EP2326765B1 - In-situ rubberized layered cable for carcass reinforcement for tyre - Google Patents

Description

The present invention relates to two-layered metal cables, 3 + N construction, used in particular for the reinforcement of rubber articles.

It also relates to metal cables of the type "gummed in situ", that is to say, gummed from the inside, during their manufacture, by rubber in the green state, before incorporation of the latter into the articles in question. rubber such as pneumatic that they are intended to reinforce.

It also relates to tires and carcass reinforcement, also called "carcasses", of these tires, in particular to reinforcement of tire carcasses for industrial vehicles such as heavy goods vehicles.

A radial tire comprises in known manner a tread, two inextensible beads, two flanks connecting the beads to the tread and a belt circumferentially disposed between the carcass reinforcement and the tread. This carcass reinforcement is constituted in known manner by at least one ply (or "layer") of rubber reinforced by reinforcement elements ("reinforcements") such as cords or monofilaments, generally of the metal type in the case of pneumatic tires for industrial vehicles.

For the reinforcement of the above carcass reinforcements, use is generally made of steel wires ( "steel cords") called "layers" ( "layered cords") consisting of a central core and one or more layers of concentric wires arranged around this soul. The most widely used layered cables are essentially M + N or M + N + P construction cables, formed of a core of M wire (s) surrounded by at least one layer of N wires which may itself be surrounded by an outer layer of P son, the M, N or P son having generally the same diameter for reasons of simplification and cost.

To fulfill their function of reinforcement of tire carcasses, the layered cables must first have good flexibility and a high endurance in flexion, which implies in particular that their son have a relatively small diameter, preferably less than 0, 30 mm, more preferably less than 0.20 mm, generally smaller than that of the son used in conventional cables for tire crown reinforcement.

These layered cables are, on the other hand, subjected to considerable stresses during the rolling of the tires, in particular to repeated bending or variations of curvature. inducing at the level of the son friction, especially as a result of contact between adjacent layers, and therefore wear, and fatigue; they must therefore have a high resistance to phenomena known as "fatigue-fretting".

Finally, it is important that they be impregnated as much as possible by the rubber, that this material penetrates into all the spaces between the wires constituting the cables. Indeed, if this penetration is insufficient, then empty channels are formed along the cables, and the corrosive agents, for example water, likely to penetrate the tires for example as a result of cuts, walk along of these channels into the carcass of the tire. The presence of this moisture plays an important role in causing corrosion and accelerating the degradation processes above (phenomena known as "fatigue-corrosion"), compared to use in a dry atmosphere.

All these phenomena of fatigue that are generally grouped under the generic term "fatigue-fretting-corrosion" are at the origin of a gradual degeneration of the mechanical properties of the cables and can affect, for the most severe driving conditions , the life of these.

On the other hand, the availability of increasingly resistant and durable carbon steels means that tire manufacturers are moving as far as possible towards the use of cables with only two layers, in particular in order to simplify the manufacture of these cables, reduce the thickness of the composite reinforcing plies and thus the hysteresis of the tires, ultimately reduce the costs of the tires themselves and reduce the energy consumption of vehicles equipped with such tires.

For all the reasons explained above, the two-layer cables most used today in the tire carcass reinforcement are essentially 3 + N construction cables consisting of a core or inner layer of 3 wires and of an outer layer of N son (for example, 8 or 9 son), the assembly may be optionally shrunk by an outer hoop thread wound helically around the outer layer.

This type of construction promotes, as is known, the external penetrability of the cable by the tire calendering rubber or other rubber article during the cooking of the latter, and consequently improves the endurance of the cables. fatigue-fretting corrosion.

Moreover, a good penetration of the cable by rubber makes it possible in a known manner, thanks to a volume of air trapped in the cable which is less, to reduce the cooking times of the tires (reduced "time in press").

However, the construction cables 3 + N have the disadvantage that they are not penetrable to the core because of the presence of a channel or capillary in the center of the three core wires, which remains empty after external impregnation with rubber and therefore conducive, by a kind of "wicking" effect, to the propagation of corrosive media such as water. This disadvantage of construction cables 3 + N is well known, it has been exposed for example in patent applications WO 01/00922 , WO 01/49926 , WO 2005/071157 , WO 2006/013077 .

To solve this problem of penetrability to the heart of 3 + N cables, the patent application US 2002/160213 proposed the production of gummed type cables in situ.

The method described in this application consists of individually sheathing (ie, single, "wire to wire") with raw rubber, upstream of the point of assembly of the three wires (or torsion point ), one or preferably each of the three son to obtain an inner layer sheathed with rubber, before the subsequent introduction of the N son of the outer layer by wiring around the inner layer and sheathed.

This process poses many problems. First of all the sheathing of only one wire out of three (as illustrated for example in FIGS. 11 and 12 of this document), does not make it possible to guarantee a sufficient filling by the rubber of the final cable, and thus to obtain a resistance optimal corrosion and endurance. Then, the sheathing wire to wire of each three wires (as illustrated for example in figures 2 and 5 of this document), if it actually leads to a filling of the cable, leads to the use of too much gum. The overflow of rubber at the periphery of the final cable then becomes unacceptable under industrial wiring and scrubbing conditions.

Due to the very strong adhesiveness of the rubber in the green state, the cable thus erased becomes unusable because of a parasitic sticky effect on the manufacturing tools or between the turns of cable during the winding of the latter on a reception coil, not to mention the final impossibility of properly calender the cable. It will be recalled here that calendering consists in transforming the cable, by incorporation between two layers of rubber in the green state, into a rubberized metal fabric used as a semi-finished product for any subsequent manufacture, for example for making a tire. .

Another problem posed by the insulated cladding of each of the three son is the large size imposed by the use of three extrusion heads. Due to such a bulk, the production of cables with cylindrical layers (that is to say not p ₁ and p ₂ different from one layer to another, or step p ₁ and p ₂ identical but with different twist directions from one layer to another) must necessarily be carried out in two discontinuous operations: (i) individual wrapping of the wires then wiring and winding of the inner layer at first, (ii) wiring of the outer layer around the inner layer in a second time. Also due to the high stickiness of the rubber in the green state, the winding and intermediate storage of the inner layer require the use of spacers and significant steps when winding on the intermediate reel, for avoid parasitic bonding between the wound layers or between the turns of the same layer.

All the above constraints are highly penalizing from the industrial point of view and antithetical to the search for high production rates.

Continuing their research, the Applicants have discovered a new 3 + N layered cable, gummed in situ, whose specific structure combined with a particular manufacturing process, overcomes the aforementioned drawbacks.

• 0,08 < d₁ < 0,30 ;
• 0,08 < d₂ ≤ 0,20 ;
• p₁ / p₂ ≤ 1 ;
• 3 < p₁ < 30 ;
• 6 < p₂ < 30 ;
• la couche interne est gainée par une composition de caoutchouc diénique dite "gomme de remplissage" qui, pour toute longueur de câble de 2 cm ou plus, est présente dans le canal central formé par les trois fils d'âme et dans chacun des interstices situés entre les trois fils d'âme et les N fils de la couche externe (Ce) ;
• le taux de gomme de remplissage dans le câble est compris entre 5 et 35 mg par g de câble ;
• le câble est dépourvu de gomme de remplissage à sa périphérie.

Accordingly, a first object of the invention is a two-layer metal cable (Ci, Ce) of construction 3 + N, gummed in situ, comprising an inner layer (Ci) consisting of three core wires of diameter d ₁ wound together helically in a pitch p ₁ and an outer layer (Ce) of N wires, N varying from 6 to 12, of diameter d ₂ wound together in a helix in a pitch p ₂ around the inner layer (Ci), said cable having the following characteristics (d ₁ , d ₂ , p ₁ , p ₂ are expressed in mm):

• 0.08 <d ₁ <0.30;
• 0.08 <d ₂ ≤ 0.20;
• p ₁ / p ₂ ≤ 1;
• 3 <p ₁ <30;
• 6 <p ₂ <30;
• the inner layer is sheathed by a diene rubber composition called "filling rubber" which, for any cable length of 2 cm or more, is present in the central channel formed by the three core wires and in each of the interstices located between the three core wires and the N wires of the outer layer (Ce);
• the rate of filling rubber in the cable is between 5 and 35 mg per gram of cable;
• the cable has no filling rubber at its periphery.

