Single-ply multi-strand cord with improved energy at break and improved total elongation

Abstract

The present invention relates to a multi-strand cord (50) having a 1×N structure comprising a single layer (52) of N strands (54) helically wound around a main axis (A), each strand (54) having one layer (56) of metal filaments (F1) and comprising M>1 metal filaments helically wound around an axis (B), the cord comprising: The cord (50) has a total elongation At>8.10%, and the energy index Er at break of the cord (50) is TIFF2023509076000015.tif14150, where σ(Ai) is the tensile stress in MPa measured at elongation Ai, dAi is the strain at Er of 52 MJ / m 3 This is a more strictly increasing stretch.

Description

[Technical Field]

[0001] The present invention relates to cords, reinforcement products, and tires containing these cords. [Background technology]

[0002] A tire for construction plant vehicles having a radial carcass reinforcement, comprising a tread, two inelastic beads, two sidewalls connecting the beads to the tread, and a crown reinforcement arranged circumferentially between the carcass reinforcement and the tread, is known from the prior art, in particular from document WO 2016 / 131862. This crown reinforcement comprises several plies reinforced by reinforcing elements such as metal cords, the cords of one ply being embedded in the elastomeric matrix of the ply.

[0003] The crown reinforcement includes a working reinforcement, a protective reinforcement, and possibly other reinforcements, such as a hoop reinforcement.

[0004] The protective reinforcement comprises one or more protective plies containing several protective filamentary reinforcing elements. Each protective filamentary reinforcing element is a cord with a 1xN structure. This cord comprises a single layer of N=4 strands spirally wound with a pitch of p3=20 mm. Each strand comprises an inner layer of M=3 inner filaments spirally wound with a pitch of p1=6.7 mm, as well as an outer layer of V=8 outer filaments spirally wound around the inner layer with a pitch of p2=10 mm. Each inner and outer filament has a diameter equal to 0.35 mm, and the total elongation of the cord is 6%.

[0005] On the other hand, when the tire passes over obstacles, for example in the form of rocks, these obstacles run the risk of perforating the tire up to the extent of the crown reinforcement. These perforations can allow corrosive agents to enter the crown reinforcement of the tire, shortening its service life. On the other hand, it has been found that the cords of the protective ply can exhibit breakage resulting from the relatively large deformations and loads exerted on them, especially when the tire passes over obstacles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 131862 [Patent Document 2] International Publication No. 2016083265 [Patent Document 3] International Publication No. 2016083267 [Patent Document 4] European Patent No. 0548539 [Patent Document 5] European Patent No. 1000194 [Patent Document 6] European Patent No. 0622489 [Patent Document 7] International Publication No. 2012055677 [Patent Document 8] Japanese Patent Application Laid-Open No. 2007092259 [Patent Document 9] International Publication No. 2007128335 [Patent Document 10] Japanese Patent Application Laid-Open No. 06346386 [Patent Document 11] European Patent No. 0143767 [Patent Document 12] French Patent No. 2 419 181 [Patent Document 13] French Patent No. 2 419 182 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is a cord that makes it possible to reduce or eliminate the number of breaks and perforations. [Means for solving the problem]

[0008] To this end, one subject of the invention is a multistrand cord having a 1 × N structure comprising a single layer of N strands helically wound around a main axis (A), each strand having one layer of metal filaments, and comprising M > 1 metal filaments helically wound around an axis (B), The cord has a total elongation At>8.10% as defined by 2014 ASTM Standard D2969-04; The energy index Er at the time of cord breakage is TIFF0007737379000001.tif14150where σ(Ai) is the tensile stress in MPa measured at elongation Ai, dAi is the stress at Er of 52 MJ / m 3 The elongation is strictly greater than

[0009] Due to their relatively high total elongation and relatively high cord breaking energy, cords according to the present invention reduce punctures and therefore extend the life of the tire. Specifically, the inventors have discovered that cords with lower stiffness than prior art cords perform better against obstacles. Rather than attempting to stiffen and strengthen the cord to the greatest extent possible to resist the deformation caused by the obstacle, as is commonly taught in the prior art, the inventors have found that it is more effective to wrap the obstacle with a cord of lower stiffness. By wrapping the obstacle, the load placed on the obstacle is reduced, and therefore the risk of the tire being punctured is also reduced. This stiffness reduction effect is shown in Figure 7, where, under stress, cords according to the present invention exhibit good deformability under light loads as a result of the radial spacing of the filaments.

[0010] Due to the relatively high total elongation and relatively high breaking energy, the cord according to the present invention can also reduce the number of breaks. Specifically, the inventors behind the present invention discovered that the determining criterion for reducing cord breakage is not only the force at break, as widely taught in the prior art, but also the energy at break index, which is represented by the area under the stress curve as a function of elongation, as partially shown in FIG. 4 of the present application. Specifically, prior art cords either have a relatively high force at break and a relatively low elongation at break, or a relatively high elongation at break and a relatively low force at break. In either case, prior art cords break with a relatively low energy at break index. Due to the relatively high total elongation, the cord according to the present invention necessarily exhibits a relatively high elongation at break. Synergistically, the relatively low modulus of elasticity allows the elongation at break to be pushed back due to the relatively low slope of the stress-elongation curve in the elastic region. Lastly, and among other things, the inventors have discovered that increasing the total elongation not only pushes back the elongation at break, but also allows for a higher energy at break by increasing the stress, as shown in the comparative tests below.

[0011] Any range of values ​​expressed as "between a and b" refers to a range of values ​​greater than a and less than b (i.e., excluding the endpoints a and b), whereas any range of values ​​expressed as "from a to b" refers to a range of values ​​from the endpoint "a" to the endpoint "b", i.e., strictly including the endpoints "a" and "b".

