cord according to the invention is obtained by embedding in a polymer matrix a bare cord without polymer matrix as defined above. The polymer matrix, preferably elastomer matrix, is based on a polymer, preferably elastomer, composition.

[037] In an extracted cord according to the invention, the enclosure of the cord that is delimited by the strands and corresponds to the volume delimited by a theoretical circle that is both radially on the inside of each strand and tangent to each strand is filled with the polymer matrix, preferably elastomer matrix.

[038] A polymer matrix is understood to be a matrix comprising at least one polymer. The polymer matrix is thus based on a polymer composition.

[039] An elastomer matrix is understood to be a matrix with elastomeric behaviour resulting from the crosslinking of an elastomer composition. The preferred elastomer matrix is thus based on the elastomer composition.

[040] The expression "based on" should be understood as meaning that the composition comprises the compound and/or the product of the in situ reaction of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, at least partially, during the various phases of manufacture of the composition; the composition thus being able to be in the fully or partially crosslinked state or in the non-crosslinked state.

[041] A polymer composition is understood as meaning that the composition comprises at least one polymer. Preferably, such a polymer may be a thermoplastic, for example a polyester or a polyamide, a thermosetting polymer, an elastomer, for example natural rubber, a thermoplastic elastomer or a combination of these polymers.

[042] An elastomer composition is understood as meaning that the composition comprises 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 used for these plies are conventional compositions for the skim coating 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 vulcanizing system, preferably comprising sulfur, stearic acid and zinc oxide, and optionally a vulcanization accelerant and/or retarder and/or various additives. The adhesion between the metal threads and the matrix in which they are embedded is afforded for example by a metal coating, for example a layer of brass.

[043] The values of the features described in the present application for the extracted cord are measured on or determined from cords extracted from a polymer matrix, in particular an elastomer matrix, for example of a tyre. Thus, for example on a tyre, the strip of material radially on the outside of the cord that is to be extracted is removed in order to be able to see the cord that is to be extracted radially flush with the polymer matrix. This removal can be done by stripping using cutters and grippers, or by planing. Next, the end of the cord that is to be extracted is uncovered using a knife. The cord is then pulled so as to extract it from the matrix, applying a relatively shallow angle in order not to plasticize the cord that is to be extracted. The extracted cords are then carefully cleaned, for example using a knife, so as to detach any remains of polymer matrix locally adhering to the cord, while taking care not to damage the surface of the metal threads.

[044] In one preferred embodiment, As' 1.05% and more preferably As' 1.10%. Thus, the energy-at-break indicator of the cord in the polymer matrix is increased even further and therefore the risk of breakage is reduced.

[045] Optionally, As' 5 1.50% and preferably As' 5 1.40%. By limiting the structural elongation, it is ensured that the cord in the polymer matrix can nevertheless absorb sufficient loads for relatively low deformations.

[046] In one preferred embodiment, MC' 5 77 GPa. By further reducing the modulus indicator MC', the elastic portion is extended even further and therefore the energy-at break indicator is increased.

[047] Advantageously, MC' 60 GPa, preferably MC' 65 GPa and more preferably MC' 68 GPa. With a relatively high modulus indicator MC', it is ensured that the cord in the polymer matrix can nevertheless absorb sufficient loads for relatively low deformations.

[048] Advantageously, the extracted cord exhibits a force at break Fr' such that Fr' 8500 N, preferably Fr' 9000 N. The force at break is measured on the extracted cord according to the standard ASTM D2969-04.

[049] Advantageously, the extracted cord exhibits an elongation at break Ar' such that Ar' 3.70%, preferably Ar' 3.80% and more preferably Ar' e 3.90%. The elongation at break is measured on the extracted cord according to the standard ASTM D2969-04.

[050] Very preferably, the extracted cord exhibits an energy-at-break indicator Er' equal to the product of the force at break Fr' of the extracted cord, expressed in N, and the elongation at break Ar'of the extracted cord, expressed in %, such that Er' 33 000 N.%, preferably Er' 35 000 N.% and more preferably Er' 36 000 N.%.

[051] Very advantageously, the extracted cord exhibits an energy-at-break indicator Er' equal to the product of the force at break Fr' of the extracted cord, expressed in N, and the elongation at break Ar'of the extracted cord, expressed in %, and a diameter D expressed in mm such that Er'/D 8500, preferably Er'/D 8800, more preferably Er'/D 9000 and very preferably Er'/D - 9100. Thus, the extracted cord exhibits an advantageous compromise between energy at break and bulk, in particular in order to reduce the thickness of the ply in which the cord will be located and therefore the weight of the tyre.

[052] The advantageous features described below apply both to the bare cord and to the extracted cord as described above.

[053] Preferably, the mechanical strength of at least 60% of the metal threads, preferably of at least 70% of the metal threads and more preferably of each metal thread of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 for a metal thread of diameter D2.

[054] Advantageously, the mechanical strength of at least 50% of the metal threads, preferably of at least 60% of the metal threads, more preferably of at least 70% of the metal threads and very preferably of each metal thread of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3600 2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3600-2000 x

D2 for a metal thread of diameter D2.

[055] In preferred constructions, N=3 or N=4, and preferably N=4.

[056] In preferred constructions, M=3, 4 or 5, and preferably M=3.

[057] In preferred constructions, P=7, 8, 9, 10 or 11, and preferably P=8.

[058] In preferred constructions, with the M>1 internal threads being wound in a helix at the pitch p1, p1 ranges from 3 to 11 mm, preferably from 5 to 9 mm.

[059] In preferred constructions, with the P external threads being wound in a helix at the pitch p2, p2 ranges from 6 to 14 mm, preferably from 8 to 12 mm.

[060] In preferred constructions, with the strands being wound in a helix at the pitch p3, p3 ranges from 10 to 30 mm, preferably from 15 to 25 mm and more preferably from 15 to 19 mm.

[061] Ina very preferred embodiment, the external layer of each strand is desaturated, preferably completely unsaturated.

[062] By definition, a layer of threads that is desaturated is such that there is enough space left between the threads to allow a polymer composition, for example an elastomer composition, to pass through. Thus, a layer that is desaturated means that the threads in this layer do not touch and that there is enough space between two adjacent threads in the layer to allow a polymer composition, for example an elastomer composition, to pass through the layer. By contrast, a layer of threads that is saturated is such that there is not enough space between the threads in the layer to allow a polymer composition, for example an elastomer composition, to pass through, for example because the threads in the layer touch one another in pairs.

[063] Advantageously, the inter-thread distance of the external layer of each strand is greater than or equal to 5 pm. Preferably, the inter-thread distance of the external layer of each strand is greater than or equal to 15 pm, more preferably greater than or equal to 35 pm, even more preferably greater than or equal to 50 pm.

[064] The fact that the external layer of each strand is desaturated advantageously makes it easier for a polymer composition, for example an elastomer composition, to pass as far as the centre of the strand and therefore to make the strand less sensitive to corrosion.

