Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/0042—Reinforcements made of synthetic materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C9/08—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship the cords extend transversely from bead to bead, i.e. radial ply
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B1/00—Constructional features of ropes or cables
  • D07B1/02—Ropes built-up from fibrous or filamentary material, e.g. of vegetable origin, of animal origin, regenerated cellulose, plastics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C2009/0071—Reinforcements or ply arrangement of pneumatic tyres characterised by special physical properties of the reinforcements
  • B60C2009/0085—Tensile strength
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C2009/0071—Reinforcements or ply arrangement of pneumatic tyres characterised by special physical properties of the reinforcements
  • B60C2009/0092—Twist structure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C2009/0269—Physical properties or dimensions of the carcass coating rubber
  • B60C2009/0276—Modulus; Hardness; Loss modulus or "tangens delta"
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C2009/0416—Physical properties or dimensions of the carcass cords
  • B60C2009/0425—Diameters of the cords; Linear density thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C2009/0416—Physical properties or dimensions of the carcass cords
  • B60C2009/0441—Density in width direction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C2009/0416—Physical properties or dimensions of the carcass cords
  • B60C2009/045—Tensile strength
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C2009/0416—Physical properties or dimensions of the carcass cords
  • B60C2009/0458—Elongation of the reinforcements at break point
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
  • B60C9/02—Carcasses
  • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
  • B60C2009/0475—Particular materials of the carcass cords
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C2200/00—Tyres specially adapted for particular applications
  • B60C2200/02—Tyres specially adapted for particular applications for aircrafts
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B2205/00—Rope or cable materials
  • D07B2205/20—Organic high polymers
  • D07B2205/2046—Polyamides, e.g. nylons
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B2501/00—Application field
  • D07B2501/20—Application field related to ropes or cables
  • D07B2501/2046—Tyre cords

Definitions

• the field of the present invention is that of tires for radial carcass reinforcement, intended in known manner to be inflated to relatively high pressures and carry very heavy loads at high speed.
• the textile is used as reinforcement since the origins of the tire.
• Textile reinforcements made from continuous textile fibers such as nylon fibers, play an important role in tires, especially in aircraft tires. To meet the requirements of these tires, they must have a high mechanical strength, good endurance and finally excellent adhesion to rubber matrices they are likely to strengthen.
• the radial carcass reinforcement of aircraft tires generally comprise several textile plies, which are anchored in each bead to at least one bead or annular reinforcing element.
• the textile reinforcements of these reinforcements and plies are wrapped around the rod by forming reversals whose respective ends are radially spaced relative to the axis of rotation of the tire.
• the severe conditions under which the tires are used for aircraft are such that a very high endurance of these carcass reinforcement is necessary.
• the first group comprises the plies of the axially inner carcass reinforcement in the area of the flanks and beads, said plies being then wrapped around an anchor rod in each bead from the inside to the outside of the tire;
• the second group consists of axially outer plies in the above zone, plies generally partially wound around the rod from the outside to the inside of the tire.
• Each carcass reinforcement ply is, for its part, reinforced by unidirectional textile reinforcements in the form of "cords” or “twists” (the two terms being synonymous), most often of aliphatic polyamide or nylon, each cabled being composed of several twisted strands together in a helix.
• cords or "twists” (the two terms being synonymous)
• the mechanical properties in extension (in particular breaking strength and toughness) and the fatigue strength (endurance in extension, flexion, compression) of these cords are paramount; in general, for a given material, they are even higher than the linear densities (titles) and the twists of the cords are important.
