Two-ply multi-strand cord with inner sheath layer for improved permeability

Abstract

The present invention relates to a two-ply multi-strand cord (50) comprising an inner layer of cords (CI) composed of K≧1 inner strands (TI) and an outer layer of cords (CE) composed of L>1 outer strands (TE) wound around the inner layer of cords (CI) with a helix radius R2. The middle and outer layers (C2, C2', C3, C3') of each inner and outer strand (TI, TE) are desaturated. The cord (50) is obtained by a method comprising the steps of producing a sheath inner layer (CIG), the inner layer (CI) being surrounded by an elastomeric composition having a thickness G and then by an outer layer (CE), such that R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer (CET) that would be obtained when the inner layer (CI) is in direct contact with the theoretical outer layer (CET), and a step (400) of approximating the outer layer (CE) of the cord to a circle circumscribed by the inner layer (CI) of the cord so that the ratio R2 / Rt is in the range of 1.00 to 1.10.

Description

[Technical Field]

[0001] The present invention relates to a multi-strand cord that can be used inter alia to reinforce tires, especially tires for large industrial vehicles. [Background technology]

[0002] A tire with a radial carcass reinforcement comprises a tread, two inextensible beads, two sidewalls connecting the beads to the tread, and a belt or crown reinforcement circumferentially disposed between the carcass reinforcement and the tread, said crown reinforcement comprising a number of plies made of an elastomeric composition potentially reinforced with reinforcing elements such as cords or filaments of the metallic or textile type.

[0003] The crown reinforcement generally comprises at least two superimposed crown plies, sometimes called working plies or cross plies, whose generally metallic reinforcing elements are arranged substantially parallel to one another within the plies but cross from one ply to the other, i.e. inclined symmetrically or asymmetrically by an angle generally comprised between 10° and 45° relative to the median circumferential plane. The working plies generally comprise reinforcing elements that exhibit very low elongation so as to perform their function of guiding the tire.

[0004] The crown reinforcement may also comprise various other auxiliary plies or layers of elastomeric composition, possibly with a width that varies and which may or may not contain reinforcing elements. Mention may be made, by way of example, of what is known as a protective ply, which serves to protect the remaining part of the belt from external attacks or perforations, or what is known as a hooping ply (known as a "zero degree" ply), which contains reinforcing elements oriented substantially in the circumferential direction, whether they are radially outer or inner relative to the working ply. The protective plies generally comprise reinforcing elements that exhibit a high degree of elongation, so that they deform under the influence of stresses applied by an indenter, for example a rock.

[0005] A working ply reinforcing element comprising a two-layer multistrand metal cord of structure 189.23 is known from the prior art. This cord comprises an inner layer of cords made of an inner strand and an outer layer of cords made of six outer strands wound helically around the inner layer of cords. Similarly, patent application WO2019243691 discloses a two-layer multistrand metal cord of structure 171.26 comprising an inner layer of cords made of an inner strand and an outer layer of cords made of six outer strands wound helically around the inner layer of cords.

[0006] Each of the inner and outer strands comprises an inner layer of strands made of 3 inner threads, a middle layer of strands made of 9 threads, and an outer layer of strands made of 15 outer threads, each thread having a diameter equal to 0.23 mm.

[0007] Tyres for large industrial vehicles, especially those of construction plants, are subject to many attacks. In particular, tyres of this type are usually driven on uneven road surfaces, which sometimes result in perforations of the tread. These perforations allow the ingress of corrosive agents, such as air and water, which oxidize the metal reinforcing elements of the crown reinforcement, especially of the crown ply, and thus significantly reduce the lifespan of the tyre.

[0008] A solution to extending the life of a tire is to increase the strength of the cord at break. Typically, the strength at break is increased by increasing the diameter of the threads that make up the cord and / or by increasing the number of threads and / or the individual strength of each thread. However, increasing the thread diameter even further, for example beyond the required 0.45 mm as in patent application WO2016051669, leads to a decrease in the flexibility of the cord, which is undesirable. Increasing the number of threads usually leads to a decrease in the ability of the elastomer composition to penetrate the strand. Finally, increasing the individual strength of each thread requires a significant investment in the equipment used to manufacture the thread.

[0009] Another solution to extending tire life is to combat the spread of these corrosive agents.

[0010] That is, it can be provided that during the manufacture of the cord, each metal thread is covered with an elastomeric composition. During this process, the elastomeric composition present penetrates the capillaries present between each layer of each strand, thus preventing the spread of corrosive agents. Such cords, generally called in-situ rubberized cords, are known from the prior art.

[0011] It is also possible to increase the distance between the threads on the middle and outer layers of the inner and / or outer strands to encourage the filling of the capillaries with the elastomeric composition of the ply during tire curing. This can be achieved by removing one or more threads from the layer or by using threads of decreasing diameter on the layer of strands. Reducing the number of threads leads to a decrease in the breaking strength of the cord, which is undesirable.

[0012] Finally, it is possible to increase the interstrand distance between the outer strands to allow the elastomeric composition better access to the inner strands. This can be achieved by using inner strands with a larger diameter than the outer strands. This solution can lead to the need to manage multiple different thread diameters during cord manufacturing or to different configurations between one or more of the inner and outer strands, which is undesirable. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2019 / 243691 [Patent Document 2] International Publication No. 2016 / 051669 [Patent Document 3] French Patent No. 2419181 [Patent Document 4] French Patent No. 2419182 Summary of the Invention [Problem to be solved by the invention]

[0014] The object of the present invention is a cord which exhibits improved permeability of its outer strands and better accessibility to the inner strands by the elastomeric composition compared to cord 189.23, so as to make it possible to reduce the penetration and spread of corrosive agents into and along the cord, without, in doing so, compromising the strength of the cord at break. [Means for solving the problem]