[065] By definition, a completely unsaturated layer of threads is such that there is sufficient room in this layer to add at least one (P+1)th thread having the same diameter as the P threads of the layer thereto, it thus being possible for a plurality of threads to be in contact, or not in contact, with one another. The fact that the external layer of each strand is completely unsaturated makes it possible to maximize the penetration of a polymer composition, for example an elastomer composition, into each strand and therefore to make each strand even less sensitive to corrosion. Thus, advantageously, the sum S12 of the inter-thread distances of the external layer of each strand is such that S12 > D2. The sum S12 is the sum of the inter-thread distances between each pair of adjacent threads in the layer. The inter-thread distance of a layer is defined, in a section of the cord perpendicular to the main axis of the cord, as being the shortest distance, on average, between two adjacent threads of the layer. Thus, the inter-thread distance is calculated by dividing the sum S12 by the number of spaces between the threads in the layer.

[066] Advantageously, and for tyres that are intended to equip construction plant vehicles, the diameter D1, D2 of each metal thread ranges from 0.25 mm to 0.50 mm, preferably from 0.30 mm to 0.45 mm and more preferably from 0.32 mm to 0.40 mm.

[067] In preferred embodiments, each internal thread has a diameter D1 greater than or equal to the diameter D2 of each external thread. The use of diameters such that D1>D2 makes it possible to promote the penetrability of the polymer composition, for example the elastomer composition, through the external layer. The use of diameters such that D1=D2 makes it possible to limit the number of different threads to be managed in the manufacture of the cord.

[068] Advantageously, the layer of N strands is desaturated, preferably incompletely unsaturated.

[069] By definition, a layer of strands that is desaturated is such that there is enough space left between the strands to allow a polymer composition, preferably an elastomer composition, to pass through. A layer of strands that is desaturated means that the strands do not touch and that there is enough space between two adjacent strands to allow a polymer composition, preferably an elastomer composition, to pass as far as into the enclosure. By contrast, a layer of strands that is saturated is such that there is not enough space between the strands of the layer to allow a polymer composition, preferably an elastomer composition, to pass through, for example because the strands of the layer touch one another in pairs.

[070] Advantageously, the inter-strand distance of the layer of strands, defined, on a cross section of the cord perpendicular to the main axis of the cord, as being the shortest distance, on average, between the circular envelopes in which two adjacent strands are inscribed, is, for a desaturated layer of strands, greater than or equal to 30 pm. Preferably, the mean inter-strand distance between two adjacent strands is greater than or equal to 70 pm, more preferably greater than or equal to 100 pm, even more preferably greater than or equal to 150 pm and very preferably greater than or equal to 200 pm.

[071] An incompletely unsaturated layer of strands is such that there is not enough space in this layer to add at least one (N+1)th strand having the same diameter as the N strands of the layer thereto.

[072] According to the invention, each strand is of the type not rubberized in situ. Not rubberized in situ means that, before the strands are assembled with one another, each strand is made up of the threads of the various layers and does not exhibit any polymer composition, in particular elastomer composition.

[073] Advantageously, each metal thread of the at least 50%, preferably of the at least 60%, more preferably of the at least 70% of the metal threads, and very preferably each metal thread of the cord comprises a steel core having a composition according to the standard NF EN 10020 of September 2000, and a carbon content C > 0.80%, preferably C > 0.82%. Such steel compositions combine non-alloyed steels (points 3.2.1 and 4.1 of the standard NF EN 10020 of September 2000), stainless steels (points 3.2.2 and 4.2 of the standard NF EN 10020 of September 2000) and other alloyed steels (points 3.2.3 and 4.3 of the standard NF EN 10020 of September2000). Arelatively high carbon content makes it possible to achieve the mechanical strength of the metal threads of the cords according to the invention. It would also have been possible to modify the method for manufacturing the metal threads, in particular by work-hardening each metal thread further, in order to increase the mechanical strength of the metal threads. Whereas modifying the method for manufacturing the metal threads involves relatively significant industrial investment, the use of a relatively high carbon content does not require any investment. Moreover, the use of a relatively high carbon content makes it possible to maintain the bending-compression endurance of the metal threads, unlike a method in which, by work-hardening the metal threads further, this bending compression endurance would be appreciably reduced.

[074] Advantageously, C 5 1.10%, preferably C 5 1.00% and more preferably C 5 0.90%. The use of an excessively high carbon content is not only relatively expensive but also causes a drop in the fatigue-corrosion endurance of the metal threads.

[075] Preferably, the bare or extracted cord has a diameter D such that D < 4 mm, preferably such that 3.5 mm 5 D 5 4 mm. The diameter D is measured on the bare or extracted cord according to the standard ASTM D2969-04.

[076] Advantageously, the bare cord or the extracted cord is obtained by a method comprising: - a step of individually assembling each of the N strands, during which, and in chronological order: - when M>1, the M internal metal threads are wound in a helix to form the internal layer, - the P external metal threads are wound in a helix around the internal layer to form the external layer, and - a step of collectively assembling the N strands by twisting, during which the N strands are wound in a helix at a pitch p3.

[077] Advantageously, the step of individually assembling each of the N strands is carried out by twisting.

[078] In this advantageous embodiment, during the individual assembly step, the M internal metal threads are wound in a helix at a pitch p10 ranging from 5 to 15 mm, preferably from 8 to 12 mm.

[079] Still in this advantageous embodiment, during the individual assembly step, the P external metal threads are wound in a helix at a pitch p20 ranging from 12 to 27 mm, preferably from 17 to 23 mm.

[080] In one particularly preferred embodiment, the bare cord or the extracted cord is obtained by a method comprising, after the collective assembly step, a step of aerating the cord, in which: - the N strands are overtwisted so as to pass from the pitch p3 to a temporary overtwisting pitch p3'such that p3'<p3, and - the N strands are untwisted so as to pass from the temporary overtwisting pitch p3'to an intermediate pitch p3" such that p3">p3'.

[081] In certain preferred embodiments, p3">p3.

[082] The aeration step makes it possible, by virtue of an additional twist, to shorten the pitch p3 down to the temporary overtwisting pitch p3', and also implicitly each pitch p1 and p2 down to temporary overtwisting pitches p1' and p2', respectively. The untwisting step makes it possible to reduce the additional twist and to obtain an intermediate pitch p3", and also implicitly to obtain intermediate pitches p1" and p2". The succession and the order of the overtwisting and then untwisting steps makes it possible to plastically deform the metal threads and confer relatively significant aeration on the cord, promoting the penetrability of the cord for example by a polymer composition, in particular an elastomer composition.

[083] Very preferably, the bare cord or the extracted cord is obtained by a method comprising, after the step of aerating the cord, a balancing step in which: - the N strands are untwisted so as to pass from the intermediate pitch p3" to a temporary balancing pitch p3"' such that p3"'>p3 and p3"'>p3', and - the N strands are twisted so as to pass from the temporary balancing pitch p3"' to the pitch p3.