The invention also relates to the use of such a cable for the reinforcement of articles or semi-finished products of rubber, for example webs, pipes, belts, conveyor belts, tires.

The cable of the invention is particularly intended to be used as reinforcing element of a tire carcass reinforcement intended for industrial vehicles such as vans and vehicles known as "HGVs", that is to say vehicles metro, bus, road transport equipment such as trucks, tractors, trailers, or off-the-road vehicles, agricultural or civil engineering machinery, and any other type of transport or handling vehicle.

The invention further relates to these articles or semi-finished rubber products themselves when reinforced by a cable according to the invention, in particular tires for industrial vehicles such as vans or HGVs.

• en coupe transversale, un câble de construction 3+9 conforme à l'invention, du type compact (Fig. 1) ;
• en coupe transversale, un câble de construction 3+9 conventionnel, également du type compact (Fig. 2) ;
• en coupe transversale, un câble de construction 3+9 conforme à l'invention, du type à couches cylindriques (Fig. 3) ;
• en coupe transversale, un câble de construction 3+9 conventionnel, également du type à couches cylindriques (Fig. 4) ;
• un exemple d'installation de retordage et gommage in situ utilisable pour la fabrication de câbles du type compacts conformes à l'invention (Fig. 5) ;
• en coupe radiale, une enveloppe de pneumatique poids lourd à armature de carcasse radiale, conforme ou non à l'invention dans cette représentation générale (Fig. 6).

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments, as well as Figures 1 to 6 relating to these examples which schematize, respectively:

• in cross section, a construction cable 3 + 9 according to the invention, of the compact type ( Fig. 1 );
• in cross-section, a conventional 3 + 9 construction cable, also of the compact type ( Fig. 2 );
• in cross-section, a construction cable 3 + 9 according to the invention, of the type with cylindrical layers ( Fig. 3 );
• in cross-section, a conventional 3 + 9 construction cable, also of the cylindrical layer type ( Fig. 4 );
• an example of a twisting and in situ scrubbing installation that can be used for the manufacture of compact type cables according to the invention ( Fig. 5 );
• in radial section, a heavy-duty pneumatic tire with a radial carcass reinforcement, conforming or not to the invention in this general representation ( Fig. 6 ).

I. MEASUREMENTS AND TESTS I-1. Dynamometric measurements

For metal wire and cable, the breaking force measurements denoted Fm (maximum load in N), tensile strength Rm (in MPa) and elongation at break denoted At (total elongation in %) are made in tension according to ISO 6892 of 1984.

With regard to the rubber compositions, the modulus measurements are carried out in tension, unless otherwise indicated according to ASTM D 412 of 1998 (test piece "C"): it is measured in second elongation (ie after one cycle). accommodation) the secant modulus "true" (i.e., reduced to the actual section of the test specimen) at 10% elongation, noted E10 and expressed in MPa (normal conditions of temperature and hygrometry according to ASTM D 1349 of 1999).

1-2. Air permeability test

This test makes it possible to determine the longitudinal permeability to the air of the cables tested, by measuring the volume of air passing through a specimen under constant pressure for a given time. The principle of such a test, well known to those skilled in the art, is to demonstrate the effectiveness of the treatment of a cable to make it impermeable to air; it has been described for example in ASTM D2692-98.

The test is here performed either on raw manufacturing cables, or on cables extracted from tires or rubber sheets they reinforce, so already coated with rubber in the cooked state.

In the first case, the raw manufacturing cables must first be coated from the outside with a so-called coating gum. For this, a series of 10 cables arranged in parallel (inter-cable distance: 20 mm) is placed between two skims (two rectangles of 80 x 200 mm) of a rubber composition in the raw state, each skim having a thickness 3.5 mm; the whole is then locked in a mold, each of the cables being kept under a sufficient tension (for example 2 daN) to ensure its straightness during the establishment in the mold, using clamping modules; then the vulcanization (baking) is carried out for 40 min at a temperature of 140 ° C and a pressure of 15 bar (rectangular piston 80 x 200 mm). After that, the assembly is demolded and cut 10 pieces of cables thus coated, for example in the form of parallelepipeds of dimensions 7x7x20 mm, for characterization.

A conventional rubber composition for tires based on natural rubber (peptized) and carbon black N330 (65 phr), comprising the following usual additives: sulfur (7 phr), sulfenamide accelerator, is used as a coating rubber. (1 phr), ZnO (8 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), cobalt naphthenate (1.5 phr); the E10 module of the coating gum is approximately 10 MPa.

The test is carried out for example on 2 cm of cable length, thus coated by its surrounding rubber composition (or coating gum), in the following manner: air is sent to the cable entry, under a pressure of 1 bar, and the volume of air at the outlet is measured using a flow meter (calibrated for example from 0 to 500 cm ³ / min). During the measurement, the cable sample is locked in a compressed seal (eg a dense foam or rubber seal) in such a way that only the amount of air passing through the cable from one end to the other, along its longitudinal axis, is taken into account by the measure; the tightness of the seal is checked beforehand with the aid of a solid rubber specimen, that is to say without cable.

The average air flow measured (average of the 10 specimens) is even lower than the longitudinal imperviousness of the cable is high. As the measurement is made with an accuracy of ± 0.2 cm ³ / min, the measured values less than or equal to 0.2 cm ³ / min are considered as zero; they correspond to a cable that can be described as airtight (totally airtight) along its axis (ie, in its longitudinal direction).

1-3. Rate filling gum

The amount of filling compound is measured by difference between the weight of the initial cable (thus erased in situ) and the weight of the cable (and therefore that of its threads) whose filling rubber has been eliminated by a suitable electrolytic treatment.

A sample of cable (length 1 m), wound on itself to reduce its bulk, constitutes the cathode of an electrolyzer (connected to the negative terminal of a generator), while the anode (connected to the positive terminal ) consists of a platinum wire. The electrolyte consists of an aqueous solution (demineralized water) comprising 1 mole per liter of sodium carbonate.

The sample, immersed completely in the electrolyte, is energized for 15 min under a current of 300 mA. The cable is then removed from the bath, rinsed thoroughly with water. This treatment allows the rubber to be easily detached from the cable (if it is not the case, we continue the electrolysis for a few minutes). The eraser is carefully removed, for example by simply wiping with an absorbent cloth, while detaching one by one the son of the cable. The threads are again rinsed with water and then immersed in a beaker containing a mixture of deionized water (50%) and ethanol (50%); the beaker is immersed in an ultrasonic tank for 10 minutes. The threads thus devoid of any trace of gum are removed from the beaker, dried under a stream of nitrogen or air, and finally weighed.

From the calculation, the filling rate in the cable, expressed in mg (milligram) of filling rubber per g (gram) of initial cable, is calculated and averaged over 10 measurements (i.e. total cable meters).

1-4. Belt test

The "belt" test is a known fatigue test which has been described for example in the applications EP-A-0 648 891 or WO98 / 41682 , the test steel cables being incorporated in a rubber article which is vulcanized.

Its principle is as follows: the rubber article is an endless belt made with a known rubber-based mixture, similar to those commonly used for radial tire carcasses. The axis of each cable is oriented in the longitudinal direction of the belt and the cables are separated from the faces of the latter by a gum thickness of about 1 mm. When the belt is arranged to form a cylinder of revolution, the cable forms a helical winding of the same axis as this cylinder (for example, not the helix equal to about 2.5 mm).

This belt is then subjected to the following stresses: the belt is rotated around two rollers, so that each elementary portion of each cable is subjected to a tension of 12% of the initial breaking force and undergoes cycles of a variation of curvature that changes it from an infinite radius of curvature to a radius of curvature of 40 mm and this for 50 million cycles. The test is carried out under a controlled atmosphere, the temperature and humidity of the air in contact with the belt being maintained at about 20 ° C and 60% relative humidity. The duration of the stresses for each belt is of the order of 3 weeks. At the end of these stresses, the cables are extracted from the belts, by shelling, and the residual breaking strength of the tired cable wires is measured.

On the other hand, a belt is identical to the previous one and it is peeled in the same way as before but this time without subjecting the cables to the fatigue test. The initial breaking strength of the non-fatigued cables is thus measured.

Finally, the force-failure decay after fatigue (denoted ΔFm and expressed in%) is calculated by comparing the residual breaking force with the initial breaking force. This decay ΔFm is in a known manner due to the fatigue and the wear of the wires caused by the joint action of the stresses and the water coming from the ambient air, these conditions being comparable to those which are subjected the cables of reinforcement in tire carcasses.