[0015] Code according to the present invention

[0016] To this end, one subject of the present invention is an inner layer made of internal metal threads Q=2, 3 or 4; an intermediate layer made of M intermediate metal threads of diameter d2 wound on the inner layer; an outer layer made of N outer metal threads of diameter d3 wound on an intermediate layer; an outer layer of cord made of L>1 outer strands wound on an inner layer of cord, the outer strands having a helix radius R2, each outer strand being a three-ply strand; and - an inner layer made of internal metal threads with Q'=2, 3 or 4, an intermediate layer made of M' intermediate metal threads of diameter d2' wound on the inner layer, and an outer layer made of N' outer metal threads of diameter d3' wound on an intermediate layer, the outer layer of the cord comprising: A two-layer multi-strand cord comprising: the intermediate layer of the or each internal strand is desaturated so that the sum SI2 of the inter-thread distances I2 of the intermediate layer of the or each internal strand is greater than or equal to the diameter d2; the outer layer of the or each inner strand is desaturated so that the sum SI3 of the inter-thread distances I3 of the outer layer of the or each inner strand is greater than or equal to the diameter d3; the intermediate layer of the or each outer strand is desaturated so that the sum SI2' of the inter-thread distances I2' of the intermediate layer of the or each outer strand (TE) is greater than or equal to the diameter d2'; the outer layer of each outer strand is desaturated so that the sum SI3' of the inter-thread distances I3' of the outer layer of each outer strand is greater than or equal to the diameter d3'; -The code is - manufacturing a sheath inner layer, the inner layer being surrounded by an elastomer composition having a thickness G, which is then surrounded by an outer layer, the thickness G of the elastomer composition being such that the ratio R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer that would be obtained when the inner layer is in direct contact with the theoretical outer layer; - bringing the outer layer of the cord closer to the circle circumscribing the inner layer of the cord (CI) so that the ratio R2 / Rt is in the range of 1.00 to 1.10; The method is obtained by the method comprising:

[0017] A range of values ​​indicated by the expression "between a and b" denotes a range of values ​​extending from greater than a to less than b (i.e., excluding the endpoints a and b), whereas a range of values ​​indicated by the expression "from a to b" means a range of values ​​extending from the endpoint "a" to the endpoint "b", i.e., including the exact endpoints "a" and "b".

[0018] By definition, the helix radius R2 of the outer layer of the cord is the radius of a theoretical circle that passes through the centers of the outer strands of the outer layer in a plane perpendicular to the axis of the cord.

[0019] By definition, the diameter of a strand is the diameter of the smallest circle that the strand can be inscribed in.

[0020] By definition, a desaturated layer of threads is one in which there is sufficient space between the metal threads to allow the passage of the non-crosslinked elastomeric composition. According to the present invention, the outer layer of each strand is desaturated, meaning that the metal threads of the outer layer do not touch, and there is sufficient space between two adjacent outer metal threads to allow the passage of the elastomeric composition, i.e., the sum of the inter-thread distances is equal to or greater than the diameter of the thread. The inter-thread distance of a layer is defined as the shortest distance that, on average, separates two adjacent threads of the layer in a cross section of the cord perpendicular to the cord's major axis. Therefore, the inter-thread distance is calculated by dividing the sum of the inter-thread distances by the number of thread gaps in the layer. In other words, a layer may be desaturated if the inter-thread distance is 5 μm or greater.

[0021] Preferably, the inter-thread distance I2 of the middle layer of the or each inner strand is 15 μm or more, more preferably 35 μm or more, more preferably 50 μm or more, and most preferably 60 μm or more.

[0022] Preferably, the inter-thread distance I2' of the middle layer of each outer strand is 15 μm or more, more preferably 35 μm or more, more preferably 50 μm or more, and most preferably 60 μm or more.

[0023] Preferably, the inter-thread distance I3 of the outer layer of the or each inner strand is 15 μm or more, more preferably 35 μm or more, more preferably 50 μm or more, and most preferably 60 μm or more.

[0024] Preferably, the inter-thread distance I3' of the outer layer of each outer strand is 15 μm or more, more preferably 35 μm or more, more preferably 50 μm or more, and most preferably 60 μm or more.

[0025] Preferably, the inter-thread distance in the outer layer of each strand is 100 μm or less.

[0026] In contrast, a saturated layer of threads is such that there is not enough space between the metal threads to allow the elastomer composition to pass through, i.e., the sum of the inter-thread distances is strictly less than the thread diameter, in other words, the saturated layer of threads can be such that the inter-thread distance is less than 5 μm.

[0027] In the present invention, the cord has two layers of strands, which means that it comprises an assembly made of two layers of strands, not more, not less, and that the assembly has only two layers of strands, not one, not three.

[0028] Direct contact with the theoretical outer layer means that there is no sheath between the inner layer and the theoretical outer layer.

[0029] By elastomeric or elastomeric composition is meant that the composition comprises at least one elastomer or one rubber (the two terms are synonymous) and at least one other component.

[0030] The inner layer of cord is surrounded by an elastomeric composition of thickness G, which is in turn surrounded by an outer layer.

[0031] The cord according to the present invention offers improved permeability compared to cord 189.23, which is not permeable because there is no elastomeric composition between the inner and outer layers. The inventors behind the present invention hypothesize that this initial ratio R2 / Rt in the range of 1.02 to 1.25 allows for a sufficient thickness of elastomeric composition to penetrate into the inner strands and fill the gaps during tire curing. This is possible due to the desaturation of the middle and outer layers of the inner and outer strands, which allows the elastomeric composition to penetrate between the outer strands on the one hand and between the outer and inner strands on the other hand, thus driving the elastomeric composition from the sheath into the inner strands up to the central capillary. Therefore, with the help of this final step that allows the outer strands to approach the inner layer, the cord diameter can be reduced and at the same time the cord can be very well permeated.

[0032] Advantageously, the or each inner strand has a cylindrical layer.

[0033] Advantageously, the or each outer strand comprises a cylindrical layer.

[0034] Very advantageously, the or each inner strand and each outer strand has a cylindrical layer. It will be recalled that such a cylindrical layer is obtained when the various layers of the strand are wound with different pitches and / or when the winding direction of these layers differs from layer to layer. A strand with a cylindrical layer has a very high permeability, unlike a strand with dense layers in which all layers have the same pitch and all layers have the same winding direction, which shows a much lower permeability.

[0035] As is known, it will be recalled that the pitch of a strand denotes the length of this strand measured parallel to the axis of the cord, after which a strand with this pitch makes one complete revolution around the said axis of the cord.Similarly, the pitch of a thread denotes the length of this thread measured parallel to the axis of the strand in which it is located, after which a thread with this pitch makes one complete revolution around the said axis of the strand.

