EP2449169A2

EP2449169A2 - Three-layer steel cord that is rubberized in situ and has a 3+m+n structure

Info

Publication number: EP2449169A2
Application number: EP10727446A
Authority: EP
Inventors: Jérémy TOUSSAIN; Thibaud Pottier
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2009-07-03
Filing date: 2010-07-02
Publication date: 2012-05-09
Also published as: WO2011000951A2; CN102472000A; US20120186715A1; FR2947577B1; WO2011000951A3; JP2012531539A; KR20120051667A; EA201270123A1; BR112012000117A2; BR112012000117A8; FR2947577A1

Abstract

The invention relates to a steel cord (C-1) with three layers (C1, C2, C3) and a 3+M+N structure, that is rubberized in situ and comprises: a first layer or central layer (C1) formed by two wires (10) of diameter d₁ assembled in a helix at a pitch p₁; a second layer (C2) formed by M wires (11) of diameter d₂, which are wound around the central layer (C1) in a helix at a pitch p₂; and a third layer (C3) formed by N wires (12) of diameter d₃, which are wound around the second layer in a helix at a pitch p₃. The cord is characterised in that it has the following characteristics: (d₁, d₂, d₃, p₁, p₂ and p₃ being expressed in mm): - 0.08 ≤ d₁ ≤ 0.5; - 0.08 ≤ d₂ ≤ 0.5; - 0.08 ≤ d₃ ≤ 0.5; - 3 < p₁ < 50; - 6 < p₂ < 50; - 9 < p₃ < 50; for any 3 cm-length of cord, a rubber composition known as "filling rubber" (13) is present in each of the capillaries in the central channel (14) defined by the three wires of the first layer (C1) and in each of the capillaries (15) defined by the 3 wires of the first layer (C1) and the M wires of the second layer (C2) and by the M wires of the second layer (C2) and the N wires of the third layer (C3); and the level of filling rubber in the cord is between 10 and 50 mg per gram of cord. The invention also relates to the method for producing one such cord and to a multi-strand cord, in which at least one of the strands is a three-layer steel cord (C-1) rubberized in situ in accordance with the invention.

Description

METAL CABLE WITH THREE LAYERS GOMMÉ IN SITU

BUILDING 3 + M + N

The present invention relates to three-layered metal cables, which can be used in particular for reinforcing rubber articles such as tires for industrial vehicles.

It is more particularly related to three-layer metal cables of the type "gummed in situ", that is to say, gummed from the inside, during their manufacture, by rubber or a rubber composition in the non-state. reticulated (raw).

This invention is more specifically related to three-layer metal cables of specific construction 3 + M + N, and their use in carcass reinforcement, also called "carcasses", tires for industrial 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 reinforcing the carcass reinforcement above, steel cords ("layered cords") consisting of a central layer and one or more layers are generally used. concentric threads disposed around this central layer. The most widely used three-layer cables are essentially L + M + N construction cables, formed of a central layer of L-wire (s) surrounded by at least one layer of M-wire itself surrounded by a layer external of N son.

The three-layer cables most used today in industrial vehicle tire carcass reinforcement, in cases where the highest mechanical strengths are targeted and consequently a larger number of wires are required, are essentially 3 + M + N construction consisting of a central layer of 3 son surrounded by an intermediate layer of M son itself surrounded by an outer layer of N son, the assembly may be optionally fretted by an external wire hoop helically wrapped around the outer layer. As is well known, these layered cables are 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". It is particularly important in addition that they are impregnated as much as possible by the rubber, that this material penetrates the best in all spaces between the son constituting the cables. Indeed, if this penetration is insufficient, then empty channels are formed along the cables, and corrosive agents such as water or even oxygen in the air, which can penetrate the tires, for example as a result of cuts, they run along these empty 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. To overcome the above drawbacks, the application WO 2005/071157 proposed cables with three layers of L + M + N construction, with L varying from 1 to 4, M from 3 to 12 and N from 8 to 20, in particular of construction 1 + M + N, one of the essential characteristics is that a sheath made of a rubber composition covers at least the intermediate layer consisting of M son, the central layer of L son can be itself covered or no rubber. Thanks to this specific architecture, not only an excellent penetrability by the rubber is obtained, limiting the corrosion problems, but also the fatigue-fretting endurance properties are significantly improved compared to the cables of the prior art. The longevity of tires for industrial vehicles and that of their carcass reinforcement are thus very significantly improved.

However, the processes described for the manufacture of these cables, as well as the cables that come from them, are not without drawbacks.

First of all, these three-layer cables are obtained in several steps which have the disadvantage of being discontinuous, firstly by producing an intermediate cable L + M (in particular 1 + M), then by sheathing via an extrusion head of this intermediate cable, finally by a final operation of wiring the remaining N son around the core thus sheathed, for forming the outer layer. To avoid the problem of "green sticky" rubber sheath before wiring the outer layer around the core, should be used further a plastic interlayer film during intermediate operations of winding and unwinding. All these successive manipulations are penalizing from the industrial and antinomic point of view of the search for high production rates.

On the other hand, if one wants to be able to guarantee a high penetration rate by the rubber inside the cable to obtain a permeability to the air of the cable, along its axis, which is as low as It has been found necessary, according to these prior art methods, to use relatively large amounts of rubber during sheathing. Such quantities lead to a spurious overflow, more or less pronounced, of the raw rubber at the periphery of the finished cable manufacturing.

However, as already mentioned above, because of the high tackiness of the raw (ie uncrosslinked) rubber, such a spurious overflow in turn generates significant disadvantages. during the subsequent handling of the cable, in particular during the calendering operations that will follow for the incorporation of the cable into a rubber band itself in the green state, before the final operations of manufacturing the tire and cooking final.

All the disadvantages described above, of course, slow industrial speeds and penalize the final cost of the cables and tires they reinforce.