[084] The aeration step generates a residual twisting torque within the cord. The untwisting step makes it possible, by virtue of a reverse twist, to lengthen the intermediate pitch p3" up to the temporary balancing pitch p3"', and also implicitly each intermediate pitch p1" and p2" up to temporary balancing pitches p1"' and p2"', respectively. The twisting step makes it possible to eliminate the reverse twist and to return to the initial pitch p3, and also implicitly to return to the initial pitches p1 and p2. The succession and the order of the untwisting and then twisting steps makes it possible to eliminate the residual twisting torque. Thus, the cord obtained at the end of the balancing step exhibits substantially zero residual twisting torque. The substantially zero residual twisting torque corresponds to the fact that the cord is torsionally balanced so as to be able to be used in the subsequent steps using the cord. The residual twisting torque is expressed in turns per metre, is measured according to the standard ASTM D2969-04 and corresponds to the number of turns that a cord of predetermined length can make about its main axis when it is left free to move.

[085] Advantageously, p3/p3'>p3"'/p3. Thus, the amplitude of the additional twist is greater than the amplitude of the reverse twist so as to allow balancing while having as little negative effect on the aeration of the cord as possible.

[086] Another subject of the invention is a tyre for a construction plant vehicle, comprising at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above.

[087] Yet another subject of the invention is a tyre for a construction plant vehicle, comprising at least one filamentary reinforcing element obtained by embedding a bare cord as defined above in a polymer matrix. As described above, the bare cord, once embedded in the polymer matrix, forms a cord which, once extracted from the tyre, forms an extracted cord according to the invention.

[088] Another subject of the invention is a tyre for a construction plant vehicle, comprising at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and obtained by embedding a bare cord as defined above in a polymer matrix.

[089] In one preferred embodiment, the tyre comprises: - a crown comprising a tread and a crown reinforcement, - two sidewalls, - two beads, each sidewall connecting each bead to the crown, the tyre comprising a carcass reinforcement that is anchored in each of the beads and extends in the sidewalls and in the crown, the crown reinforcement being radially interposed between the carcass reinforcement and the tread, the crown reinforcement comprising the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[090] In one embodiment, the carcass reinforcement comprises at least one carcass ply comprising carcass filamentary reinforcing elements extending from one bead to the other so as to form an angle ranging from 80 to 90 with the circumferential direction of the tyre.

[091] In this embodiment, the crown reinforcement extends preferably, in the circumferential direction of the tyre, around the entire circumference of the tyre.

[092] Advantageously, the crown reinforcement comprises a protective reinforcement arranged radially on the outside of the crown reinforcement. Thus, the crown reinforcement does not comprise any other reinforcement reinforced by filamentary reinforcing elements that is arranged radially on the outside of the protective reinforcement.

[093] Preferably, the protective reinforcement comprises the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[094] More preferably, the protective reinforcement comprises at least one protective ply comprising one or more protective filamentary reinforcing elements that make an angle greater than or equal to 10°, preferably ranging from 10° to 45 and more preferably from 15° to 40°, with the circumferential direction of the tyre, the or each protective filamentary reinforcing element being formed by the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[095] In one preferred embodiment, the protective reinforcement comprises two protective plies, each protective ply comprising one or more protective filamentary reinforcing elements that make an angle greater than or equal to 10, preferably ranging from 100 to 45 and more preferably from 15 to 40, with the circumferential direction of the tyre, the or each protective filamentary reinforcing element being formed by the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[096] Preferably, the orientation of the angle made by the protective filamentary reinforcing elements with the circumferential direction of the tyre in one protective ply is opposite to the orientation of the angle made by the protective filamentary reinforcing elements with the circumferential direction of the tyre in the other protective ply. In other words, the protective filamentary reinforcing elements in one protective ply are crossed with the protective filamentary reinforcing elements in the other protective ply. The orientation of an angle means the direction, clockwise or anticlockwise, in which it is necessary to rotate from a reference straight line, in this case the circumferential direction of the tyre, defining the angle in order to reach the other straight line defining the angle.

[097] In certain preferred embodiments, the crown reinforcement comprises a hoop reinforcement arranged radially on the inside of the protective reinforcement.

[098] Advantageously, the hoop reinforcement comprises the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[099] In one preferred embodiment, the protective reinforcement and the hoop reinforcement each comprise at least one metal filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[0100] Advantageously, the hoop reinforcement comprises at least one hooping ply comprising one or more hooping filamentary reinforcing elements that make an angle less than or equal to 10, preferably less than or equal to 5° and more preferably substantially zero, with the circumferential direction of the tyre, the or each filamentary hooping filamentary reinforcing element being formed by the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix. The use of a cord according to the invention in the hoop reinforcement makes it possible to ensure absorption of the loads associated with the inflation pressure and to limit the radial expansion of the tyre. This absorption and this limitation are, given the relatively flexible nature of the at least one metal filamentary reinforcing element, even more effective when the angle made by the hooping filamentary reinforcing elements with the circumferential direction of the tyre is low.

[0101] In one preferred embodiment, the hoop reinforcement comprises two hooping plies, each hooping ply comprising one or more hooping filamentary reinforcing elements that make an angle less than or equal to 10°, preferably less than or equal to 50 and more preferably substantially zero, with the circumferential direction of the tyre, the or each filamentary hooping filamentary reinforcing element being formed by the at least one filamentary reinforcing element formed, after extraction from the tyre, by an extracted cord as defined above and/or obtained by embedding a bare cord as defined above in a polymer matrix.

[0102] In one embodiment, the two layers are formed by a continuous circumferential ply, the ply being wound over at least two complete circumferential turns, each complete circumferential turn forming a layer.

[0103] Preferably, when the angle made by the hooping filamentary reinforcing elements is substantially non-zero, the orientation of the angle made by the hooping filamentary reinforcing elements with the circumferential direction of the tyre in one hooping ply is opposite to the orientation of the angle made by the hooping filamentary reinforcing elements with the circumferential direction of the tyre in the other hooping ply. In other words, the hooping filamentary reinforcing elements in one hooping ply are crossed with the hooping filamentary reinforcing elements in the other hooping ply.

[0104] In preferred embodiments, the crown reinforcement comprises a working reinforcement arranged radially on the inside of the protective reinforcement.

[0105] Advantageously, the working reinforcement comprises at least one working ply comprising one or more working filamentary reinforcing elements that make an angle less than or equal to 70, preferably less than or equal to 60 and more preferably ranging from 15° to 40°, with the circumferential direction of the tyre.

[0106] In one preferred embodiment, the working reinforcement comprises two working plies, each working ply comprising one or more working filamentary reinforcing elements that make an angle less than or equal to 70°, preferably less than or equal to 60° and more preferably ranging from 15° to 40°, with the circumferential direction of the tyre.

[0107] Preferably, the orientation of the angle made by the working filamentary reinforcing elements with the circumferential direction of the tyre in one working ply is opposite to the orientation of the angle made by the working filamentary reinforcing elements with the circumferential direction of the tyre in the other working ply. In other words, the working filamentary reinforcing elements in one working ply are crossed with the working filamentary reinforcing elements in the other working ply. The orientation of an angle means the direction, clockwise or anticlockwise, in which it is necessary to rotate from a reference straight line, in this case the circumferential direction of the tyre, defining the angle in order to reach the other straight line defining the angle.

