EP2366048B1 - Method and device for manufacturing a multiple wire strand for tire reinforcement filled with a filler during stranding - Google Patents

Description

The present invention relates to processes and devices for manufacturing three-layer metal cables, of M + N + P construction, used in particular for the reinforcement of rubber articles, in particular tires.

It is more particularly related to processes and devices for manufacturing metal cables of the type "gummed in situ", that is to say, gummed from the inside, during their manufacture, by rubber in the uncrosslinked state, in order to improve their resistance to corrosion and consequently their endurance, in particular in carcass reinforcement of 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 carrying heavy loads.

For the reinforcement of the above carcass reinforcements, use is generally made of steel wires ( "steel cords") called "layers" ( "layered cords") consisting of a core layer and one or more layers of concentric wires arranged around this central layer. The most used three-layer cables are essentially M + N + P construction cables, formed of a central layer of M wire (s), M varying from 1 to 4, surrounded by an intermediate layer of N wires, N typically ranging from 3 to 12, itself surrounded by an outer layer of P son, P typically ranging from 8 to 20, the assembly may be optionally shrunk by an external hoop wound helically around the outer layer .

In a well-known manner, these layered cables are subjected to considerable stresses during the rolling of the tires, in particular to repeated flexures or variations of curvature inducing at the level of the strands of friction, in particular as a result of the contacts between adjacent layers, and therefore of wear, as well as fatigue; they must therefore have a high resistance to phenomena known as "fatigue-fretting".

It is particularly important that they are impregnated as much as possible with the rubber, that this material penetrates all the spaces between the wires constituting the cables. Indeed, if this penetration is insufficient, then channels or empty capillaries, along and inside the cables, and corrosive agents such as water or even oxygen in the air, which may penetrate the tires for example as a result of cuts in their tread , walk 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 disadvantages, the demand WO 2005/071157 proposed cables with three layers of 1 + M + N construction, in particular of construction 1 + 6 + 12, one of the essential characteristics is that a sheath consisting of a rubber composition covers at least the intermediate layer consisting of M son, the core (or unit wire) of the cable may itself be covered or not 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 the tires 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 1 + M (in particular 1 + 6), then by sheathing via an extrusion head of this intermediate cable or core, finally by a final operation of wiring the N (in particular 12 son) remaining around the core thus sheathed, for forming the outer layer. To avoid the problem of "raw tights" of the rubber sheath before wiring the outer layer around the core, should be further used 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 rubber (non-crosslinked), 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 to a strip of rubber itself in the green state, before the final operations of manufacturing the tire and final baking.

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

Continuing their research, the Applicants have discovered an improved manufacturing process that overcomes the aforementioned drawbacks.

• une étape d'assemblage par retordage des N fils autour de la première couche (C1), pour formation en un point, dit « point d'assemblage » d'un câble intermédiaire dit « toron d'âme » de construction M+N ;
• en aval du point d'assemblage, une étape de gainage du toron d'âme M+N par une composition de caoutchouc dite « gomme de remplissage », à l'état non réticulé ;
• une étape d'assemblage par retordage des P fils de la troisième couche (C3) autour du toron d'âme ainsi gainé ;

une étape d'équilibrage final des torsions.Accordingly, a first object of the invention is a method of manufacturing a metal cable with three concentric layers (C1, C2, C3), of construction M + N + P, comprising a first inner layer (C1) consisting of M son of diameter d ₁ , M ranging from 1 to 4, around which are surrounded together helically in a pitch p ₂ , in a second intermediate layer (C2), N son of diameter d ₂ , N ranging from 3 to 12 , around which are surrounded together in a helix in a step p ₃ , in a third outer layer (C3), P son of diameter d ₃ , P varying from 8 to 20, said method comprising the following steps operated online:

• a step of assembly by twisting the N son around the first layer (C1), for formation at a point, called "assembly point" of an intermediate cable said "core strand" of M + N construction;
• downstream of the assembly point, a step of sheathing the core strand M + N by a rubber composition called "filling rubber", in the uncrosslinked state;
• a step of assembly by twisting the P son of the third layer (C3) around the core strand and sheathed;

a final balancing step of the twists.