1-5 Endurance test in pneumatic

The endurance of fatigue-fretting-corrosion cables is evaluated in carcass plies of heavy-duty tires by a rolling test of very long duration.

For this purpose, heavy-duty tires are manufactured whose carcass reinforcement consists of a single rubberized web reinforced by the cables to be tested. These tires are mounted on suitable known rims and inflated to the same pressure (with an overpressure relative to the nominal pressure) with air saturated with moisture. These tires are then rolled on an automatic rolling machine, under a very high load (overload with respect to the nominal load) and at the same speed, during a determined number of kilometers. At the end of rolling, the cables are extracted from the carcass of the tire, by shelling, and the residual breaking force is measured both on the yarns and on the cables thus fatigued.

On the other hand, identical tires are made to the previous ones and they are peeled in the same way as before, but this time without subjecting them to rolling. Thus, after dehulling, the initial breaking force of the non-fatigued wires and cables is measured.

Finally, the force-failure decay after fatigue (denoted ΔFm and expressed in%) is calculated by comparing the residual breaking force with the initial breaking force. This decay ΔFm is due to the fatigue and the wear (reduction of section) of the wires caused by the joint action of the various mechanical stresses, in particular of the intense work of the contact forces between the wires, and of the water from the ambient air, in other words the fatigue-fretting-corrosion experienced by the cable inside the tire, when driving.

It is also possible to conduct the rolling test until the forced destruction of the tire, due to a rupture of the carcass ply or some other type of damage occurring earlier (for example a break-down).

II. DETAILED DESCRIPTION OF THE INVENTION

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight.

On the other hand, 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. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

II-1. 3 + N cable of the invention

• une couche interne (Ci) constituée de trois fils d'âme de diamètre d₁ enroulés ensemble en hélice selon un pas p₁ ; et
• une couche externe (Ce) de N fils, N variant de 6 à 12, de diamètre d₂ enroulés ensemble en hélice selon un pas p₂ autour de la couche interne (Ci).

The two-layer metal cable (Ci, Ce) of the invention, of construction 3 + N, therefore comprises:

• an inner layer (Ci) consisting of three core wires of diameter d ₁ wound together in a helix in a pitch p ₁ ; and
• an outer layer (Ce) of N wires, N varying from 6 to 12, of diameter d ₂ wound together helically in a pitch p ₂ around the inner layer (Ci).

• 0,08 < d₁ < 0,30 ;
• 0,08 < d₂ ≤ 0,20 ;
• p₁ / p₂ ≤ 1 ;
• 3 < p₁ < 30 ;
• 6 < p₂ < 30 ;
• la couche interne est gainée par une composition de caoutchouc diénique dite "gomme de remplissage" qui, pour toute longueur de câble de 2 cm ou plus, est présente dans le canal central formé par les trois fils d'âme et dans chacun des interstices situés entre les trois fils d'âme et les N fils de la couche externe (Ce) ;
• le taux de gomme de remplissage dans le câble est compris entre 5 et 35 mg par g de câble ;
• le câble est dépourvu de gomme de remplissage à sa périphérie.

It also has the following essential features:

• 0.08 <d ₁ <0.30;
• 0.08 <d ₂ ≤ 0.20;
• p ₁ / p ₂ ≤ 1;
• 3 <p ₁ <30;
• 6 <p ₂ <30;
• the inner layer is sheathed by a diene rubber composition called "filling rubber" which, for any cable length of 2 cm or more, is present in the central channel formed by the three core wires and in each of the interstices located between the three core wires and the N wires of the outer layer (Ce);
• the rate of filling rubber in the cable is between 5 and 35 mg per gram of cable;
• the cable has no filling rubber at its periphery.

This cable of the invention can thus be described as gummed cable in situ: its inner layer Ci and its outer layer Ce are separated radially by a filling rubber sheath which fills, at least in part, each of the interstices or cavities present between the inner layer Ci and the outer layer Ce. In addition, its central capillary formed by the three wires of the inner layer is also penetrated by the filling rubber.

The cable of the invention has another essential feature that its filling rubber level is between 5 and 35 mg of gum per g of cable.

Below the minimum indicated, it is not possible to guarantee that, for any length of cable of at least 2 cm, the filling rubber is present, at least in part, in each of the interstices of the cable, while beyond the maximum indicated, one is exposed to the various problems described above due to the overflow of the filling rubber at the periphery of the cable. For all these reasons, it is preferred that the level of filling gum be between 5 and 30 mg, for example in a range of 10 to 25 mg per g of cable.

Such a rate of filling rubber and its control within the limits indicated above is made possible only by the implementation of a specific twisting-gumming method, adapted to the geometry of the cable 3 + N, which will be discussed in detail later.

The implementation of this specific process, while allowing to obtain a cable whose amount of filling rubber is controlled, ensures the presence of internal partitions (continuous or discontinuous in the axis of the cable) or rubber stoppers in the cable of the invention, in particular in its central channel, in sufficient number; thus, the cable of the invention becomes impervious to the propagation, along the cable, of any corrosive fluid such as water or oxygen from the air, thereby removing the wicking effect described in the introduction to this memo.

According to a particularly preferred embodiment of the invention, the following characteristic is verified: on any cable length of 2 cm or more, the cable is sealed or almost airtight in the longitudinal direction. In other words, each interstice (or cavity) of the cable 3 + N, including the central channel formed by the three core wires, comprises at least one plug (or internal partition) of filling rubber every 2 cm. such that said cable (when coated from the outside by a polymer such as rubber) is watertight or substantially airtight in its longitudinal direction.

In the air permeability test described in paragraph 1-2, a 3 + N cable, referred to as "airtight", is characterized by an average air flow rate of less than or equal to 0.2 cm ³ / min. while a cable 3 + N said "almost airtight" is characterized by an average air flow of less than 2 cm ³ / min, more preferably less than 1 cm ³ / min.

According to the invention, the cable of the invention is devoid of filling rubber at its periphery. By such an expression, it is meant that no particle of filling compound is visible, with the naked eye, at the periphery of the cable, that is to say that the person skilled in the art does not make any difference , with the naked eye and at a distance of two meters or more, between a 3 + N cable coil which is in accordance with the invention and a conventional 3 + N cable coil not gummed in situ, at the output of manufacture.

• 0,10 < d₁ < 0,25 ;
• 0,10 < d₂ ≤ 0,20 .

For an optimized compromise between strength, feasibility, rigidity and flexural endurance of the cable, it is preferred that the diameters of the wires of the layers Ci and Ce, whether these wires have an identical diameter or not from one layer to another, verify the following relationships:

• 0.10 <d ₁ <0.25;
• 0.10 <d ₂ ≤ 0.20.

• 0,10 < d₁ < 0,20 ;
• 0,10 < d₂ < 0,20.

More preferably still, the following relationships are verified:

• 0.10 <d ₁ <0.20;
• 0.10 <d ₂ <0.20.

The wires of the layers Ci and Ce may have an identical diameter or different from one layer to another. Wire of the same diameter is preferably used from one layer to the other (ie d ₁ = d ₂ ), which simplifies in particular the manufacture and reduces the cost of the cables.

Preferably, the following relationship is satisfied: 0.5 ≤ p ₁ / p ₂ ≤ 1.

It will be recalled here that in a known manner the pitch "p" represents the length, measured parallel to the axis of the cable, at the end of which a wire having this pitch performs a complete revolution about said axis of the cable.

According to a particular embodiment, the p ₁ and p ₂ are equal (p ₁ = p ₂ ). This is particularly the case for cables of the compact type of layer as described for example in the figure 1 , in which the two layers Ci and Ce have the other characteristic of being wound in the same direction of torsion (S / S or Z / Z). In such compact-layer cables, the compactness is such that virtually no distinct layer of wires is visible; as a result, the cross-section of such cables has an outline which is polygonal and non-cylindrical, as illustrated for example on the figure 1 (compact cable 3 + 9 according to the invention) or the figure 2 (compact cable 3 + 9 control, that is to say, not gummed in situ).

The pitch p ₂ is chosen more preferably between 6 and 25 mm, for example in a range of 8 to 20 mm, in particular when d ₁ = d ₂ . In such a case, the pitch p ₁ is chosen more preferably between 3 and 25 mm, for example in a range of 4 to 20 mm, in particular when d ₁ = d ₂ .