[0108] In one embodiment, with the working reinforcement comprising two working plies, the hoop reinforcement is arranged radially between the two working plies.

[0109] In one embodiment, the tyre has a size of the W R U type, where U>35, preferably U49 and more preferably U57. This designation of the size of the tyre is in accordance with the nomenclature of the ETRTO ("European Tyre and Rim Technical Organisation").

[0110] The invention will be understood better from reading the following description, which is given solely by way of non-limiting example and with reference to the drawings, in which: - Figure 1 is a simplified view in cross section of a tyre according to the invention; - Figure 2 is a detail view of the part II of the tyre in Figure 1; - Figure 3 is a schematic view in cross section perpendicular to the axis of the cord (which is assumed to be straight and at rest) of an extracted cord according to the invention; - Figure 4 is a force-elongation curve of the extracted cord in Figure 3; - Figure 5 is a schematic view in cross section perpendicular to the axis of the cord (which is assumed to be straight and at rest) of the cord in Figure 3 in its bare state and according to the invention; - Figure 6 is a force-elongation curve of the bare cord in Figure 5; - Figures 7 and 8 are schematic views of an installation and a method for manufacturing the bare cord and the extracted cord according to the invention.

[0111] A frame of reference X, Y, Z corresponding to the usual axial, radial and circumferential orientations, respectively, of a tyre has been depicted in the figures.

[0112] The median circumferential 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, and passes through the middle of the crown reinforcement.

[0113] Figures 1 and 2 show a tyre for a construction plant-type vehicle, for example of the "dumper" type, denoted by the overall reference 10. Thus, the tyre 10 has a size of the W R U type, for example 40.00 R 57 or 59/80 R 63.

[0114] In a manner known to a person skilled in the art, W: - when it is in the form H/B, denotes the nominal aspect ratio H/B as defined by the ETRTO (H being the height of the section of the tyre and B being the width of the section of the tyre) and, - when it is in the form H.00 or B.00, in which H=B, H and B being as defined above. U represents the diameter, in inches, of the rim seat on which the tyre is intended to be mounted, and R denotes the type of carcass reinforcement of the tyre, in this case radial. U35, preferably U49 and more preferably UW57.

[0115] The tyre 10 comprises a crown 12 comprising a tread 22 and a crown reinforcement 14. The tread 22 is arranged radially on the outside of the crown reinforcement 14. The crown reinforcement 14 extends, in the circumferential direction Z of the tyre 10, around the entire circumference of the tyre 10.

[0116] The tyre 10 also comprises two sidewalls 16 and two beads 18, each of these beads 18 being reinforced with an annular structure, in this case a bead wire 20. Each sidewall 16 connects each bead 18 to the crown 12.

[0117] The tyre 10 also comprises a carcass reinforcement 24 which is anchored in each of the two beads 18, is wound in this case around the two bead wires 20 and comprises a turnup 26 disposed towards the outside of the tyre 20, which is shown here mounted on a wheel rim 28. The carcass reinforcement 24 extends in the sidewalls 16 and in the crown 12. The crown reinforcement 14 is radially interposed between the carcass reinforcement 24 and the tread 22.

[0118] The carcass reinforcement 24 comprises at least one carcass ply 30 that comprises carcass filamentary reinforcing elements 31 and extends from one bead 18 to the other so as to make an angle ranging from 80 to 90 with the circumferential direction Z of the tyre 10.

[0119] The tyre 10 also comprises a sealing ply 32 made up of an elastomer (commonly known as "inner liner") which defines the radially internal face 34 of the tyre 10 and which is intended to protect the carcass ply 30 from the diffusion of air coming from the space inside the tyre 10.

[0120] The crown reinforcement 14 comprises a protective reinforcement 36 arranged radially on the inside of the tread 22, a working reinforcement 38 arranged radially on the inside of the protective reinforcement 36 and a hoop reinforcement 50 arranged radially on the inside of the protective reinforcement 36. The protective reinforcement 36 is thus radially interposed between the tread 22 and the working reinforcement 38. The protective reinforcement 36 is thus likewise arranged radially on the outside of the crown reinforcement 14.

[0121] The protective reinforcement 36 comprises first and second protective plies 42, 44, the first ply 42 being arranged radially on the inside of the second ply 44. Each first and second protective ply 42, 44 respectively comprises first and second protective filamentary reinforcing elements 43, 45 arranged substantially parallel to one another in each first and second protective ply 42, 44. Each first and second protective filamentary reinforcing element 43, 45 makes an angle greater than or equal to 10°, preferably ranging from 10° to 45 and preferentially from 15 to 40, with the circumferential direction Z of the tyre 10. Optionally, the first and second protective filamentary reinforcing elements 43, 45 are crossed from one protective ply to the other. In this instance, each first protective filamentary reinforcing element 43 makes an angle equal to +33° with the circumferential direction Z of the tyre 10 and each second protective filamentary reinforcing element 45 makes an angle equal to -33° with the circumferential direction Z of the tyre 10.

[0122] The working reinforcement 38 comprises first and second working plies 46, 48, the first ply 46 being arranged radially on the inside of the second ply 48. Each first and second working ply 46, 48 respectively comprises first and second working filamentary reinforcing elements 47, 49 arranged substantially parallel to one another in each first and second working ply 46, 48. Each first and second working metal filamentary reinforcing element 47, 49 makes an angle less than or equal to 70, preferably less than or equal to 60 and more preferably ranging from 15° to 40°, with the circumferential direction Z of the tyre 10. Optionally, the first and second working filamentary reinforcing elements 47, 49 are crossed from one working ply to the other. In this instance, each first working metal filamentary reinforcing element 47 makes an angle equal to +19° with the circumferential direction Z of the tyre 10 and each second working filamentary reinforcing element 49 makes an angle equal to -33° with the circumferential direction Z of the tyre 10. Examples of such working reinforcing elements are described in the documents EP0602733 and also EP0383716.

[0123] The hoop reinforcement 50, also referred as the limiting block, comprises first and second hooping plies 52, 54, each first and second hooping ply 52, 54 respectively comprising first and second hooping filamentary reinforcing elements 53, 55 arranged substantially parallel to one another in each first and second hooping ply 52, 54. Each first and second hooping filamentary reinforcing element 53, 55 makes an angle less than or equal to 10°, preferably less than or equal to 5° and more preferably substantially zero, with the circumferential direction Z of the tyre 10. In this instance, each first and second hooping filamentary reinforcing element 53, 55 makes a substantially zero angle with the circumferential direction Z of the tyre 10.

[0124] In the embodiment illustrated, the hoop reinforcement 50 is advantageously arranged radially between the two working plies 46, 48.

[0125] With reference to Figure 3, each protective reinforcing element 43, 45 and each hooping reinforcing element 53, 55 is formed, after extraction from the tyre 10, by an extracted cord 60'as described below. The cord 60'is for its part obtained by embedding a bare cord 60 illustrated in Figure 5 in a polymer matrix, in this instance in an elastomer matrix respectively forming each elastomer matrix of each protective ply 42, 44 and of each hooping layer 52, 54 in which the protective reinforcing elements 43, 45 and the hooping reinforcing elements 53, 55 are respectively embedded.

