EP1246964A1

EP1246964A1 - Multilayer steel cable for a tire carcass

Info

Publication number: EP1246964A1
Application number: EP00991642A
Authority: EP
Inventors: François-Jacques CORDONNIER; Alain Domingo; Henri Barguet; Le Tu Anh Vo
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Priority date: 1999-12-30
Filing date: 2000-12-27
Publication date: 2002-10-09
Anticipated expiration: 2020-12-27
Also published as: MXPA02006360A; WO2001049926A1; US6837289B2; BR0016868A; JP4705302B2; KR20020063611A; EP1246964B1; AU3366701A; RU2227187C2; JP2003519299A; US20040108038A1; CA2395899A1; ATE267908T1; CN1238581C; DE60011141T2; CN1415036A; DE60011141D1

Abstract

A multi-layer cable having an unsaturated outer layer, usable as a reinforcing element for a tire carcass reinforcement, comprising a core of diameter d0 surrounded by an intermediate layer (C1) of four or five wires (M=4 or 5) of diameter d1 wound together in a helix at a pitch p1, this layer C1 itself being surrounded by an outer layer (C2) of N wires of diameter d2 wound together in a helix at a pitch p2, N being less by 1 to 3 than the maximum number Nmax of wires which can be wound in one layer about the layer C1, this cable having the following characteristics (d0, d1, d2, p1 and p2 in mm):The invention furthermore relates to the articles or semi-finished products made of plastics material and/or rubber which are reinforced by such a multi-layer cable, in particular to tires intended for industrial vehicles, more particularly truck tires and their carcass reinforcement plies.

Description

MULTILAYERED STEEL CABLE FOR TIRE CARCASS

The present invention relates to steel cables ("steel cords") which can be used for reinforcing rubber articles such as tires. It relates more particularly to so-called "layered" cables which can be used to reinforce the carcass reinforcement of tires for industrial vehicles such as truck tires.

The steel cables for tires generally consist of wires made of perlitic (or ferrito-perlitic) carbon steel, hereinafter referred to as "carbon steel", the carbon content of which is generally between 0.2% and 1.2%, the diameter of these wires being most often between approximately 0.10 and 0.40 mm (millimeter). These wires are required to have a very high tensile strength, generally greater than 2000 MPa. preferably greater than 2500 MPa. obtained thanks to the structural hardening occurring during the wire hardening phase. These wires are then assembled in the form of cables or strands, which requires the steels used that they also have sufficient torsional ductility to support the various wiring operations.

For the reinforcement of the carcass reinforcements of HGV tires, most commonly used today are so-called "layered cords" or "multilayer" steel cables consisting of a central core and one or more layers of concentric wires arranged around this core. These layered cables, which favor longer contact lengths between the wires, are preferred to the older so-called "strand cords" because of their greater compactness, on the one hand part of a lower sensitivity to wear by fretting. Among the layered cables, there are in particular, in a known manner, cables with a compact structure and cables with tubular or cylindrical layers.

The most common layered cables in truck tire carcasses are cables of formula (L + M) or (L + M + N), the latter being generally intended for larger tires. These cables are formed in a known manner of a core of L wire (s) surrounded by at least one layer of M wires, possibly itself surrounded by an outer layer of N wires, with in general L varying from 1 to 4. , M varying from 3 to 12, N varying from 8 to 20 if applicable, the assembly possibly being hooped by an external hoop wire wound helically around the last layer.

Such layered cables which can be used for reinforcing carcass reinforcements of radial tires, in particular of truck tires, have been described in a very large number of publications. Reference will be made in particular to documents US-A-3,922,841; US-A-4,158,946; US-A-4,488,587; EP-A-0 168 858; EP-A-0 176 139 or US-A-4 651 513; EP-A-0 194 01 1; EP-A-0 260 556 or US-A-4 756 151; EP-A-0 362 570; EP-A-0 497 612 or US-A-5 285 836; EP-A-0 568 271; EP-A-0 648 891; EP-A-0 669 421 or US-A-5 595 057; EP-A-0 675 223; EP-A-0 709 236 or US-A-5 836 145; EP-A-0 719 889 or US-A-5 697 204; EP-A-0 744 490 or US-A-5 806 296 or US-A-5 822 973; EP-A-0 779 390 or US- A-5,802,829; EP-A-0 834 613 or US-A-6 102 095; WO98 / 41682; RD (Research Disclosure) N ° 34054, August 1992, pp. 624-33; RD N ° 34370, November 1992, pp. 857-59.

To fulfill their function of reinforcing the carcass reinforcement of radial tires, the layered cables must first of all have good flexibility and a high endurance in bending, which implies in particular that their wires have a relatively small diameter, normally less than 0.28 mm, in particular smaller than that of the wires used in conventional cables for the crown reinforcement of tires.

These layered cables are moreover subjected to significant stresses during the rolling of the tires, in particular to repeated bending or variations in curvature inducing friction in the wires, in particular as a result of contacts between adjacent layers, and therefore of the wear and tear; they must therefore have a high resistance to the so-called "fatigue-fretting" phenomena.

Finally, it is important that they are impregnated as much as possible with 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, capable of penetrating into the tires for example following cuts, travel along of these channels into the carcass reinforcement of the tire. The presence of this moisture plays an important role in causing corrosion and accelerating the above degradation processes (so-called "fatigue-corrosion" phenomena), compared to use in a dry atmosphere.

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

In order to improve the endurance of layered cables in the carcass reinforcements of HGV tires, where in known manner the stresses in repeated bending can be particularly severe, it has long been proposed to modify their construction in order to increase in particular their penetration by rubber, and thus limit the risks due to corrosion and fatigue-corrosion.

Were for example proposed or described cables with construction layers (3 + 9) or (3 + 9 + 15) constituted by a 3-wire core surrounded by a first layer of 9 wires and, where appropriate, by a second layer of 15 wires, as described for example in EP-A-0 168 858, EP-A-0 176 139, EP-A-0 497 612, EP-A-0 669 421. EP-A-0 709 236 , EP-A-0 744 490, EP-A-0 779 390, the diameter of the core wires being or not different from that of the wires of the other layers. These cables cannot be penetrated to the core because of the presence of a channel or capillary in the center of the three core wires, which remains empty after impregnation with the rubber, and therefore conducive to the propagation of corrosive media such as the water.

The publication RD No. 34370 describes for example cables of structure [1 + 6 + 12], of the compact type or of the type with concentric tubular layers, consisting of a core formed by a single wire, surrounded by an intermediate layer of 6 wires itself surrounded by an outer layer of 12 wires. The penetrability by the rubber can be improved by using different wire diameters from one layer to another, or even within the same layer. Construction cables [1 + 6 + 12] whose penetration is improved thanks to an appropriate choice of the diameters of the wires, in particular the use of a core wire of larger diameter, have been described for example in EP -A-0 648 891 or WO98 / 41682.

To further improve, compared to these conventional cables, the penetration of rubber inside the cable, multilayer cables have been proposed or described with a central core surrounded by at least two concentric layers, in particular cables of formula [1 + M + N] (for example [1 + 5 + 10]) whose outer layer is unsaturated (incomplete), thus ensuring better penetration by the rubber (see for example the aforementioned applications EP-A-0 675 223, EP- A-0 719 889, EP-A-0 744 490, WO98 / 41682). The proposed constructions allow the elimination of the hoop wire, thanks to a better penetration of the rubber through the external layer and the self-fretting which results therefrom. However, experience shows that these cables are not penetrated to the core by the rubber, in any case still insufficiently.

In any event, an improvement in penetration by the rubber is not sufficient to guarantee a sufficient level of performance. When used for reinforcing the carcass reinforcement of tires, the cables must not only resist corrosion but also satisfy a large number of criteria, sometimes contradictory, in particular of toughness, resistance to fretting, high adhesion to rubber, uniformity, flexibility, endurance in repeated bending, stability under strong bending, etc.