• the present invention concerns (according to the references given in FIGS. 1 to 3 appended) a radial tire for an airplane (1), defining three main directions, circumferential (X), axial (Y) and radial (Z ), comprising an apex (2) surmounted by a tread (3), two sidewalls (4), two beads (5), each sidewall (4) connecting each bead (5) to the top (2), an armature carcass (7) anchored in each of the beads (5) to at least one rod (6) and extending in the flanks (4) to the top (2), a crown reinforcement or belt (10) s' extending in the crown (2) in the circumferential direction (X) and situated radially between the carcass reinforcement (7) and the tread (3), this so-called radial carcass reinforcement (7) comprising at least one so-called carcass ply in the form of a rubber matrix reinforced by radially oriented reinforcing elements, said radially reinforcing textile reinforcements the latter being wholly or
• N is greater than 2
• Tei of each strand is greater than 75 cN / tex;
• Te 2 of each twist is greater than 60 cN / tex;
• the helix angle denoted a of each twist is greater than 20 °.
• the invention also relates to the use, for the reinforcement of a carcass reinforcement of a radial tire for aircraft, of a nylon textile twister as defined above.
• a conventional (or spun) multifilament textile fiber in cross-section, a conventional (or spun) multifilament textile fiber, first in the initial state (15) that is to say devoid of torsion, then after a first torsion operation T1 in the direction D1, in the form of a spun yarn on itself or "strand" (20) (Fig. 2);
• FIG. 40 in cross section, another representation of a final textile cord (40), less schematic than the previous one, illustrating that the final section of a textile cord (here, for example consisting of 4 strands), once formed and at a minimum tension, it is closer in fact to a section with a circular contour, because of the high lateral plasticity provided by the multifilament nature of the starting material (FIG.
• rubber or "elastomer” (both terms being considered synonymous): any type of elastomer, whether of the diene type or of the non-diene type, for example thermoplastic;
• rubber composition or “rubber composition” means a composition which comprises at least one rubber and a filler
• layer means a sheet, strip or other element of relatively small thickness with respect to its other dimensions, preferably having a ratio of the thickness to the largest of the other dimensions less than 0.5, more preferably less than at 0.1;
• axial direction means a direction substantially parallel to the axis of rotation of the tire
• circumferential direction means a direction that is substantially perpendicular both to the axial direction and to a radius of the tire (in other words, tangent to a circle whose center is on the axis of rotation of the tire);
• radial direction means a direction along a radius of the tire, that is to say any direction passing through the axis of rotation of the tire and substantially perpendicular to that direction, that is to say with a perpendicular at this direction an angle not diverging by more than 5 degrees (thus zero or at most equal to 5 degrees); "oriented along an axis or a direction” by speaking of any element such as a reinforcement, an element which is oriented substantially parallel to this axis or this direction, that is to say making with this axis or this direction an angle not more than 5 degrees apart;
• oriented perpendicular to an axis or direction speaking of any element such as a reinforcement, an element which is oriented substantially perpendicular to that axis or direction, that is to say making with a perpendicular to this axis or direction an angle not more than 5 degrees apart;
• M Median circumferential plane
• unidirectional reinforcements reinforcements essentially parallel to each other, that is to say oriented along the same axis.
• x and / or y means “x” or “y” or both (i.e., “x and y”). Any range of values designated by the expression “between a and b” represents the range of values from more than “a” to less than “b” (i.e., “a” and “b” terminals excluded ) while any range of values referred to as “a to b” means the range of values from “a” to "b” (ie including the strict "a” and “a” limits). "B”). - -
• FIG. 1 very schematically represents (that is to say, without respect of a specific scale) a radial section of a tire (1) for aircraft whose radial carcass reinforcement ( 7) is reinforced by nylon textile twists according to the invention.
• This radial tire for aircraft (1) defining three main directions, circumferential (X), axial (Y) and radial (Z), comprises a crown (2) surmounted by a tread (3), two sidewalls (4). ), two beads (5), each flank (4) connecting each bead (5) to the top (2), a carcass reinforcement (7) anchored in each of the beads (5) to at least one rod (6) and s extending in the flanks (4) to the top (2), a crown reinforcement or belt (10) extending in the crown (2) in the circumferential direction (X) and radially located between the carcass reinforcement (7) and the tread (3).