[0126] The bare cord 60 and the extracted cord 60' exhibit a xN structure comprising a single layer 61 of N strands 62 wound in a helix defining an internal enclosure 64 of the cord. In the cord 60', the internal enclosure 64 is filled with a filling material 66 for filling the internal enclosure 64. The filling material 66 is based on a polymer composition, in this case based on an elastomer composition identical to the composition of the elastomer matrix of each protective ply 42, 44 and of each hooping ply 52, 54 in which each protective reinforcing element 43, 45 and hooping reinforcing element 53, 55, in this case each cord 60, is respectively embedded.

[0127] Each strand 62 has two layers of metal threads and comprises an internal layer C1 made up of M1 internal metal threads F1 of diameter D1 and an external layer C2 made up of P>1 external metal threads F2 of diameter D2 wound around the internal layer C1.

[0128] In this case, the bare cord 60 and the extracted cord 60'have a diameter D such that D 5 4 mm, preferably such that 3.5 mm 5 D 5 4 mm. In this instance, D=3.89 mm.

[0129] Also, N=3 or N= 4 and in this case preferably N=4. In addition, M=3, 4 or 5, and in this case preferably M=3. Moreover, P=7, 8, 9, 10 or 11 and in this case preferably P=8.

[0130] Each diameter D1, D2 of each metal thread F1, F2 ranges from 0.25 mm to 0.50 mm, preferably from 0.30 mm to 0.45 mm and more preferably from 0.32 mm to 0.40 mm. In this instance, D1=D2=0.35 mm. Each metal thread F1, F2 comprises a steel core exhibiting an unalloyed steel composition according to the standard NF EN 10020 of September 2000 and a carbon content C > 0.80%, preferably C 0.82% and such that C 5 1.10%, preferably C 1.00% and more preferably C 0.90%. In this instance, C=0.86%. According to the invention, the mechanical strength Rm of at least 50% of the metal threads F1, F2 of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1, preferably 3600-2000 x D1, and greater than or equal to 3500-2000 x D2, preferably 3600-2000 x D2, respectively, for each metal thread of diameter D1, D2. In this instance, each metal thread F1, F2 exhibits a mechanical strength Rm, measured according to the standard ASTM D2969-04, greater than or equal to 3600-2000 x D1 and greater than or equal to 3600-2000 x D2, respectively, for each metal thread of diameter D1, D2. In this case, the mechanical strength Rm of each thread F1, F2 is equal to 2960 MPa.

[0131] The layer 61 of N strands is desaturated, preferably incompletely unsaturated. The distance between two adjacent strands 62 is equal to 200 pm.

[0132] The external layer C2 of each strand 62 is desaturated, preferably completely unsaturated. In this instance, the distance between two adjacent external threads F2 is equal to 60 pm.

[0133] The M>1 internal metal threads F1 are, in the bare cord 60 and the extracted cord 60', wound in a helix with the pitch p1. The pitch p1 ranges from 3 to 11 mm, preferably from 5 to 9 mm and in this case p1=6.4 mm. The corresponding helix angle P of each internal metal thread F1 in the internal layer C1 ranges from 6 to 22, preferably from 80 to 15° and in this case P=11.2.

[0134] The P external metal threads F2 are, in the bare cord 60 and the extracted cord 60', wound in a helix with the pitch p2. The pitch p2 ranges from 6 to 14 mm, preferably from 8 to 12 mm and in this case p2=9.5 mm. The corresponding helix angle y of each external metal thread F2 in the external layer C2 ranges from 13 to 30°, preferably from 160to 230 and in this case y=20.0°.

[0135] The strands 62 are wound in a helix with the pitch p3. The pitch p3 ranges from 10 to 30 mm, preferably from 15 to 25 mm and more preferably from 15 to 19 mm and in this case p3=18 mm. The helix angle a of each strand 62 in the bare cord 60 and the extracted cord 60' ranges from 13 to 39, preferably from 16 to 27 and more preferably from 21 to 270and in this case a=23.2°.

[0136] The cord 60'exhibits a force at break Fr'such that Fr' 8500 N, preferably Fr'

! 9000 N and in this case Fr'=9133 N. The cord 60' exhibits an elongation at break Ar' such that Ar' 3.70%, preferably Ar' - 3.80% and more preferably Ar' 3.90% and in this case Ar'= 3.96%. The cord 60'exhibits an energy-at-break indicator Er'equal to the product of the force at break Fr', expressed in N, and the elongation at break Ar', expressed in %, such that Er' 33 000 N.%, preferably Er' 35 000 N.% and more preferably Er' 36 000 N.% and in this case Er'=36 137 N.%. The ratio of the energy at-break indicator Er' to the diameter D expressed in mm is such that Er'/D 8500, preferably Er'/D 8800, more preferably Er'/D 9000 and very preferably Er'/D 9100. In this instance, Er'/D=9297.

[0137] According to the invention and as illustrated in Figure 4, the cord 60' has a structural elongation As' greater than or equal to 1.00%, preferably As' 1.05% and more preferablyAs' 1.10%. Moreover, As' 1.50% and preferably As' 1.40%. In this instance, As'=1.20%.

[0138] According to the invention and as illustrated in Figure 4, the cord 60' has an elastic modulus MC' s80 GPa and preferably MC' s77 GPa. Moreover, MC' 60 GPa, preferably MC' -65 GPa and more preferably MC' 68 GPa. In this instance, MC'=74 GPa.

[0139] With reference to Figure 6, the cord 60 exhibits a force at break Fr such that Fr 8500 N, preferably Fr - 9000 N, more preferably Fr 9350 N and even more preferably

Fr - 9600 N and in this case Fr=9835 N. The cord 60 exhibits an elongation at break Ar such that Ar 6.50%, preferably Ar 6.75% and more preferably Ar e 6.90% and in this instance Ar= 6.99%. The cord 60 exhibits an energy-at-break indicator Er equal to the product of the force at break, expressed in N, and the elongation at break, expressed in %, such that Er - 60 000 N.%, preferably Er 63 000 N.% and more preferably Er 64 000 N.% and in this instance Er=68 747 N.%.

[0140] The cord 60 exhibits a ratio of the energy-at-break indicator Er to the diameter D expressed in mm such that Er/D 15 000, preferably Er/D 15 800, more preferably Er/D 16 000 and very preferably Er/D 16 500 and in this instance Er/D=17 673.

[0141] According to the invention, MC 5 127 and preferably MC 5 125. Moreover, MC 100, preferably MC 110 and more preferably MC 115. In this instance, MC=117. 4(a) x [M x (D1 / 2)2x cos 4 (p) The modulus indicator MC is defined by MC= 200 x cos

+ P x (D2 / 2)2 x cos 4(y)] / [M x (D1 / 2)2 + P x (D2 / 2)2] where D1 and D2 are expressed in mm, a is the helix angle of each strand 62 in the cord 60, P is the helix angle of each internal metal thread D1 in the internal layer C1, and y is the helix angle of each external metal thread D2 in the external layer C2.