[0036] The winding direction of a layer of strands or layers of threads is the direction that the strands or threads make with respect to the axis of the cord or strand. Winding direction is commonly designated by the letters Z or S.

[0037] The pitch, winding direction, and diameter for threads and strands are determined in accordance with ASTM standard D2969-04(2014).

[0038] Preferably, the strands are not subjected to preforming.

[0039] Advantageously, the cord is made of metal. The term "metallic cord" is understood to mean, by definition, a cord formed by threads that are mainly (i.e., more than 50% of these threads) or completely (100% of the threads) composed of metallic material. Such a metallic cord is preferably implemented as a steel cord, more preferably a cord that can be made of pearlitic (or ferritic-pearlitic) carbon steel, hereinafter referred to as "carbon steel", or a cord that can be made of stainless steel (by definition, stainless steel comprises at least 11% chromium and at least 50% iron). However, it is of course also possible to use other steels or other alloys.

[0040] When carbon steel is used advantageously, its carbon content (% by weight of steel) is preferably between 0.05% and 1.2%, in particular between 0.4% and 1.1%, these contents representing a good compromise between the mechanical properties required for the tire and the feasibility of threading.

[0041] The metal or steel used, whether it is in particular carbon steel or stainless steel, can itself be coated with a metal layer that improves, for example, the processability properties of the metal cord and / or its components, or the use properties of the cord and / or the tire itself, such as adhesion, corrosion resistance or ageing resistance. According to a preferred embodiment, the steel used is covered with a layer of brass (Zn-Cu alloy) or zinc.

[0042] Preferably, the threads in the same layer of a given (inner or outer) strand all have substantially the same diameter. Advantageously, the outer strands all have substantially the same diameter. By "substantially the same diameter" it is meant that the threads or strands have the same diameter within industrial tolerances.

[0043] Advantageously, the outer strand is wound helically around the inner strand with a pitch lying in the range 40 mm to 100 mm, preferably in the range 50 mm to 90 mm.

[0044] In a first embodiment of the invention, the outer layer of the cord is saturated so that the inter-strand distance E of the outer strands, defined as the shortest distance separating on average the circular envelopes inscribed by two adjacent outer strands on a cross section of the cord perpendicular to the main axis of the cord, is strictly less than 20 μm.

[0045] By definition, a saturated layer of the cord is such that the interstrand distance with respect to the outer strands is strictly less than 20 μm. The interstrand distance of the outer layer of outer strands is defined as the shortest distance that separates, on average, the circular envelopes inscribed by two adjacent outer strands on a cross section of the cord perpendicular to the main axis of the cord. This construction of the cord therefore makes it possible to guarantee good structural stability of the outer layer, and the saturation of the outer layer ensures that the outer layer comprises a relatively large number of outer strands and therefore exhibits a relatively high breaking force.

[0046] In contrast, the desaturated layer of the cord is such that the interstrand distance E for the outer strands is greater than or equal to 20 μm.

[0047] In a second embodiment according to the invention, L is less than or equal to the maximum number Lmax of outer strands that can be laid on a theoretical outer layer having a helical radius Rt, and L is such that the outer layer is incompletely unsaturated.

[0048] By definition, an incompletely undersaturated layer is such that there is not enough space in this layer to add at least one (P+1)th strand having the same diameter as the P strands of this layer. In this particular example, there is not enough space in the outer layer to add at least one (L+1)th outer strand having the same diameter as the L outer strands of the outer layer. This structure of the cord therefore makes it possible to guarantee good structural stability of the outer layer, and the incomplete undersaturation of the outer layer makes it possible to ensure that the outer layer has a relatively large number of outer strands and therefore exhibits a relatively high force at break.

[0049] A fully undersaturated layer, as opposed to a partially undersaturated layer, provides sufficient space within the layer to add at least one (P+1)th strand having the same diameter as the P strands in the layer, and thus the strands may or may not be touching one another. In this particular example, there is sufficient space in the outer layer to add at least one (L+1)th outer strand having the same diameter as the L outer strands in the outer layer.

[0050] Preferably, L is equal to the maximum number Lmax of outer strands that can be laid on a theoretical outer layer having a helix radius Rt, L being such that the outer layer is incompletely unsaturated. The outer layer comprises many outer strands and therefore exhibits a relatively high breaking force.

[0051] Advantageously, the thickness G of the sheath of elastomer composition is strictly greater than 0 mm, preferably greater than or equal to 0.01 mm. The greater the thickness G of the elastomer composition, the better the permeability in the inner layer.

[0052] Advantageously, the thickness G of the sheath of elastomeric composition is less than or equal to 0.8 mm, preferably less than or equal to 0.60 mm and more preferably less than or equal to 0.52 mm, which makes it possible to limit the outer diameter of the cord while optimizing the permeability of the inner layer.

[0053] Advantageously, the elastomeric composition comprises an elastomer selected from the group consisting of polybutadiene, natural rubber, synthetic polyisoprene, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

[0054] Preferably, the elastomeric composition comprises an elastomer selected from the group consisting of natural rubber, synthetic polyisoprene, isoprene copolymers, and mixtures of these elastomers.

[0055] Preferably, the elastomer composition also contains a vulcanization system and a filler. More preferentially, the elastomer is a diene-based elastomer.

[0056] Preferably, the elastomer comprises carbon black as a reinforcing filler.

[0057] Advantageously, K=1, 2, 3 or 4, preferably K=1, 2 or 3, more preferably K=1 or 3.

[0058] Advantageously, L=6, 7, 8, 9 or 10, preferably L=6, 7, 8 or 9, more preferably L=6 or 9.

[0059] In a first variant, K=1 and L=6. In a cord with K=1, the presence of the elastomeric composition allows good permeability and also reduces the contact pressure on the inner strands due to the severe lateral loads that the outer strands exert on them.

[0060] In a second variant, K=2 and L=7 or 8, preferably K=2 and L=8.

[0061] In a third variant, K=3 and L=7, 8 or 9, preferably K=3 and L=9.

[0062] In a fourth variant, K=4 and L=9 or 10, preferably K=4 and L=10.