The outer layer Ce has the preferential characteristic of being a saturated layer, that is to say that, by definition, there is not enough room in this layer to add at least one (N _max +1) th wire d ₂ diameter, N _max representing the maximum number of windable son in a layer around the inner layer Ci. This construction has the advantage of limiting the risk of overflowing gum filling at its periphery and to offer, for a given diameter of the cable, a higher resistance.

Thus, the number N of wires can vary to a very large extent according to the particular embodiment of the invention, for example from 6 to 12 wires, it being understood that the maximum number of wires N _max will be increased if their diameter d ₂ is reduced compared to the diameter d ₁ core son, to preferentially keep the outer layer in a saturated state.

• pour N = 8 : 0,7 ≤ (d₁ / d₂) ≤ 1 ;
• pour N = 9 : 0,9 ≤ (d₁ / d₂) ≤ 1,2 ;
• pour N = 10 : 1,0 ≤ (d₁ / d₂) ≤ 1,3.

According to a preferred embodiment, the layer Ce comprises from 8 to 10 wires, in other words the cable of the invention is chosen from the group of construction cables 3 + 8, 3 + 9 and 3 + 10. More preferably, the son of the layer Ce then verify the following relationships

• for N = 8: 0.7 ≤ (d ₁ / d ₂ ) ≤ 1;
• for N = 9: 0.9 ≤ (d ₁ / d ₂ ) ≤ 1.2;
• for N = 10: 1.0 ≤ (d ₁ / d ₂ ) ≤ 1.3.

Are particularly selected from the cables above those consist of son having substantially the same diameter from one layer to another (or d ₁ = d ₂ ).

According to a particularly preferred embodiment, the outer layer has 9 wires.

The 3 + N cable of the invention, like all layer cables, can be of two types, namely of the compact type or the type with cylindrical layers.

Preferably, all the wires of the layers Ci and Ce are wound in the same direction of torsion, that is to say either in the direction S (arrangement "S / S"), or in the direction Z (disposition "Z / Z "). The winding in the same direction of the layers Ci and Ce advantageously makes it possible to minimize the friction between these two layers and therefore the wear of the wires which constitute them.

More preferably still, the two layers are wound in the same direction (S / S or Z / Z), ie at the same pitch (p ₁ = p ₂ ), to obtain a cable of the compact type as represented by example to the figure 1 , or at different steps to obtain a cable of the cylindrical type as represented for example in the figure 3 .

The construction of the cable of the invention advantageously allows the removal of the wire hoop, thanks to a better penetration of the rubber in its structure and self-hooping resulting.

By wire rope, is meant by definition in the present application a cable formed of son constituted mainly (that is to say for more than 50% in number of these son) or integrally (for 100% son) a metallic material. The wires of the layer Ci are preferably made of steel, more preferably of carbon steel. Independently, the wires of the layer Ce are themselves made of steel, preferably carbon steel. But it is of course possible to use other steels, for example a stainless steel, or other alloys.

When carbon steel is used, its carbon content is preferably between 0.4% and 1.2%, especially between 0.5% and 1.1%. It is more preferably between 0.6% and 1.0% (% by weight of steel), such a content representing a good compromise between the mechanical properties required for the composite and the feasibility of the son. It should be noted that a carbon content of between 0.5% and 0.6% makes such steels ultimately less expensive because easier to draw. Another advantageous embodiment of the invention may also consist, depending on the applications concerned, of using steels with a low carbon content, for example between 0.2% and 0.5%, in particular because of a cost lower and easier to draw.

The metal or steel used, whether it is in particular a carbon steel or a stainless steel, may itself be coated with a metal layer improving for example the properties of implementation of the wire rope and / or its constituent elements, or the properties of use of the cable and / or the tire themselves, such as adhesion properties, corrosion resistance or resistance to aging. According to a preferred embodiment, the steel used is covered with a layer of brass (Zn-Cu alloy) or zinc; it is recalled that during the wire manufacturing process, the coating of brass or zinc facilitates the drawing of the wire, as well as the bonding of the wire with the rubber. But the son could be covered with a thin metal layer other than brass or zinc, for example having the function of improving the resistance to corrosion of these son and / or their adhesion to rubber, for example a thin layer of Co, Ni, Al, an alloy of two or more compounds Cu, Zn, Al, Ni, Co, Sn.

The cables of the invention are preferably carbon steel and have a tensile strength (Rm) preferably greater than 2500 MPa, more preferably greater than 3000 MPa. The total elongation at break (At) of the cable, the sum of its structural, elastic and plastic elongations, is preferably greater than 2.0%, more preferably at least 2.5%.

The diene elastomer (or indistinctly "rubber", both of which are considered synonymous) of the filling compound is preferably a diene elastomer chosen from the group consisting of polybutadienes (BR), natural rubber (NR), polyisoprenes of synthesis (IR), the various butadiene copolymers, the various isoprene copolymers, and the mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), whether the latter are prepared by emulsion polymerization (ESBR) or in solution (SSBR), the isoprene-butadiene copolymers (BIR), copolymers of isoprene-styrene (SIR) and copolymers of isoprene-butadiene-styrene (SBIR).

A 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 preferably natural rubber or synthetic polyisoprene of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. According to other preferred embodiments, the diene elastomer may consist, in whole or in part, of another diene elastomer such as, for example, an SBR elastomer used in or with another elastomer, for example type BR.

The filling rubber may contain one or more diene elastomer (s), which may be used in combination with any type of synthetic elastomer other than diene, or with polymers other than elastomers.

The filling rubber is of the crosslinkable type, that is to say that it generally comprises a crosslinking system adapted to allow the crosslinking of the composition during its baking (i.e., its hardening). Preferably, the system for crosslinking the rubber sheath is a so-called vulcanization system, that is to say based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator. To this basic 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, more preferably between 1 and 8 phr, the primary vulcanization accelerator, for example a sulfenamide, is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr.

But the invention also applies to cases where the filling gum is free of sulfur and even of any other crosslinking system, it being understood that could be sufficient, for its own crosslinking, the crosslinking or vulcanization system already present in the matrix. rubber that the cable of the invention is intended to reinforce, and capable of migrating by contact of said surrounding matrix to the filling rubber.

The filling rubber may also comprise, in addition to said crosslinking system, all or part of the additives normally used in rubber matrices intended for the manufacture of tires, such as, for example, reinforcing fillers such as carbon black or inorganic fillers such as silica, coupling agents, anti-aging agents, antioxidants, plasticizing agents or extension oils, whether the latter are of aromatic or non-aromatic nature, especially very low or non-aromatic oils, for example of naphthenic or paraffinic type, high or preferably low viscosity, MES or TDAE oils, plasticizing resins with high Tg greater than 30 ° C, agents facilitating the implementation (processability) of compositions in the raw state , tackifying resins, anti-eversion agents, methylene acceptors and donors such as, for example, HMT (hexamethylenethane) etramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimide), known adhesion promoter systems such as metal salts, for example, in particular cobalt, nickel or lanthanide salts.

The level of reinforcing filler, for example carbon black or a reinforcing inorganic filler such as silica, is preferably greater than 50 phr, for example included between 60 and 140 phr. It is more preferably greater than 70 phr, for example between 70 and 120 phr. As carbon blacks, for example, all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called pneumatic 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 reinforcing inorganic fillers are in particular silica (SiO ₂ ) type inorganic fillers, in particular precipitated or fumed silica having a BET surface area of less than 450 m ² / g, preferably from 30 to 400 m ² / g.

Those skilled in the art will know, in the light of the present description, adjust the formulation of the filling rubber in order to achieve the desired levels of properties (including modulus of elasticity), and adapt the formulation to the application specific consideration.

According to a first embodiment of the invention, the formulation of the filling rubber can be chosen to be identical to the formulation of the rubber matrix that the cable of the invention is intended to reinforce; thus, there is no problem of compatibility between the respective materials of the filling rubber and said rubber matrix.

According to a second embodiment of the invention, the formulation of the filling gum may be chosen different from the formulation of the rubber matrix that the cable of the invention is intended to reinforce. In particular, the formulation of the filling gum may be adjusted by using a relatively high quantity of adhesion promoter, typically for example from 5 to 15 phr of a metal salt such as a cobalt salt, a nickel salt or a lanthanide salt such as neodymium (see, in particular, application WO 2005/113666 ), and advantageously reducing the amount of said promoter (or even removing it completely) in the surrounding rubber matrix. Of course, it will also be possible to adjust the formulation of the filling compound in order to optimize its viscosity and thus its penetration inside the cable during manufacture of the latter.