[0012] The total elongation At, a parameter well known to those skilled in the art, can be determined, for example, by applying the 2014 ASTM standard D2969-04 to a cord tested to obtain a stress-elongation curve. At is derived from the resulting curve as the elongation (in %) corresponding to the point on the stress-elongation curve at which the cord breaks, i.e., the point at which the load increases to the maximum stress value and then suddenly decreases after break, projected onto the elongation axis. A decrease in stress beyond a certain level indicates that cord breakage has occurred.

[0013] The energy index Er at the time of cord breakage is determined by the following relationship: This energy-to-break index is calculated by calculating the area under the tensile stress curve as a function of elongation using the tensile stress function. 3 The area is traditionally determined by the rectangular method, where the tensile stress σ(Ai) is measured at the elongation Ai, which is expressed in a dimensionless percentage and is expressed in MPa, such that when i=0: Ai=0=A0=0% elongation, and when i=t: Ai=t=At: the total elongation at break of the cord. The energy index at break Er is therefore the sum of (1 / 2σ(Ai)+σ(Ai+1))×(Ai+1-Ai), for i between 0 and t. In this integration, the rectangular sampling is defined so that the width defined by (Ai+1-Ai) is substantially equal to 0.025%, i.e., four rectangles for an elongation of 0.1%, as depicted in FIG. 4.

[0014] In the present invention, a cord comprises a single layer of N strands, which means that it comprises an assembly made up of exactly one layer of strands, and that the assembly has only one single layer of strands, not zero or two.

[0015] Advantageously, the winding direction of each strand is opposite to the winding direction of the cord.

[0016] The winding direction of a layer of strands is defined as the direction in which the strands form relative to the axis of the cord. The winding direction is generally indicated by the letter Z or the letter S.

[0017] The winding direction of the strands is determined in accordance with the 2014 ASTM standard D2969-04.

[0018] The cord according to the present invention has a single helix. By definition, a single helix cord is a cord in which the axis of each strand in a layer describes a single helix about a major axis, as opposed to a double helix cord in which the axis of each strand describes a first helix about the axis of the cord and a second helix about the helix described by the axis of the cord. In other words, when a cord extends in a substantially linear direction, it comprises a single layer of helically wound strands, each strand of the layer describing a helical path about a major axis parallel to the substantially linear direction, such that in a cross-sectional plane substantially perpendicular to the major axis, the distance between the center of each strand of the layer and the major axis is substantially constant and identical for all strands of the layer. In contrast, when a double helix strand extends in a substantially linear direction, the distance between the center of each strand of the layer and the substantially linear direction is different for all strands of the layer.

[0019] As described above for cords, each strand according to the present invention has a single helix. By definition, a single helix strand is one in which the axis of each metal filament element in the layer describes a single helix, as opposed to a double helix strand in which the axis of each metal filament element describes a first helix around the axis of the strand and a second helix around the helix described by the axis of the strand. In other words, when a strand extends in a substantially linear direction, it comprises a single layer of helically wound metal filament elements, each metal filament element in the layer describing a helical path around a major axis parallel to the substantially linear direction, such that, in a cross-sectional plane substantially perpendicular to the major axis, the distance between the center of each metal filament element in the layer and the major axis is substantially constant and identical for all of the metal filament elements in the layer. In contrast, when a double helix strand extends in a substantially linear direction, the distance between the center of each metal filament element in the layer and the substantially linear direction is different for all of the metal filament elements in the layer.

[0020] The cord according to the present invention does not have a metal central core. This cord is also called a 1×N cord, where N is the number of strands, or an "open cord" (a cord with an open structure). In the cord according to the present invention, the inner enclosure is empty, and therefore there is no filler material, and in particular no elastomer composition. As a result, it is called a cord without filler material.

[0021] Filament elements are defined as elements extending longitudinally along a major axis and having a cross section perpendicular to the major axis, the largest dimension G of which is relatively small compared to the dimension L along the major axis. By relatively small we mean that L / G is 100 or more, preferably 1000 or more. This definition covers both filament elements having a circular cross section and filament elements having a non-circular cross section, such as a polygonal or oval cross section. Highly preferably, each metal filament element has a circular cross section.

[0022] By definition, the term metallic means a filament element that is predominantly (i.e., more than 50% of its weight) or entirely (100% of its weight) composed of metallic material. Each metallic filament element is preferably made of steel, more preferably pearlitic or ferritic-pearlitic carbon steel, commonly referred to by those skilled in the art as carbon steel, or stainless steel (which by definition contains at least 10.5% chromium).

[0023] Preferably, the metal filaments and strands are not subjected to preforming, in other words the cord is obtained by a method that does not include a step of preforming each of the metal filament elements and each of the strands individually.

[0024] Advantageously, the total elongation At is At≧8.30%, preferably At≧8.50%.

[0025] Advantageously, the total elongation At is At≦20.00%, preferably At≦16.00%.

[0026] Advantageously, the cord (50) has an energy index at break Er of 55 MJ / m 3 That's all.

[0027] Preferably, the cord (50) has an energy index Er at break of 200 MJ / m 3 or less, preferably 150MJ / m 3 The following is the result.

[0028] Preferably, the cord has a structural elongation As determined by 2014 ASTM standard D2969-04 such that As>4.30%, preferably As≧4.50%, more preferably As≧4.60%.

[0029] Preferably, the cord has a structural elongation As determined by 2014 ASTM standard D2969-04 such that As≦10.0%, preferably As≦9.50%.