Thus, for all the reasons explained above, and despite the various recent improvements which have been made here or there on such or such determined criterion, the best cables used today in the carcass reinforcements of HGV tires remain limited to a small number of cables with very conventional structure layers, of the compact type or with cylindrical layers, with a saturated outer layer (complete); these are essentially construction cables [3 + 9], [3 + 9 + 15] or [1 + 6 + 12] as described above.

However, the Applicant has found during its research a new layered cable, of the unsaturated outer layer type, which unexpectedly further improves the overall performance of the best known layered cables for reinforcing the carcasses of heavy goods vehicle tires. This cable of the invention has, thanks to a specific architecture, not only excellent penetration by rubber, limiting the problems of corrosion. but also fatigue-fretting endurance properties which are significantly improved compared to cables of the prior art.

The longevity of HGV tires and that of their carcass reinforcement can thus be significantly improved. Consequently, a first object of the invention is a multilayer cable with an unsaturated outer layer, usable as a reinforcing element for a tire carcass reinforcement, comprising a core (denoted C0) of diameter d ₀ , surrounded by a layer intermediate (denoted Cl) of four or five wires (M = 4 or 5) of diameter d, wound together in a helix at a pitch p, this layer Cl being itself surrounded by an external layer (denoted C2) of N wires of diameter d ₂ wound together in a helix at a pitch p ₂ , N being 1 to 3 less than the maximum number N _max of wires windable in a layer around the layer Cl, this cable being characterized in that it has the following characteristics (d ₀ , d ,,

- (i) 0.08 <d ₀ <0.28;

- (ii) 0.15 <d, <0.28;

- (iii) 0.12 <d ₂ <0.25;

- (iv) for M = 4: 0.40 <(d ₀ / d,) <0.80; for M = 5: 0.70 <(do / d,) <1.10;

- (v) 4.8 π (d ₀ + d,) <p, <p ₂ <5.6 π (d ₀ + 2d, + d ₂ );

- (vi) the wires of layers C1 and C2 are wound in the same direction of twist.

The invention also relates to the use of a cable according to the invention for the reinforcement of articles or semi-finished products made of plastic and / or rubber, for example plies, pipes, belts, conveyor belts, tires, more particularly tires intended for industrial vehicles usually using a metal carcass reinforcement.

The cable of the invention is very particularly intended to be used as a reinforcing element for a tire carcass reinforcement intended for industrial vehicles chosen from vans, "HGVs" - Le., Metro, bus, transport vehicles road (trucks, tractors, trailers), off-road vehicles -, agricultural or civil engineering machinery, airplanes, other transport or handling vehicles.

The invention further relates to these semi-finished articles or products made of plastic and / or rubber themselves when they are reinforced with a cable according to the invention, in particular the tires intended for the industrial vehicles mentioned above. , more particularly truck tires and their carcass reinforcement plies.

The invention and its advantages will be easily understood in the light of the description and of the exemplary embodiments which follow, as well as of FIGS. 1 and 3 relating to these examples which schematize, respectively:

- a cross section of a structural cable [1 + 5 + 10] according to the invention (Figure 1);

- a cross section of a cable of compact structure of the prior art (Figure 2);

- a radial section through a truck tire tire with a radial carcass reinforcement (Figure 3). I. MEASUREMENTS AND TESTS

1-1. Namometric measurements

With regard to metallic wires or cables, the measurements of breaking strength noted Fm (maximum load in N), of breaking strength noted Rm (in MPa) and elongation at break noted At (total elongation in %) are carried out in tension according to ISO 6892 standard of 1984. With regard to rubber compositions, the modulus measurements are carried out in tension according to standard AFNOR-NFT-46002 of September 1988: we measure in second elongation (ie , after an accommodation cycle) the nominal secant module (or apparent stress, in MPa) at 10% elongation, noted M10 (normal conditions of temperature and hygrometry according to standard AFNOR-NFT-40101 of December 1979) .

1-2. Air permeability test

The air permeability test makes it possible to measure a relative index of air permeability denoted "Pa". It constitutes a simple means of indirect measurement of the penetration rate of the cable by a rubber composition. It is carried out on cables extracted directly, by shelling, from the vulcanized rubber sheets which they reinforce, therefore penetrated by the cooked rubber.

The test is carried out on a determined cable length (for example 2 cm) in the following manner: air is sent to the cable inlet, under a given pressure (for example 1 bar), and the quantity is measured air at the outlet, using a flow meter; during the measurement the cable sample is blocked in a tight seal so that only the quantity of air passing through the cable from one end to the other, along its longitudinal axis, is taken into account by the measurement. The measured flow is lower the higher the penetration rate of the cable by the rubber.

1-3. Belt test

The “belt” test is a known fatigue test which has been described for example in the above-mentioned applications EP-A-0 648 891 or WO98 / 41682, the steel cables to be tested being incorporated in a rubber article that the we vulcanize.

Its principle is as follows: the rubber article is an endless belt made with a known mixture based on rubber, similar to those which are commonly used for the carcasses of radial tires. 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 rubber thickness of approximately 1 mm. When the belt is arranged so as to form a cylinder of revolution, the cable forms a helical winding of the same axis as this cylinder (for example, not of the helix equal to approximately 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 variation of curvature which make it pass from an infinite radius of curvature to a radius of curvature of 40 mm and this during 50 million cycles. The test is carried out under a controlled atmosphere, the temperature and the humidity of the air in contact with the belt being maintained at approximately 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 force of the wires of the tired cables is measured.

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

One finally calculates the lapse of force-rupture after fatigue (noted ΔFm and expressed in%), by comparing the residual force-rupture with the initial force-rupture.

This lapse ΔFm is in 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 to which the cables of reinforcement in tire carcasses.

1-4. Corrugated tensile test

The "wavy traction" test is a fatigue test well known to those skilled in the art, in which the tested material is tired in pure uni-axial extension (extension-extension), that is to say without stress compression.

The principle is as follows: a sample of the cable to be tested, held at each of its two ends by the two jaws of a traction machine is subjected to a tensile stress or extension whose intensity σ varies cyclically and symmetrically (σ _moy ± σ _a ) around an average value (σ _m0 y), between two extreme values σ _mιn (σ _mo - σ _a ) and σ _max (σ _mo + σ _a ) framing this average value, in a relation load "R" = (σ _mιn / σ _max ) determined. The average stress σ _moy is therefore linked to the charge ratio R and to the amplitude σ _a by the relation σ _m0 y ≈ σ _a (l + R) / (lR).

In practice, the test is carried out as follows: a first stress amplitude σ _a is chosen (generally in a range of the order of 1/4 to 1/3 of the resistance R of the cable) and the test is launched fatigue for a maximum number of 10 ⁵ cycles (frequency 30 Hz), the load ratio R being chosen equal to 0.1. Depending on the result obtained - ie breakage or non-breakage of the cable after these 10 ⁵ cycles maximum - a new amplitude σ _a (lower or higher than the previous one, respectively) is applied to a new test piece, by varying this value σ _a according to the so-called staircase method (Dixon & Mood: Journal of the American statistical association, 43, 1948, 109-126). A total of 17 iterations are thus carried out, the statistical treatment of the tests defined by this staircase method leads to the determination of an endurance limit - denoted σ, j - which corresponds to a probability of cable breakage of 50% after 10 ⁵ fatigue cycles. For this test, a tensile fatigue machine from the company Schenk (model PSA) is used; the useful length between the two jaws is 10 cm; the measurement is carried out under a controlled dry atmosphere (relative humidity rate less than or equal to 5%; temperature of 20 ° C).

1-5. Tire endurance test

The endurance of cables in fatigue-fretting-corrosion is evaluated in carcass plies of truck tires by a very long running test.