Preferably, the filling rubber has, in the crosslinked state, a secant modulus in extension E10 (at 10% elongation) which is between 2 and 25 MPa, more preferably between 3 and 20 MPa, in particular included in a range of 3 to 15 MPa.

The invention relates of course to the previously described cable both in the green state (its filling rubber then being uncured) than in the cooked state (its filling rubber then being vulcanized). However, it is preferred to use the cable of the invention with a filling compound in the green state until it is subsequently incorporated into the product. semi-finished or finished product such as pneumatic to which this cable is intended, so as to promote the connection during the final vulcanization between the filling rubber and the surrounding rubber matrix (for example the calendering rubber).

The figure 1 schematically, in section perpendicular to the axis of the cable (assumed rectilinear and at rest), an example of a preferred cable 3 + 9 according to the invention.

This cable (noted C-1) is of the compact type, that is to say that its inner layers Ci and external Ce are wound in the same direction (S / S or Z / Z according to a recognized nomenclature) and moreover at the same step (p ₁ = p ₂ ). This type of construction has the consequence that the inner (10) and outer (11) wires form two concentric layers which each have a substantially polygonal contour (represented in dotted lines) (triangular for the Ci, hexagonal layer for the Ce layer), and not cylindrical as in the case of cables with cylindrical layers which will be described later.

The filling rubber (12) fills the central capillary (13) (symbolized by a triangle) formed, delimited by the three core wires (10) by spreading them very slightly, while completely covering the internal layer Ci formed by the three wires (10). It also fills each interstice or cavity (also symbolized by a triangle) formed, delimited either by a core wire (10) and the two external wires (11) which are immediately adjacent to it, or by two core wires (10). ) and the outer wire (11) adjacent thereto; in total, 12 interstices are thus present in this cable 3 + 9, to which is added the central capillary (13).

According to a preferred embodiment, in the cable 3 + N of the invention, the filling rubber extends in a continuous manner around the layer Ci it covers.

For comparison, the figure 2 recalls the section of a cable 3 + 9 (noted C-2) conventional (ie, not gummed in situ), also of the compact type. The absence of filling rubber makes practically all the son (20, 21) in contact with each other, which leads to a particularly compact structure, moreover very difficult to penetrate (not to say impenetrable) from the outside by rubber. The characteristic of this type of cable is that the three core wires (20) form a central channel or capillary (23) which is empty and closed and thus conducive, by "wicking" effect, to the propagation of corrosive media such as that water.

The figure 3 schematizes another example of a preferential cable 3 + 9 according to the invention.

This cable (noted C-3) is of the type with cylindrical layers, that is to say that its inner layers Ci and external Ce are either wound at the same pitch (p ₁ = p ₂ ) but in a different direction (S / Z or Z / S), or wound in a different pitch (p ₁ # p ₂ ) regardless of the torsion directions (S / S or Z / Z or S / Z or Z / S). In known manner, this type of As a result of the construction, the wires are arranged in two adjacent, concentric, tubular layers (Ci and Ce) giving the cable (and the two layers) a cylindrical, non-polygonal contour (shown in dotted lines).

The filling rubber (32) fills the central capillary (33) (symbolized by a triangle) formed by the three core wires (30) slightly apart, while completely covering the inner layer Ci formed by the three wires ( 30). It also fulfills, at least in part (here, in this example, totally) each interstice or cavity formed, delimited either by a core wire (30) and the two external wires (31) which are immediately adjacent thereto (the most close), or by two core wires (30) and the outer wire (31) adjacent thereto.

For comparison, the figure 4 recalls the section of a cable 3 + 9 (noted C-4) conventional (ie, not gummed in situ), also of the type with two cylindrical layers. The absence of filling rubber causes the three wires (40) of the inner layer (Ci) to come into close contact with each other, which leads to a central, empty and closed capillary 43, which is impenetrable. on the outside by rubber and propitious on the other hand to the propagation of corrosive media.

The cable of the invention could be provided with an outer hoop, constituted for example by a single wire, metallic or not, helically wound around the cable in a shorter pitch than that of the outer layer, and a sense of winding opposite or identical to that of this outer layer.

However, thanks to its specific structure, the cable of the invention, already self-shrunk, generally does not require the use of an external hoop, which advantageously solves the wear problems between the hoop and son the outermost layer of the cable.

However, if a hoop wire is used, in the general case where the son of the outer layer are carbon steel, then one can advantageously choose a stainless steel wire hoop to reduce the fretting wear of these son carbon steel in contact with the stainless steel band, as taught for example in the application WO-A-98/41682 , the stainless steel wire may be optionally replaced, in an equivalent manner, by a composite wire of which only the skin is made of stainless steel and the carbon steel core, as described for example in the document EP-A-976 541 . It is also possible to use a hoop consisting of a polyester or a thermotropic aromatic polyester amide, as described in the application WO-A-03/048447 .

II-2. Manufacture of the cable 3 + N of the invention

• tout d'abord, une étape d'assemblage par retordage des trois fils d'âme, pour formation de la couche interne (Ci) en un point d'assemblage ;
• puis, en aval dudit point d'assemblage des trois fils d'âme, une étape de gainage de la couche interne (Ci) par la gomme de remplissage à l'état cru (c'est-à-dire non réticulée) ;
• suivie d'une étape d'assemblage par retordage des N fils de la couche externe (Ce) autour de la couche interne (Ci) ainsi gainée ;
• puis d'une étape d'équilibrage final des torsions.

The cable of the invention of construction 3 + N previously described can be manufactured according to a method comprising the following four steps operated online:

• firstly, a step of assembly by twisting the three core son, for forming the inner layer (Ci) at an assembly point;
• then, downstream of said assembly point of the three core wires, a step of sheathing the inner layer (Ci) with the filling gum in the green state (that is to say uncrosslinked);
• followed by a step of assembly by twisting the N son of the outer layer (Ce) around the inner layer (Ci) and sheathed;
• then a final balancing step of the twists.

• soit par câblage : dans un tel cas, les fils ne subissent pas de torsion autour de leur propre axe, en raison d'une rotation synchrone avant et après le point d'assemblage ;
• soit par retordage : dans un tel cas, les fils subissent à la fois une torsion collective et une torsion individuelle autour de leur propre axe, ce qui génère un couple de détorsion sur chacun des fils.

It is recalled here that there are two possible techniques for assembling metal wires:

• or by wiring: in such a case, the wires are not twisted around their own axis, due to a synchronous rotation before and after the assembly point;
• either by twisting: in such a case, the son undergo both a collective twist and an individual twist around their own axis, which generates a torque of detorsion on each son.

An essential feature of the above method is to use, both for the assembly of the inner layer and for that of the outer layer, a twisting step.

During the first step, the three core wires are twisted together (direction S or Z) to form the inner layer Ci, in a manner known per se; the son are delivered by feeding means such as coils, a distribution grid, coupled or not to a connecting grain, intended to converge the core son in a common point of torsion (or point of assembly).

The inner layer (Ci) thus formed is then sheathed with filling gum in the green state, provided by an extrusion screw at an appropriate temperature. The filling rubber can thus be delivered at a fixed point, unique and compact, by means of a single extrusion head, without using an individual sheathing son upstream of the assembly operations, before forming the inner layer, as described in the prior art.

This method has the significant advantage of not slowing down the conventional assembly process. It makes the complete initial twisting, scrubbing and final twisting operation possible in one step, irrespective of the type of cable produced (compact cable as a cylindrical layer cable), all at high speed. The above process can be put implemented at a speed (running speed of the cable on the twisting-scrub line) greater than 50 m / min, preferably greater than 70 m / min.

Upstream of the extrusion head, the tension exerted on the three son, substantially identical from one thread to the other, is preferably between 10 and 25% of the breaking force of the son.

The extrusion head may comprise one or more dies, for example an upstream guide die and a downstream die calibration. It is possible to add continuous measurement and control means of the diameter of the cable connected to the extruder. Preferably, the extrusion temperature of the filling rubber is between 60 ° C and 120 ° C, more preferably between 60 ° C and 100 ° C.

The extrusion head thus defines a cladding zone having the shape of a cylinder of revolution whose diameter is preferably between 0.15 mm and 0.8 mm, more preferably between 0.2 and 0.6 mm, and whose length is preferably between 4 and 10 mm.