[0030] The structural elongation As, a parameter well known to those skilled in the art, is determined, for example, by applying the 2014 ASTM Standard D2969-04 to a cord tested to obtain a force-elongation curve. As is derived from the resulting curve as the elongation (in %) corresponding to the projection onto the elongation axis of the intersection between a tangent to the structural portion of the force-elongation curve and a tangent to the elastic portion of the force-elongation curve. It should be noted that the force-elongation curve includes a structural portion, an elastic portion, and a plastic portion as it progresses toward increasing elongation. The structural portion corresponds to the structural elongation resulting from the breathability of the cord, i.e., the void space between the various metal strands that make up the cord. The elastic portion corresponds to the elastic elongation resulting from the cord's structure, particularly the various layer angles and strand diameters. The plastic portion corresponds to the plastic elongation resulting from the plasticity (irreversible deformation beyond the elastic limit) of one or more metal filament elements of the strand.

[0031] Preferably, the cord has a secant modulus in the range of 3.0 to 10.0 GPa, and preferably in the range of 3.5 to 8.5 GPa.

[0032] The cord according to the present invention can therefore have a large deformation with respect to a small force and a low first stiffness.

[0033] The secant modulus of elasticity E1 is the slope of the line connecting the origin of the stress-elongation curve obtained under the conditions of the 2014 ASTM Standard D 885 / D 885M - 10a to the 1% abscissa point of this same curve.

[0034] Preferably, the cord has a tangent modulus of elasticity E2 in the range of 50 to 180 GPa, preferably 55 to 150 GPa.

[0035] Thus, the cord according to the invention has a minimum stiffness that allows it to absorb or transmit loads.

[0036] The tangent modulus of elasticity, E2, is calculated as follows on the force-elongation curve obtained under the conditions of 2014 ASTM Standard D 885 / D 885M - 10a: E2 corresponds to the maximum tangent modulus of elasticity of the cord on the force-elongation curve.

[0037] Another subject of the invention is a cord drawn from a polymer matrix, the drawn cord having a 1×N structure comprising a single layer of N strands helically wound around a main axis (A), each strand having one layer of metal filaments, and comprising M>1 metal filaments helically wound around a main axis (B), The extracted cord (50') has a total elongation At' of 5.00% or more as defined by the 2014 ASTM standard D2969-04; The breaking energy index Er' of the extracted cord (50') is Defined by TIFF0007737379000003.tif14150, where σ(Ai) is the tensile stress in MPa measured at elongation Ai, and dAi is the stress at which Er' is 35 MJ / m 3 This is a more strictly increasing stretch.

[0038] Preferably, the polymer matrix is ​​an elastomeric matrix.

[0039] The polymer matrix, preferably the elastomeric matrix, is based on a polymer, preferably an elastomeric composition.

[0040] A polymer matrix is ​​understood to be a matrix comprising at least one polymer. A polymer matrix is ​​thus based on a polymer composition.

[0041] The definition of an elastomeric matrix is ​​a matrix containing at least one elastomer. Thus, preferred elastomeric matrices are based on elastomeric compositions.

[0042] The expression "based on" is to be understood to mean that the composition comprises compounds and / or products of in situ reactions of the various components used, some of which can and / or are intended to react at least partially with one another during the various stages of the preparation of the composition, and thus the composition can be in a fully or partially crosslinked or non-crosslinked state.

[0043] A polymer composition is understood to mean that the composition comprises at least one polymer, preferably such a polymer may be a thermoplastic, such as a polyester or a polyamide, a thermosetting polymer, an elastomer, such as natural rubber, a thermoplastic elastomer, or a combination of these polymers.

[0044] An elastomeric composition is understood to mean 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 that can be used for these plies are conventional compositions for skim coating filamentous reinforcing elements, and include a diene elastomer, such as natural rubber, a reinforcing filler, such as carbon black and / or silica, a crosslinking system, such as a vulcanization system, preferably sulfur, stearic acid, and zinc oxide, and optionally vulcanization accelerators and / or retarders and / or various additives. Adhesion between the metal filaments and the matrix in which they are embedded is provided, for example, by a metal coating, such as a brass layer.

[0045] The values ​​of the characteristics described in this application for extracted cords are measured on or determined from cords extracted from a polymer matrix, in particular an elastomeric matrix, such as a tire. Thus, for example, in a tire, a strip of material radially outside the extracted cord is removed, leaving the extracted cord visible radially flush with the polymer matrix. This removal can be done by stripping with a cutter and knife or by planing. The ends of the extracted cord are then cut off using a knife. The cord is then pulled out of the matrix, applying a relatively shallow angle so as not to plasticize the extracted cord. The extracted cord is then carefully cleaned, for example with a knife, to remove any remnants of the polymer matrix locally adhering to the cord, taking care not to damage the surface of the metal filaments.

[0046] Preferably, the total elongation At' is such that At'≥5.20%.

[0047] Preferably, the cord (50) has an energy index Er' at break of 40 MJ / m 3 That's all.

[0048] The advantageous features described herein apply equally to the codes defined above and to the extracted codes.

[0049] Advantageously, the cord has strands defining an internal cord enclosure of diameter Dv, each strand having a diameter Dt and a helical radius of curvature Rt defined by Rt = Pe / (πxSin(2αe)), where Pe is the pitch of each strand expressed in millimeters, αe is the helix angle (54) of each strand, Dv, Dt and Rt expressed in millimeters: 25≦Rt / Dt≦180 and 0.10≦Dv / Dt≦0.50.

[0050] The cord according to the invention exhibits excellent longitudinal compressibility and, all other things being equal, exhibits a relatively small diameter.

[0051] The inventors behind the present invention assert that, firstly, the cord is well ventilated due to the sufficiently large radius of curvature Rt relative to the diameter Dt of each strand, and the relatively large spacing of each strand from the longitudinal axis of the cord reduces the risk of buckling, which allows the strands to accommodate a relatively high longitudinal compressive deformation due to the helical configuration. In contrast, the radius of curvature Rt of each strand of the prior art cord is relatively small compared to the diameter Dt, so that the metal filament elements are close to the longitudinal axis of the cord and, due to the helical configuration, can accommodate a much lower longitudinal compressive deformation than the cord according to the present invention.