[0063] In embodiments not according to the invention, particularly where K=3 or 4, there is a risk of seeing a very significant spread of corrosive agents between the K=3 or 4 internal strands that define a central capillary that significantly facilitates their extension along the cord if the cord is insufficiently penetrated. This drawback can be overcome by providing a sheath around the K internal strands that makes them permeable with the elastomeric composition, thereby preventing corrosive agents from accessing the central capillary that is itself perforated, and thus preventing these corrosive agents from spreading along the cord.

[0064] In a cord with K>1, the most severe lateral load that the cord experiences when tensioned is the lateral load between the internal strands. Cords with many external strands are known in the prior art, which present a structure with K>1 and saturate the external layer of the cord in order to maximize the breaking strength by adding the maximum number of external strands. Due to the desaturation of the external layer of the strands, the cord, on the one hand, has spaces between the external threads that allow the elastomeric composition to pass through, thus making the cord less susceptible to corrosion. On the other hand, although the number of external threads is reduced, the desaturation of the external layer of the strands, on the one hand, allows the elastomeric composition to penetrate between the external threads, and, on the other hand, allows the elastomeric composition of the sheath to be forced between the internal strands, forming a cushion of elastomeric composition that at least partially absorbs the lateral load between the internal strands. Therefore, better corrosion resistance is achieved compared to similar cords with saturated external cord layers.

[0065] Inner strand of the cord according to the invention

[0066] In one preferred embodiment, Q>1, preferably Q=2, 3, or 4. In instances where Q is equal to 1, there would be a risk of seeing the inner thread of the inner strand radially separate from the inner strand and even from the cord under the action of repeated compressive loads applied to the cord. This risk is reduced due to the presence of multiple threads in the inner layer of the inner strand (Q>1), in which case the compressive load is distributed over the multiple threads of the inner layer.

[0067] Advantageously, M=7, 8, 9 or 10, preferably M=7, 8 or 9.

[0068] Advantageously, N=12, 13, 14, 15 or 16, preferably N=12, 13 or 14.

[0069] Preferably, Q=4, M=9, and N=14.

[0070] Outer strand of the cord according to the invention

[0071] Advantageously, M'=7, 8, 9 or 10, preferably M'=7, 8 or 9.

[0072] Advantageously, N'=12, 13, 14, 15 or 16, preferably N'=12, 13 or 14.

[0073] Preferably, Q'=3, M'=9, and N'=14.

[0074] Advantageously, Q=4, M=9, and N=14; each internal metal thread of each internal strand has a diameter d1 equal to the diameter d2 of each intermediate thread of each internal strand and equal to the diameter d3 of each external thread of each internal strand; Q'=3, M'=9, and N'=14; each intermediate metal thread of each outer strand has a diameter d2' equal to the diameter d3' of each outer thread of each outer strand; -d1=d2=d3=d1'.

[0075] Advantageously, each metal thread has a respective diameter d1, d1', d2, d2', d3, d3' ranging from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferentially from 0.15 mm to 0.42 mm.

[0076] Method for manufacturing a cord according to the present invention

[0077] Another subject of the invention is a method for producing a two-layer multi-strand cord, - step, by twisting or plying, K≧1 inner strands are helically braided to form an inner layer of the cord; the or each inner strand is a three-layer strand, comprising an inner layer made of Q=2, 3 or 4 inner metal threads, an intermediate layer made of M intermediate metal threads having a diameter d2 wound around the inner layer, the sum SI2 of the inter-thread distances I2 of the intermediate layer of the or each inner strand being greater than or equal to the diameter d2, and an outer layer made of N outer metal threads having a diameter d3 wound around the intermediate layer, the sum SI3 of the inter-thread distances I3 of the outer layer of the or each inner strand being greater than or equal to the diameter d3; - forming a sheath inner layer by surrounding the inner layer with an elastomer composition having a thickness G, the thickness G of the elastomer composition being such that the ratio R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer obtained when the inner layer is in direct contact with the theoretical outer layer; - step involves spirally assembling L>1 outer strands around an inner layer of the cord by twisting or plying; each outer strand is a two-layered strand and comprises an inner layer made of Q'=2, 3 or 4 inner metal threads, an intermediate layer made of M' intermediate metal threads with a diameter d2' wound around the inner layer, the total SI2' of the inter-thread distances I2' of the intermediate layer of each outer strand being greater than or equal to the diameter d2', and an outer layer made of N' outer metal threads with a diameter d3' wound around the intermediate layer, the total SI3' of the inter-thread distances I3' of the outer layer of each outer strand being greater than or equal to the diameter d3'; In the -step, means are used to approximate the outer layer of the cord to a circle circumscribed by the inner layer of the cord so that the ratio R2 / Rt is in the range of 1.00 to 1.10.

[0078] Advantageously, the steps of helically braiding the K≧1 inner strands and assembling the L>1 outer strands around the inner layer of cord are performed using twisting.

[0079] Advantageously, the means employed to approximate the outer layer of cord to the circle circumscribed by the inner layer of cord consist, for example, of two rows of rollers mounted opposite each other but offset, between which the cord is passed.

[0080] In one embodiment, one row is movable and can be moved closer to the fixed row to subject the cable to a series of bends.

[0081] In another embodiment, the train of rollers can move around the axis of the cord.

[0082] Reinforced product according to the present invention

[0083] Another subject of the invention is a reinforced product comprising an elastomeric matrix and at least one cord as defined above.

[0084] Advantageously, the reinforced product comprises one or more cords according to the invention embedded in an elastomeric matrix, in the case of a plurality of cords, the cords being arranged side by side in the main direction.

[0085] Tire according to the present invention

[0086] Another subject of the invention is a tire comprising at least one cord or reinforcing product as defined above.

[0087] Preferably, the tire has a carcass reinforcement fixed to the two beads and radially surrounded by a crown reinforcement which is itself surrounded by the tread, the crown reinforcement being connected to the beads by two side walls and comprising at least one cord as defined above.

[0088] In one preferred embodiment, the crown reinforcement comprises a protective reinforcement and a working reinforcement, the working reinforcement comprising at least one cord as defined above, the protective reinforcement being radially sandwiched between the tread and the working reinforcement.

[0089] The Code is most particularly directed to "heavy vehicles", i.e. industrial vehicles selected from heavy vehicles such as subways, buses, road haulage vehicles (trucks, tractors, trailers), off-road vehicles, agricultural or construction plant vehicles, or other transport or material handling vehicles.