Thus, the amount of filling gum delivered by the extrusion head can be adjusted easily so that in the final 3 + N cable this amount is between 5 and 35 mg, preferably between 5 and 30 mg, especially in a range of 10 to 25 mg per g of cable.

Typically, at the outlet of the extrusion head, the inner layer Ci, at any point of its periphery, is covered with a minimum thickness of filling rubber which is preferably greater than 5 μm, more preferably greater than 10 μm, by example between 10 and 50 microns.

At the output of the preceding cladding step, during a third step, the final assembly is carried out, always by twisting (S or Z direction), of the N wires of the outer layer (Ce) around the inner layer (Ci) and sheathed. During the twisting, the N son come to rely on the eraser, to become embedded in the latter. The filling rubber, moving under the pressure exerted by these external son, then naturally tends to fill, at least in part, each of the interstices or cavities left empty by the son, between the inner layer (Ci) and the layer external (Ce).

At this stage, the cable 3 + N of the invention is not finished: its central channel, delimited by the three core wires, is not yet filled with filling rubber, in any case insufficiently for obtaining acceptable air impermeability.

The next essential step is to route the cable through torsion balancing means. By "torsion balancing" is meant here in known manner the cancellation of the residual torsional torques (or of the detorsion springback) exerted on each wire of the cable, in the inner layer as in the outer layer.

Torsion balancing tools are well known to those skilled in the art of twisting; they may consist for example of "trainers" and / or "twisters" and / or "twister-trainers" consisting of either pulleys for twisters or small diameter rollers for trainers, pulleys or rollers through which circulates the cable, in a single plane or preferably in at least two different planes.

It is assumed a posteriori that, when passing through these balancing tools, the torsion exerted on the three core wires is sufficient to force, to drive the filling gum in the raw state (ie, not crosslinked uncured), still hot and relatively fluid, from the outside to the core of the cable, even inside the central channel formed by the three son, ultimately offering the cable of the invention the excellent property of air impermeability that characterizes it. The additional training function, provided by the use of a trainer tool, would have the advantage that the contact of the rollers of the trainer with the son of the outer layer will exert additional pressure on the filling rubber further promoting its penetration into the central capillary formed by the three souls.

In other words, the method described above exploits the twisting of the three core wires, in the final stage of manufacture of the cable, to distribute, naturally, the filling rubber in and around the inner layer (Ci), while perfectly controlling the amount of filling compound provided. Those skilled in the art will in particular be able to adjust the arrangement, the diameter of the pulleys and / or rollers of the torsion-balancing means, in order to vary the intensity of the radial pressure acting on the various wires.

Thus, unexpectedly, it has been found possible to penetrate the filling rubber into the very core of the cable of the invention, by depositing the rubber downstream of the assembly point of the three son and not upstream as described in FIG. the prior art, while controlling and optimizing the amount of filling gum delivered through the use of a single extrusion head.

After this final step of balancing the torsion, the manufacture of the cable 3 + N of the invention is complete. This cable can be wound on a receiving reel, for storage, before being processed, for example, through a calendering installation, for preparing a metal-rubber composite fabric.

The method described above makes it possible to manufacture cables in accordance with the invention which have no filling rubber at their periphery. By such an expression, it is meant that no particle of filling compound is visible, with the naked eye, at the periphery of the cable, that is to say that the person skilled in the art does not make any difference at the end of the manufacturing process, with the naked eye and at a distance of three meters or more, or even more preferably of two meters or more, between a cable reel according to the invention and a conventional non-gummed cable reel in situ .

The method described above is of course applicable to the manufacture of compact type cables (for recall and by definition, those whose layers Ci and Ce are wound at the same pitch and in the same direction) as cables of the type with cylindrical layers (As a reminder and by definition, those whose layers Ci and Ce are wound either in different steps or in opposite directions, or in different steps and in opposite directions).

• des moyens d'alimentation des trois fils d'âme ;
• des moyens d'assemblage par retordage des trois fils d'âme pour formation de la couche interne ;
• des moyens de gainage de la couche interne ;
• en sortie de moyens de gainage, des moyens d'assemblage par retordage de N fils externes autour de la couche interne ainsi gainée, pour formation de la couche externe ;
• enfin, des moyens d'équilibrage de torsion.

An assembly and scrubbing device that can be used for carrying out the method described above is a device comprising from upstream to downstream, according to the direction of advancement of a cable being formed:

• feeding means for the three core wires;
• means for assembling by twisting the three core wires for forming the inner layer;
• means for sheathing the inner layer;
• at the outlet of the cladding means, means for assembling N external threads around the inner layer thus sheathed, for forming the outer layer;
• finally, torsion balancing means.

We see on the figure 5 an exemplary device (50) for twisting assembly, of the fixed feed and rotary receiving type, usable for the manufacture of a cable of the compact type (p ₁ = p ₂ and the same direction of twisting of the layers Ci and Ce) ) as illustrated for example in figure 1 , wherein power supply means (510) deliver three core wires (51) through a distribution grid (52) (axisymmetrical splitter), whether or not coupled to an assembly line (53), beyond of which the three core wires converge at an assembly point (54) for forming the inner layer (Ci).

The inner layer Ci, once formed, then passes through a cladding zone consisting for example of a single extrusion head (55) through which is intended to circulate the inner layer. The distance between the point of convergence (54) and the sheathing point (55) is for example between 50 cm and 1 m. Around the inner layer Ci as well gummed (56), progressing in the direction of the arrow, are then assembled by twisting the N son (57) of the outer layer (Ce), for example nine in number, delivered by supply means (570). The final cable 3 + N thus formed is finally collected on a rotary reception (59), after crossing the torsion balancing means (58) consisting for example of a trainer or twister-trainer.

It is recalled here that, in a manner well known to those skilled in the art, for the manufacture of a cable according to the invention of the type with cylindrical layers as illustrated for example in the figure 3 (Not different p ₁ and p ₂ and / or different torsion direction of the layers Ci and Ce), we will use a device comprising two bodies (supply or reception) rotating, and not a single one as described above ( Fig. 5 ) for exemple.

II-3. Use of the tire carcass reinforcement cable

As explained in the introduction to this memo, the cable of the invention is particularly intended for a tire carcass reinforcement for industrial vehicles such as trucks.

For example, the figure 6 schematically represents a radial section of a metal carcass reinforcement tire which may or may not conform to the invention, in this general representation. This tire 1 has a crown 2 reinforced by a crown reinforcement or belt 6, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a rod 5. The crown 2 is surmounted by a tread not shown in this schematic figure. A carcass reinforcement 7 is wound around the two rods 5 in each bead 4, the upturn 8 of this armature 7 being for example disposed towards the outside of the tire 1 which is shown here mounted on its rim 9. The carcass reinforcement 7 is in known manner constituted by at least one sheet reinforced by so-called "radial" metal cables, that is to say that these cables are arranged substantially parallel to each other and extend from a bead to the other so as to form an angle between 80 ° and 90 ° with the median circumferential plane (plane perpendicular to the axis of rotation of the tire which is located midway between the two beads 4 and passes through the middle of the crown frame 6).

The tire according to the invention is characterized in that its carcass reinforcement 7 comprises at least, as reinforcement of at least one carcass ply, a metal cable according to the invention. Of course, this tire 1 also comprises, in a known manner, an inner rubber or elastomer layer (commonly called "inner rubber") which defines the radially inner face of the tire and which is intended to protect the carcass ply from the diffusion of the tire. air from the interior space to the tire.

In this carcass reinforcement ply, the density of the cables according to the invention is preferably between 40 and 150 cables per dm (decimetre) of carcass ply, more preferably between 70 and 120 cables per dm of ply, the distance between two adjacent cables, axis to axis, being preferably between 0.7 and 2.5 mm, more preferably between 0.75 and 2.2 mm.

The cables according to the invention are preferably arranged in such a way that the width (denoted Le) of the rubber bridge between two adjacent cables is between 0.25 and 1.5 mm. This width represents in a known manner the difference between the calender pitch (no laying of the cable in the rubber fabric) and the diameter of the cable. Below the indicated minimum value, the rubber bridge, which is too narrow, risks being degraded mechanically during the working of the sheet, in particular during the deformations undergone in its own plane by extension or shearing. Beyond the maximum indicated, one is exposed to the risk of appearance of appearance defects on the sidewalls of the tires or penetration of objects, by perforation, between the cables. More preferably, for these same reasons, the width Le is chosen between 0.35 and 1.25 mm.