Truck tires are manufactured for this, the carcass reinforcement of which consists of a single rubberized ply 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 humidity. These tires are then rolled on an automatic rolling machine, under a very high load (overload compared to the nominal load) and at the same speed, for 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 wires and on the cables thus tired.

On the other hand, tires identical to the previous ones are produced and they are peeled in the same way as above, but this time without subjecting them to running. We thus measure, after shelling. the initial breaking force of the non-tired wires and cables.

One finally calculates the lapse of force-rupture after fatigue (noted ΔFm and expressed in%), by comparing the residual force-rupture with the initial force-rupture. This lapse ΔFm is due to the fatigue and wear (reduction in section) of the wires caused by the joint action of the various mechanical stresses, in particular the intense work of the contact forces between the wires, and of the water coming from the ambient air, in other words to the fatigue-fretting-corrosion undergone by the cable inside the tire, during rolling.

It is also possible to choose to run the rolling test until the forced destruction of the tire, due to a rupture of the carcass ply or to another type of damage occurring earlier (for example, dethatching).

II. DETAILED DESCRIPTION OF THE INVENTION

II- 1. Cable of the invention

The terms "formula" or "structure", when used in the present description to describe the cables, simply refer to the construction of these cables.

The cable of the invention is a multilayer cable comprising a core (C0) of diameter d ₀ , an intermediate layer (Cl) of 4 or 5 wires (M = 4 or 5) of diameter d, and an outer unsaturated layer (C2 ) of N wires of diameter d ₂ , N being 1 to 3 less than the maximum number N _ma of wires which can be wound up in a single layer around the layer C1. In this layered cable of the invention, the diameter of the core and that of the wires of layers C1 and C2, the helix pitches (therefore the angles) and the winding directions of the various layers are defined by the set of the following characteristics (d ₀ , d |, d ₂ , pi and p ₂ expressed in mm):

(i) 0.08 <d ₀ <0.28

(ii) 0.15 <d, <0.28

(iii) 0.12 <d ₂ <0.25

(iv) for M = 4: 0.40 <(d ₀ / d,) <0.80; for M = 5: 0.70 <(d ₀ / d,) <1.10;

(v) 4.8 π (d ₀ + d,) <p, <p ₂ <5.6 π (d ₀ + 2d, + d ₂ );

(vi) the wires of layers C1 and C2 are wound in the same direction of twist.

The characteristics (i) to (vi) above, in combination, make it possible to obtain both:

- Sufficient but limited contact forces between C0 and Cl, favorable to reduced wear and less fatigue of the wires of the Cl layer;

- reduced fretting wear between the wires of layers C 1 and C2, this despite the presence of different pitches (p, ≠ p ₂ ) between the two layers Cl and C2. - thanks in particular to an optimization of the diameter ratio (d ₀ / di) and of the helix angles formed by the wires of the layers Cl and C2, optimal penetration of the rubber through the layers Cl and C2 and up to the core C0 of the latter, ensuring on the one hand a very high protection against corrosion or its possible propagation, on the other hand minimal disorganization of the cable under stress in strong bending.

Thus, thanks to its specific structure, the cable of the invention, already self-fretted. generally does not require the use of an external hoop wire around the layer C2; this advantageously solves the wear problems between the hoop wire and the wires of the outermost layer of the cable.

But, of course, the cable of the invention could also include such an external hoop, consisting for example of a (at least one) single wire wound in a helix around the external layer C2, according to a pitch of helix preferably more shorter than that of layer C2, and a winding direction opposite or identical to that of this outer layer.

In order to further reinforce the specific hooping effect provided by the layer C2, the cable of the invention, in particular when it does not have such an external hoop wire, preferably checks the characteristic (vii) below :

(vii) 5.0 π (d ₀ + d,) <p, <p ₂ <5.0 π (d ₀ + 2d, + d ₂ )

Characteristics (v) and (vi) - different p, and p ₂ and layers C1 and C2 wound in the same direction of twist - mean that, in known manner, the wires of layers C1 and C2 are essentially arranged in two layers cylindrical (ie tubular), adjacent and concentric. By cables with so-called "tubular" or "cylindrical" layers, we mean cables made up of a core (ie. Core or central part) and one or more layers concentric, each of tubular shape, arranged around this core, in such a way that. at least in the cable at rest, the thickness of each layer is substantially equal to the diameter of the wires which constitute it; it follows that the cross section of the cable has a contour or envelope (denoted E) which is substantially circular, as illustrated for example in FIG. 1.

The cables with cylindrical or tubular layers of the invention must in particular not be confused with cables with so-called "compact" layers, assemblies of wires wound at the same pitch and in the same direction of twist; in such cables, the compactness is such that practically no distinct layer of wires is visible; it follows that the cross section of such cables has a contour (E) which is no longer circular, but polygonal, as illustrated for example in FIG. 2.

The outer layer C2 is a tubular layer of N wires called "unsaturated" or "incomplete". that is to say that, by definition, there is enough space in this tubular layer C2 to add at least one (N + 1) th wire of diameter d ₂ , several of the N wires possibly being in contact with the each other. Conversely, this tubular layer C2 would be qualified as "saturated" or "complete" if there was not enough room in this layer to add at least one (N + 1) th wire of diameter d ₂ .

Preferably, the cable of the invention is a layered cable of construction denoted [1 + M + N], that is to say that its core consists of a single wire. as shown for example in Figure 1 (cable marked C-I).

This Figure 1 shows schematically a section perpendicular to the axis (denoted O) of the core and the cable, the cable being assumed to be straight and at rest. We see that the core CO (diameter d ₀ ) is formed of a single wire; it is surrounded and in contact with an intermediate layer C1 of 5 wires of diameter di wound together in a helix at a pitch pi; this layer C1, of thickness substantially equal to d _{] 5} is itself surrounded and in contact with an external layer C2 of 10 wires of diameter d ₂ wound together in a helix at a pitch p ₂ , and therefore of thickness substantially equal to d ₂ . The wires wound around the core C0 are thus arranged in two adjacent and concentric, tubular layers (layer C1 of thickness substantially equal to d _b then layer C2 of thickness substantially equal to d ₂ ). We see that the wires of layer C l have their axes (denoted Oi) arranged practically on a first circle C _/ shown in dotted lines, while the wires of layer C2 have their axes (denoted 0 ₂ ) arranged practically on a second circle (A, also shown in dotted lines.

For an even better compromise of results, with regard in particular to the penetrability of the cable by the rubber and the contact forces between the different layers, it is preferred that the relation (vii) above be verified, this that the cable of the invention is either hooped or not by an external hoop wire.

Even more preferably, for these same reasons, the cable of the invention verifies the following relationship:

(viii) 5.3 π (d ₀ + d,) <p, <p ₂ <4.7 π (d ₀ + 2d, + d ₂ ) By thus shifting the steps and therefore the contact angles between the wires of the layer C1 on the one hand, and those of the layer C2 on the other hand, it has been found that the penetrability of the cable was further improved, by increasing the surface of the penetration channels between these two layers, while optimizing its fatigue-fretting performance.

It will be recalled here that, according to a known definition, the pitch represents the length, measured parallel to the axis O of the cable, at the end of which a wire having this pitch makes a complete revolution around the axis O of the cable; thus, if the axis O is sectioned by two planes perpendicular to the axis O and separated by a length equal to the pitch of a wire from one of the two layers Cl or C2, the axis of this wire (Oi or O ₂ , respectively) has in these two planes the same position on the two circles corresponding to the layer C1 or C2 of the wire considered.

In the cable according to the invention, a preferred embodiment consists in choosing the pitches pi and p ₂ included in a range from 5 to 15 mm, pi being notably included in a range from 5 to 10 mm and p ₂ included in an area of 10 to 15 mm.

The following relationship is more preferably verified, in particular when the cable of the invention is devoid of external hoop wire:

6 <p, <p ₂ <14.