[0090] Preferably, the tire is for a construction plant type vehicle, and therefore has a diameter of the seat of the rim on which it is intended to be mounted, measured in inches, of at least 25 inches, preferably between 39 and 63 inches.

[0091] The present invention also relates to a rubber article comprising an assembly according to the invention or an impregnated assembly according to the invention, by which is meant any kind of article made of rubber, such as a ball, a non-pneumatic object such as a non-pneumatic tire casing, a conveyor belt or a track.

[0092] A better understanding of the invention will be obtained on reading the following examples, given purely by way of non-limiting example and made with reference to the drawings in which: [Brief explanation of the drawings]

[0093] [Figure 1] 1 is a cross-sectional view perpendicular to the circumferential direction of a tire according to the present invention; [Figure 2] FIG. 2 is a detailed view of region II in FIG. 1. [Figure 3] 1 is a cross-sectional view of a product reinforced according to the present invention. [Figure 4] 1 is a schematic view of a cord (50) according to the invention in a cross section perpendicular to the axis of the cord (assumed to be straight and stationary); FIG. [Figure 5]1 is a schematic diagram of an installation for manufacturing a cord (50) according to the present invention. [Figure 6] 1 is a schematic diagram of an installation for manufacturing a cord (50) according to the present invention. [Figure 7] 4 is a schematic diagram of step 400 of approaching the outer layer of the cord (50) to the inner layer according to the present invention. [Figure 8] FIG. 10 shows a photograph of code EDIT and photographs of comparison codes C1 and C2. [Figure 9] Photographs of cords 50, 51, and 70 according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0094] Example of a tire according to the present invention

[0095] The coordinate system X, Y, Z corresponding to the axial (X), radial (Y), and circumferential (Z) directions, respectively, common to a tire, are shown in Figures 1 and 2.

[0096] The "median circumferential plane" M of the tire is the plane perpendicular to the tire's axis of rotation and equidistant from the annular reinforcing structure of each bead.

[0097] 1 and 2 show a tire, designated by the general reference numeral 10, in accordance with the present invention.

[0098] The tire 10 is for heavy vehicles of the construction plant type, for example of the "dump truck" type, and therefore has dimensions of the type 53 / 80R63.

[0099] The tire 10 has a crown 12 reinforced by a crown reinforcement 14, two sidewalls 16, and two beads 18, each of which is reinforced using an annular structure, in this example a bead wire 20. The crown reinforcement 14 is radially surrounded by a tread 22 and connected to the beads 18 by the sidewalls 16. A carcass reinforcement 24 is fixed to the two beads 18, wrapped around the two bead wires 20 in this example, and includes a turnup 26 positioned towards the outside of the tire 20, which is shown here mounted on a wheel rim 28. The carcass reinforcement 24 is radially surrounded by the crown reinforcement 14.

[0100] The carcass reinforcement 24 comprises at least one carcass ply 30 reinforced with radial carcass cords (not shown) positioned substantially parallel to one another and extending from one bead 18 to the other at an angle comprised between 80° and 90° with respect to 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).

[0101] The tire 10 also comprises a sealing ply 32 (commonly known as an "inner liner") made of elastomer that defines the radially inner surface 34 of the tire 10 and is intended to protect the carcass ply 30 from the diffusion of air coming from the interior space of the tire 10.

[0102] The crown reinforcement 14 comprises, from the outside to the inside of the tire 10 in the radial direction, a protective reinforcement 36 arranged radially inward of the tread 22, a working reinforcement 38 arranged radially inward of the protective reinforcement 36, and an additional reinforcement 40 arranged radially inward of the working reinforcement 38. The protective reinforcement 36 is thus sandwiched radially between the tread 22 and the working reinforcement 38. The working reinforcement 38 is sandwiched radially between the protective reinforcement 36 and the additional reinforcement 40.

[0103] The protective reinforcement 36 comprises first and second protective plies 42, 44 comprising protective metal cords, the first ply 42 being arranged radially inward of the second ply 44. Optionally, the protective metal cords form an angle with the circumferential direction Z of the tire that is at least equal to 10°, preferably in the range of 10° to 35°, more preferably in the range of 15° to 30°.

[0104] The operational reinforcement 38 includes first and second operational plies 46, 48, with the first ply 46 disposed radially inward of the second ply 48. Each ply 46, 48 includes at least one cord 50. Optionally, the operational metal cord 50 crosses from one operational ply to the other and forms an angle with the circumferential direction Z of the tire equal to a maximum of 60°, preferably in the range of 15° to 40°.

[0105] The additional reinforcement 40, also called limiting block, the purpose of which is to partially absorb the mechanical stresses of expansion, comprises, for example, an additional metal reinforcing element, also known per se, which forms an angle with the circumferential direction Z of the tire 10 equal to a maximum of 10°, preferably ranging from 5° to 10°, as described, for example, in FR2 419,181 or FR2 419,182.

[0106] Examples of reinforced products according to the present invention

[0107] 3 shows a reinforced product according to the present invention, designated by the general reference number 100. The reinforced product 100 comprises at least one cord 50, in this example a plurality of cords 50, embedded in an elastomeric matrix 102.

[0108] 3 depicts the elastomeric matrix 102 and the cords 50 in a coordinate system X, Y, Z, with direction Y being radial and directions X and Z being axial and circumferential. In FIG. 3, the reinforced product 100 comprises a plurality of cords 50 arranged side by side in the main direction X, extending parallel to one another within the reinforced product 100, and collectively embedded in the elastomeric matrix 102.

[0109] Code according to the present invention

[0110] 4 shows a cord 50 according to the present invention, depicted before step 400 of approximating the outer layer CE of the cord to the circle inscribed by the inner layer CI of the cord.

[0111] The cord 50 is metallic and is of the multi-strand type having two cylindrical layers, so it will be understood that the strands of which the cord 50 is made are two layers, no more and no less.

[0112] The cord 50 comprises an inner layer CI of the cord with inner strands TI, K≧1. In this particular example, K=1, 2, 3, or 4, preferably K=1, 2, or 3, more preferably K=1 or 3, where K=3. The inner layer CI is surrounded by an elastomeric composition of thickness G, thus forming a sheathed inner layer CIG. The outer layer CE comprises outer strands TE, L>1, wound with a helical radius R2 around the sheathed inner layer CIG of the cord. In this particular example, L=6, 7, 8, 9, or 10, preferably L=6, 7, 8, or 9, more preferably L=6 or 9, where L=9. Here, R2 is equal to 1.69 mm.