Preferably, the rubber composition used for the fabric of the carcass reinforcement ply has, in the vulcanized state (ie, after curing), a secant modulus in extension E10 which is between 2 and 25 MPa, more preferably between 3 and 20 MPa, especially in a range of 3 to 15 MPa, when the fabric is intended to form a carcass reinforcement ply.

III. EXAMPLES OF CARRYING OUT THE INVENTION

The following tests demonstrate the ability of the invention to provide cables whose endurance, in particular tire carcass reinforcement, is significantly increased thanks to an excellent property of impermeability to air, along their longitudinal axis.

III-1. Test 1 - Manufacture of cables

In the following tests, 3 + 9 layered cables are used as shown schematically in FIG. figure 1 , consisting of fine wire made of carbon steel coated with brass.

The carbon steel wires are prepared in a known manner, for example starting from machine wires (diameter 5 to 6 mm) that are first cold-rolled, by rolling and / or drawing, up to an intermediate diameter of about 1 mm. The steel used is a known carbon steel (USA AISI 1069 standard) with a carbon content of 0.70%.

The intermediate diameter son undergo a degreasing treatment and / or pickling, before further processing. After deposition of a brass coating on these intermediate son, is carried on each wire a so-called "final" work hardening (ie, after the last patenting heat treatment), by cold drawing in a moist medium with a drawing lubricant which is for example in the form of an aqueous emulsion or dispersion.

The steel wires thus drawn have the following diameter and mechanical properties: <b> Table 1 </ b> Steel φ (mm) Fm (N) Rm (MPa) NT 0.18 68 2820

The brass coating that surrounds the son has a very small thickness, significantly less than one micrometer, for example of the order of 0.15 to 0.30 microns, which is negligible compared to the diameter of the steel son. Of course, the composition of the wire steel in its various elements (eg C, Cr, Mn) is the same as that of the steel of the starting wire.

These wires are then assembled in the form of 3 + 9 layer cables (referenced C-1 to Fig. 1 and C-2 at the Fig. 2 ) whose construction conforms to the representations of Figures 1 and 2 and whose mechanical properties are given in Table 2. <b> Table 2 </ b> Cable p ₁ (mm) p ₂ (mm) Fm (daN) Rm (MPa) At (%) C-1 12.5 12.5 78.5 2720 1.9 C-2 6.3 12.5 81.0 2770 1.9

The cable of the invention 3 + 9 (C-1), as shown schematically in FIG. Fig. 1 , is formed of 12 wires in total, all of diameter 0.18 mm, which were wound at the same pitch (p ₁ = p ₂ = 12.5 mm) and in the same direction of twist (S) to obtain a cable of the compact type. The rate of filling rubber, measured according to the method indicated previously in paragraph 1-3, is about 24 mg per gram of cable. This filling gum fills the central channel or capillary formed by the three core wires by spreading them slightly, while completely covering the inner layer Ci formed by the three son. It also fills, at least partially if not totally, each of the twelve interstices formed either by a core wire and the two outer wires which are immediately adjacent thereto, or by two core wires and the outer wire which is adjacent to them. This cable C-1 of the invention is devoid of external hoop wire.

For the manufacture of this cable, we used a device as described previously and schematized in the figure 5 . The filling gum is a conventional rubber composition for a tire carcass reinforcement, having the same formulation as that of the carcass rubber ply that the C-1 cable is intended to reinforce in the following test. This composition was extruded at a temperature of about 82 ° C. through a 0.410 mm calibration die.

The control cable 3 + 9 (C-2), as shown schematically in FIG. Fig. 2 , is formed of 12 wires total of diameter 0.18 mm. It comprises an inner layer Ci of 3 wires wound together in a helix (direction S) in a pitch p ₁ equal to about 6.3 mm, this layer Ci being in contact with a cylindrical outer layer of 9 wires themselves wound together helically (S direction) around the core in a double pitch p ₂ equal to about 12.5 mm. It furthermore comprises a unitary external hoop wire of small diameter (0.15 mm diameter, no 3.5 mm pitch), not shown in FIG. figure 2 for simplification, intended in particular, in known manner, to increase the buckling resistance of the cable and in particular the endurance of the carcass in rolling under low pressure; this control cable is not penetrable from the outside to its center, it is devoid of filling rubber.

III-2. Test 2 - Endurance of the cables in test belt

In this test, the C-1 and C-2 layered cables are then incorporated by calendering with rubber "skims" consisting of a composition conventionally used for the manufacture of radial tire carcass reinforcement plies. for vehicles Trucks. This composition is based on natural rubber (peptized) and carbon black N330 (55 phr); it also comprises the following usual additives: sulfur (6 phr), sulfenamide accelerator (1 phr), ZnO (9 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), cobalt naphthenate (1 phr) pce); the module E10 of the composition is about 6 MPa.

The composite and calendered fabrics thus comprise a rubber matrix formed of two thin layers (thickness approximately 0.6 mm) of rubber superimposed on both sides of the cables. The calender pitch (no laying of the cables in the rubber fabric) is about 1.5 mm. Given the diameter of the cables (approximately 0.73 and 1.02 mm for the C-1 and C-2 cables respectively), the thickness of the rubber on the back of the cables is between 0.15 and 0.25 mm approximately. .

The rubberized fabrics thus prepared were then subjected to the belt test described in paragraph 1-4 above; after dehulling, the following results were obtained: <b> Table 3 </ b> cables ΔFm (%) on individual layers and cable This This Cable C-1 6.3 5.3 5.6 C-2 11 18 16

As can be seen from Table 3, whatever the zone of the cable analyzed (inner layer Ci or external Ce), the best results (the smallest lapses) are systematically recorded on the cables C-1 conforming to the invention. In particular, it can be observed that the overall decay ΔFm of the cable of the invention is approximately three times less than that of the control cable.

III-3. Test 3 - Endurance of cables in tire carcass reinforcement

In this new test, another cable according to the invention, denoted C-3, identical to the previous cable C-1, except for its pitches p ₁ and p ₂ (in this test, equal to 6 and 10 mm respectively) is manufactured. ). Since the pitches p ₁ and p ₂ are different, the structure of this cable is of cylindrical type, as illustrated for example in FIG. figure 3 . Its gum filling rate is about 27 mg per g of cable.

This cable C-3 has the properties shown in Table 4 which follows. <b> Table 4 </ b> Cable p ₁ (mm) p ₂ (mm) Fm (daN) Rm (MPa) At (%) C-3 6 10 79.2 2745 2.4

The C-2 and C-3 layered cords are then calendered to rubberized rubber skims (skims) as described previously in Test 2, followed by two sets of rolling tests. heavy vehicle tires (noted respectively P-2 and P-3), of dimensions 225/90 R17.5, with in each series of tires intended for driving, others for dehulling on a new tire. The carcass reinforcement of these tires consists of a single radial ply consisting of the rubberized fabrics above.

The tires P-3 reinforced by the C-3 cables of the invention are therefore the tires according to the invention. The tires P-2 reinforced by the control cables C-2 constitute the control tires of the prior art; these P-2 tires constitute, because of their recognized performance, a control of choice for this test.

The tires P-2 and P-3 are therefore identical with the exception of the cables C-2 and C-3 which reinforce their carcass reinforcement 7.

Their crown reinforcement or belt 6, in particular, is in a manner known per se consisting of two triangulation half-plies reinforced with metal cables inclined by 65 degrees, surmounted by two "superimposed" working plies crossed. These working plies are reinforced by known metal cables arranged substantially parallel to each other and inclined by 26 degrees (radially internal ply) and 18 degrees (radially external ply). The two working plies are furthermore covered by a protective ply reinforced with conventional metal cables (high elongation) inclined at 18 degrees. All angles of inclination indicated are measured relative to the median circumferential plane.

These tires are subjected to a severe rolling test as described in paragraph 1-5, conducting the test to a total distance of 250,000 km. Such mileage equates to a continuous run of nearly 8 months and more than 100 million fatigue cycles.

After rolling, it is carried out a shelling that is to say a removal of the cables out of the tires. The cables are then subjected to tensile tests, each time measuring the initial breaking force (cable extracted from the new tire) and the residual breaking force (cable extracted from the rolling tire) of each type of wire, according to the position of the wire in the cable, and for each of the cables tested.