[0052] Secondly, if the radius of curvature Rt of each strand is too large, the cord according to the invention will have insufficient longitudinal stiffness in compression to ensure its reinforcing role, for example for tires.

[0053] Furthermore, if the inner enclosure diameter Dv is too large, the cord will be too large in diameter relative to the strand diameter.

[0054] The values ​​of the properties Dt, Dv, and Rt, as well as the other properties described below, are measured or determined from the cord immediately after it is produced, i.e., before embedding it in an elastomeric matrix, or when it is extracted from an elastomeric matrix, e.g., a tire, and the elastomeric matrix is ​​subjected to a cleaning process in which the cord, particularly the material present inside the cord, is removed. To ensure its original condition, the adhesive interface between each metal filament element and the elastomeric matrix must be removed, for example, by electrochemical treatment in a sodium carbonate bath. Effects associated with the molding step of the tire manufacturing process described below, particularly cord elongation, are eliminated by extracting the plies and cords, thereby substantially restoring their properties from before the molding step during extraction.

[0055] The enclosure of the cord according to the invention corresponds to the volume delimited by the strands and by a theoretical circle radially inside each strand on the one hand and tangent to it on the other hand, the diameter of this theoretical circle being equal to the diameter Dv of the enclosure.

[0056] The helix angle αe of each strand is a parameter well known to those skilled in the art and can be determined using the following calculation: tan αe=2xπ x Re / Pe, where Pe is the pitch in millimeters at which each strand is wound, Re is the helix radius of each strand in millimeters, tan is the tangent function, and αe is expressed in degrees.

[0057] The helix diameter De, expressed in millimeters, is calculated using the relationship: De = Pe x Tan(αe) / π, where Pe is the pitch, expressed in millimeters, at which each strand is wound, αe is the helix angle of each strand determined above, and Tan is the tangent function. The helix diameter De corresponds to the diameter of a theoretical circle passing through the centers of the strands of the layer in a plane perpendicular to the major axis of the cord.

[0058] The enclosure diameter Dv, expressed in millimeters, is calculated using the relationship: Dv=De-Dt, where Dt is the diameter of each strand and De is the helix diameter, both expressed in millimeters.

[0059] The radius of curvature Rt, expressed in millimeters, is calculated using the relationship: Rt = Pe / (πxSin(2αe)), where Pe is the pitch of each strand in millimeters, αe is the helix angle of each internal strand, and Sin is the sine function.

[0060] It will be recalled that the pitch around which each strand is wound is the length measured parallel to the axis of the cord covered and disposed by this filament element, and that the strand with this pitch then makes a complete revolution around said axis of the cord.

[0061] Advantageously, the cord is such that the metal filament elements define an internal enclosure for strands of diameter Dvt, each metal filament element having a diameter Df and a helical radius of curvature Rf defined by Rf=P / (πxSin(2α)), where P is the pitch of each metal filament element expressed in millimeters and α is the helix angle of each metal filament element (F1), Dvt, Df and Rf expressed in millimeters, and the cord satisfies the following relationships: 9≦Rf / Df≦30 and 1.30≦Dvt / Df≦4.50.

[0062] The enclosure of each strand corresponds to the volume delimited by the metal filaments and by a theoretical circle radially inside each metal filament element on the one hand and tangent to each metal filament element on the other hand, the diameter of this theoretical circle being equal to the enclosure diameter Dvt.

[0063] The helix angle α of each metal filament element is a parameter well known to those skilled in the art and can be determined using the following calculation: tan α=2×π×R / P, where P is the pitch in millimeters at which each strand is wound, R is the helix radius of each strand in millimeters, tan denotes the tangent function, and α is expressed in degrees.

[0064] The helix diameter Dh, expressed in millimeters, is calculated using the relationship: Dh = P x Tan(α) / π, where P is the pitch, expressed in millimeters, at which each metal filament element is wound, α is the helix angle of each metal filament element determined above, and Tan is the tangent function. The helix diameter Dh corresponds to the diameter of a theoretical circle passing through the center of the metal filament element of the layer in a plane perpendicular to the major axis of the cord.

[0065] The enclosure diameter Dvt of the strand, expressed in millimeters, is calculated using the relationship: Dvt=Dh-Df, where Df is the diameter of each metal filament element and Dh is the helix diameter, both expressed in millimeters.

[0066] The radius of curvature Rf, expressed in millimeters, is calculated using the relationship: Rf=P / (πxSin(2α)), where P is the pitch of each metal filament element in millimeters, α is the helix angle of each metal filament element, and Sin is the sine function.

[0067] It will be recalled that the pitch around which each metal filament element is wound is the length measured parallel to the axis of the cord covered and disposed by this filament element, at the end of which a filament element having this pitch makes a complete revolution around said axis of the cord.

[0068] The optional features described below can be combined with each other, provided that such combinations are technically compatible.

[0069] In one advantageous embodiment, all the metal filament elements have the same diameter Df.

[0070] Another subject of the invention is a method for manufacturing a cord, comprising the steps of: The method comprises: producing N strands; providing a transient assembly including a layer composed of M'>1 metal filaments helically wound around a transient core; The transitional assembly a first divided assembly including a layer of M1'≧1 spirally wound metal filaments, the M1' metal filaments originating from a layer of M'>1 metal filaments of a transitional assembly; a second divided assembly including a layer of M2'>1 spirally wound metal filaments, the M2' metal filaments originating from a layer of M'>1 metal filaments of the transitional assembly; the transitional core or one or more assemblies including the transitional core; and separating the reassembling the first segment assembly with the second segment assembly to form a strand having a layer of metal filaments and including M>1 metal filaments; carried out by The method further comprises: The method includes assembling the N strands by cabling to form a cord.