Another disadvantage that is added, this time specific to construction cables 3 + M + N, is that these cables are not penetrable to the heart because of the presence of a channel or capillary in the center of three wires the central layer, which remains empty after impregnation with rubber and therefore conducive, by a kind of "wicking" effect, to the propagation of corrosive media such as water or oxygen.

This disadvantage of construction cables 3 + M or 3 + M + N is well known; it has been disclosed for example in patent applications WO 01/00922, WO 01/49926, WO 2005/071157. Continuing their research, the Applicants have discovered an improved three-layer cable, obtained through a specific manufacturing process, which overcomes the aforementioned drawbacks.

Accordingly, a first object of the invention is a three-layer metal cable (C1, C2, C3) of construction 3 + M + N, gummed in situ, comprising a first layer (Cl) consisting of three di diameter wires. helically assembled in a pitch p _b central layer around which are helically wound in a pitch p ₂ , in a second layer (C2), M son of diameter d ₂ , second layer around which are helically wound in a step p ₃ , in a third layer (C3), N son of diameter d ₃ , said cable being characterized in that it has the following characteristics (di, d ₂ , d ₃ , pi, p ₂ and p ₃ being expressed in mm): - AT - ;

- 0.08 <d ₂ <0.50;

- 0.08 <d ₃ <0.50;

- 3 <p! <50;

- 6 <p ₂ <50;

- 9 <p ₃ <50;

over any length of cable equal to 3 cm, a rubber composition called "filling rubber" is present in the central channel defined by the three son of the first layer (Cl) and in each of the capillaries delimited on the one hand by the 3 wires of the first layer (C1) and the M son of the second layer (C2), on the other hand by the M son of the second layer (C2) and N son of the third layer (C3);

the rate of filling rubber in the cable is between 10 and 50 mg per gram of cable.

This three-layer cable of the invention, compared to the three-layer gummed in situ cables of the prior art, has the notable advantage of having a reduced amount of filling rubber, which guarantees a better compactness, this eraser being further distributed uniformly inside the cable, inside each of its capillaries, thus conferring on it optimal impermeability along its axis.

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 of industrial vehicles (ie, carrying heavy loads) chosen from vans and vehicles called "heavy vehicles" it is - ie metro vehicles, buses, road transport vehicles 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 with a cable according to the invention, in particular tires for industrial vehicles such as vans or heavy vehicles.

The invention also relates to a method of manufacturing the cable of the invention, said method comprising at least the following steps: a first step of assembling by twisting the three son of the central layer to form a first point called "first assembly point" of the first layer or central layer (Cl);

a second assembly step by twisting the M son around the central layer (Cl), for formation in a second point called "second assembly point" of an intermediate cable (C1 + C2) said "strand soul ", Of construction 3 + M;

downstream of the first assembly point, a step of sheathing the central layer (C1) and / or the core strand (C1 + C2) with the filling rubber in the green state, this cladding being conducted either upstream, either downstream or both upstream and downstream of the second assembly point;

followed by a third assembly step by twisting or wiring the N son around the core strand and sheathed;

- Then a final balancing step of the twists.

The invention as well as its advantages will be easily understood in the light of the description and the following exemplary embodiments, as well as FIGS. 1 to 6 relating to these examples which schematize, respectively: in cross-section, a construction cable + 9 + 15 according to the invention, gummed in situ, compact type (Figure 1);

in cross-section, a conventional 3 + 9 + construction cable, not gummed in situ, also of the compact type (Fig. 2);

in cross section, a construction cable 3 + 9 + 15 according to the invention, gummed in situ, of the type with cylindrical layers (FIG 3);

an example of a twisting and in situ scrubbing installation that can be used for the manufacture of compact type cables, in accordance with the invention (FIG.

- In radial section, a heavy-duty pneumatic tire with radial carcass reinforcement, conforming or not to the invention in this general representation (FIG 5).

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 diene rubber compositions, the modulus measurements are carried out in tension, unless otherwise indicated according to the ASTM D 412 standard of 1998 (test piece "C"): one measures in second elongation (that is to say after a cycle of accommodation) the secant modulus "true" (that is to say, brought back to the real section of the specimen) at 10% elongation, denoted ElO 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 carried out either on cables extracted from tires or rubber sheets which they reinforce, thus already coated from the outside by rubber in the fired state, or on raw manufacturing cables, which have been coated and subsequent cooking.

In the second case, the raw cables must be, before the test, 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 minutes at a temperature of 140 ^° C. and at a pressure of 15 bar (rectangular piston of 80 × 200 mm). After which, the assembly is demolded and cut 10 pieces of cables thus coated, in the form of parallelepipeds of appropriate dimensions (for example 7x7x20 or 7x7x30 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) (phr parts per hundred parts of elastomer) ; the ElO module of the coating gum is approximately 10 MPa. The test is carried out over a predetermined length (for example 3 cm or even 2 cm) of cable, thus coated by its surrounding rubber composition (or coating gum) in the fired state, as follows: at the inlet of the cable, 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 itself 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. Filling rate

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 this 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).

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. Cable of the invention

The metal cable of the invention therefore comprises three concentric layers:

a first layer or central layer (Cl) consisting of 3 di diameter wires assembled together in a helix according to a pitch pi;

a second layer (C2) having M son of diameter d ₂ helically assembled, in a pitch p ₂ , around the first layer;

- A third layer (C3) having N son diameter diameter d ₃ helically assembled in a pitch p ₃ around the second layer.

In a known manner, the first and second assembled layers (C1 + C2) constitute what is usually called the cable core, which supports the outermost layer (C3).