[0142] According to the invention and as illustrated in Figure 6, the cord 60 has a structural elongation As - 3.00% and preferably As - 3.10%. Moreover, As 5 4.00%, preferably As5 3.75% and more preferably As 5 3.50%. In this instance, As=3.20%.

[0143] Each bare cord 60 and extracted cord 60' is obtained by a method comprising, first of all, a step of individually assembling each of the N strands 62 by twisting, during which, and in chronological order, the M internal metal threads F1 are wound in a helix at a pitch P10 to form the internal layer C1, p10 ranging from 5 to 15 mm and preferably from 8 to 12 mm and in this case p10=10 mm. Next, the P external metal threads F2 are wound in a helix around the internal layer C2 at a pitch p20 to form the external layer C2, the pitch p20 ranging from 12 to 27 mm, preferably from 17 to 23 mm and in this case p20=20 mm. The method also comprises a step of collectively assembling the N strands 62, formed beforehand, by twisting, during which the N strands 62 are wound in a helix at a pitch p3 as described above. During this collective assembly step, the pitch of the internal metal threads F1 and external metal threads F2 passes from p10 and p20 to the pitches p1 and p2, respectively, as described above.

[0144] After the collective assembly step, the method comprises a step of aerating the bare cord 60, in which, first of all, the N strands 62 are overtwisted so as to pass from the pitch p3 to a temporary overtwisting pitch p3' such that p3'<p3, where in this case p3'=10 mm. Next, in the aeration step, the N strands 62 are untwisted so as to pass from the temporary overtwisting pitch p3'to an intermediate pitch p3" such that p3">p3' and such that p3">p3, where in this case p3"=p3=18 mm.

[0145] After the aeration step, the method comprises a balancing step in which, first of all, the N strands are untwisted so as to pass from the intermediate pitch p3" to a temporary balancing pitch p3"'such that p3"'>p3 and p3"'>p3', where in this case p3"'=23 mm. Next, in the balancing step, the N strands are twisted so as to pass from the temporary balancing pitch p3"' to the pitch p3. In this case, advantageously, p3/p3'>p3"'/p3.

[0146] The tyre 10 is for its part obtained by a manufacturing method comprising, in addition to the above-described steps of the method for manufacturing the cord, a step of embedding the cord 60 in the polymer matrix, in this case the elastomer matrix, for example by skim coating, in order to form at least one ply or one layer comprising the cord embedded in the matrix. Next, the method for manufacturing the tyre 10 comprises the steps of assembling the ply or the layer with at least other products in order to form an uncrosslinked green form of tyre. Next, the method for manufacturing the tyre 10 comprises a crosslinking step in which the uncrosslinked green form is crosslinked, in this case by vulcanization.

[0147] Figures 7 and 8 illustrate an installation 68 for manufacturing the bare cord 60 as described above.

[0148] The installation 68 comprises an installation 70 for individually assembling each strand 62, shown in Figure 7, and an installation 72 for collectively assembling the strands 62, shown in Figure 8.

[0149] It will be recalled that there are two possible techniques for assembling metal threads: - either by cabling: in which case the metal threads or strands undergo no twisting about their own axis, because of a synchronous rotation before and after the assembling point; - or by twisting: in which case the metal threads or the strands undergo both a collective twist and an individual twist about their own axis, thereby generating an untwisting torque on each of the metal threads and on the strand or the cord itself.

[0150] The method for manufacturing the bare cord 60 uses twisting and not cabling.

[0151] The installation 70 for individually assembling each strand 62 comprises, from upstream to downstream in the direction in which the strand 62 passes, means 74 for feeding the M internal metal threads F1, means 76 for assembling the M internal metal threads F1 by twisting, means 77 for setting the assembled M internal metal threads in rotation, means 78 forfeeding the P external metal threads F2, means 80 for assembling the P external metal threads F2 around the internal layer C1 by twisting, means 81 for setting the strand 62 in rotation, means 83 for tensioning the strand 62 and means 84 for storing the strand 62.

[0152] The assembly 72 for collectively assembling the strands 62 comprises, from upstream to downstream in the direction in which the bare cord 60 passes, means 86 for feeding the N strands 62, means 88 for assembling the N strands 62 together by twisting, means 90 for setting the bare cord 60 in rotation, means 92 for aerating the bare cord 60, means 94 for balancing the bare cord 60, means 96 for tensioning the bare cord 60 and means 98 for storing the bare cord 60.

[0153] With reference to Figure 7, the means 74 for feeding the M internal metal threads F1 comprise reels 102 for unwinding each internal metal thread Fl. The means 76 for assembling the M internal metal threads F1 comprise a distributor 104 and an assembly guide 106 defining an assembly point P1. The means 77 for setting in rotation comprise two flywheels 107 arranged downstream of the assembly point P1.

[0154] The means 78 for feeding the P external metal threads F2 comprise reels 108 for unwinding each external metal thread F2. The means 80 for assembling the P external metal threads F2 comprise a distributor 110 and an assembly guide 112 defining an assembly point P2. The means 81 for setting in rotation comprise two flywheels 113 arranged downstream of the assembly point P2.

[0155] The means 83 for tensioning the strand 62 comprise one or more winches 118 and the means 84 for storing the strand 62 comprise a reel 120 for winding each strand 62.

[0156] Each strand 62 is in this case assembled by twisting.

[0157] With reference to Figure 8, the means 86 for feeding the N strands 62 comprise reels 122 for unwinding each strand 62. The means 88 for assembling the N strands 62 together comprise a distributor 124 and an assembly guide 126 defining an assembly point P3. The means 90 for setting the bare cord 60 in rotation comprise two flywheels 128 arranged downstream of the assembly point P3. The aeration means 92 comprise a twister 130. The balancing means 94 comprise a twister 132. The means 96 for tensioning the bare cord 60 comprise one or more winches 134 and the means 98 for storing the bare cord 60 comprise a reel 136 for winding the bare cord 60.

[0158] COMPARATIVE TESTS

[0159] A prior art cord TO as disclosed in W02016/131862, six control cords T1 to T6 and two cords 11 and 12 according to the invention were compared below. For each of these cords, certain features thereof were measured, in the bare state and in the state extracted from a tyre. It will be noted that the cord 12 corresponds, in its bare state, to the cord 60 described above and, once extracted from the tyre, to the cord 60'described above.

[0160] Each cord TO, T2, T3, T5 and 11 was manufactured by a method in which an aeration step as described above was not implemented. By contrast, each cord T2, T4, T6 and 12 was manufactured by a method in which an aeration step as described above was implemented.