• the so-called radial carcass reinforcement (7) comprises at least one so-called “carcass ply” ply in the form of a matrix or rubber composition reinforced by substantially radially oriented reinforcing elements, called radial textile reinforcements, of which at least a part consists of specific nylon textile twists.
• radial textile reinforcements of which at least a part consists of specific nylon textile twists.
• the latter constitute all of the radial textile reinforcements used in said carcass ply (7).
• these nylon textile twists having a number N of multifilament strands twisted together in a helix, combine the following characteristics: N is greater than 2;
• the Tei tenacity of each strand is greater than 75 cN / tex;
• Te 2 of each twist is greater than 60 cN / tex;
• helix angle denoted a (alpha) of each twist is greater than 20 °.
• the nylon or polyamide aliphatic is chosen from polyamides 4-6, 6, 6-6, 11 or 12; more preferably nylon 6 or 6-6, more particularly nylon 6-6 is used.
• the specific nylon twisted or wired used to reinforce the carcass plies of the aircraft tire of the invention therefore has the essential first characteristic that it comprises more than two, that is to say three or more strands. . - -
• N is 3 or 4. More preferably, N is 3.
• FIG. 2 schematizes, in cross-section, a conventional multifilament textile fiber (15) in the initial state, that is to say without torsion; as is well known, such a fiber or "spun” (in English “yarn") is formed of a plurality of elementary filaments (50), typically several tens to several hundred, of very fine diameter, generally less than 35 ⁇ .
• twists or cords textile at least double twist (Tl, T2) and this is illustrated by way of example in Figures 2 and 3, are prepared from such a yarn, by a so-called twisting process in which: during a first step (FIG.
• each yarn (15) constituting the final cord is first of all individually pretensioned on itself (according to a twist initial Tl) in a given direction Dl (respectively S or Z direction according to a recognized nomenclature designating the orientation of the turns along the transverse bar of an S or Z), to form a multifilament strand (in English "strand”) or "ply”) also called surtors (in English "folded yarn”) (20) in which the elementary filaments (50) are imposed a helical deformation around the fiber axis (or axis of the strand);
• N strands or surtors for example three in number (20a, 20b, 20c) in Figure 3, are then twisted this time all together in a final twist T2 (which may be equal to or different from T1) in the opposite direction D2 (respectively Z or S direction), for obtaining the cord or twisted (in English "cord” or "pliedyarn”) (30) final N strands.
• the role of the twisting is to adapt the properties of the material in order to create the transverse cohesion of the reinforcement, to increase its resistance to fatigue and also to improve the adhesion with the reinforced matrix.
• FIG. 4 represents, again in cross-section, another representation of a textile cord (40), less schematic than the previous one, recalling the well-known fact that the section of a textile cord (for example here consisting of 4 strands or surtors 20a, 20b, 20c, - -
• twists can be measured and expressed in different ways, either simply and in a number of revolutions per meter (rpm), and this is more rigorous when desired. compare materials of different types (density) and / or titer, at a helix angle (a) of the filaments or, what is equivalent, in the form of a torsion factor K.
• the helix angle ⁇ (relative to the axis of the twist) can be measured directly by visual observation on the twist, or its tangent (Tan) calculated in a known manner by the equation below in which T represents the torsion (in r / m) of the elementary filaments constituting the twist, and Re (in m) the winding radius of the strands or surtors in the final twist:
• the torsion factor K is linked to the torsion T (T1 or T2 depending on whether the factor is calculated on a strand or on the twist) according to the following well-known relation (T in r / m, Ti in tex, p in g / cm 3 ):
• the Ti titer of each strand or surtors constituting the twist is greater than 180 tex.
• Ti is greater than 200 tex, more preferably - - greater than 220 tex. More preferably still, Ti is greater than 240 tex, in particular greater than 260 tex.