This cable of the invention also has the following characteristics (di, d ₂ , d ₃ , p ₁ , p ₂ and p ₃ being expressed in mm): ;

- 0.08 <d ₂ <0.50;

- 0.08 <d ₃ <0.50;

- 3 < _P <50;

- 6 <p ₂ <50;

- 9 <p ₃ <50; over any length of cable equal to 3 cm, a rubber composition called "filling rubber" is present in the central channel defined by the three son of the first layer (Cl) and in each of the capillaries delimited on the one hand by the 3 wires of the first layer (C1) and the M son of the second layer (C2), on the other hand by the M son of the second layer (C2) and N son of the third layer (C3);

- The rate of filling rubber in the cable (C-I) is between 10 and 50 mg per gram of cable. This cable of the invention can be qualified cable gummed in situ, that is to say, it is erased from the inside, during its manufacture itself (so in the raw state of manufacture), by the rubber filling. In other words, the central channel or capillary delimited by the three son of the first layer (Cl) and each of the capillaries or interstices (the two interchangeable terms designating the voids, free spaces in the absence of filling rubber) located between, delimited by both the first (C1) and the second (C2) layers, both the second (C2) and the third (C3) layers, are filled at least in part, continuously or not according to the cable axis, by the filling rubber.

According to a preferred embodiment, on any cable portion of length equal to 3 cm, more preferably equal to 2 cm, the central channel and each capillary or interstice described above comprise at least one rubber stopper; in other words and preferentially, there is at least one rubber stopper every 3 cm, preferably every 2 cm of cable, which obstructs the capillary or central channel and each other capillary or interstice of the cable so that, at air permeability test (according to paragraph 1-2), this cable of the invention has an average air flow rate less than

2 cm ³ / min, more preferably less than or less than 0.2 cm ³ / min.

Another essential feature of the cable of the invention is that its level of filling rubber is between 10 and 50 mg of gum per g of cable. Below the minimum indicated, it is not possible to guarantee that, on any cable length of 3 cm, preferably 2 cm, the filling rubber is present, at least in part, in each of the interstices or capillaries of the cable to preferentially form at least one plug, while beyond the maximum indicated, it 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 rubber is between 15 and 45 mg, more preferably between 15 and 40 mg of filling gum per g of cable. Such a rate of filling rubber and its control within the limits indicated above is only possible thanks to the implementation of a specific twisting-gumming method, adapted to the geometry of the cable, which will be exposed 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 capillaries of the cable of the invention, this in a 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 in the air, thereby eliminating the wicking effect described in the introduction to this memo .

Thus, the following characteristic is preferably verified: over any cable length of 3 cm, preferably 2 cm, the cable is sealed or substantially airtight in the longitudinal direction. In other words, each capillary of the cable preferably comprises at least one plug (or internal partition) of filling rubber on this given length, such that said cable (once coated with the outside by a polymer such as rubber) is watertight or almost airtight in its longitudinal direction. In the air permeability test described in paragraph 1-2, an "airtight" cable in the longitudinal direction is characterized by an average air flow rate of not more than 0.2 cm ³ / min while a cable called "almost airtight" in the longitudinal direction is characterized by an average air flow less than 2 cm ³ / min, preferably less than 1 cm ³ / min.

For an optimized compromise between strength, feasibility, rigidity and bending endurance of the cable, it is preferred that the diameters of the son of the layers C1, C2 and C3, these son have a diameter identical or not from one layer to another, check the following relations (di, d ₂ , d ₃ being expressed in mm): ;

- 0.10 <d ₂ <0.40;

- 0.10 <d ₃ <0.40. More preferably still, the following relationships are verified: ;

- 0.10 <d ₂ <0.30;

- 0.10 <d ₃ <0.30. The wires of the layers C1, C2 and C3 may have an identical diameter or different from one layer to another; wires of the same diameter are preferably used from one layer to another (ie di = d ₂ = d ₃ ), which simplifies in particular the manufacture and reduces the cost of the cables. The steps p ₂ and p ₃ are chosen more preferably in a range of 8 to 25 mm, more preferably still in a range of 10 to 20 mm, in particular when d ₂ = d ₃ .

According to another preferred embodiment, the p ₂ and p ₃ are equal, the pitch pi may be identical to or different from p ₂ . In other possible embodiments, pi = p ₂ ≠ p ₃ or pi ≠ p ₂ ≠ p ₃ .

According to another preferred embodiment, for a better compromise between resistance and flexibility of the cable, the following characteristics are verified: ;

- 6 <p ₂ <30;

- 9 <p ₃ <30.

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 three steps pi, p ₂ and p ₃ are equal. This is particularly the case for cables of the compact type of layer as schematized for example in Figure 1, wherein the three layers C1, C2 and C3 further have the characteristic of being wound in the same direction of torsion ( S / S / S or Z / 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 a contour which is polygonal and non-cylindrical, as illustrated by way of example in FIG. 1 (compact cable 3 + 9 + 15 according to the invention) or in FIG. (compact cable 3 + 9 + 15 control, that is to say, not gummed in situ).

The third or outer layer C3 has the preferred 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 + l) ^th wire d ₃ diameter, N _max representing the maximum number of windable son in a layer around the second layer C2. This construction has the significant advantage of further limiting the risk of overfilling gum filling at its periphery and offer, for a given diameter of the cable, a higher strength. However, the invention also applies to cases where the outer layer (C3) is an unsaturated layer.

Thus, the number N of wires can vary to a very large extent according to the particular embodiment of the invention, it being understood that the maximum number N _max of wires N will be increased if their diameter d ₃ is reduced compared to the diameter d ₂ threads of the second layer, in order to preferentially keep the outer layer in a saturated state.

According to a preferred embodiment, the second layer (C2) has 6 to 12 son and the third layer (C3) has 12 to 18 son. Are particularly selected from the above cables those consisting of son having substantially the same diameter of the layer C2 to the layer C3 (or d ₂ = di).

According to a more particularly preferred embodiment, the second layer (C2) has 8 or 9 wires (ie M equal to 8 or 9) and the third layer (C3) has 14 or 15 wires (ie N equal to 14 or 15) . The cable of the invention is particularly preferred constructions 3 + 8 + 14 and 3 + 9 + 15.