[0113] The thickness G of the elastomer composition is such that the ratio R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer CET obtained when the inner layer CI is in direct contact with the theoretical outer layer CET, where R2=1.69 and R2 / Rt=1.06.

[0114] The cord 50 is finally obtained by a method comprising a step 500 of approximating the outer layer CE of the cord to the circle circumscribed by the inner layer CI of the cord so that the ratio R2 / Rt is in the range of 1.00 to 1.10, where R2=1.67 and R2 / Rt=1.05.

[0115] The cord 50 also comprises a wrapper F (not shown) made of a single wrapping wire.

[0116] Code 50 inner strand TI

[0117] The inner strand is a three-layer strand and comprises an inner layer C1 made of Q=2, 3, or 4 inner metal threads F1, a middle layer C2 made of M intermediate metal threads wound around the inner layer C1, and an outer layer C3 made of N outer metal threads wound around the middle layer C2.

[0118] Here, Q=4.

[0119] M=7, 8, 9, or 10, preferably M=7, 8, or 9. Here, M=9.

[0120] N=12, 13, 14, 15, or 16, and preferably N=12, 13, or 14. Here, N=14.

[0121] The middle layer C2 of each inner strand TI is desaturated, or incompletely desaturated. Because it is desaturated, the inter-thread distance of the outer layer of each inner strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, and here equal to 43 μm. The sum SI2 of the inter-thread distances I2 of the middle layer of each inner strand is greater than or equal to the diameter d2 of the middle thread of the middle layer of each inner strand. Here, the sum SI2 = 0.39 mm is greater than d2 = 0.26 mm.

[0122] The outer layer C3 of each inner strand TI is desaturated, incompletely desaturated. Being desaturated, the interthread distance of the outer layer of each inner strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, more preferably greater than or equal to 50 μm, and here equal to 53 μm. The sum SI3 of the interthread distances I3 of the outer layer of each inner strand is greater than or equal to the outer thread diameter d3 of the outer layer of each inner strand. Here, the sum SI3 = 0.74 mm is greater than d3 = 0.26 mm.

[0123] Each inner, middle, and outer thread of each inner strand TI has a diameter d1, d2, and d3, respectively. Each inner thread diameter d1, middle thread diameter d2, and outer thread diameter d3 of each inner strand TI ranges from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferably from 0.15 mm to 0.42 mm. Here, d1 = d2 = d3 = 0.26 mm.

[0124] Outer strand TE of code 50

[0125] Each outer strand TE has three layers, comprising an inner layer C1' made of Q'=2, 3 or 4 inner metal threads, an intermediate layer C2' made of M' intermediate metal threads wound on the inner layer C1', and an outer layer C3' made of N' outer metal threads wound on the intermediate layer C2'.

[0126] Here, Q'=3.

[0127] M'=7, 8, 9, or 10, preferably M'=7, 8, or 9. Here, M'=9.

[0128] N'=12, 13, 14, 15, or 16, preferably N'=12, 13, or 14. Here, N'=14.

[0129] The intermediate layer C2' of each outer strand TE is desaturated, or incompletely desaturated. Because it is desaturated, the inter-thread distance of the outer layer of each outer strand is 15 μm or more, more preferably 35 μm or more, and here is equal to 43 μm. The sum SI2' of the inter-thread distances I2' of the intermediate layer of each outer strand is equal to or greater than the diameter d2' of the intermediate thread of the intermediate layer of each outer strand. Here, the sum SI2' = 0.39 mm, which is greater than d2' = 0.23 mm.

[0130] The outer layer C3 of each outer strand TE is desaturated, or incompletely desaturated. Because it is desaturated, the inter-thread distance of the outer layer of each outer strand is 15 μm or more, more preferably 35 μm or more, more preferably 50 μm or more, and here equals 50 μm. The sum SI3′ of the inter-thread distances I3′ of the outer layer of each outer strand is equal to or greater than the outer thread diameter d3′ of the outer layer of each outer strand. Here, the sum SI3′=0.70 mm, which is greater than d3′=0.23 mm.

[0131] The inner, middle, and outer threads of each outer strand TE have diameters d1', d2', and d3', respectively. The inner thread diameter d1', middle thread diameter d2', and outer thread diameter d3' of each inner and outer strand TE range from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferably from 0.14 mm to 0.42 mm. Here, d1'=0.26 mm, d2'=d3'=0.23 mm.

[0132] Code 50 looks like this: Q=4, M=9, and N=14; each internal metal thread of each internal strand has a diameter d1 equal to the diameter d2 of each intermediate thread of each internal strand and equal to the diameter d3 of each external thread of each internal strand; Q'=3, M'=9, and N'=14; each intermediate metal thread of each outer strand has a diameter d2' equal to the diameter d3' of each outer thread of each outer strand; -d1=d2=d3=d1'.

[0133] The outer layer CE of the cord is desaturated. The average inter-strand distance E separating two adjacent outer strands TE is therefore equal to or greater than 20 μm. Preferably, the average inter-strand distance E separating two adjacent outer strands TE is equal to or greater than 40 μm, more preferably equal to or greater than 50 μm. Here, the inter-strand distance E is equal to 170 μm.

[0134] Each thread has a breaking strength, expressed as Rm, such that 2500≦Rm≦3100 MPa. The steel for these threads is said to be of the SHT (“ultra-high tensile”) grade. Other threads can be used, for example, lower grades such as NT (“normal tensile”) or HT (“high tensile”) grades, as well as higher grades such as UT (“ultra-high tensile”) or MT (“mega tensile”) grades.