The average decay ΔFm is given in% in Table 5 below; it is calculated both for the wires of the inner layer Ci and for the wires of the outer layer Ce. Global ΔFm decays are also measured on the cables themselves. <b> Table 5 </ b> tires cables ΔFm (%) on individual layers and cable This This Cable P-2 C-2 11 22 18 P-3 C-3 4.8 7.8 7.0

When reading Table 5, we see again that, whatever the zone of the cable analyzed (inner layer Ci or outer Ce), the best results (ie the smallest lapses), and by far are obtained on the cables C-3 according to the invention. In particular, it is noted that the global decay ΔFm of the cable of the invention is reduced by a factor of approximately 2.5 with respect to the control cable.

Correlatively to these results, a visual examination of the different wires shows that the phenomena of wear or fretting (erosion of material at the contact points), which result from the repeated friction of the wires between them, are clearly reduced in the cables C-3 by compared to C-2 cables.

In summary, the use of the cable C-3 according to the invention makes it possible to increase the longevity of the carcass quite sensibly, which is already excellent in the control tire reinforced by the cable C-2.

In conclusion, as demonstrated by the preceding tests, the cables of the invention make it possible to significantly reduce the phenomena of fatigue-fretting-corrosion of the cables in the carcass reinforcement of the tires, in particular of the heavy-duty tires, and to improve the longevity of these tires.

Finally, and this is not the least, it has furthermore been found that these cables according to the invention, thanks to their particular construction (as a reminder, requiring no external hoop wire) and probably a greatly improved buckling resistance. , provided to the carcass reinforcement of tires a significantly improved endurance, by a factor of two to three, in rolling under reduced pressure.

All the improved endurance results described above also appear to be very well correlated with the rate of penetration of the cables by the rubber, as explained hereafter in the test 4.

III-4. Trial 4 - Tests of air permeability

The cables C-1 of the invention have moreover been subjected to the air permeability test described. in paragraph 1-2, by measuring the air volume (in cm ³ ) passing through the cables in 1 minute (average of 10 measurements for each cable tested).

For each cable C-1 tested and for 100% of the measurements (ie ten test pieces out of ten), a flow rate of zero or less than 0.2 cm ³ / min was measured; in other words, the cables of the invention can be described as airtight along their axis; they therefore have an optimal penetration rate by rubber.

In situ control gummed cables of the same construction as the compact cables C-1 of the invention were prepared by individually sheathing either a single wire or each of the three wires of the inner layer Ci. using extrusion dies of variable diameter (230 to 300 microns) arranged this time upstream of the assembly point (sheathing and in-line twisting) as described in the prior art; for a rigorous comparison, the amount of filling rubber was adjusted in such a way that the rate of filling rubber in the final cables (between 4 and 30 mg / g of cable, measured according to the method of the paragraph 1-3), which is close to that of the cables of the invention.

In the case of jacketing a single wire, regardless of the cable tested, it was observed that 100% of the measurements (ie, 10 test pieces out of 10) indicated an air flow rate greater than 2 cm ³ / min; the average flow rate measured varied from 2.5 to 9 cm ³ / min depending on the operating conditions used, in particular the diameter of the extrusion die tested.

In the case of the individual cladding of each of the three yarns, if the measured average flow rate has in many cases been found to be less than 2 cm ³ / min, it has nevertheless been observed that the cables obtained had a relatively large amount of filling rubber at their periphery, making them unsuitable for a calendering operation in industrial conditions.

Of course, the invention is not limited to the previously described embodiments.

For example, the cable of the invention could be used for reinforcing articles other than tires, for example pipes, belts, conveyor belts; advantageously, it could also be used for reinforcing parts of tires other than their carcass reinforcement, in particular for reinforcing the crown reinforcement of tires for industrial vehicles such as heavy goods vehicles.

In particular, the invention also relates to any multi-strand steel cable ("multi-strand broken ") whose structure incorporates at least, as elementary strand, a layered cable according to the invention.

• (1+6) (3+N) formé au total de sept torons élémentaires, un au centre et les six autres câblés autour du centre ;
• (3+9) (3+N) formé au total de douze torons élémentaires, trois au centre et les neuf autres câblés autour du centre,

mais dans lesquels chaque toron élémentaire (ou tout au moins une partie d'entre eux) constitué par un câble à couches 3+N, notamment 3+8 ou 3+9, du type compact ou du type à couches cylindriques, est un câble 3+N conforme à l'invention, gommé in situ.As examples of multi-strand cables according to the invention, which can be used, for example, in tires for industrial vehicles of the civil engineering type, in particular in their carcass or crown reinforcement, mention may be made of multi-strand cables of known general construction. in itself:

• (1 + 6) (3 + N) formed of a total of seven elementary strands, one in the center and the other six wired around the center;
• (3 + 9) (3 + N) formed in total of twelve elementary strands, three in the center and the other nine wired around the center,

but in which each elementary strand (or at least a part of them) constituted by a layered cable 3 + N, in particular 3 + 8 or 3 + 9, of the compact type or of the type with cylindrical layers, is a cable 3 + N according to the invention, gummed in situ.

Such multi-strand steel cables, in particular of the type (1 + 6) (3 + 8), (1 + 6) (3 + 9), (3 + 9) (3 + 8) or (3 + 9) ) (3 + 9), could be themselves erased in situ during their manufacture, that is to say that in this case the central strand is itself, or the strands of the center if they are several are themselves, sheathed with unvulcanized filling rubber (this filling compound being of identical or different formulation to that used for the in situ scrubbing of the elementary strands) before the wiring is put in place by the peripheral strands forming the outer layer.

Claims (15)

1. Metal cord consisting of two layers (Ci, Ce) of 3+N construction, rubberized in situ, comprising an inner layer (Ci) formed from three core wires of diameter d₁ wound together in a helix with a pitch p₁ and an outer layer (Ce) of N wires, N varying from 6 to 12, of diameter d₂, which are wound together in a helix with a pitch p₂ around the inner layer (Ci), said cord being characterized in that it has the following characteristics (d₁, d₂, p₁ and p₂ being expressed in mm):

   - 0.08 < d₁ < 0.30;

   - 0.08 < d₂ ≤ 0.20;

   - p₁ / p₂ ≤ 1;

   - 3 < p₁ < 30;

   - 6 < p₂ < 30;

   - the inner layer is sheathed with a diene rubber composition called a "filling rubber " which, for any length of cord of 2 cm or more, is present in the central channel formed by the three core wires and in each of the gaps lying between the three core wires and the N wires of the outer layer (Ce);

   - the content of filling rubber in the cord is between 5 and 35 mg per g of cord;

   - the cord has no filling rubber on its periphery.
2. Cord according to Claim 1, in which the diene elastomer of the filling rubber is chosen from the group formed by polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and blends of these elastomers.
3. Cord according to Claim 2, in which the diene elastomer is natural rubber.
4. Cord according to any one of Claims 1 to 3, in which the following relationships are satisfied (d₁ and d₂ being in mm):

   - 0.10 < d₁ < 0.25;

   - 0.10 < d2 ≤ 0.20.
5. Cord according to any one of Claims 1 to 4, in which the following relationship is satisfied:

   0.5 ≤ p₁ / p₂ ≤ 1.
6. Cord according to any one of Claims 1 to 5, in which p₁ = p₂.
7. Cord according to any one of Claims 1 to 6, in which p₂ is between 6 and 25 mm.
8. Cord according to any one of Claims 1 to 7, in which p₁ is between 3 and 25 mm.
9. Cord according to any one of Claims 1 to 8, in which the outer layer (Ce) is a saturated layer.
10. Cord according to any one of Claims 1 to 9, in which the outer layer (Ce) comprises 8, 9 or 10 wires, preferably 9 wires.
11. Cord according to any one of Claims 1 to 10, in which the content of filling rubber is between 5 and 30 mg per g of cord, preferably between 10 and 25 mg per g of cord.
12. Cord according to any one of Claims 1 to 11, characterized in that, in the air permeability test, it has an average air flow rate of less than 2 cm³/min, preferably less than or at most equal to 0.2 cm³/min.
13. Multistrand rope, at least one of the strands of which is a cord according to any one of Claims 1 to 12.
14. Tyre comprising a cord or rope according to any one of Claims 1 to 12.
15. Tyre according to Claim 14, said tyre being intended for an industrial vehicle and the cord being present in the carcass reinforcement of the tyre.

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