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

Preferably, the three layers C1, C2 and C3 are wound in the same direction of torsion, that is to say either in the S direction ("S / S / S" layout), or in the Z direction ("S" arrangement). Z / Z / Z "). The winding in the same direction of these layers advantageously allows to minimize the friction between these three layers and therefore the wear of the son constituting them. More preferably, they are wound in the same direction of torsion and at the same pitch (ie pi = p ₂ = P 3), to obtain a cable of the compact type as represented for example in FIG. Cable of the invention advantageously allows the removal of the wire hoop, through a better penetration of the rubber in its structure and self-frettage resulting therefrom.

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.

Independently of each other and from one layer to the other, the wire or wires of the central layer (C1), the wires of the second layer (C2) and the wires of the third layer (C3) are preferably steel, more 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 (% by weight of steel) is preferably between 0.4% and 1.2%, especially between 0.5% and 1.1%; these levels represent a good compromise between the mechanical properties required for the tire and the feasibility of the wires. 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 in particular carbon steel or 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 elastomer (or indistinctly "rubber", both considered to be synonymous) of the filling rubber is preferably a diene elastomer, that is to say by definition an elastomer derived at least in part (that is, a homopolymer or a copolymer) of monomer (s) diene (s) (ie, monomer (s) carrier (s) of two carbon-carbon double bonds, conjugated or not). The diene elastomer is more preferentially selected from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), various butadiene copolymers, various isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), whether they are prepared by emulsion polymerization (ESBR) or in solution (SSBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene copolymers -butadiene-styrene (SBIR). A preferred embodiment consists in using an "isoprene" elastomer, that is to say a homopolymer or 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 isoprene elastomer may also be associated with another diene elastomer such as, for example, an SBR and / or BR elastomer.

The filling rubber may contain one or more elastomer (s), especially diene (s), the latter or they may be used (s) in combination with any type of polymer other than elastomer. The filling rubber is preferably of the crosslinkable type, that is to say that it comprises by definition a crosslinking system adapted to allow the crosslinking of the composition during its baking (i.e., its hardening and not its melting); thus, in such a case, this rubber composition can be described as infusible, since it can not be melted by heating at any temperature. Preferably, in the case of a diene rubber composition, 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 at least one vulcanization accelerator. To this basic vulcanization system may be added various known vulcanization activators. Sulfur is used at a preferential rate of between 0.5 and 10 phr, more preferably between 1 and 8 phr, the vulcanization accelerator, for example a sulphenamide, is used at a preferential rate of between 0.5 and 10. pce, more preferably between 0.5 and 5.0 phr.

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 naphthenic or paraffinic type, high or preferably low viscosity, MES or TDAE oils, plasticizing resins with high Tg greater than 30 ⁰ C, agents facilitating the implementation (processability) of the compositions in the green state, tackifying resins, anti-eversion agents methylene acceptors and donors such as, for example, HMT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimide), known adhesion promoter systems such as metal salts, for example, in particular cobalt salts; or nickel.

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 between 50 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). As reinforcing inorganic fillers are especially suitable mineral fillers of the silica (SiO 2) type, 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 salt of cobalt or nickel, and reducing advantageously the amount of said promoter (or even completely suppressing it) 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 ElO (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 uncrosslinked) and in the fired state (its filling rubber then being crosslinked or vulcanized). However, it is preferred to use the cable of the invention with a filling gum in the green state until it is subsequently incorporated into the semi-finished product or finished product such as the tire for which it is intended, so as to promote the connection to the product. during the final crosslinking or vulcanization between the filling rubber and the surrounding rubber matrix (for example the calendering rubber).

Figure 1 shows schematically in section perpendicular to the axis of the cable (assumed rectilinear and at rest), an example of a preferred cable 3 + 9 + 15 according to the invention.

This cable (denoted CI) is of the compact type, that is to say that its first, second and third layers (respectively Cl, C2 and C3) son are wound in the same direction (S / S / S or Z / Z / Z according to a recognized nomenclature) and in addition at the same step (pi = p2 = P3). This type of construction has the consequence that the wires (11, 12) of the second and third layers (C2, C3) form around the three wires (10) of the central layer (Cl) two substantially concentric layers which each have a contour ( E) (shown in dotted lines) which is substantially polygonal (more precisely hexagonal) and non-cylindrical as in the case of cables with so-called cylindrical layers. It can be seen in this FIG. 1 that, while spacing the wires very slightly, the filling rubber (13) at least partially fills the central channel or capillary (14) delimited by the three wires (10) of the first layer (Cl ) as well as each of the capillaries (15) (by way of example, some of them, in particular the most central ones, are here symbolized by a triangle) which are delimited on the one hand by the 3 wires (10) of the first layer (C1) and the M son (11) of the second layer (C2), on the other hand by the M son (11) of the second layer (C2) and the N son (12) of the third layer ( C3), these wires being taken three by three. In total, we see here that 36 capillaries (15) or interstices are present in this example of cable 3 + 9 + 15, to which is added of course the central capillary (14). According to a preferred embodiment, in the cable according to the invention, the filling rubber extends in a continuous manner around the second layer (C2) that it covers.

For comparison, Figure 2 recalls the section of a cable 3 + 9 + 15 (denoted C-2) conventional (that is to say, not gummed in situ), also of the compact type. The absence of gum The result is that all the wires (20, 21, 22) are in contact with each other, which leads to a particularly compact structure, very difficult to penetrate (not to say impenetrable) from the outside by rubber. The characteristic of this type of cable is that the various wires form three to three, between two adjacent layers, channels or capillaries (25) which for the majority of them remain closed and empty, and therefore conducive by "wicking effect""to the propagation of corrosive media such as water.