A particular and advantageous embodiment then consists in choosing p, between 6 and 10 mm and p ₂ between 10 and 14 mm.

In the cable according to the invention, all the wires of layers C1 and C2 are wound in the same direction of twist, that is to say either in the direction S ("S / S" arrangement), or in the direction Z ("Z / Z" arrangement). Such an arrangement of layers C1 and C2 is rather contrary to the most conventional constructions of layered cables [L + M + N], in particular those of construction [3 + 9 + 15], which most often require crossing of the two layers Cl and C2 (either an "S / Z" or "Z / S" arrangement) so that the wires of the layer C2 come to fry the wires of the layer Cl. The winding in the same direction of the layers C1 and C2 advantageously makes it possible, in the cable according to the invention, to minimize the friction between these two layers C1 and C2 and therefore the wear of the wires which constitute them.

In the cable of the invention, the ratios (d ₀ / dι) must be fixed within given limits, according to the number M (4 or 5) of wires of the layer Cl. Too low a value of this ratio is detrimental to the wear between the core and the wires of the layer C1. A too high value harms the compactness of the cable, for a level of resistance that is ultimately little modified, as well as its flexibility; the increased rigidity of the core due to a diameter d ₀ too high would also be detrimental to the feasibility itself of the cable, during wiring operations.

The wires of layers C1 and C2 can have an identical or different diameter from one layer to another; wires of the same diameter (d, = d ₂ ) can advantageously be used, in particular to simplify the wiring process and lower costs, as shown for example in FIG. 1. The maximum number N _max of wires wound in a single saturated layer around the layer Cl is of course a function of many parameters (diameter d ₀ of the core, number M and diameter d ₍ of the wires of the layer Cl, diameter d ₂ wires of layer C2). For example, if N _max is equal to 12, N can then vary from 9 to 1 1 (for example constructions [l + M + 9], [l + M + 10] or [1 + M + l 1]); if N _{ma <} is for example equal to 1 1, N can then vary from 8 to 10 (for example constructions [l + M + 8], [l + M + 9] or [l + M + 10]).

Preferably, the number N of wires in the layer C2 is 1 to 2 less than the maximum number N _max . This allows in most cases to provide sufficient space between the wires so that the rubber compositions can infiltrate between the wires of the layer C2 and reach the layer C1. Thus, the invention is preferably implemented with a cable chosen from structural cables [1 + 4 + 8], [1 + 4 + 9], [1 + 4 + 10], [1 + 5 + 9 ], [1 + 5 + 10] or [1 + 5 + 1 1].

By way of examples of cables in accordance with the invention, mention will be made of cables having the following constructions and in particular, among them, the preferred cables satisfying at least one of the relations (vii) or (viii) mentioned above:

- [1 + 4 + 8] with d ₀ = 0, 100 mm and d, = d ₂ = 0.200 mm;

- [1 + 4 + 8] with d ₀ = 0.120 mm and d, = d ₂ = 0.225 mm;

- [1 + 4 + 9] with d ₀ = 0.120 mm and d, = d ₂ = 0.200 mm;

- [1 + 4 + 9] with d ₀ = 0, 150 mm and d, = d ₂ = 0.225 mm;

- [1 + 4 + 10] with d ₀ = 0.120 mm and d, = d ₂ = 0.175 mm; - [1 + 4 + 10] with d ₀ = 0.150 mm and d, = d ₂ = 0.225 mm;

- [1 + 5 + 9] with d ₀ = 0.150 mm and d, = d ₂ = 0.175 mm;

- [1 + 5 + 9] with d ₀ = 0.175 mm and d, = d ₂ = 0.200 mm;

- [1 + 5 + 10] with d ₀ = 0.150 mm and d, = d ₂ = 0.175 mm;

- [1 + 5 + 10] with d ₀ = d, = d ₂ = 0.200 mm; - [1 + 5 + 1 1] with d ₀ = d ₂ = 0.200 mm; d, = 0.225 mm;

- [1 + 5 + 1 1] with d ₀ = 0.200 mm and d, = d ₂ = 0.225 mm;

- [1 + 5 + 1 1] with d ₀ = d, = d ₂ = 0.225 mm;

- [1 + 5 + 1 1] with d ₀ = 0.240 mm and d, = d ₂ = 0.225 mm;

- [1 + 5 + 1 1] with d ₀ = d ₂ = 0.225 mm; di = 0.260 mm.

It will be noted that, in these cables, at least two layers out of three (C0, C 1, C2) contain wires of identical diameters (respectively d ₀ , d ,, d ₂ ).

The invention is preferably implemented in the carcass reinforcements of HGV tires, with cables of structure [1 + 5 + N], more preferably of structure [1 + 5 + 9], [1 + 5 + 10] or [1 + 5 + 1 1]. Even more preferably, cables of structure [1 + 5 + 10] or [1 + 5 + 1 1] are used.

For such cables [1 + 5 + N], an advantageous embodiment of the invention consists in using wires of the same diameter for the core and at least one of the layers C1 and C2, or even for the two layers (in this case, d ₀ = d, = d ₂ ), as shown for example in Figure 1. However, to further increase the penetrability of the cable by the rubber, the wires of layer C1 can be chosen to have a diameter greater than those of layer C2, for example in a ratio (d | / d ₂ ) preferably between 1.05 and 1.30.

For reasons of industrial strength, feasibility and cost, it is preferred that the diameter d ₀ of the core is between 0.14 and 0.28 mm.

On the other hand, for a better compromise between strength, feasibility and flexural strength of the cable, on the one hand, penetrability by rubber compositions on the other hand, it is preferred that the diameters of the wires of the layers C2 are between 0 , 15 and 0.25 mm.

For the carcass reinforcements of HGV tires, the diameter d, is preferably chosen less than or equal to 0.26 mm and the diameter d ₂ is preferably greater than 0.17 mm. A diameter d | less than or equal to 0.26 mm makes it possible to reduce the level of stresses undergone by the wires during large variations in cable curvature, whereas diameters d ₂ preferably greater than 0.17 mm are chosen for reasons, in particular , wire resistance and industrial cost; when d, and d ₂ are chosen from these preferential intervals, the diameter do of the core is then more preferably between 0.14 and 0.25 mm.

The invention can be implemented with any type of steel wire, for example carbon steel wire and / or stainless steel wire as described for example in applications EP-A-0 648 891 or WO98 / 41682 cited above. Carbon steel is preferably used, but it is of course possible to use other steels or other alloys.

When carbon steel is used, its carbon content (% by weight of steel) is preferably between 0.50% and 1.0%, more preferably between 0.68% and 0.95%; these contents represent a good compromise between the mechanical properties required for the tire and the feasibility of the wire. It should be noted that in applications where the highest mechanical strengths are not necessary, it is advantageous to use carbon steels whose carbon content is between 0.50% and 0.68%, in particular varies from 0, 55% to 0.60%, such steels being ultimately less expensive because they are easier to draw. Another advantageous embodiment of the invention may also consist, depending on the intended applications, 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.

When the cables of the invention are used to reinforce the carcass reinforcements of tires for industrial vehicles, their wires preferably have a tensile strength greater than 2000 MPa, more preferably greater than 3000 MPa. In the case of tires of very large dimensions, one will especially choose cords whose tensile strength is between 3000 MPa and 4000 MPa. Those skilled in the art know how to manufacture, for example, carbon steel wires having such a resistance, in particular by adjusting the carbon content of the steel and the final work hardening rates (ε) of these wires.

The cable of the invention may include an external hoop, for example consisting of a single wire, metallic or not, wound helically around the cable in a shorter pitch than that of the outer layer, 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-fretted. generally does not require the use of an external hoop wire, which advantageously solves the problems of wear between the hoop and the wires of the outermost layer of the cable.