[0071] Each strand is manufactured according to the method and by employing the equipment described in documents WO2016083265 and WO2016083267. Such methods, which implement a dividing step, should be distinguished from conventional cable processes, which involve a single assembly step in which the metal filament elements are spirally wound, and which are preceded by a step of individually preforming each metal filament element, in particular to increase the value of the structural elongation. Such methods and equipment are described in documents EP0548539, EP1000194, EP0622489, WO2012055677, JP2007092259, WO2007128335, JPH06346386 or EP0143767. In these methods, the metal monofilaments are individually preformed in order to obtain the greatest possible structural elongation. However, this step of separately preforming the metal monofilaments not only requires specific equipment and makes the method relatively unproductive, without making it possible to achieve superior structural elongation compared to methods without a separate preforming step, but also has a negative effect on the metal monofilaments preformed in this way due to friction against the preforming tool. Such a negative effect can create break initiation points on the surface of the metal monofilament, thus adversely affecting the durability of the metal monofilament, especially its durability under compression. The presence or absence of such preforming marks can be observed with an electron microscope after the manufacturing method, or more simply, by knowing the method used to manufacture the cord.

[0072] Due to the manufacturing method used, each metal filament element of the cord is free from preforming marks. Such preforming marks include, in particular, flat portions. The preforming marks also include cracks extending in a cross-sectional plane substantially perpendicular to the major axis along which each metal filament element extends. Such cracks extend radially from the radially outer surface of each metal filament element toward the inside of each metal filament element in the cross-sectional plane substantially perpendicular to the major axis. As mentioned above, such cracks are generated by the bending load imposed by the mechanical preforming tool, i.e., perpendicular to the major axis of each metal filament element, and are extremely detrimental to durability. In contrast, in the methods described in WO2016083265 and WO2016083267, the metal filament elements are preformed together on a transitional core, and the preforming load is applied in a torsional state and therefore not perpendicular to the major axis of each metal filament element. Any cracks that occur do not extend radially from the radially outer surface of each metal filament element toward the inside of each metal filament element, but rather along the radially outer surface of each metal filament element, preventing a decrease in durability.

[0073] Advantageously, the cord has a diameter D such that D≦6.00 mm, preferably D≦5.00 mm.

[0074] The diameter or apparent diameter (denoted D) is measured by clamping the cord between two perfectly straight rods of 200 mm length and measuring the space between which the cord is driven using a comparator, as described below. For example, for the KAEFER model JD50 / 25, an accuracy of 1 / 100 mm can be achieved, equipped with type a contacts and a contact pressure of approximately 0.6 N. The measurement protocol consists of a series of three measurements (perpendicular to the axis of the cord and under zero tension) repeated three times.

[0075] In one embodiment, each metal filament element includes a single metal monofilament. Here, each metal filament element is preferably composed of a metal monofilament. In a variant of this embodiment, the metal monofilament is directly coated with a layer of a metal coating containing copper, zinc, tin, cobalt or an alloy of these metals, such as brass or bronze. In this variant, each metal filament element then consists of, for example, a metal monofilament made of steel and forms a core directly coated with a metal coding layer.

[0076] In this embodiment, each metal strand is preferably made of steel as described above and has a mechanical strength in the range of 1000 MPa to 5000 MPa. Such mechanical strength corresponds to steel grades commonly encountered in the field of tires, namely NT (Normal Tensile), HT (High Tensile), ST (Super Tensile), SHT (Super High Tensile), UT (Ultra Tensile), UHT (Ultra High Tensile) and MT (Mega Tensile) grades. Using a high mechanical strength potentially enables an improvement in the reinforcement of the matrix into which the cord is embedded and a reduction in the weight of the matrix reinforced in this way.

[0077] Advantageously, the layer is composed of N strands wound in a spiral, where N ranges from 2 to 6.

[0078] The process of assembling the N strands is carried out by cable wiring. The definition of cable wiring is that due to synchronous rotation before and after assembly, the strands do not twist around their own axes. This not only increases the ductility of the cord but also has the main advantage of achieving a greater breaking force than in the case of open cord strands alone.

[0079] In a first embodiment that enables partial reassembly of the M' metal filament elements, the separation step and the reassembly step are carried out such that M1'+M2'<M'.

[0080] In a second embodiment allowing for complete reassembly of the M' metal filament elements, the separation and reassembly steps are carried out such that M1'+M2'=M'.

[0081] The advantageous features described below apply equally to the methods of the first and second embodiments described above.

[0082] Preferably, M=M1′+M2′ is in the range of 3-18, preferably 4-15.

[0083] Advantageously, in an embodiment in which the transitional core is separated into two parts each associated with a first and second split assembly, to facilitate extraction of the transitional core, the following is done. When M'=4 or M'=5, M1'=1, 2 or 3 and M2'=1, 2 or 3; when M'≧6, M1'≦0.75×M'; When M'≧6, M2'≦0.75×M'.

[0084] In embodiments in which the transitional core is separated into two parts associated with the first and second assemblies, M'≧6, M1'≦0.70×M', and M2'≦0.70×M' to further facilitate extraction of the transitional core.

[0085] Very preferentially, the step of providing a transient assembly comprises assembling by twisting M'>1 metallic filament elements wound helically around a transient core.

[0086] Advantageously, the step of providing the transient assembly includes a step of balancing the transient assembly. In this way, since the balancing step is performed on the transient assembly including the M' metallic filament element and the transient core, the balancing step is implicitly performed upstream of the step of separating into the first and second divided assemblies. This avoids the need to manage residual twists imposed during the step of assembling the transient assembly in the paths followed by the various assemblies downstream of the assembling step, in particular via guide means, e.g. pulleys.