• the title Ti can of course be adjusted by a preliminary grouping, usually in packets of 2, 3 or even 4, of several yarns of lower basic title. For example, it is customary to prepare a strand or surtres of 188 tex by grouping, prior to any twisting operation, 2 spun yarns of elementary title 94 tex; a strand or surtres of 280 tex can be prepared by grouping 2 yarns of elementary title 140 tex.
• the title Ti indicated in the present application is always that of the final yarn (after possible regrouping) serving as strand for the operation of first twist (pretorsion) in the manufacture of the twisted yarn.
• the toughness (as a reminder, breaking strength divided by the title) denoted Tei of each strand is greater than 75 cN / tex. Preferably, it is greater than 80 cN / tex, more preferably greater than 85 cN / tex. In particular, it is greater than 90 cN / tex, more particularly greater than 95 cN / tex.
• the elongation at break Ari of each strand is greater than 14%.
• Ari is greater than 16%, more preferably greater than 18%, in particular greater than 20%.
• nylon fibers examples include “T728” or “T802” fibers from Kordsa, “T654" from Nexis, or “T7” from Asahi, which can be available according to different titles.
• the tenacity Te 2 of the plied yarn is greater than 60 cN / tex, preferably greater than 65 cN / tex, still more preferably greater than 70 cN / tex. In particular, it is greater than 75 cN / tex, more particularly greater than 80 cN / tex.
• the elongation at break Ar 2 of each twist is greater than 18%.
• Ar 2 is preferably greater than 20%, more preferably greater than 22%, in particular greater than 24%.
• the helix angle ⁇ of each twist is greater than 20 °; preferably, a is greater than 22 °, more preferably greater than 24 °.
• the torsion factor (denoted Ks) of each strand or surtors, thus calculated on the surtors as present (twisted) in the twist is greater than 90, more preferably greater than 100, in particular greater than 110. - -
• Prior conditioning means the storage of the cables for at least 24 hours, before measurement, in a standard atmosphere according to the European standard DIN EN 20139 (temperature of 20 ⁇ 2 ° C, hygrometry of 65 ⁇ 2%).
• the title of the elementary strands or cords is determined on at least three samples, each corresponding to a length of 50 m, by weighing this length. As a reminder, the title (or linear density) is the weight in grams of 1000 m of product, it is expressed in tex (0, 111 tex equals 1 denier).
• the mechanical properties in extension are measured in known manner using an "INSTRON" traction machine equipped with "4D” type clamping tongs (for a force rupture less than 100 daN) or “4E” (for a breaking force of at least 100 daN), unless otherwise specified in ASTM D885 (2010).
• the tested samples are pulled over an initial length of 400 mm for 4D pliers and 800 mm for 4E pliers, at a nominal speed of 200 mm / min, under a standard pretension of 0.5 cN / tex. All results given are an average of 10 measurements.
• the mechanical properties indicated for the plies are those measured on the plies in their given (stable) torsion state (under a helix angle) while the properties mechanical (Ti, Te ls Ari) indicated for the multifilamentary strands are those measured on the constituent yarns of the strands once the twists at first and then in a second time the strands themselves untwisted;
• the yarns then simply undergo, in a well-known manner, a very slight prior twisting, referred to as "protective twist” (corresponding to a helix angle of the filaments of about 6 degrees) before positioning and pulling in. the clamps.
• the rubber compositions used as matrices in the carcass reinforcement plies of the aircraft tires of the invention are conventional compositions for calendering textile reinforcements, typically based on at least one rubber, a reinforcing filler such as carbon black. and / or silica, generally a vulcanization system and customary additives.
• any suitable adhesive system may be used, for example a textile glue of the "RFL” type (resorcinol- - - formaldehyde latex) or any equivalent adhesive known to confer a satisfactory adhesion between rubber and nylon, such as the more recent adhesive compositions described in applications WO 2013/017421, WO 2013/017422, WO 2013/017423 , WO 2015/007641, WO 2015/007642.