However, if a hoop wire is used, in the general case where the wires of layer C2 are made of carbon steel, it is then advantageously possible to choose a hoop wire of stainless steel in order to reduce the wear by fretting of these wires. made of carbon steel in contact with the stainless steel hoop, as taught by the aforementioned application WO98 / 41682, the stainless steel wire being able to 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 patent application EP-A-0 976 541.

II-2. Fabric and tire of the invention

The invention also relates to tires intended for industrial vehicles, more particularly truck tires as well as rubberized fabrics usable as carcass reinforcement plies of these truck tires.

By way of example, FIG. 3 schematically represents a radial section of a truck tire 1 with a radial carcass reinforcement which may or may not conform to the invention, in this general representation. This tire 1 has a crown 2, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a bead wire. The crown 2. surmounted by a tread (not shown in this schematic figure) is so known per se reinforced by a crown reinforcement 6 consisting for example of at least two superimposed crossed plies, reinforced by known metal cables. A carcass reinforcement 7 is wound around the two rods 5 in each bead 4, the reversal 8 of this reinforcement 7 being for example disposed towards the outside of the tire 1 which is here shown mounted on its rim 9. The carcass reinforcement 7 consists of at least one ply reinforced by so-called "radial" cables, that is to say that these cables are arranged practically parallel to one another and extend from one bead to the other so 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 reinforcement 6 ).

The tire according to the invention is characterized in that its carcass reinforcement 7 comprises at least one carcass ply whose radial cables are multi-layer steel cables according to the invention.

In this carcass ply, the density of the cables according to the invention is preferably between 40 and 100 cables per dm (decimeter) of radial ply, more preferably between 50 and 80 cables per dm, the distance between two adjacent radial cables , from axis to axis, thus preferably being between 1.0 and 2.5 mm, more preferably between 1.25 and 2.0 mm. The cables according to the invention are preferably arranged in such a way that the width (denoted "i") of the rubber bridge, between two adjacent cables, is between 0.35 and 1 mm. This width l represents in known manner the difference between the calendering pitch (no laying of the cable in the rubber fabric) and the diameter of the cable. Below the minimum value indicated, the rubber bridge, which is too narrow, risks being mechanically degraded during the working of the ply, in particular during the deformations undergone in its own plane by extension or shearing. Beyond the maximum indicated, there is a risk of appearance defects appearing on the sidewalls of the tires or of objects penetrating, by perforation, between the cables. More preferably, for these same reasons, the width "d" is chosen to be between 0.4 and 0.8 mm.

The values recommended above for cable density, distance between adjacent cables and rubber bridge width are those measured both on the fabric as it is in the raw state (ie. Before incorporation into the tire) and in the tire itself, in the latter case measured under the bead of the tire.

Preferably, the rubber composition used for the fabric of the carcass ply has, in the vulcanized state (ie, after baking), a secant module in extension M10 which is less than 8 MPa, more preferably between 4 and 8 MPa. It is in such a field of modules that the best endurance compromise has been recorded between the cables of the invention on the one hand, and the reinforced fabrics of these cables on the other hand.

For example, for the manufacture of the tires of the invention, the procedure is as follows. The above-layered cables are incorporated by calendering into a rubberized fabric formed of a known composition based on natural rubber and carbon black as reinforcing filler, conventionally used for the manufacture of the carcass reinforcement plies of tires Weight - heavy radial. The tires are then manufactured in a known manner and are as shown diagrammatically in FIG. 3, already commented on. Their radial carcass reinforcement 7 is, for example, made up of a single radial ply formed of the above rubberized fabric, the radial cables of the invention being arranged at an angle of about 90 ° with the circumferential plane median. Their vertex frame 6 is. in a manner known per se, consisting of two overlapping work plies crossed, reinforced with metal cables inclined by 22 degrees, these two work plies being covered by a protective top ply reinforced with "elastic" metallic cables (ie, cables with high elongation). In each of these crown reinforcement plies, the metal cables used are known conventional cables, arranged substantially parallel to one another, and the angles of inclination indicated are measured relative to the median circumferential plane.

III. EXAMPLES OF EMBODIMENT OF THE INVENTION

III- 1. Nature and properties of the wires used

For carrying out the examples of cables conforming or not conforming to the invention to the invention, fine carbon steel wires are used, prepared according to known methods as described for example in applications EP-A-0 648 891 or WO98 / 41682 cited above. starting from commercial wires with an initial diameter of approximately 1 mm. The steel used is a known carbon steel (USA standard AISI 1069), the carbon content of which is approximately 0.7%, comprising 0.5% manganese and approximately 0.2% silicon, the remainder consisting of iron and the usual unavoidable impurities associated with the steel manufacturing process.

The commercial starting wires first undergo a known degreasing and / or pickling treatment before their subsequent implementation. At this stage, their breaking strength is approximately 1150 MPa. their elongation at break is approximately 10%. Copper is then deposited on each wire, followed by a zinc deposit, by electrolytic means at room temperature, and then heat is heated by Joule effect to 540 ° C. to obtain brass by diffusion of copper and zinc, the weight ratio (phase) / (phase α + phase β) being equal to approximately 0.85. No heat treatment is carried out on the wire after obtaining the brass coating.

A so-called "final" work hardening is then carried out on each wire (ie, implemented after the last heat treatment), by cold wire drawing in a wet environment with a wire drawing lubricant which is in the form of an emulsion in water. This wet drawing is carried out in a known manner in order to obtain the final work hardening rate (denoted ε) calculated from the initial diameter indicated previously for the starting commercial wires.

By definition, the rate of a hardening noted ε is given by the formula ε = Ln (Sj / Sf), in which Ln is the natural logarithm, S \ represents the initial section of the wire before this hardening and Sf the final section of wire after this work hardening.

By adjusting the final work hardening rate, two groups of wires of different diameters are thus prepared, a first group of wires of average diameter φ equal to about 0.200 mm (ε = 3.2) for wires of index 1 (wires denoted Fl) and a second group of wires of average diameter φ equal to about 0.175 mm (ε = 3.5) for the wires of index 2 (wires denoted F2).

The steel wires thus drawn have the mechanical properties indicated in Table 1.

The elongation At indicated for the wires is the total elongation recorded when the wire breaks, that is to say integrating both the elastic part of the elongation (Hooke's law) and the plastic part of the elongation.

The brass coating which surrounds the wires has a very small thickness, clearly less than a micrometer, for example of the order of 0.15 to 0.30 μm, which is negligible compared to the diameter of the steel wires. Of course, the composition of the steel of the wire in its various elements (for example C, Mn, Si) is the same as that of the steel of the starting wire. It will be recalled that, during the wire manufacturing process, the brass coating facilitates the wire drawing, as well as the bonding of the wire with, the rubber. Of course, the wires could be covered with a thin metallic layer other than brass, for example having the function of improving the corrosion resistance of these wires and / or their adhesion to rubber. for example a thin layer of Co. Ni, Zn, Al, an alloy of two or more of the Cu compounds. Zn, Al, Ni, Co, Sn.

III-2. Cable realization

The above wires are then assembled in the form of layered cables, of structure [1 + 5 + 10] for the cable according to the invention (cable marked CI), of structure [1 + 6 + 12] for the cable of the 'prior art (cable noted C-II); the wires F1 are used to form the core CO of these cables CI and C-II, as well as the layers Cl and C2 of the cable CI according to the invention, while the wires F2 are used to form the layers Cl and C2 of the C-II indicator cable.

These cables are manufactured with wiring devices (Barmag cabling machine) and according to methods well known to those skilled in the art which are not described here for the simplicity of the description. Cable C-II is produced in a single wiring operation (pi = p ₂ ) whereas the CI cable requires, due to different pi and p ₂ pitch, two successive operations (manufacture of a cable [1 + 5] then wiring the last layer around this cable [1 + 5]), these two operations can advantageously be carried out online using two stranding machines arranged in series.