[0135] Method for manufacturing a cord according to the present invention

[0136] An example of a method for manufacturing the multi-strand cord 50 will now be described with reference to FIGS. Each of the above-mentioned inner strands is manufactured according to a known method involving the following steps, preferably carried out continuously in-line: a first stage of assembling, by twisting, Q=2, 3 or 4 internal threads F1 of the internal layer C1 in the Z direction with a pitch p1 to form the internal layer C1 at a first assembly point; a second stage of subsequently assembling, by twisting or twisting, the M intermediate threads F2 around the Q internal threads F1 of the internal layer C1 in the Z direction with a pitch p2 to form an intermediate layer C2 at a second assembly point; a third stage of subsequently assembling, by twisting or twisting, the N outer threads F3 in the Z direction around the M intermediate threads F2 of the intermediate layer C2 with a pitch p3 to form the outer layer C3 at a third assembly point; - Preferably a final twist-balancing step.

[0137] In step 100, K≧1 inner strands TI are helically braided by twisting to form an inner layer CI of the cord.

[0138] In step 200, the inner layer CI is surrounded by an elastomer composition having a thickness G to form a sheath inner layer CIG, the thickness G of the elastomer composition being such that the ratio R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer CET that would be obtained when the inner layer CI is in direct contact with the theoretical outer layer CET.

[0139] Each of the above-mentioned outer strands is manufactured according to a known method, preferably carried out continuously in-line, involving the following steps: - a first stage of assembling, by twisting, Q'=2, 3 or 4 internal threads F1' of the internal layer C1' in the Z direction with a pitch p1' to form the internal layer C1' at a first assembly point; a second stage of subsequently assembling, by twisting or twisting, M' intermediate threads F2' in the Z direction around the Q' internal threads F1' of the internal layer C1' with a pitch p2' to form an intermediate layer C2' at a second assembly point; a third stage of subsequently assembling, by twisting or twisting, the N' outer threads F3' around the M' intermediate threads F2' of the intermediate layer C2' in the Z direction with a pitch p3' to form the outer layer C3' at a third assembly point; - Preferably a final twist-balancing step.

[0140] By "twist-balancing" herein is meant, as known to those skilled in the art, the elimination of residual torque (or elastic return of twist) on each thread of the strand in the middle layer as in the outer layer.

[0141] After this final twist-balancing step, the production of the strands is complete, and each strand is wound onto one or more receiving reels for storage prior to the subsequent operation of assembling the elementary strands by twisting to obtain a multi-strand cord.

[0142] In step 300, the outer strands TE, L>1, are assembled helically around the inner layer CI of the cord by twisting. In step 400, means 500 are used to make the outer layer CE of the cord approximate a circle circumscribed by the inner layer CIG of the cord, so that the ratio R2 / Rt is in the range of 1.00 to 1.10.

[0143] This step 400 is explained with reference to FIG.

[0144] The means 500 employed to bring the outer layer CE of the cord closer to the circle circumscribed by the inner layer CI of the cord may consist, for example, of two rows of rollers mounted opposite but offset from one another, between which the cord is threaded. Each row contains between six and eight rollers. One row is movable and can be brought closer to the fixed row so that the cord undergoes a series of bends. These roller rows may be fixed or movable around the axis of the cord.

[0145] The cord is therefore subjected to a series of bending actions which enable it to reduce its diameter as shown in FIG.

[0146] L is equal to the maximum number Lmax of outer strands TE that can be laid on a theoretical outer layer CET with a helical radius Rt, L being such that the outer layer CE is incompletely unsaturated, where Lmax=6 and L=Lmax=6.

[0147] The thickness G of the sheath of the elastomer composition is strictly greater than 0 mm, preferably 0.01 mm or more, and the thickness G is 0.80 mm or less, preferably 0.60 mm or less, more preferably 0.52 mm or less, where G=0.08 mm.

[0148] The elastomer composition contains a vulcanization system, a filler, and a diene-based elastomer.

[0149] The elastomer composition used is a diene-based elastomer composition conventionally used in tires, based on natural (deflocculated) rubber and carbon black N330 (65 phr), and also contains the following customary 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 means parts by weight per 100 parts by weight of elastomer); the coating elastomer composition has an E10 modulus of approximately 10 MPa.

[0150] In some cases, in the final assembly stage, a wrapper F is wound around the previously obtained assembly in the S direction with a pitch pf.

[0151] The cords are then incorporated by skimming into a composite substrate made from a known composition based on natural rubber and carbon black as reinforcing fillers conventionally used in the manufacture of crown reinforcements for radial tires, which composition essentially contains, in addition to the elastomer and reinforcing filler (carbon black), antioxidants, stearic acid, extending oil, cobalt naphthenate as adhesion promoter, and finally a vulcanization system (sulfur, accelerators, and ZnO).

[0152] These cord-reinforced composite fabrics have an elastomeric matrix formed from two thin layers of elastomeric composition, each having a thickness ranging between 1 mm and 4 mm, overlaid on either side of the cord. The skim pitch (the spacing at which the cords are laid in the elastomeric composition fabric) ranges from 4 mm to 8 mm.

[0153] These composite fabrics are then used as working plies in the crown reinforcement during the process of manufacturing tires, steps which are otherwise known to those skilled in the art.

[0154] Table 1 below summarizes the characteristics of the various codes 50, 51, 60, and 70. [Table 1]

[0155] Comparative Test

[0156] Air Permeability Test

[0157] This test makes it possible to determine the longitudinal air permeability of the tested cord by measuring the volume of air passing through the test specimen in a given time under a constant pressure. The principles of such a test are known to those skilled in the art and are intended to determine the effectiveness of a cord treatment to make the cord impermeable to air, and are described, for example, in ASTM standard D2692-98.

[0158] These tests are carried out on as-manufactured, unaged cords. The raw cords are first coated on the outside with an elastomer composition, referred to as the coating composition. For this purpose, 10 consecutive parallel-aligned cords (cord spacing: 20 mm) are placed between two layers or "skims" (two rectangles, each 80 x 200 mm long) of the raw diene-based elastomer composition, each 5 mm thick. The whole is then clamped in a mold, and the cords are held under tension (e.g., 3 daN) using a clamping module to ensure that they lie straight when placed in the mold. A vulcanization (curing) treatment is then carried out at a temperature of approximately 110 °C and a pressure of 15 bar (rectangular piston, 80 x 200 mm long) for approximately 8 hours. The whole is then removed from the mold, and 10 specimens of the coated cord are cut into parallelepipeds, each 7 x 7 x 60 mm long, for characterization.