[0087] Advantageously, the method includes a step of balancing the final assembly downstream of the reassembly step.

[0088] Advantageously, the method includes a step of maintaining rotation about the direction of movement of the final assembly, which step of maintaining rotation is performed downstream of the step of isolating the transitional assembly and upstream of the step of balancing the final assembly.

[0089] Preferably, the method does not include a step of individually preforming each of the metal filament elements. In prior art methods that use a step of individually preforming each of the metal filament elements, the metal filament elements are given a shape by preforming tools, such as rollers, which cause defects on the surface of the metal filament elements. These defects significantly reduce the durability of the metal filament elements and therefore the durability of the final assembly.

[0090] Highly preferably, the transitional core is a metal filament element. In a preferred embodiment, the transitional core is a metal monofilament. The diameter of the spaces between the metal filament elements, and therefore the geometric characteristics of the final assembly, are accordingly very precisely controlled, in contrast to transitional cores made of fibrous materials, such as polymeric materials, whose compressibility can cause variations in the geometric characteristics of the final assembly.

[0091] In another, equally advantageous embodiment, the transitional core is a woven filament element. Such a woven filament element comprises at least one multifilament woven ply or, in a variant, is composed of woven monofilaments. Fiber filaments that can be used are selected from polyesters, polyketones, aliphatic or aromatic polyamides, and blends of fiber filaments containing these materials. This reduces the risk of breakage of the transitional core due to friction of the metal filament element against the transitional core and the torsion applied to the transitional core.

[0092] Reinforced product according to the present invention

[0093] A further subject of the present invention is a reinforced product comprising a polymer matrix and at least one extracted cord as defined above.

[0094] Advantageously, the reinforced product comprises one or more cords according to the invention embedded in a polymer matrix, in the case of a plurality of cords, the cords being arranged side by side in the main direction.

[0095] Tire according to the present invention

[0096] A further subject of the present invention is a tire comprising at least one extracted cord as defined herein or a reinforcement product as defined herein.

[0097] Preferably, the tire comprises a carcass reinforcement anchored to the two beads and radially borne by a crown reinforcement which is itself borne by the tread, the crown reinforcement being joined to said beads by two sidewalls and comprising at least one cord as defined above.

[0098] 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 herein, and the protective reinforcement being positioned radially between the tread and the working reinforcement.

[0099] The Code specifically contemplates industrial vehicles selected from "heavy vehicles" - i.e., heavy vehicles such as subways, buses, road transport vehicles (lorries, tractors, trailers), off-road vehicles - i.e., agricultural or construction plant vehicles, or other transport or processing vehicles.

[0100] Preferably, the tire is for a construction plant type vehicle, and therefore has a size such that the seat diameter (in inches) of the rim on which the tire is intended to be mounted is 30 inches or greater.

[0101] The present invention also relates to a rubber article comprising an assembly according to the invention or an impregnated assembly according to the invention, the definition of which is any type 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 caterpillar track.

[0102] The invention will be better understood on reading the following description, given purely by way of non-limiting example and with reference to the drawings, in which: [Brief explanation of the drawings]

[0103] [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 reinforced product according to the present invention. [Figure 4] FIG. 2 shows a portion of the stress-elongation curve of a cord (50) according to the present invention. [Figure 5] 1 is a schematic cross-sectional view perpendicular to the axis of a cord (50) according to a first embodiment of the present invention (assumed to be straight and stationary). FIG. [Figure 6] FIG. 6 is a view similar to FIG. 5 of a cord (60) according to a second embodiment of the present invention. [Figure 7]FIG. 6 is a schematic diagram showing the effect of deformability of the cord (50) of FIG. 5 under light tensile load due to radial clearance of the filaments. [Figure 8] FIG. 6 is a schematic representation of a method according to the invention that allows the production of the cord (50) of FIG. 5. [Figure 9] FIG. 6 is a schematic representation of a method according to the invention that allows the production of the cord (50) of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0104] Example of a tire according to the present invention

[0105] An X, Y, Z frame of reference corresponding to the typical axial (X), radial (Y) and circumferential (Z) directions of the tire are depicted in FIGS.

[0106] 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.

[0107] 1 and 2 show a tire according to the invention and are designated by the general reference P.

[0108] The tire P is intended for heavy vehicles of the construction plant type, for example for heavy vehicles of the "dumper" type. The tire P therefore has dimensions of the type 53 / 80R63.

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

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

[0111] The tire P also includes a sealing ply 32 (commonly known as an "inner liner") constructed of an elastomer that defines the radially inner surface 34 of the tire P and is intended to protect the carcass ply 30 from the diffusion of air emanating from the space inside the tire P.

[0112] The crown reinforcement 14 comprises, from the radially outer side to the radially inner side of the tire P, a protective reinforcement 36 arranged radially inside the tread 22, a working reinforcement 38 arranged radially inside the protective reinforcement 36, and an additional reinforcement 40 arranged radially inside the working reinforcement 38. Thus, the protective reinforcement 36 is arranged radially between the tread 22 and the working reinforcement 38. The working reinforcement 38 is interposed radially between the protective reinforcement 36 and the additional reinforcement 40.

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

[0114] The working reinforcement 38 comprises first and second working 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 working metal cord 50 crosses from one working ply to another, forming an angle with the circumferential direction Z of the tire equal to 60° at most, preferably an angle in the range of 15° to 40°.

[0115] The additional reinforcement 40, also called limiting block, the purpose of which is to partially absorb the mechanical stresses of expansion, consists for example of an additional metal reinforcing element, known per se, as described for example in FR 2 419 181 or FR 2 419 182, which is at an angle to the circumferential direction Z of the tire P of at most 10°, preferably between 5° and 10°.