This method of the invention makes it possible to manufacture, online and continuously, a three-layer cable which, compared to the in situ three-layer gummed in-line cables of the prior art, has the notable advantage of having a reduced amount of gum filling, which guarantees a better compactness, this gum being further distributed evenly inside the cable, inside each of its capillaries, thus conferring on it a longitudinal impermeability further improved.

• des moyens d'alimentation d'une part des M fils de la première couche (C1), d'autre part des N fils de la deuxième couche (C2) ;
• des premiers moyens d'assemblage par retordage des N fils pour mise en place de la deuxième couche (C2) autour de la première couche (C1), en un point dit point d'assemblage, pour formation d'un câble intermédiaire dit « toron d'âme » de construction M+N ;
• en aval dudit point d'assemblage, des moyens de gainage du toron d'âme M+N ;
• en sortie des moyens de gainage, des seconds moyens d'assemblage par retordage des P fils autour du toron d'âme ainsi gainé, pour mise en place de la troisième couche (C3) ;
• en sortie des seconds moyens d'assemblage, des moyens d'équilibrage de torsion.

The invention also relates to an assembly device and in-line scrubbing, usable for implementing the method of the invention, said device comprising upstream downstream, according to the direction of advancement of the cable being formed:

• feeding means on the one hand M son of the first layer (C1), on the other hand N son of the second layer (C2);
• first assembly means by twisting the N son for setting up the second layer (C2) around the first layer (C1), at a point called said point of assembly, for forming an intermediate cable called "strand soul "of construction M + N;
• downstream of said assembly point, cladding means of the core strand M + N;
• at the output of the cladding means, second assembly means by twisting the P son around the core strand and sheathed, for implementation of the third layer (C3);
• at the output of the second assembly means, torsion balancing means.

• un exemple de dispositif de retordage et gommage in situ utilisable pour la fabrication d'un câble à trois couches du type compact, selon un procédé conforme à l'invention (Fig. 1) ;
• en coupe transversale, un câble de construction 1+6+12, gommé in situ, du type compact, susceptible d'être fabriqué par le procédé de l'invention (Fig. 2) ;
• en coupe transversale, un câble de construction 1+6+12 conventionnel, non gommé in situ, également du type compact (Fig. 3).

The invention as well as its advantages will be readily understood in the light of the description and the following exemplary embodiments, as well as Figures 1 to 4 relating to these examples which schematize, respectively:

• an example of an in situ twisting and scrubbing device that can be used for the manufacture of a cable of three layers of the compact type, according to a method according to the invention ( Fig. 1 );
• in cross-section, a construction cable 1 + 6 + 12, gummed in situ, of the compact type, which can be manufactured by the process of the invention ( Fig. 2 );
• in cross-section, a conventional 1 + 6 + 12 construction cable, not gummed in situ, also of the compact type ( Fig. 3 ).

I. 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).

• tout d'abord, une étape d'assemblage par retordage des N fils autour de la première couche (C1), pour formation en un point, dit «point d'assemblage» d'un câble intermédiaire dit « toron d'âme » de construction M+N ;
• puis, en aval du point d'assemblage, une étape de gainage du toron d'âme M+N par une composition de caoutchouc dite « gomme de remplissage » à l'état non réticulé (c'est-à-dire à l'état cru) ;
• une étape d'assemblage par retordage des P fils de la troisième couche (C3) autour du toron d'âme ainsi gainé ;
• une étape d'équilibrage final des torsions.

The method of the invention is intended for the manufacture of a metal cable with three concentric layers (C1, C2, C3), of construction M + N + P, comprising a first inner layer (C1) consisting of M diameter wires d ₁ , M ranging from 1 to 4, around which are surrounded together helically in a pitch p ₂ , in a second intermediate layer (C2), N son of diameter d ₂ , N varying from 3 to 12, around which are surrounded together in a helix in a step p ₃ , in a third outer layer (C3), P son of diameter d ₃ , P varying from 8 to 20, said method comprising the following steps operated online:

• firstly, a step of assembly by twisting the N son around the first layer (C1), for formation at a point, called "assembly point" of an intermediate cable called "strand soul" of M + N construction;
• then, downstream from the assembly point, a step of sheathing the core strand M + N by a rubber composition called "filling rubber" in the uncrosslinked state (that is to say at the raw state);
• a step of assembly by twisting the P son of the third layer (C3) around the core strand and sheathed;
• a final balancing step of the twists.