FIG. 3 schematizes, again in section perpendicular to the axis of the cable (assumed to be rectilinear and at rest), another example of a preferential cable 3 + 9 + 15 (denoted C-3) according to the invention, this time of the type with cylindrical layers that is to say that the son (respectively 31, 32) of the second and third layers (C2, C3) form around the three son (30) of the central layer (Cl) two substantially concentric layers each having an outline (E) (shown in dotted lines) which is substantially cylindrical and non-hexagonal as previously for FIG.

FIG. 3 shows that the filling rubber (33), while spacing the wires very slightly, at least partially fills the central channel (34) delimited by the three wires (30) of the first layer (Cl) and that each of the capillaries or interstices (35) (for example, some of them, especially the most central are here symbolized by a triangle) located between, delimited by on the one hand the 3 son (30) of the first layer (C1) and the M son (31) of the second layer (C2), on the other hand the M son (31) of the second layer (C2) and the N son (32) of the third layer (C3 ), these son being taken at least in groups of 3 adjacent son (3, 4, 5 or even 6 in this case, according to the examples of capillaries or interstices shown in Figure 3).

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 (C3), and a winding direction opposite or identical to that of this outer layer. However, thanks to its specific structure, the cable of the invention, already self-shrinking, does not generally require the use of an external hoop wire, which advantageously solves the wear problems between the hoop and the wires. 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 hoop, as taught for example in the application WO-A-98/41682, the stainless steel wire may optionally be replaced, in an equivalent manner, by a composite yarn 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.

Those skilled in the art will understand that the cable of the invention described above could be optionally gummed in situ with a filling rubber based on elastomers other than diene, especially thermoplastic elastomers (TPE) such as for example polyurethane elastomers. (TPU) do not require a known manner of crosslinking or vulcanization but which have, at the operating temperature, properties similar to those of a vulcanized diene elastomer.

However, and particularly preferably, the present invention is implemented with a filling rubber based on diene elastomers such as previously described, thanks in particular to a specific manufacturing process which is particularly suitable for such elastomers; this manufacturing process is described in detail below.

II-2. Manufacture of the cable of the invention

The cable of the invention described above, gummed preferentially in situ by a diene elastomer, is capable of being manufactured according to a process comprising the following steps, preferably carried out online and continuously: a first assembly step by twisting of the three wire of the central layer for forming a first point called "first assembly point" of the first layer or central layer (Cl);

downstream of the first assembly point, a step of sheathing the central layer

(Cl) and / or the core strand (C1 + C2) by filling rubber in the uncrosslinked state (raw), this cladding being conducted either upstream or downstream, or both upstream and downstream of the second assembly point;

- then a final step of balancing the twists.

Preferably, the step of sheathing by the filling rubber is conducted on the single central layer (Cl), downstream of the first assembly point and upstream of the second assembly point, the filling rubber being delivered in a only once in sufficient quantity for obtaining the cable according to the invention. A possible embodiment may consist in operating, downstream of the second assembly point, an additional step of sheathing the core strand (C1 + C2). However, it is preferred to use only one cladding step. It is recalled here that there are two possible techniques for assembling metal wires:

or by wiring: in such a case, the wires do not undergo torsion around their own axis, because of a synchronous rotation before and after the assembly point; or 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 of the son and on the cable itself.

An essential characteristic of the above method is to use a twisting step for both the assembly of the first layer (Cl) and the second layer (C2) around the central layer (Cl). .

The assembly of the third layer (C3) around the second layer (C2) can be made by twisting or cabling. It is preferred to use a twisting operation as for the first two assembly operations (layers C1 and C2).

If the third layer (C3) is assembled by wiring, the cable is then preferably manufactured in two discontinuous steps (twisting of the first two layers, and subsequent wiring of the third layer); in this case it is preferred to use two cladding steps, a first cladding of the central layer (Cl), a second subsequent cladding on the core strand (C 1 + C2).

By way of example, the procedure is as follows.

The wires of the central layer are twisted together (direction S or Z) for forming the first layer (Cl), 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 3 son in a common point of torsion (or first point of assembly ). The first layer (C1) thus formed is then sheathed with green filling gum 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. 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 50 ^° C. and 120 ^° C., more preferably between 50 ^° C. and 100 ^° C.

The extrusion head thus defines a cladding zone having, for example, in the preferred case of a single cladding step conducted on the central layer (Cl), the shape of a cylinder of revolution whose diameter is preferably comprised between 0.15 mm and 1.2 mm, more preferably between 0.2 and 1.0 mm, and whose length is preferably between 4 and 10 mm.

The amount of filling compound delivered by the extrusion head can be adjusted easily so that in the final cable this amount is between 10 and 50 mg per g of final cable, that is to say finished from manufacturing, gummed in situ.

Below the indicated minimum, it is not possible to guarantee that the filling rubber is present in each of the capillaries or interstices of the cable, while beyond the maximum indicated, one can expose oneself to the various problems previously described due to the overflow of the filling rubber at the periphery of the cable, according to the particular conditions of implementation of the invention and the specific construction of the cables manufactured. For all these reasons, it is preferred that the amount of filling gum delivered be between 15 and 45 mg, more preferably between 15 and 40 mg per g of cable.

Downstream of the first assembly point, the tension stress exerted on the core strand is preferably between 10 and 25% of its breaking force.

In the preferred case of a single cladding step conducted on the central layer (Cl), at the outlet of the extrusion head, the central layer of the cable, at any point of its periphery, is preferably covered with a minimum thickness filling rubber that is greater than 20 microns, more preferably greater than 30 microns, especially between 30 and 80 microns. At the output of the preceding cladding step, the M son of the second layer (C2) are twisted together (direction S or Z) around the central layer (Cl) thus sheathed to form the core strand (C1 + C2); as previously for the 3 wires of the central layer, the M son of the second layer (C2) are delivered by feeding means such as distribution grid coils, intended to converge around the central layer, the M son in a common torsion point (or second assembly point). During this twisting, the M son come to rely on the filling rubber, to become embedded in the gum sheath covering the central layer (Cl). This filling rubber, in sufficient quantity, then naturally fills the capillaries that form between the central layer (C1) and the second layer (C2).