[0116] Examples of reinforced products according to the present invention

[0117] Figure 3 shows a reinforced product according to the invention and is designated by the general reference R. The reinforced product R comprises at least one cord 50', in this example a plurality of cords 50', embedded in a polymer matrix Ma.

[0118] 3 depicts the polymer matrix Ma and the cords 50' in a frame of reference X, Y, Z, with direction Y being the radial direction and directions X and Z being the axial and circumferential directions. In FIG. 3, the reinforced product R comprises a plurality of cords 50' juxtaposed in the main direction X and extending parallel to one another within the reinforced product R, and is entirely embedded in the polymer matrix Ma. In this example, the polymer matrix Ma is an elastomeric matrix based on an elastomeric compound.

[0119] Code according to a first embodiment of the present invention

[0120] FIG. 5 shows a code 50 according to a first embodiment of the present invention.

[0121] Once extracted from the tire 10, each protective reinforcing element 43, 45 and each hoop reinforcing element 53, 55 is formed from the extracted cord 50' as explained below. The cord 50 is obtained in this example by embedding it in the polymer matrix forming the respective polymer matrix of each protective ply 42, 44 and each hoop layer 52, 54, respectively, in which the protective reinforcing elements 43, 45 and each hoop reinforcing element 53, 55, respectively, are embedded.

[0122] The cord 50 and the extracted cord 50' are made of metal with a single layer.

[0123] The cord 50 or cord 50' comprises a layer of 1xN construction including a single layer 52 of N=3 strands 54 helically wound around a main axis (A), each strand 54 comprising a single layer of metal filaments 56F1, and M>1 metal filaments helically wound around an axis (B), where M=5 in this example.

[0124] As mentioned above, the value At is determined by plotting the force-elongation curve of Code 50 applying the 2014 ASTM standard D2969-04.

[0125] The cord 50 has a total elongation At>8.10%, preferably At≧8.30%, more preferably At≧8.50%, and a total elongation At≦20.00%, preferably At≦16.00%, in this example At=13.4%.

[0126] From this stress-elongation curve, the area under the curve is derived as described herein. Figure 4 illustrates the rectangular method for determining the energy-to-break index of cord 50.

[0127] The energy index Er at break for Code 50 is as follows: It looks like TIFF0007737379000004.tif10150, TIFF0007737379000005.tif14150, which is exactly 52 MJ / m 3 Greater than 55MJ / m 3 More than 200MJ / m 3 or less, and preferably 150 MJ / m 3 The following is the result.

[0128] The cord 50 has a structural elongation As such that As>4.30%, preferably As≧4.50%, more preferably As≧4.60%, and As≦10.0%, preferably As≦9.50%. In this example, As=9.3%.

[0129] The cord 50 has a secant elastic modulus E1 in the range of 3.0 to 10.0 GPa, preferably 3.5 to 8.5 GPa. In this example, E1=4.0 GPa.

[0130] The tangent elastic modulus E2 of the cord 50 is in the range of 50 to 180 GPa, preferably in the range of 55 to 150 GPa. In this example, E2=73 GPa.

[0131] The drawn cord 50' has a total elongation At'>5.00%, preferably At'≧5.20%, where At'=10% in this example.

[0132] The energy index Er' at break of the extracted cord 50' is TIFF0007737379000006.tif7170, which is Virtually equal to TIFF0007737379000007.tif14150. , which is exactly 35MJ / m 3 Greater than 40MJ / m 3 That's all.

[0133] The strands 54 define an internal enclosure 59 of the cord 50; 50' of diameter Dv, with each strand 54 having a diameter Dt and a helical radius of curvature Rt defined by Rt = Pe / (π x Sin(2αe)) = 80 / (π x sin(2 × 5.3 × π / 180) = 138 mm.

[0134] Rt / Dt=138 / 2.03=68≦180, 68≧25.

[0135] Dv / Dt = 0.32 / 2.03 = 0.16 ≤ 0.50 and 0.16 ≥ 0.10.

[0136] The metal filament element F1 of each strand 52 defines an internal enclosure 58 of the strand 52 of diameter Dvt, with each metal filament element F1 having a diameter Df and a helical radius of curvature Rf defined by Rf = P / (πxSin(2α)) = 10 4 / (πxSin(2 × 25 8 × π / 180) = 4 2 mm.

[0137] Rf / Df=4.2 / 0.46=9≦30.

[0138] TIFF0007737379000008.tif6157

[0139] Method for manufacturing a cord according to the present invention

[0140] Next, an example of a method for manufacturing the multi-strand cord 50 as illustrated in FIGS. 8 and 9 will be described.

[0141] First, the filament element F1 and the transitional core 16 are unwound from the supply means.

[0142] Next, the method includes a step 100 of providing a transient assembly 22, which includes, on the one hand, a step of assembling the M' metallic filament elements F1 by twisting a single layer of the M' metallic filament elements F1 around the transient core 16, and, on the other hand, a step of balancing the transient assembly 22, which is carried out by means of a twister.

[0143] The method includes step 110 of separating the transient assembly 22 into a first divided assembly 25, a second divided assembly 27, a transient core 16, or one or more assemblies including a transient core 16, in this case the transient core 16.

[0144] Downstream of the supply means 11, step 110 of separating the transient assembly 22 into a first divided assembly 25, a second divided assembly 27 and a transient core 16 includes step 120 of separating the transient assembly 22 into a precursor assembly, a second divided assembly 27 and finally the transient core 16.

[0145] Downstream of the separating step 122, the step 120 of separating the transitional assembly into precursor and split assemblies includes a step 124 of separating the split assemblies into a second split assembly 27 and a transitional core 16. In this case, the separating step 124 includes dividing the split assemblies into a second split assembly 27, a transitional core 16, and a complementary assembly.