[0159] The composition used as the coating elastomer composition is a diene-based elastomer composition conventionally used in tires, based on natural (deflocculated) rubber and carbon black N330 (65 phr), and further containing the following customary 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 means parts by weight per 100 parts by weight of elastomer); the coating elastomer composition has an E10 modulus of approximately 10 MPa.

[0160] The test is carried out on a 6 cm long cord that has been coated with the surrounding elastomer composition (or coating elastomer composition) in the cured state in the following manner: 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 (e.g., 0-500 cm 3 During the measurement, the cord sample is fixed in a compressed airtight seal (for example a high-density foam or rubber seal) 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 in the measurement; the airtightness of the airtight seal itself is checked beforehand using a test piece of solid elastomer composition, i.e. without the cord.

[0161] The more longitudinally impermeable the cord, the smaller the average air flow rate (averaged over 10 specimens) measured. Measurements are made with an accuracy of ±0.2 cm³ / min, so measurements below 0.2 cm³ / min are considered zero and correspond to cords that can be described as airtight (completely airtight) along their axis (i.e., in their longitudinal direction).

[0162] Table 2 summarizes the characteristics of the comparative codes T1 and T2 and the prior art EDT (189.23) code.

[0163] [Table 2]

[0164] Table 3 below summarizes the results of permeability tests for prior art cord EDT, various comparative cords C1 and C2, and cords 50, 60, and 70 according to the present invention, respectively. Comparative cord C1 is a version of prior art cord 189.23 with a desaturated thread layer and a different thread diameter to improve permeability. Cord C2 is another version of prior art cord 189.23. These test results are presented on a 100 basis. Thus, a result above 100 for any one of these tests indicates that the tested cord exhibits greater impermeability than the control cord; in this case, control cord C1 is being compared to cords C2, 50, 51, 60, and 70.

[0165] [Table 3]

[0166] It is noted that cords 50, 51, 60, and 70 according to the invention show a very significantly better penetration than cord EDT, and significantly better than comparative cords C1 and C2, which is solely the result of the ratio R2 / Rt according to the invention. Furthermore, it can be further noted that in Figure 9, in the case of cords 50, 51, and 70, the central capillary is almost completely penetrated, whereas in Figure 8 this is not the case for cord EDT and comparative cords C1, C2, the dark areas being areas devoid of elastomeric composition.

[0167] Table 3 therefore shows that for various sheath thicknesses, the penetration of the elastomeric composition into the cord and therefore its access to the inner strands is significantly improved for the ratio R2 / Rt according to the invention due to the presence of a sheath of thickness G compared to the versions represented by the prior art cord with R2 / Rt=1 and the control cords C1 and C2.

[0168] Of course, the invention is not limited to the exemplary embodiments described above.

[0169] For reasons of industrial feasibility, cost, and overall performance, the present invention is preferably practiced with linear threads having a conventional circular cross section, i.e., straight threads.

[0170] It will also be possible to combine features of the various embodiments described or envisaged above, provided that these features are compatible with one another. [Explanation of symbols]

[0171] 50 Code according to the present invention C1 Inner layer of inner strand C2 Middle layer of inner strand C3 Outer layer of inner strand CET Theoretical Outer Layer

Claims

1. A method for manufacturing a two-ply multi-strand cord (50), comprising: In step (100), K≧1 internal strands (TI) are helically braided by twisting or twisting to form an internal layer (CI) of the cord, the or each internal strand (TI) being a three-layer (C1, C2, C3) strand, and comprising an internal layer (C1) made of Q=2, 3 or 4 internal metal threads (F1) and an intermediate layer (C2) made of M intermediate metal threads (F2) of diameter d2 wound around the internal layer (C1), so that an intermediate layer (C2) in which the sum SI2 of the inter-thread distances I2 of the intermediate layer of the internal strand (TI) or of each internal strand (TI) is greater than or equal to the diameter d2; and an outer layer (C3) made of N outer metal threads (F3) with a diameter d3 wound around the intermediate layer (C2), so that the sum SI3 of the inter-thread distances I3 of the outer layer of the internal strand (TI) or of each internal strand (TI) is greater than or equal to the diameter d3. In step (200), the inner layer (CI) is surrounded by an elastomeric composition having a thickness G to form a sheath inner layer (CIG), the thickness G of the elastomeric composition being such that the ratio R2 / Rt is in the range of 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer (CET) obtained when the inner layer (CI) is in direct contact with the theoretical outer layer, and the thickness G of the sheath of elastomeric composition is less than or equal to 0.8 mm, In step (300), L>1 outer strands (TE) are spirally assembled around the inner layer (CI) of the cord by twisting or twisting, each outer strand (TE) being a three-layer (C1', C2', C3') strand, with an inner layer (C1') made of Q'=2, 3 or 4 inner metal threads (F1') and an intermediate layer (C2') made of M' intermediate metal threads (F2') of diameter d2' wound around the inner layer (C1'), so that an intermediate layer (C2') in which the sum SI2' of the inter-thread distances I2' of the intermediate layer (C2') of each outer strand (TE) is greater than or equal to the diameter d2', and an outer layer (C3') made of N' outer metal threads (F3') with a diameter d3' wound around the intermediate layer (C2'), so that the sum SI3' of the inter-thread distances I3' of the outer layer (C3') of each outer strand (TE) is greater than or equal to the diameter d3', In step (400), means (500) are used for approximating the outer layer (CE) of the cord to a circle circumscribed by the inner layer (CI) of the cord so that the ratio R2 / Rt is in the range of 1.00 to 1.

10. A method for producing a two-layer multi-strand cord (50) comprising:

2. A method for manufacturing a two-ply multi-strand cord (50) as described in claim 1, characterized in that L is equal to the maximum number of outer strands (TE) that can be laid on the theoretical outer layer (CET) having a helical radius Rt, and L is such that the outer layer (CE) is incompletely unsaturated.

3. A method for manufacturing a two-layer multi-strand cord (50) as described in claim 1, characterized in that the thickness G of the sheath of the elastomer composition is strictly greater than 0 mm.

4. A method for manufacturing a two-layer multi-strand cord (50) as described in claim 1, characterized in that K = 1, 2, 3, or 4.

5. A method for manufacturing a two-layer multi-strand cord (50) as described in claim 1, characterized in that L = 6, 7, 8, 9, or 10.

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