During a third step, the final assembly is carried out, always by twisting (direction S or Z), N son of the third layer or outer layer (C3) around the core strand (C1 + C2) previously formed.

At this stage of the process, the cable of the invention is not yet finished: the capillaries or channels delimited by the M son of the second layer (C2) and the N son of the third layer (C3), are not still filled with filling rubber, in any case insufficiently to obtain a cable having an impervious to air that is optimal.

The next important step is to pass the cable, thus provided with its filling rubber in the green state, through torsion balancing means to obtain a cable said to be balanced in torsion (ie that is, virtually without residual torsion); "Torsional balancing" here means, in a known manner, the cancellation of the residual torsional torques (or of the detorsional springback) exerted on each wire of the cable in the twisted state, in its respective layer. Torsion balancing tools are 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, during the passage through the different balancing means above, the latter generate, on the M and N son of the second and third layers (C2 and C3), a torsion and radial pressure which are sufficient to redistribute the filling gum in the uncured (ie, uncrosslinked, uncured) state, still hot and relatively fluid, by transferring it in part, capillaries formed by the central layer (Cl) and the M son of the second layer (C2), towards the inside of the capillaries formed by the M son of the second layer (C2) and the N son of the third layer (C3), finally offering the cable of the invention the excellent impermeability property to the air that characterizes it. The dressing function, provided by the use of a trainer tool, would also have the advantage that the contact of the rollers of the trainer with the son of the outer layer (C3) will exert an additional radial pressure on the filling rubber promoting again its optimal distribution in the capillaries present between the second layer (C2) and the third layer (C3) of the cable. In other words, the method described above exploits the twisting of the son and the radial pressure exerted on the latter at the final stage of manufacture of the cable, to radially distribute the filling rubber inside the cable, while by 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 proved possible to make the filling rubber penetrate the heart of the cable of the invention and into all of its capillaries, by depositing the rubber downstream of the first assembly point of the 3-wire for forming the first layer or core layer (Cl), 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 of the invention, gummed in situ by its filling rubber in the green state, is complete.

Preferably, in this finished cable, the thickness of filling rubber between two adjacent wires of the cable, whatever they are, is greater than 1 micron, preferably between 1 and 10 microns. This cable can be wound on a receiving reel, for storage, before being treated, for example, through a calendering installation, for preparing a metal-rubber composite fabric that can be used as a tire carcass reinforcement, or else to be assembled as a multistrand cable. The method described above has the advantage of making possible the complete operation of initial twisting, exfoliation and subsequent twisting in line and in a single step, regardless of the type of cable manufactured (compact cable as cable with cylindrical layers), all this at high speed. The above method can be 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, especially greater than 100 m / min.

This method of course applies to the manufacture of compact type cables (for recall and by definition, those whose layers C1, C2 and C3 are wound at the same pitch and in the same direction) as the manufacture of cables of the type with cylindrical layers (for recall and by definition, those whose layers C1, C2 and C3 are wound either at different steps (whatever their torsion directions, identical or not), or in opposite directions (whatever their not, identical or different)).

The process described above makes it possible, according to a particularly preferred embodiment, to manufacture cables that may be lacking (or virtually devoid of) gum filling 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 output of the manufacturing process, with the naked eye and at a distance of three meters or more, between a cable reel according to the invention and a conventional cable reel not gummed in situ.

An assembly and scrubbing device preferably used for the implementation of this method, is a device comprising upstream downstream, according to the direction of advancement of a cable being formed: feed means and first assembly means by twisting of the three central son for forming the first layer (C1) at a point called said first point of assembly,;

supply means and second assembly means by twisting the M son of the second layer (C2) around the central layer (Cl), at a point called said second point of assembly, for forming an intermediate cable said "strand of soul" of C1 + C2 construction;

cladding means for the central layer (C1) and / or the core strand (C1 + C2), arranged either upstream or downstream, or both upstream and downstream of the second assembly point;

feeding means and third assembly means by twisting of the

N son around the core strand, for setting up the third layer (C3);

at the output of the third assembly means, torsion balancing means. FIG. 4 shows an exemplary device (40) for twisting assembly, of the fixed feed and rotary receiving type, usable for the manufacture of a three-layer cable of construction 3 + M + N, compact type (pi = p ₂ = P3 and the same direction of torsion of the layers C2 and C3) as shown for example in Figure 1 commented previously. In this device (40), supply means (110) deliver three wires (10) through a distribution grid (111) (axisymmetric splitter), whether or not coupled to an assembly line (112), beyond which converge the three son (10) at an assembly point (113) for forming the first layer or central layer (Cl). The central layer (C1) thus formed then passes through a cladding zone (114) consisting for example of an extrusion head. The distance between the sheathing point (114) and the convergence point (113) is for example between 1 and 5 meters. Feeding means (115) then deliver, around the central layer (Cl) thus sheathed, M son (11), for example through a distribution grid coupled to an assembly grain, beyond which converge the M (for example 9) son of the second layer into a second point assembly (116) for forming the core strand (C1 + C2) of construction 3 + M (eg 3 + 9).

Around the core strand (C1 + C2) thus formed and progressing in the direction of the arrow F, are then assembled by twisting the N son (12) of the outer layer (C3), for example of the number 15, delivered by feeding means (117). The final cable (C1 + C2 + C3) is finally collected on the rotary reception (119), after passing through the torsion balancing means (118) consisting for example of a trainer or a twister-trainer. It will be recalled here that, in a manner well known to those skilled in the art, for the manufacture of a cable of the type with cylindrical layers (not p ₂ and p ₃ different and / or torsion direction different layers C2 and C3) such As illustrated in FIG. 3, for example, a device comprising two coupled rotating (power supply or receiving) devices and not a single one as described above (FIG.