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

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

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

An essential feature of the above method is to use a twisting step both for assembling the second layer (C2) around the first layer (C1) and for assembling the third layer or outer layer (C3 ) around the second layer (C2).

During the first step, the N son of the second layer (C2) are twisted together (direction S or Z) around the first layer (C1) for formation of the core strand (C1 + C2), in a known manner in itself; the son are delivered by supply means such as coils, a distribution grid, coupled or not to a connecting grain, intended to converge around the core N son in a common point of torsion (or point d 'assembly).

Preferably, the diameter d ₂ of the N son is within a range of 0.08 to 0.45 mm and the twisting pitch p ₂ is within a range of 5 to 30 mm.

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.

Downstream of the assembly point (and therefore, in particular, upstream of the extrusion head), the tension stress exerted on the core strand is preferably between 10 and 25% of its breaking force.

The core strand (C1 + C2) thus formed is then sheathed with non-cross-linked 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 the shape of a cylinder of revolution whose diameter is preferably 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 gum delivered by the extrusion head is adjusted in a preferred range between 5 and 40 mg, especially between 5 and 30 mg per gram of final cable (i.e., finished 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 5 and 25 mg, more preferably still within a range of 10 to 25 mg per g of cable (especially 10 to 20 mg per g of cable ).

Typically, at the outlet of the extrusion head, the core (C1 + C2) of the cable (or core strand M + N), at any point of its periphery, is covered with a minimum thickness of gum of filling which is preferably greater than 5 microns, more preferably greater than 10 microns, especially between 10 and 80 microns.

The elastomer (or indistinctly "rubber", both of which are considered synonymous) of the filling rubber is preferably a diene elastomer, that is to say by definition an elastomer derived at least in part (ie 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 chosen from the group consisting of butadiene-styrene copolymers (SBR), whether the latter are prepared by emulsion polymerization (ESBR) or in solution (SSBR), the isoprene-butadiene copolymers (BIR ), isoprene-styrene copolymers (SIR) and isoprene-butadiene-styrene copolymers (SBIR).

A preferred embodiment consists in using an "isoprene" elastomer, that is to say a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR). , the synthetic polyisoprenes (IR), the various isoprene copolymers and the mixtures of these elastomers. The isoprene elastomer is preferably natural rubber or synthetic polyisoprene of the cis-1,4 type. Among these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. According to other preferred embodiments, the 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 cooking (ie, 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. The filling rubber may also comprise all or part of the usual additives intended for the matrices of tire rubber, such as, for example, reinforcing fillers such as carbon black or silica, antioxidants, oils, plasticizers, anti-eversion agents, resins, adhesion promoters such as cobalt salts.

The level of reinforcing filler, for example carbon black or a reinforcing inorganic filler such as silica, is preferably greater than 50 phr, for example 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). Suitable reinforcing inorganic fillers are in particular silica (SiO ₂ ) type inorganic fillers, in particular precipitated or fumed silica having a BET surface area of less than 450 m ² / g, preferably from 30 to 400 m ² / g.

At the output of the preceding cladding step, during a third step, the final assembly is carried out, always by twisting (direction S or Z), P wires of the third layer or outer layer (C3) around the core strand (C1 + C2) and sheathed. During the twisting, the P son come to rely on the eraser, to become embedded in the latter. The filling rubber, moving under the pressure exerted by these outer P, then naturally tends to fill, at least in part, each of the capillaries or cavities left empty by the son, between the core strand (C1 + C2) and the outer layer (C3).

Preferably, the diameter d ₃ of P son is in a range of 0.08 to 0.45 mm and the twisting pitch p ₃ is greater than or equal to p ₂ , in particular in a range of 5 to 30 mm.