[0161] Each of the cords was tested in an air permeability test. Such a permeability test is well known to those skilled in the art and makes it possible to determine the longitudinal permeability to air of the cords tested, by measuring the volume of air passing along a test specimen under constant pressure over a given period of time. The principle of such a test, which is well known to those skilled in the art, is to demonstrate the effectiveness of the treatment of a cord to make it impermeable to air; it has been described for example in the standard ASTM D2692-98. Such a test is carried out on as-manufactured and non-aged cords. The raw cords are coated on the outside beforehand with an elastomer composition referred to as coating composition. For this purpose, a series of 10 cords laid parallel (inter-cord distance: 20 mm) is placed between two layers or "skims" (two rectangles measuring 80 x 200 mm) of a diene elastomer composition composition in the raw state, each skim having a thickness of 5 mm; all of this is then immobilized in a mould, with each of the cords being kept under sufficient tension (for example 3 daN) to ensure that it lies straight as it is being placed in the mould, using clamping modules; it is then vulcanized (cured) for around 10 to 12 hours at a temperature of around 120°C and under a pressure of 15 bar (rectangular piston measuring 80 x 200 mm). After that, the entirety is removed from the mould and 10 test specimens of cords thus coated are cut out, for characterizing, in the shape of parallelepipeds measuring 7x7x60 mm. The coating elastomer composition used is a diene elastomer composition conventionally used in tyres, based on natural (peptized) rubber and carbon black N330 (65 phr), also containing the following usual additives: sulfur (7 phr), sulfenamide accelerator (1 phr), ZnO (8 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), cobalt naphthenate (1.5 phr) (phr meaning parts by weight per hundred parts of elastomer); the E10 modulus of the coating elastomer composition is around 10 MPa. The test is carried out on a 6 cm length of cord, which is therefore coated with its surrounding elastomer composition (or coating elastomer composition) in the cured state, in the following way: air is injected into the inlet end of the cord at a pressure of 1 bar and the volume of air at the outlet end is measured using a flow meter (calibrated for example from 0 to 500 cm 3 /min). During the measurement, the sample of cord is immobilized in a compressed airtight seal (for example, a seal made of dense foam or of rubber) so that only the amount of air passing along the cord from one end to the other, along its longitudinal axis, is taken into account by the measurement; the airtightness of the airtight seal itself is checked beforehand using a solid test specimen of elastomer composition, that is to say one without a cord. The higher the longitudinal impermeability of the cord, the lower the mean air flow rate measured (averaged over the 10 test specimens). The cord TO is identified with a relative measurement "=". A cord that is more permeable than the cord TO and is therefore less penetrable is identified with a relative measurement "-" and a cord that is even more permeable than the cord TO and is therefore not very penetrable is identified with a relative measurement "- -". By contrast, a cord that is less permeable than the cord TO and is therefore more penetrable is identified with a relative measurement "+" and a cord that is even less permeable than the cord TO and is therefore very penetrable is identified with a relative measurement "+ +". The result of this test is given in the line entitled "APA". All of the results of the comparative tests are collated in Table 1 below.

Cord TO T1 T2 T3 T4 T5 T6 11 12 N/M/P 4/3/8 4/3/8 4/3/8 4/3/8 4/3/8 4/3/8 4/3/8 4/3/8 4/3/8 D1/D2 0.35 0.35/ 0.35/ 0.35/ 0.35/ 0.35/ 0.35/ 0.35/ 0.35/ (mm) /0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 p10/ 10/20 10/20 10/20 10/20 10/20 10/20 10/20 10/20 10/20 p20 (mm) p1/p2/ 6.7/10/ 6.7/10/ 6.3/9.2 6.7/10/ 6.7/10/ 7/10.7/ 7/10.7/ 6.3/9.2 6.4/9.5 p3 (mm) 20 20 /17 20 20 23 23 /17 /18 al 20.3/ 20.3/ 23.7/ 20.3/ 20.3/ 18.9/ 18.9/ 23.7/ 23.2/ P/ 10.7/ 10.7/ 11.4/ 10.7/ 10.7/ 10.3/ 10.3/ 11.4/ 11.2/ Y( 0 ) 19.1 19.1 20.6 19.1 19.1 17.9 17.9 20.6 20 Aeration No Yes No No Yes No Yes No Yes C (%) 0.80 0.80 0.80 0.86 0.86 0.86 0.86 0.86 0.86 Rm (MPa) 2765 2765 2765 2960 2960 2960 2960 2960 2960 D (mm) 3.83 3.97 3.78 3.95 4.04 4.14 4.09 3.87 3.89 APA = + = + ++ + ++ + ++

Bare cord As(%) 2.54 2.70 2.79 2.92 2.9 2.67 2.63 3.31 3.20 MC 129 129 114 129 129 137 137 114 117 Fr(N) 9538 9432 9185 9927 9726 10158 10032 9241 9835 Ar (%) 6.33 6.99 7.32 6.30 6.30 5.90 5.90 6.95 6.99 Er (N.%) 60376 65930 67234 62540 61 274 59932 59189 64225 68747 Er/D 15764 16607 17787 15849 15174 14466 14486 16578 17673 Extracted cord

As'(%) 0.70 0.80 0.90 0.98 0.97 0.75 0.81 1.21 1.20 MC'(GPa) 88 80 75 81 82 93 93 70 74 Fr'(N) 9165 9092 8703 9350 9298 9735 9674 9108 9133 Ar' (%) 3.26 3.62 3.69 3.70 3.70 3.30 3.30 4.31 3.96 Er'(N.%) 29878 32913 32114 34595 34403 32126 31 924 39255 36167 Er'/D 7801 8290 8496 8767 8520 7754 7813 10133 9297

Table 1

[0162] It will be noted that the use of a relatively short pitch p3 in the cords 11 and 12 makes it possible to increase the As of the cords compared with the control cords. Such an increase makes it possible, as explained above, to increase the elongation at break Ar and therefore the energy-at-break indicator of the cord while allowing absorption of the deformations caused by the obstacles. Moreover, a relatively short pitch p3 makes it possible to obtain a relatively modest modulus and therefore to extend the elastic portion of the force-elongation curve and, as explained above, to increase the elongation at break Ar and therefore the energy-at-break indicator Er of the cord while allowing absorption of the deformations caused by the obstacles.

[0163] It will be noted, on comparing the cords TO and T3, but also the cords T2 and 11, that the use of metal threads having relatively high mechanical strength (2960 MPa) in place of metal threads having lower mechanical strength (2765 MPa) does not, for the bare cords, cause an increase in the energy-at-break indicator that corresponds to the increase in mechanical strength. In the case of the cords T2 and 11, no change in this energy-at-break indicator is even observed. The inventors explain this by the fact that the metal threads and the strands, within the bare cable, are in contact with one another and that, for a given method for manufacturing the metal threads, the higher the mechanical strength, the more the metal threads are sensitive to the contact loads, thereby reducing the elongation at break Ar and/or the force at break Fr of the cord in spite of the increase in mechanical strength of each metal thread. Nevertheless, once the cord has been filled with the polymer composition, the filling material, in this case the polymer matrix, prevents contact between the metal threads and the strands, making it possible, on account of the use of metal threads having relatively high mechanical strength (2960 MPa), to increase the energy-at-break indicator Er' of the cord through an increase in the elongation at break Ar'and/or in the force at break Fr'.