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 an industrial vehicle.

By way of example, FIG. 5 very schematically represents a radial section of a tire with a metal carcass reinforcement that 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 reinforcing element of at least one carcass ply, a metal cable according to the invention. Of course, this tire 1 also comprises in known manner a layer of rubber or inner elastomer (commonly called "inner rubber") which defines the radially inner face of the tire and which is intended to protect the carcass ply of the air diffusion from the interior space to the tire .

III. EXAMPLES OF CARRYING OUT THE INVENTION

The following tests demonstrate that the three-layer cables according to the invention, compared to the in situ three-layered gummed cables of the prior art, have the significant advantage of having a reduced amount of filling rubber, which makes them guarantees a better compactness, this gum being further distributed uniformly inside the cable, inside each of its capillaries, thus conferring on them an optimal longitudinal impermeability.

In these tests, 3 + 9 + construction layer wires made of brass-coated carbon steel thin wires are used. The carbon steel wires are prepared in a known manner, for example starting from machine wires (diameter 5 to 6 mm) which are first cold-rolled, by rolling and / or drawing, to a neighboring intermediate diameter. of 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 emulsion or an aqueous dispersion. 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. The steel wires thus drawn have the diameter and the mechanical properties indicated in Table 1 below.

Table 1

These wires are then assembled in the form of 3 + 9 + compact layer cables, the construction of which is in accordance with the representation of FIG. 1 and whose mechanical properties are given in table 2. Table 2 The example (CI) of cable 3 + 9 + 15 prepared according to the process previously described, as shown diagrammatically in FIG. 1, is thus formed of a total of 27 wires, all of diameter 0.18 mm, which have been wound in three concentric layers at the same pitch (pi = p ₂ = P3 = 15 mm) and in the same direction of torsion (S) to obtain a cable of the compact type. The rate of filling rubber, measured according to the method indicated previously in paragraph II-1C, is equal to about 20 mg per g of cable. This filling rubber is present in each of the capillaries of the cable, that is to say that it fills all or at least part of each of these capillaries so that it exists at least on any portion of cable of length equal to 3 cm (preferably even reduced to 2 cm), a rubber stopper in each capillary.

For the manufacture of this cable, a device as described previously and schematized in FIG. 4. The filling rubber is a conventional rubber composition for a tire carcass reinforcement for industrial vehicles, having the same formulation as that of the carcass rubber ply that the C-I cable is intended to reinforce; 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 ElO modulus of the composition is about 6 MPa. This composition was extruded at a temperature of about 85 ° C through a sizing die with a diameter of about 0.450 mm.

The CI cables thus prepared were subjected to the air permeability test described in paragraph II-1-B, by measuring the volume of air (in cm ³ ) passing through the cables in 1 minute (average of 10 measurements for each cable tested). For each CI cable 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, these examples of cables prepared according to the method of the invention described above can be qualified as airtight along their longitudinal axis; they therefore have an optimal penetration rate by rubber. On the other hand, control gummed cables in situ, of the same construction as the CI compact cables above, were prepared according to the method described in the aforementioned application WO 2005/071157, in several discontinuous steps, by sheathing via a head. extruding the intermediate core strand 3 + 9, and then, in a second step, wiring the remaining 15 wires around the core thus sheathed, for forming the outer layer. These control cables were then subjected to the air permeability test of section 1-2. It was found first of all that none of these control cables showed 100% of the measurements (ie ten test pieces out of ten) with a flow rate of zero or less than 0.2 cm / min, in other words that none of these control cables could not be qualified as airtight (totally airtight) along its axis. It has been observed, on the other hand, that among these control cables, those having the best imperviousness results (ie an average flow rate of approximately 2 cm ³ / min), all had a relatively large amount of parasitic filling rubber overflowing with their periphery, rendering them unsuitable for a satisfactory calendering operation in industrial conditions.

In summary, the method of the invention allows the manufacture of 3 + M + N construction cables gummed in situ which, thanks to an optimal penetration rate by rubber, on the one hand have a high endurance in carcass reinforcement of pneumatic, on the other hand can be implemented effectively under industrial conditions, especially without the difficulties associated with overflowing of rubber during their manufacture.

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

Thus, for example, at least one (ie one or more) wire of the cable of the invention, whatever the layer considered (Cl, C2 or C3), could be replaced by a preformed wire or deformed, or more generally by a wire of different section than the other son diameter di and / or d ₂ and / or d ₃ , for example to further improve the penetrability of the cable by rubber or any other material, the bulk diameter of this replacement wire may be smaller, equal to or greater than the diameter (di and / or d ₂ and / or d ₃ ) of the other constituent wires of the layer (C1 and / or C2 and / or C3) concerned.

Without the spirit of the invention being modified, part of the son constituting the cable according to the invention could be replaced by son other than son steel, metal or not, including son mineral or organic material to high mechanical strength, for example monofilaments organic polymers liquid crystal.

The invention also relates to any multi-strand steel cable ("multistrand rope") whose structure incorporates at least, as elementary strand, a layered cable according to the invention. As examples of multi-strand cables in accordance with 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 two-layer multistrand cables (J + K) strands of general construction known per se, for example:

(1 + 5) x (3 + M + N) formed in total of six elementary strands, one in the center and the other five wired around the center;

(1 + 6) x (3 + M + N) formed in total of seven elementary strands, one in the center and the other six wired around the center;

- (2 + 7) x (3 + M + N) formed in total of nine elementary strands, two in the center and the other seven wired around the center;

(2 + 8) x (3 + M + N) formed in total of ten elementary strands, two in the center and eight others wired around the center;

(3 + 8) x (3 + M + N) formed in total of eleven elementary strands, three in the center and eight others wired around the center;

(3 + 9) x (3 + M + N) formed in total of twelve elementary strands, three in the center and the other nine wired around the center;

(4 + 9) x (3 + M + N) formed in total of thirteen elementary strands, three in the center and nine others wired around the center;

- (4 + 10) x (3 + M + N) formed in total of fourteen elementary strands, four in the center and the other ten wired around the center, but in which each elementary strand (or at least, at least some of them) is constituted by a cable with three layers 3 + M + N, in particular 3 + 8 + 14 or 3 + 9 + 15, which is in accordance with the invention.