According to another particular embodiment of the invention, there is the following relationship which is verified (d ₁ , d ₂ , d ₃ , p ₂ and p ₃ being expressed in mm): $$\mathrm{5}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}\right)<{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{2}}\le {\mathrm{p}}_{\mathrm{3}}<\mathrm{10}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+\mathrm{2}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}+{\mathrm{d}}_{\mathrm{3}}\right)\mathrm{.}$$

In particular, we have the following relation which is verified: $$\mathrm{5}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}\right)<{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{2}}\le {\mathrm{p}}_{\mathrm{3}}<\mathrm{10}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+\mathrm{2}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}+{\mathrm{d}}_{\mathrm{3}}\right)\mathrm{.}$$

Advantageously, the steps p ₂ and p ₃ are equal, which simplifies the manufacturing process.

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 may be chosen to be identical to the formulation of the rubber matrix that the final cable 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 compound may be chosen different from the formulation of the rubber matrix that the final cable 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 E10 (at 10% elongation) which is between 2 and 25 MPa, more preferably between 3 and 20 MPa, in particular included in a range of 3 to 15 MPa.

Preferably, the third 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 ( P _max +1) th wire of diameter d ₃ , P _max representing the maximum number of wires rollable in a third layer (C3) around the second layer (C2). This construction has the advantage of limiting the risk of overfilling gum filling at its periphery and offer, for a given diameter of the cable, a higher strength.

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

Preferably, the first layer (C1) consists of a unitary yarn (ie, M = 1) and the diameter d ₁ is within a range of 0.08 to 0.50 mm. According to another preferred embodiment, the second layer (C2) has 5 to 7 wires (ie, N varies from 5 to 7). According to another particularly preferred embodiment, the layer C3 comprises from 10 to 14 wires; are particularly selected from the cables above those consisting of son having substantially the same diameter of the layer C2 to the C3 layer (ie d ₂ = d ₃ ).

According to another more preferred embodiment, the first layer (C1) comprises a single wire (M equal to 1), the second layer (C2) has 6 wires (N equal to 6) and the third layer (C3) comprises 11 or 12 wires (P equal to 11 or 12). In other words, the cable of the invention has the preferred constructions 1 + 6 + 11 or 1 + 6 + 12.

The M + N + P cable, like any layer cable, can be of two types, namely of the compact layer type or of the cylindrical layer type.

According to a particularly preferred embodiment of the invention, the son of the third layer (C3) are helically wound at the same pitch (p ₂ = p ₃ ) and in the same direction of torsion (that is to say either in the direction S ("S / S" arrangement) or in the Z direction ("Z / Z" arrangement)) and the second intermediate layer (C2) wires, in order to obtain a layered cable compact type as schematized for example in the figure 2 .

In such compact-layer cables, the compactness is such that virtually no distinct layer of wires is visible; as a result, the cross-section of such cables has an outline that is polygonal and non-cylindrical, as illustrated for example in figure 2 (compact cable 1 + 6 + 12 gummed in situ) and figure 3 (compact cable 1 + 6 + 12 conventional, that is to say not gummed in situ).

At this stage, the cable of the invention is not finished: the capillaries present inside the core, delimited by the M son of the first layer (C1) and the N son of the second layer (C2 ), are not yet filled with filling rubber, in any case insufficiently to obtain a cable having an impervious to air that is optimal.

The next essential step is to route the cable through torsion balancing means. By "torsion balancing" is meant here in a known manner the cancellation of the residual torsional torques (or 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 and / or rollers through which circulates the cable.

It is assumed a posteriori that, when passing through these balancing tools, the torsion exerted on the N son of the second layer (C2) is sufficient to force, to drive the still hot and relatively fluid filling rubber of the outside towards the inside of the cable, even within the capillaries formed by the M wires of the first layer (C1) and the N wires of the second layer (C2), which finally provide the cable of the invention. excellent air impermeability property that characterizes it. The dressing function, provided by the use of a trainer tool, would also have the advantage that the contact of the trainer rollers with the son of the third layer (C3) will exert additional pressure on the filling rubber further promoting its penetration into the capillaries present between the second layer (C2) and the third layer (C3) of the cable of the invention.