• RTL resorcinol- - - formaldehyde latex
• the rubber is a diene rubber, that is to say for all elastomeric recall (single elastomer or elastomer mixture) which is derived, at least in part (ie, a homopolymer or a copolymer), monomers dienes that is to say monomers bearing two carbon-carbon double bonds, whether the latter are conjugated or not.
• elastomeric recall single elastomer or elastomer mixture
• monomers dienes that is to say monomers bearing two carbon-carbon double bonds, whether the latter are conjugated or not.
• This diene elastomer is more preferably selected from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.
• Such copolymers being especially chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-copolymers.
• SBIR butadiene-styrene
• a particularly preferred embodiment consists in using an "isoprene" elastomer, that is to say a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR ), the synthetic polyisoprenes (IR), the various isoprene copolymers and the mixtures of these elastomers.
• the isoprene elastomer is more preferably natural rubber or a synthetic polyisoprene of cis-1,4 type.
• polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are used in particular.
• each layer of rubber composition comprises 50 to 100 phr of natural rubber.
• Each rubber composition may comprise one or more diene elastomer (s), also all or part of the additives usually used in rubber matrices for the manufacture of tires, such as, for example, reinforcing fillers such as carbon black.
• plasticizing agents or extension oils whether these are aromatic or non-aromatic in nature (in particular very low or non-aromatic oils, for example of the naphthenic or paraffinic type, with high or preferably low viscosity, MES or TDAE oils), plasticizing resins with a high glass transition temperature (greater than 30 ° C.), agents facilitating the use (processability ) green compositions, tackifying resins, anti-eversion agents, methylene acceptors and donors such as, for example, H MT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or - - bismaleimide), adhesion promoter systems, a crosslinking or vulcanization system.
• aromatic or non-aromatic oils in particular very low or non-aromatic oils, for example of the naphthenic or paraffinic type, with high or preferably low viscosity, MES or TDAE oils
• the crosslinking system of the rubber composition is a so-called vulcanization system, that is to say based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator.
• a vulcanization system may be added various known secondary accelerators or vulcanization activators.
• the sulfur is used at a preferential rate of between 0.5 and 10 phr
• the primary vulcanization accelerator for example a sulfenamide
• the level of reinforcing filler for example carbon black and / or silica, is preferably greater than 30 phr, especially between 30 and 100 phr.
• Carbon blacks are suitable for all carbon blacks, especially blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called tire grade blacks). Among the latter, mention will be made more particularly of carbon blacks of (ASTM) grade 300, 600 or 700 (for example N326, N330, N347, N375, N683, N772).
• Suitable silicas are in particular precipitated or pyrogenic silicas having a BET surface area of less than 450 m 2 / g, preferably from 30 to 400 m 2 / g.
• each rubber composition has, in the crosslinked state, a secant modulus in extension noted Ms, at 10% elongation, which is between 4 and 25 MPa, more preferably between 4 and 20 MPa; values in particular between 5 and 15 MPa have proved particularly suitable.
• the measurements of this secant modulus are carried out in tension, unless otherwise indicated according to the ASTM D 412 standard of 1998 (test-tube "C"): one measures in second elongation (that is to say after a cycle of accommodation) the secant modulus "true” (that is to say, reduced to the actual section of the test piece) at 10% elongation, noted here Ms and expressed in MPa (normal temperature and humidity conditions according to ASTM standard D 1349 of 1999).
• the tire of the invention has another preferred feature that the density of the radial textile plies reinforcing said (at least one) radial carcass ply, measured in the axial direction Y, is between 50 and 80 threads / dm of ply (per decimeter i.e., 100 mm wide rubber web), preferably 60 to 75 threads / dm web.
• the use of an aircraft tire is characterized, as is known, by particularly high pressure, load and speed conditions.