Such multi-strand steel cables, in particular of the type (1 + 5) (3 + 8 + 14), (1 + 6) (3 + 8 + 14), (2 + 7) (3 + 8 + 14) ), (2 + 8) (3 + 8 + 14), (3 + 8) (3 + 8 + 14), (3 + 9) (3 + 8 + 14), (4 + 9) (3 + 8) +14), (4 + 10) (3 + 8 + 14), (1 + 5X3 + 9 + 15), (1 + 6) (3 + 9 + 15), (2 + 7) (3 + 9 + 15), (2 + 8) (3 + 9 + 15), (3 + 8X3 + 9 + 15), (3 + 9) (3 + 9 + 15), (4 + 9) (3 + 9 + 15) ) or (4 + 10) (3 + 9 + 15), could be themselves gummed in situ during their manufacture, that is to say that in this case the central strand is itself, or the strands from the center if there are several of them themselves, sheathed with unvulcanized filling rubber (this filling rubber being of the same or different formulation as that used for the in situ scrubbing of the elementary strands) before the setting in place by wiring the peripheral strands forming the outer layer.

Claims

1. Three-layer metal cable (Cl, C2, C3) of construction 3 + M + N, gummed in situ, comprising a first layer or central layer (Cl) consisting of three di diameter wires helically assembled in a pitch _b central layer around which are helically wound in a pitch p ₂ , in a second layer (C2), M son of diameter d ₂ , second layer around which are helically wound in a pitch p ₃ , in a third layer (C3), N son of diameter d ₃ , said cable being characterized in that it has the following characteristics (di, d ₂ , d ₃ , pi, p ₂ and p ₃ being expressed in mm): ;

- 0.08 <d ₂ <0.50;

- 0.08 <d ₃ <0.50;

- 3 < _P <50;

- 6 <p ₂ <50;

- 9 <p ₃ <50;

- On any length of cable equal to 3 cm, a rubber composition called "filling rubber" is present in the central channel defined by the three son of the first layer (Cl) and in each of the delimited capillaries on the one hand by the 3 wires of the first layer (C1) and the M son of the second layer (C2), on the other hand by the M son of the second layer (C2) and the N son of the third layer (C3);

- The rate of filling rubber in the cable is between 10 and 50 mg per gram of cable.

2. Cable according to claim 1, wherein the rubber of the filling rubber is a diene elastomer.

3. Cable according to claim 2, wherein the diene elastomer is selected from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. .

4. Cable according to claim 3, wherein the diene elastomer is an isoprene elastomer, preferably natural rubber.

5. A cable according to any one of claims 1 to 4, wherein the following characteristics are satisfied (pi, p _2, p ₃ being expressed in mm): - 3 < _P1 <30;

- 6 <p ₂ <30;

- 9 <p ₃ <30.

The cable of any one of claims 1 to 5, wherein: •

7. Cable according to any one of claims 1 to 6, wherein the following characteristics are verified (di, d ₂ , d ₃ in mm): ;

- 0.10 <d ₂ <0.40;

- 0.10 <d ₃ <0.40.

8. Cable according to any one of claims 1 to 7, wherein the 3, M and N son of the first (C1), second (C2) and third (C3) layers are wound in the same direction of torsion.

9. Cable according to any one of claims 1 to 8, wherein di = d ₂ ⁼ d ₃ .

Cable according to any one of claims 1 to 9, wherein p ₂ = p ₃ .

11. Cable according to any one of claims 1 to 10, wherein the second layer (C2) has 6 to 12 son and the third layer (C3) comprises 12 to 18 son.

12. Cable according to claim 11, wherein the second layer (C2) has 8 or 9 son and the third layer has 14 or 15 son.

13. Cable according to any one of claims 1 to 12, wherein the third layer (C3) is a saturated layer.

14. Cable according to any one of claims 1 to 13, wherein the level of gum filling is between 15 and 45 mg, preferably between 15 and 40 mg per g of cable.

15. Cable according to any one of claims 1 to 14, characterized in that, in the air permeability test (according to paragraph 1-2), it has a mean air flow less than

2 cm / min.

16. Cable according to claim 15, characterized in that, in the air permeability test (according to paragraph 1-2), it has an air flow rate of less than or equal to 0.2 cm ³ / min.

17. A method of manufacturing a cable according to any one of claims 1 to 16, comprising at least the following steps:

a first assembly step by twisting the three wires of the first layer for forming into a first point called "first point of assembly" of the first layer or central layer (Cl);

a second assembly step by twisting the M wires around the central layer (Cl), for forming a second point called "second assembly point" of an intermediate cable (C1 + C2) called "strand of soul ', of construction

2 + M;

- Then a final balancing step of the twists.

18. Multistrand cable at least one of the strands is a cable according to any one of claims 1 to 16.

19. Use of a cable according to any one of claims 1 to 16 and 18, for the reinforcement of an article or semi-finished product of rubber.

The use of claim 19, wherein the rubber article is a tire.

Pneumatic tire comprising a cable according to any one of claims 1 to 16 and 18.

22. A tire according to claim 21, said tire being an industrial vehicle tire.

23. A tire according to claim 20 or 21, the cable being present in the carcass reinforcement or the crown reinforcement of the tire.