[0164] Lastly, it will be noted that the implementation of a method comprising an aeration step makes it possible, all things being equal, to significantly improve the penetrability of the cord with a polymer composition, in this case with an elastomer composition.

[0165] The invention is not limited to the above-described embodiments.

[0166] Specifically, a cord could also be used in which at least 50%, preferably at least 60% and more preferably at least 70% has a carbon content C such that C>0.80%, preferably C0.82% and such that C51.10%, preferably C51.00% and more preferably C50.90%, without departing from the scope of the invention.

[0167] Similarly, a cord could be used in which the mechanical strength of at least 50%, preferably of at least 60%, more preferably of at least 70% of the metal threads of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 and preferably greater than or equal to 3600-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 and preferably greater than or equal to 3600-2000 x D2 for a metal thread of diameter D2, without departing from the scope of the invention.

[0168] This is because it is enough for a sufficient number of metal threads of the assembly to have sufficiently high mechanical strength to make it possible to achieve the desired properties, in particular the energy-at-break properties.

Claims

1. Cord (60) exhibiting a 1xN structure comprising a single layer (61) of N strands (62) wound in a helix, each strand (62) having two layers of metal threads (Fl, F2) and comprising: - an internal layer (Cl) made up ofM1 internal metal thread(s) (Fl) of diameter D1, - an external layer (C2) made up of P>1 external metal threads (F2) of diameter D2 wound around the internal layer (Cl), characterized in that - the cord (60) exhibits a structural elongation As determined by applying the standard ASTM D2969-04 of 2014 such that As 3.00%, - the cord (60) satisfies MC 5 127, where MC= 200 x cos4 (a) x [M x (D1 / 2)2 x

cos 4 (p) + P x (D2 / 2)2 x cos4(y)] / [M x (D1 / 2)2 + P x (D2 / 2)2], where: - D1 and D2 are expressed in mm, - a is the helix angle of each strand (62) in the cord (60), - P is the helix angle of each internal metal thread (Fl) in the internal layer (Cl), and - y is the helix angle of each external metal thread (F2) in the external layer (C2), - the mechanical strength of at least 50% of the metal threads (Fl, F2) of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 for a metal thread of diameter D2.

2. Cord (60) according to the preceding claim, which exhibits a force at break Fr such that Fr 8500 N, preferably Fr 9000 N, more preferably Fr 9350 N and even more preferably Fr 9600 N.

3. Cord (60) according to either one of the preceding claims, which exhibits an elongation at break Ar such that Ar 6.50%, preferably Ar 6.75% and more preferably Ar 6.90%.

4. Cord (60) according to any one of the preceding claims, which exhibits an energy-at-break indicator Er equal to the product of the force at break of the cord, expressed in N, and the elongation at break of the cord, expressed in %, such that Er 60 000 N.%, preferably Er 63 000 N.% and more preferably Er 64 000 N.%.

5. Cord (60) according to any one of the preceding claims, which exhibits: - an energy-at-break indicator Er equal to the product of the force at break of the cord, expressed in N, and the elongation at break of the cord, expressed in %, and

- a diameter D expressed in mm, such that Er/D - 15 000, preferably Er/D 15 800, more preferably Er/D 16 000 and very preferably Er/D 16 500.

6. Cord (60') extracted from a polymer matrix, the extracted cord (60') exhibiting a 1xN structure comprising a single layer (61) of N strands (62) wound in a helix, each strand (62) having two layers of metal threads (Fl, F2) and comprising: - an internal layer (Cl) made up ofM1 internal metal thread(s) (Fl) of diameter D1, - an external layer (C2) made up of P>1 external metal threads (F2) of diameter D2 wound around the internal layer (Cl), characterized in that - the extracted cord (60') exhibits a structural elongation As' determined by applying the standard ASTM D2969-04 of 2014 such that As' 1.00%, - the extracted cord (60') exhibits an elastic modulus MC' s80 GPa, - the mechanical strength of at least 50% of the metal threads (Fl, F2) of diameter D1 and D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3500-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3500-2000 x D2 for a metal thread of diameter D2.

7. Extracted cord (60') according to Claim 6, which exhibits a force at break Fr' such that Fr' 8500 N, preferably Fr' 9000 N.

8. Extracted cord (60') according to Claim 6 or 7, which exhibits an elongation at break Ar'such thatAr' 3.70%, preferablyAr' 3.80% and more preferablyAr' 3.90%.

9. Extracted cord (60') according to any one of Claims 6 to 8, which exhibits an energy-at-break indicator Er' equal to the product of the force at break of the extracted cord, expressed in N, and the elongation at break of the extracted cord, expressed in %, such that Er' 33 000 N.%, preferably Er' 35 000 N.% and more preferably Er' 36 000 N.%.

10. Extracted cord (60') according to any one of Claims 6 to 9, which exhibits: - an energy-at-break indicator Er' equal to the product of the force at break of the extracted cord, expressed in N, and the elongation at break of the extracted cord, expressed in %, and - a diameter D expressed in mm, such that Er'/D 8500, preferably Er'/D 8800, more preferably Er'/D 9000 and very preferably Er'/D 9100.

11. Cord (60, 60') according to any one of the preceding claims, wherein the mechanical strength of at least 50% of the metal threads (Fl, F2) of diameter D1 and

D2, measured according to the standard ASTM D2969-04, is greater than or equal to 3600-2000 x D1 for a metal thread of diameter D1 and greater than or equal to 3600 2000 x D2 for a metal thread of diameter D2.

12. Cord (60, 60') according to any one of the preceding claims, which is obtained by a method comprising: - a step of individually assembling each of the N strands (62), during which, and in chronological order: - when M>1, the M internal metal threads (Fl) are wound in a helix to form the internal layer (Cl), - the P external metal threads (F2) are wound in a helix around the internal layer (C2) to form the external layer (C2), and - a step of collectively assembling the N strands (62) by twisting, during which the N strands (62) are wound in a helix at a pitch p3.

13. Cord (60, 60') according to the preceding claim, which is obtained by a method comprising, after the collective assembly step, a step of aerating the cord, in which: - the N strands (62) are overtwisted so as to pass from the pitch p3 to a temporary overtwisting pitch p3'such that p3'<p3, and - the N strands (62) are untwisted so as to pass from the temporary overtwisting pitch p3' to an intermediate pitch p3" such that p3">p3'.

14. Cord (60, 60') according to the preceding claim, which is obtained by a method comprising, after the step of aerating the cord, a balancing step in which: - the N strands (62) are untwisted so as to pass from the intermediate pitch p3" to a temporary balancing pitch p3"' such that p3"'>p3 and p3"'>p3', and - the N strands (62) are twisted so as to pass from the temporary balancing pitch p3"' to the pitch p3.

15. Tyre (10) for a construction plant vehicle, characterized in that it comprises at least one filamentary reinforcing element (43, 45, 53, 55): - formed, after extraction from the tyre (10), by an extracted cord (60') according to any one of Claims 6 to 14, and/or - obtained by embedding a cord (60) according to any one of Claims 1 to 5 or according to any one of Claims 11 to 14 in a polymer matrix.