• tire for aircraft is preferably meant in the present application a tire whose nominal pressure is greater than 9 bar and the nominal deflection greater than 30%. - -
• the nominal pressure is the nominal inflation pressure of the tire as defined, for example, by the Tire and Rim Association (or TRA) standard.
• the nominal deflection is the radial deformation of a tire, or radial height variation, when it moves from an unfilled inflated state to a statically loaded inflated state under the nominal pressure and load conditions as defined. for example, by the TRA standard. It is expressed as a relative deflection, defined by the ratio of this variation of the radial tire height to half of the difference between the outside diameter of the tire and the maximum diameter of the rim measured on the rim flange. . The outer diameter of the tire is measured statically in an unfilled condition inflated to the nominal pressure.
• the TRA standard defines in particular the crushing of an airplane tire by its crushed radius, that is to say by the distance between the axis of the tire wheel and the plane of the ground with which the tire is in contact under nominal pressure and load conditions.
• the radial carcass reinforcement (7) preferably comprises a plurality of radially superimposed carcass plies, the number of superimposed carcass plies being more preferably in a range from 3 to 10.
• the specificity of the cord or nylon twists used in the carcass reinforcement of the aircraft tire of the invention compared with the twists used hitherto in the carcass reinforcement of the aircraft tires of the prior art, is that it combines the essential characteristics previously mentioned. , namely: - it consists of at least three strands;
• each strand is very high, greater than 180 tex; its tenacity is greater than 75 cN / tex; its elongation at break is greater than 14%;
• the tenacity of each twist is greater than 60 cN / tex, its elongation at break is greater than 18%; its helix angle a is greater than 20 °.
• the 280 tex yarns were thus assembled by two strands (N equal to 2), those of 188 tex were assembled by three strands (N equal to 3 ).
• N the number of strands
• N the number of strands
• three different cords were manufactured by varying the helix angle (calculated according to the equation given above) according to three increasing values, from 23.5 ° to 28 ° (T2 torsion varies from about 245 tr / m to 320 tr / m depending on the case).
• the six nylon cords denoted Cl to C6 in the following table, were all characterized by a double twist construction; they have been conventionally manufactured by assembling 2 or 3 strands (N equal to 2 or 3) according to the final twist T2 and the direction D2 (direction S). Each of these strands had previously been manufactured by an initial twisting operation (T1 equal to T2) of the yarn on itself in the opposite direction Dl (Z direction).
• the belt comprises two layers of the cord to be tested, in a known rubber compound (composition) of the type commonly used for reinforcing tires.
• composition of the type commonly used for reinforcing tires.
• the axis of each cord is oriented in the longitudinal direction of the belt and the cords are separated from the faces of this - - last by a thickness of gum of about 1 mm.
• This belt is then subjected to the following stresses: the belt around a roller of a given diameter (in this case 15 mm) is cyclically driven, using a crank-handle system, so that each elementary portion of the belt is subjected to a given tension (here, about 15 daN) and undergo cycles of variation of curvature which pass it from an infinite radius of curvature to a given radius of curvature and this during 190 000 cycles, at a frequency of 7 Hz.
• This variation of curvature of the belt causes the cord of the inner layer, the one closest to the roller, a given geometric compression ratio (here, about 13%) depending on the diameter of the roller chosen.
• the cords of the inner layer are peeled off and the decay (denoted AFR) of force is measured on breaking the cords once tired.
• the "Disc Fatigue Test” essentially consists in incorporating the cords to be tested in rubber blocks, and then, after cooking, to fatigue the rubber specimens thus formed in compression, between two rotating discs inclined relative to each other. the other (here, 3.5 ° is about 28% of maximum compression ratio between the two discs) a very large number of cycles (in the examples which follow, 600 000 cycles at 33 cycles / s). After fatigue, the cords are extracted from the test pieces; their residual breaking strength is measured and the decay (AFR) of force at break is deduced therefrom.

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