The cable C-I according to the invention has the following characteristics:

- structure [1 + 5 + 10] d ₀ = d, = d ₂ = 0.200; (d ₀ / d,) = 1.00; p, = 8 (Z); p ₂ = ll (Z).

The C-II control cable has the following characteristics:

structure [1 + 6 + 12] d ₀ = 0.200; d, = d ₂ = 0.175; - (d ₀ / d,) = 1.14; p, = 10 (Z); p ₂ = 10 (Z).

Whatever the cables, the wires F2 of layers C1 and C2 are wound in the same direction of twist (direction Z).

The two cables tested have no hoop and have a diameter of approximately 1.0 mm for the CI cable, approximately 0.90 mm for the C-II cable. The core of these cables has the diameter d ₀ the same diameter as that of its single wire F1, practically devoid of twist on itself. The cable of the invention CI is a cable with tubular layers as shown schematically in cross section in Figure 1, already discussed above. It differs from the usual cables of the prior art in particular by the fact that its intermediate layers C1 and external C2 comprise, respectively, one and two wires less than a conventional saturated cable, and that its pitches p, and p ₂ are different while also checking the above relation (v). In this CI cable. N is 2 less than the maximum number (here N _max = 12) of wires which can be wound up in a single saturated layer around layer C 1.

The control cable C-II is a compact layered cable as shown diagrammatically in FIG. 2. It can be seen in particular in this cross section of FIG. 2 that the cable C-II. although of neighboring construction, due to its wiring method (wires wound in the same direction and not p, and p ₂ equal) a structure much more compact than that of the CI cable; it follows that no tubular layer of wires is visible for this cable, the cross section of this cable C-II having a contour E which is no longer circular but hexagonal.

It is noted that the cable of the invention C-I (M = 5) verifies the following characteristics:

- (i) 0.08 <d ₀ <0.28 - (ii) 0.15 <d, <0.28 - (iii) 0.12 <d ₂ <0.25 - (iv) for M = 4 : 0.40 <(d ₀ / d,) <0.80; for M = 5: 0.70 <(d ₀ / d,) <1.10;

- (v) 4.8 π (do + d,) <p, <p ₂ <5.6 π (d ₀ + 2d, + d ₂ );

- (vi) the wires of layers C1 and C2 are wound in the same direction of twist.

This C-I cable also checks each of the following preferential relationships:

d ₂ >0.17; d, <0.26;

0.14 <d ₀ <0.25;

6 <p, <p ₂ <14.

It also checks each of the relationships (vii) and (viii) above.

The mechanical properties of cables C-I and C-II are indicated in table 2 below:

Table 2

The elongation At indicated for the cable is the total elongation recorded at the break of the cable, that is to say integrating both the elastic part of the elongation (Hooke's law), the plastic part of the elongation and the so-called structural part of the elongation inherent in the specific geometry of the cable tested. - 1!

III-3. Endurance tests (belt test ^" )

The above-layered cables are incorporated by calendering into a rubberized fabric formed of a known composition based on natural rubber and carbon black as reinforcing filler, conventionally used for the manufacture of the carcass reinforcement plies of tires Weight -heavy radial (module M10 equal to approximately 6 MPa, after firing). This composition essentially comprises, in addition to the elastomer and the reinforcing filler, an antioxidant, stearic acid, an extension oil, cobalt naphthenate as an adhesion promoter, finally a vulcanization system ( sulfur, accelerator, ZnO). In the rubber fabric, the cables are arranged parallel in a known manner, according to a cable density of the order of 63 cables per dm (decimeter) of ply, which. taking into account the diameter of the cables, equivalent to a width “£” of the rubber bridges, between two adjacent cables, of approximately 0.6 mm for the cable of the invention, of approximately 0.7 mm for the control cable .

The fabrics thus prepared are subjected to the belt test described in paragraph 1-3. After fatigue, shelling is carried out, that is to say an extraction of the cables from the belts. The cables are then subjected to tensile tests, each time measuring the residual tensile strength (cable extracted from the belt after fatigue) of each type of wire. according to the position of the wire in the cable, and for each of the cables tested, and by comparing it to the initial tensile strength (cables extracted from new belts).

The average lapses ΔFm are given in% in table 3; they are calculated both for the core wires (C0) and for the wires of layers C1 and C2. The overall ΔFm lapses are also measured on the cables themselves.

Table 3

On reading Table 3, it can be seen that, whatever the zone of the cable analyzed (core C0, layers Cl or C2), the best results are recorded on the cable C-I according to the invention. If the lapses ΔFm remain fairly similar as regards the external layer C2 (although lower in the cable according to the invention), it is noted that the more one penetrates inside the cable (layer Cl and core C0), the more the gaps widen in favor of the cable according to the invention; the lapses ΔFm of the core and of the layer C 1 are almost twice lower in the cable of the invention. The overall lapse of the cable of the invention is significantly lower than that of the control cable (8% instead of 14%).

Correlatively to the above 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 Repeated friction between the wires, are significantly reduced in the CI cable compared to the C-II cable.

These results are unexpected insofar as those skilled in the art could on the contrary expect that the choice of different propeller pitch pi and p ₂ in the cable according to the invention, and therefore the presence of angles of different contact between the layers C1 and C2 - which have the effect of reducing the contact surfaces and therefore of increasing the contact pressures between the wires of the layers Cl and C2 - on the contrary result in an increase in friction and therefore of wear between the wires, and ultimately penalize the cable according to the invention. It is not so.

III-4. Air permeability tests

The endurance results described above appear to be well correlated with the penetration rate of the cables by the rubber, as explained below.

Cables C-I and C-II not tired (after extraction from new belts) were subjected to the air permeability test described in paragraph 1-2. by measuring the amount of air passing through the cables in 1 minute (average of 10 measurements). The permeability indices Pa obtained are reported in Table 4 (in relative units); the values indicated correspond to the average of 10 samples taken at different points on the belts, the base 100 being used for the C-II control cables.

Table 4

It is noted that the cable according to the invention has a significantly lower air permeability index Pa (factor 5 approximately) than that of the control C-II, and consequently a significantly higher rate of penetration by the rubber.

Its specific construction makes it possible, during the molding and / or the curing of the tires, an almost complete migration of the rubber inside the cable, to the heart of the latter, without the formation of empty channels. The cable, thus made impermeable by the rubber, is protected from the oxygen and humidity flows which pass for example from the sidewalls or the tread of the tires to the areas of the carcass reinforcement, where the cable in known manner is subjected to the most intense mechanical work.

III-5. Other cables and endurance tests (wavy traction test and belt test)

In this new series of tests, three layered cables, denoted C-III to CV, of construction [1 + 5 + 10] are prepared, these cables being in accordance with the invention, in order to submit them to the fatigue test. in wavy traction (paragraph 1-4). These cables, prepared from :; son Fl previously described, have the following characteristics.

• Cable C-III (according to the invention): structure [1 + 5 + 10] d ₀ = d, = d ₂ = 0.200;

(d ₀ / d,) = 1.00; p, = 8 (S); p ₂ = ll (S).

Cable C-IV (control): structure [1 + 5 + 10] d ₀ = d, = d ₂ = 0.200; (do / d,) = 1.00; p, = 5.5 (S); p ₂ = 1 1 (S).

• CV cable (indicator): structure [1 + 5 + 10] d ₀ = d, = d ₂ = 0.200; (d ₀ / d,) = 1.00; p, = 7.5 (S); p ₂ = 15 (S).

The cable C-III has a construction similar to that of the cable C-I previously tested.