[0146] Downstream of the supplying step 100, the step 110 of separating the transitional assembly into a first divided assembly 25, a second divided assembly 27 and a transitional core 16 includes a step 130 of separating the precursor assembly into a first divided assembly 25 and a complementary assembly.

[0147] Downstream of separation steps 110, 120, 124, and 130, the method includes step 140 of reassembling the first split assembly 25 with the second split assembly 27 to form strand 54. In this embodiment, reassembly step 140 is a step of reassembling the first split assembly 25 with the second split assembly 27 to form strand 54 and includes metal filaments F1 where M > 1, where M is from 3 to 18, preferably from 4 to 15, and where M = 5 here.

[0148] In this embodiment, supply step 100, separation step 110, and reassembly step 140 are performed such that all M' metal filament elements F1 have the same diameter Dfi, are helically wound with the same pitch P, and have the same helical radius of curvature Rf as described above.

[0149] In this embodiment that allows for partial reassembly of the M' metal filament elements, separation step 110 and reassembly step 140 are performed such that M1' + M2' < M'. Here, M1' = 1, M2' = 4: M1' + M2' = 5 < 8. Finally, it can be seen that M1' ≤ 0.70 × M' = 0.70 × 8 = 5.6 and M2' ≤ 0.70 × M' = 0.70 × 8 = 5.6.

[0150] Execute a final balance adjustment step.

[0151] Finally, strand 54 is stored on a storage spool. Similarly, N strands 54 are manufactured.

[0152] Regarding the temporary core 16, the method includes a step of recycling the temporary core 16. In this recycling step, downstream of separation step 110, in this case downstream of separation step 124, the temporary core 16 is recovered and the previously recovered temporary core is introduced upstream of the assembly step. This recycling step is continuous.

[0153] Note that the method as thus described does not have a step of preforming each of the metal filament elements F1 individually.

[0154] To form the cord 50, an assembly step 300 is performed which involves assembling N strands 54 in a cabling manner, where in this example N=3.

[0155] It should be noted that the method thus described does not include preforming each of the strands 54 individually.

[0156] Code according to a second embodiment of the present invention

[0157] FIG. 6 illustrates a cord 60 according to a second embodiment of the present invention.

[0158] Unlike the first embodiment described herein, the code 60 according to the second embodiment is such that N=4.

[0159] The properties of the various cords 50, 50', 60, 60', 51, 52, 53, 53', 54 according to the invention and the prior art cords EDT1, EDT1', EDT2, EDT2' are summarised in Tables 1, 2 and 3 below.

[0160] Comparative Test

[0161] Evaluation of total cord elongation and energy at break index

[0162] The stress-elongation curves of the cords were plotted using the 2014 ASTM standard D2969-04, and the total elongation and energy-to-break index were calculated for the various cords 50, 50', 60, 60', 51, 52, 53, 53', 54 according to the invention and the prior art cords EDT1, EDT1', EDT2 and EDT2'.

[0163] In Table 3, "NA" means that the parameter was not measured.

[0164] [Table 1]

[0165] [Table 2]

[0166] [Table 3]

[0167] Tables 1, 2 and 3 demonstrate that cords 50, 50', 60, 60', 51, 52, 53, 53', 54 according to the present invention have improved energy-to-break index and better deformability compared to prior art cords EDT1, EDT1', EDT2 and EDT2'.

[0168] Thus, the code according to the invention is able to solve the problem mentioned in the preamble.

[0169] The present invention is not limited to the above-described embodiments. [Explanation of symbols]

[0170] 50 Code 52 hoop layers 54 hoop layers 56 Metal Filament 59 Internal Enclosure

Claims

1. A multi-strand cord (50) having a 1×N structure comprising a single layer (52) of N strands (54) helically wound around a main axis (A), A cord (50) in which each strand (54) has one layer (56) of metal filaments (F1) and comprises M>1 metal filaments helically wound around an axis (B), The cord (50) has a total elongation At>8.10% as defined by the 2014 ASTM standard D2969-04; The breaking energy index Er of the cord (50) is where σ(Ai) is the tensile stress in MPa measured at elongation Ai, and dAi is the elongation such that Er is strictly greater than 52 MJ / m A code (50).

2. The cord (50) of claim 1, wherein the total elongation At is At > 8.30%.

3. The cord (50) according to claim 1, wherein the cord (50) has an energy index at break Er of 55 MJ / m3 or more.

4. 2. The cord (50) of claim 1, having a structural elongation, As, as defined by 2014 ASTM Standard D2969-04, such that As>4.30%.

5. The cord (50) of claim 1, having a secant modulus of elasticity E1 in the range of 3.0 to 10.0 GPa.

6. The cord (50) of claim 1, having a tangent modulus of elasticity E2 in the range of 50 to 180 GPa.

7. A cord (50') drawn from a polymer matrix, said drawn cord (50') having a 1xN structure comprising a single layer (52) of N strands (54) helically wound around a main axis (A), each strand (54) having one layer (56) of metal filaments (F1) and comprising M>1 metal filaments helically wound around an axis (B), The drawn cord (50') has a total elongation At'≧5.00% as defined by the 2014 ASTM standard D2969-04; The energy index Er' at break of the extracted cord (50') is where σ(Ai) is the tensile stress in MPa measured at elongation Ai, and dAi is the elongation such that Er′ is strictly greater than 35 MJ / m An extracted cord (50') characterized in that:

8. The drawn cord (50') according to claim 7, wherein the total elongation At' is such that At'≧5.20%.

9. A reinforced product (R) comprising a polymer matrix (Ma) and at least one extracted cord (50') according to claim 7.

10. A tire (P), characterized in that it comprises at least one extracted cord (50') according to claim 7 or a reinforcement product according to claim 9.

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