Cables with a structure [1 + 5 + 10] close to or similar to that of the control cables C-IV or CV above, characterized inter alia by a pitch p ₂ double of the pitch p _{l 5} are known to those skilled in the art. job ; they have for example been described in the aforementioned applications EP-A-0 675 223 or EP-A-0 744 490. These known cables do not verify all of the characteristics (i) to (vi) of the cables of the invention, in particular the essential characteristic (v) relating to the offset between

None of the three cables tested has a hoop. Their properties are those indicated in Table 5 below:

Table 5

These three cables therefore have very similar constructions and mechanical properties at break: in the three cases, N is 2 less than the maximum number (here N _max = 12) of wires wound in a single saturated layer around the layer Cl; they all have a construction with tubular layers as illustrated in FIG. 1; the steps p, and p ₂ are different in each cable. However, only the cable C-III verifies the above-mentioned relation (v), as well as the preferential characteristics of the relations (vii) and (viii).

In the wavy traction fatigue test, these three cables gave the results in Table 6; σ < _j y is expressed in MPa as well as in relative units (ur), the base 100 being retained for the cable of the invention C-III.

Table 6

It is noted that, in spite of very close constructions, the cable of the invention C-III is distinguished by a fatigue life significantly superior to that of the control cables, in particular that of the control cable C-IV which it should be noted that only the pitch p, differs (5.5 mm instead of 8 mm).

The three cables of this test were also subjected to the belt test previously applied to cables C-I and C-II (paragraph III-4). They all showed very good performance, close in terms of overall cable lapse (ΔFm at most equal to 10%). However, it was on the cable of the invention that the lowest average wear was recorded for the wires of the peripheral layer C2; this improved result must be emphasized because, in this type of cable, it is indeed the layer C2 which has the greatest number of wires and therefore supports most of the load.

In summary, the overall improved endurance of the cable of the invention C-III, compared with the control cables C-IV and CV of very similar constructions, must be attributed here, firstly, to an optimization of the angle ratios. helix (spacing between steps p, and p ₂ ) formed by the wires of layers C1 and C2. Thanks to this, an even better compromise of results is obtained with respect to the rubber penetration of the cable and the contact forces between the different layers.

III-6. Endurance in pneumatics

A rolling test is carried out here on HGV tires intended to be mounted on a rim with flat seats, dimension 12.00 R 20 XZE.

All the tires tested are identical, except for the layered cables which reinforce their carcass reinforcement 7 (see Figure 3).

The cables used for the carcass reinforcement 7 have the following characteristics • C-VI cable (according to the invention - 17 wires + 1 hoop wire): structure [1 + 5 + 1 1] d ₀ = d ₂ = 0.230; d, ≈ 0.260; - (d ₀ / d,) = 0.88; p, = 7.5 (S); p ₂ = 15 (S).

Cable C-VII (indicator - 27 wires + 1 hoop wire): structure [3 + 9 + 15] - d ₀ = d, = d ₂ = 0.230; po = 6.5 (S); p, = 12.5 (S); p ₂ = 18.0 (Z).

The cable of the invention C-VI consists of a core wire of 0.23 mm diameter, surrounded by an intermediate layer of 5 wires wound together in a helix (direction S) in a pitch of 7.5 mm , itself surrounded by an outer layer of 1 1 wires themselves wound together in a helix (direction S) in a pitch of 15 mm. This C-VI cable is wrapped by a single wire of 0.15 mm diameter (Rm = 2800 MPa) wound in a helix (direction Z) in a pitch of 5 mm. In this cable according to the invention, N is 1 less than the maximum number (here N _max = 12) of wires which can be wound up in a single saturated layer around layer C 1. It checks the relation (v) without, however, checking the preferential relationships (vii) and (viii). To further increase its penetrability by the rubber, the wires of layer C1 were chosen to have a diameter greater than those of layer C2 in a preferred ratio (d ₁ / d ₂ ) of between 1.10 and 1.20. The cable diameter (total size) is approximately 1.49 mm.

With the exception of the hoop wire (steel with 0.7% carbon), all the wires of the cable C-VI, noted F3 and F4 in Table 7 below, were made from a steel with higher carbon content (0.82% instead of 0.71% for the control cable) to partially compensate for the decrease in the number of wires by an increase in the steel's resistance.

The C-VII cable was chosen as a control for this rolling test, because of its performance recognized by a person skilled in the art for the reinforcement of large truck tires. Cables of identical or similar structure have for example been described in the aforementioned applications EP-A-0 497 612, EP-A-0 669 421, EP-A-0 675 223, EP-A-0 709 236 or even EP -A-0 779 390, to illustrate the prior art in this field. The cable C-VII is made up of 27 wires (noted F5 in table 7) of the same diameter 0.23 mm, with a core of 3 wires wound together in a helix (direction S) in a pitch of 6.5 mm, this core being surrounded by an intermediate layer of 9 wires themselves wound together in a helix (direction S) in a pitch of 12.5 mm, itself surrounded by an outer layer of 15 wires themselves wound together in a helix (direction Z) in 18.0 mm steps. This C-VII cable is wrapped by a single wire of 0.15 mm diameter (Rm = 2800 MPa) wound in a helix (direction S) in a pitch of 3.5 mm. Its diameter (total size) is approximately 1.65 mm.

The wires F3, F4 and F5 are brass-plated wires, prepared in a known manner as indicated above in paragraph III-1 for the wires F1 F2. The two cables tested and their constituent wires have the mechanical properties indicated in Table 7. Table 7

The carcass reinforcement 7 of the tires tested consists of a single radial ply formed of rubberized fabrics of the same type as those used previously for the belt test (paragraph III-3 above): composition based on natural rubber and black carbon, having a Ml 0 module of approximately 6 MPa.

The frame 7 is reinforced either by the cables according to the invention (C-VI), or by the control cables (denoted C-VII). The fabric according to the invention comprises approximately 53 cables per dm of sheet, which is equivalent to a distance between two adjacent radial cables, from axis to axis. about 1.9 mm and a width £ of rubber bridge equal to about 0.41 mm. The control fabric comprises approximately 45 cables per dm of sheet, which is equivalent to a distance between two adjacent radial cables, from axis to axis, of approximately 2.2 mm and to a width £ equal to approximately 0.55 mm.

The mass of metal in the carcass reinforcement of the tire according to the invention is thus reduced by 23% compared to the control tire, which constitutes a very significant reduction. Correlatively, thanks to the use of a "HR" type steel (0.82% carbon) for the wires of the C-VI cable, the reduction in resistance of the fabric according to the invention is only reduced by 13% about.

As for the crown reinforcement 6, it is in known manner made up of (i) two crossed overlapping working plies, reinforced with metal cables inclined by 22 degrees, these two working plies being covered by (ii) a crown ply of reinforced protection of elastic metal cables inclined by 22 degrees. In each of these crown reinforcement plies, the metal cables used are known conventional cables, arranged substantially parallel to one another, and all the angles of inclination indicated are measured relative to the median circumferential plane.

A series of two tires (denoted P-1) was reinforced by the cable C-VI, another series of two tires (denoted P-2) was reinforced by the control cable C-VII. In each series, one tire is intended for running, the other for shelling on new tires. The tires P-1 therefore constitute the series according to the invention, the tires P-2 the control series.

These tires are subjected to a severe rolling test as described in paragraph 1-5, with a total of 150,000 km traveled. The distance imposed on each type of tire is very high; it is equivalent to continuous rolling for a duration of around three months and to 50 million fatigue cycles. Despite these very severe running conditions, the two tires tested run without damage until the end of the test, n in particular without breaking the cables of the carcass ply; this illustrates in particular for the person skilled in the art the high performance of the two types of tire, including control tires.

After rolling, shelling is carried out, that is to say an extraction of the cables from the tires. The cables are then subjected to tensile tests, each time measuring the initial breaking strength (cable extracted from the new tire) and the residual breaking strength (cable extracted from the tire having rolled) of each type of wire, according to the position of the wire in the cable, and for each of the cables tested. The average lapse ΔFm given in% in Table 8. is calculated both for the core wires (CO) and for the wires of layers C1 and C2. Overall ΔFm lapses are also measured on the cables themselves.

Table 8

When reading Table 8, it can be seen that the carcass reinforcement of the tire according to the invention, although very much lighter, as well as the metal cables of the invention which reinforce it, although clearly smaller, have a overall endurance equivalent to that of the control solution, with in addition another advantage of the invention residing in less wear (half as much) of the wires of the layer C1; this reduced wear of the wires of the layer Cl is probably due to the optimized construction of the cable of the invention, namely a winding in the same direction (here S / S) of the layers Cl and C2, unlike the cross construction (S / Z) of layers C1 and C2 of the control cable.

The non-tired C-VI and C-VII cables (after extraction from new tires) were also subjected to the air permeability test (paragraph 1-2). The results in Table 9 clearly underline, if necessary, the superiority of the cable of the invention; the permeability indices Pa are expressed in relative units, the base 100 being unchanged compared to table 4 above (base 100 for the control cable C-II).

Table 9

In conclusion, as clearly demonstrated by the various tests which precede, the cables of the invention make it possible to significantly reduce the fatigue-fretting-corrosion phenomena in the carcass reinforcement of tires, in particular HGV tires, and thus improving the longevity of these reinforcements and tires. Thus, for an equivalent lifetime, the invention makes it possible to reduce the size of the cables and thus to lighten these carcass reinforcements and these tires.

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

Thus, for example, the core CO of the cables of the invention could consist of a wire with a non-circular section, for example plastically deformed, in particular a wire with a substantially oval or polygonal section, for example triangular, square or still rectangular; the core CO could also consist of a preformed wire, of circular section or not. for example a wavy, twisted, twisted, helix or zig-zag wire. In such cases, it should of course be understood that the diameter d ₀ of the core represents the diameter of the imaginary cylinder of revolution which surrounds the core wire (overall diameter), and no longer the diameter (or any other transverse size, if its section is not circular) of the core wire itself. It would be the same if the core CO was formed not of a single wire as in the previous examples, but of several wires assembled together, for example two wires arranged parallel to one another or else twisted together, in a direction of twist identical or not to that of the intermediate layer Cl.

For reasons of industrial feasibility, cost and overall performance, however, it is preferred to implement the invention with a single conventional linear core wire, of circular section.

On the other hand, the core wire being less stressed during the wiring operation than the other wires, given its position in the cable, it is not necessary for this wire to use, for example, compositions. steel with high torsional ductility; it is advantageously possible to use any type of steel, for example stainless steel, in order to end up for example with a hybrid steel cable [1 + 5 + 10] or [1 + 5 + 1 1], as taught in WO98 / 41682 cited above, comprising a stainless steel wire in the center and 15 or 16 carbon steel wires around.

Of course, one (at least one) linear wire from one of the two layers C1 and or C2 could also be replaced by a preformed or deformed wire, or more generally by a wire of section different from that of the other wires of diameter di and / or d ₂ , so as for example to further improve the penetration of the cable by rubber or any other material, the overall diameter of this replacement wire possibly being less, equal or greater than the diameter (d, and / or d ₂ ) of the other constituent wires of the layer (Cl and / or C2) concerned.

Without the spirit of the invention being modified, all or part of the wires constituting the cable according to the invention could consist of wires other than steel wires, metallic or not, in particular wires made of mineral or organic material to high mechanical strength, for example monofilaments made of organic liquid crystal polymers as described in application WO92 / 12018.

The invention also relates to any multi-strand steel cable, the structure of which incorporates at least, as an elementary strand, a layered cable according to the invention.

Claims

1. Multilayer cable with an unsaturated outer layer, usable as a reinforcing element for a tire carcass reinforcement, comprising a core (denoted CO) of diameter d ₀ surrounded by an intermediate layer (denoted Cl) of four or five wires ( M = 4 or 5) of diameter d! wound together in a helix at a pitch p _b this layer Cl being itself surrounded by an external layer (denoted C2) of N wires of diameter d ₂ wound together in a helix at a pitch p ₂ , N being less than 1 to 3 to the maximum number N _max of wires windable in a layer around the layer Cl, this cable being characterized in that it has the following characteristics (d ₀ , d _t , d ₂ , pi and p ₂ in mm):

- (i) 0.08 < d ₀ < 0.28 - (ii) 0.15 < d, < 0.28 - (iii) 0.12 < d ₂ < 0.25

- (iv) for M = 4: 0.40 < (d ₀ / d,) <0.80; for M = 5: 0.70 < (d ₀ / d,) <1.10;

- (v) 4.8 π (d ₀ + d,) < p, < p ₂ < 5.6 π (d ₀ + 2d, + d ₂ );

- (vi) the wires of layers Cl and C2 are wound in the same direction of twist.

2. Cable according to claim 1, of construction [1+M+N], the core of which consists of a single wire.

3. Cable according to claim 2, chosen from construction cables [1+4+8], [1+4+9], [1+4+10], [1+5+9], [1+5 +10] and [1+5+11].

4. Cable according to claims 2 or 3, of construction [1+5+N].

5. Cable according to claim 4, of construction [1+5+10] or [1+5+11].

6. Cable according to any one of claims 1 to 5, characterized in that the pitches P _J and p ₂ are included in a range of 5 to 15 mm.

7. Cable according to any one of claims 1 to 6, verifying the following relationship:

0.15 < d ₂ < 0.25 .

8. Cable according to claim 7, verifying the following relationships:

0.14 < d ₀ <0.25; d ₂ >0.17; d, <0.26.

9. Cable according to any one of claims 1 to 8, characterized in that it is a steel cable.

10. Cable according to claim 9, characterized in that the steel is a carbon steel.

11. Cable according to any one of claims 1 to 10, verifying the relationship:

5.0 π (d ₀ + d,) < p, < p ₂ < 5.0 π (d ₀ + 2d, + d ₂ ) .

12. Cable according to claim 1 1, verifying the relationship:

5.3 π (d ₀ + d,) < p, < p ₂ < 4.7 π (d ₀ + 2d, + d ₂ ).

13. Cable according to any one of claims 1 to 12, in which the ratio (d|/d ₂ ) is between 1.05 and 1.30.

14. Cable according to claim 13, in which the ratio (d|/d ₂ ) is between 1.10 and 1.20.

15. Use of a cable according to any one of claims 1 to 14 as a reinforcing element for articles or semi-finished products made of plastic and/or rubber.

16. Use of a cable according to any one of claims 1 to 14 as a reinforcing element of a tire carcass reinforcement intended for industrial vehicles chosen from vans, heavy goods vehicles, agricultural or civil engineering machinery, airplanes , other transport or handling vehicles.

17. Heavy-duty tire whose carcass reinforcement comprises a cable conforming to any one of claims 1 to 14.

18. Composite fabric usable as a heavy-duty tire carcass reinforcement ply, comprising a matrix of rubber composition reinforced with a cable according to any one of claims 1 to 14.

19. Fabric according to claim 18, its cable density being between 40 and 100 cables per dm of fabric.

20. Fabric according to claim 19, the density of cables being between 50 and 80 cables per dm of fabric.

21. Fabric according to any one of claims 18 to 20, the width denoted £ of the rubber composition bridge, between two adjacent cables, being between 0.35 and 1 mm.

22. Fabric according to claim 21, the width £ being between 0.4 and 0.8 mm.

23. Fabric according to any one of claims 18 to 22, the rubber composition having, in the vulcanized state, a secant modulus in extension M10 which is less than 8 MPa.

24. Fabric according to claim 23, the rubber composition having, in the vulcanized state, a modulus M10 of between 4 and 8 MPa.

25. Fabric according to any one of claims 18 to 24, the rubber being natural rubber.

26. Heavy-duty tire whose carcass reinforcement comprises, as a reinforcing ply, at least one fabric according to any one of claims 18 to 25.