In other words, the process described above exploits the twisting of the wires in the final stage of manufacture of the cable, in order to distribute the filling rubber naturally, evenly, inside the cable, while perfectly controlling the quantity of filling rubber provided.

Thus, unexpectedly, it has been found possible to make the filling rubber penetrate the heart of the cable of the invention, in all of its capillaries, by depositing the rubber downstream of the N-joint point. son around the first layer or core (C1), 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 is complete. Preferably, in this finished cable, the thickness of filling rubber between two adjacent wires of the cable, whatever they are, varies from 1 to 10 microns. This cable can be wound on a receiving reel, for storage, before being processed, for example, through a calendering installation, for preparing a metal-rubber composite fabric that can be used, for example, as a tire carcass reinforcement.

Thus prepared, the cable M + N + P can be qualified as airtight: at the air permeability test described in paragraph II-1-B which follows, it is characterized by an average air flow rate. less than 2 cm ³ / min, preferably less than or equal to 0.2 cm ³ / min.

The method of the invention has the advantage of making possible the complete operation of initial twisting, scrubbing and final twisting in line and in a single step, regardless of the type of cable produced (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.

The method of the invention makes it possible to manufacture cables which may be lacking (or virtually devoid of) filling gum at their periphery. By such an expression, it is meant that no particle of filling compound is visible, with the naked eye, at the periphery of the cable, that is to say that the person skilled in the art does not make any difference at the end of the manufacturing process, 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.

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

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 another, the core wire (s) (C1), the wires of the second layer (C2) and the wires of the third layer (C3) are preferably made of 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.

• des moyens d'alimentation d'une part des M fils de la première couche (C1), d'autre part des N fils de la deuxième couche (C2) ;
• des premiers moyens d'assemblage par retordage des N fils pour mise en place de la deuxième couche (C2) autour de la première couche (C1), en un point dit point d'assemblage, pour formation d'un câble intermédiaire dit « toron d'âme » de construction M+N ;
• en aval dudit point d'assemblage, des moyens de gainage du toron d'âme M+N ;
• en sortie des moyens de gainage, des seconds moyens d'assemblage par retordage des P fils autour du toron d'âme ainsi gainé, pour mise en place de la troisième couche (C3) ;
• en sortie des seconds moyens d'assemblage, des moyens d'équilibrage de torsion.

An assembly and scrubbing device preferably used for implementing the method of the invention described above, is a device comprising upstream downstream, according to the direction of advancement of a cable being formed:

• feeding means on the one hand M son of the first layer (C1), on the other hand N son of the second layer (C2);
• first assembly means by twisting the N son for setting up the second layer (C2) around the first layer (C1), at a point called said point of assembly, for forming an intermediate cable called "strand soul "of construction M + N;
• downstream of said assembly point, cladding means of the core strand M + N;
• at the output of the cladding means, second assembly means by twisting the P son around the core strand and sheathed, for implementation of the third layer (C3);
• at the output of the second assembly means, torsion balancing means.

We see on the figure 1 attached an example of device (10) for assembly by twisting, of the fixed feed and rotary receiving type, usable for the manufacture of a cable of the compact type (p ₂ = p ₃ and the same direction of twist of the layers C2 and C3). In this device (10), supply means (110) deliver, around a single core wire (C1), N wires (11) through a grid (12) distribution (axisymmetric splitter), coupled or not to a connecting grain (13), gate beyond which converge the N (for example six) wires of the second layer at an assembly point (14), for formation of the core strand (C1 + C2 ) of construction 1 + N (eg 1 + 6).

The core strand (C1 + C2), once formed, then passes through a cladding zone consisting for example of a single extrusion head (15). The distance between the point of convergence (14) and the sheathing point (15) is for example between 50 cm and 1 m. Around the core strand thus gummed (16) and progressing in the direction of the arrow, are then assembled by twisting the P son (17) of the outer layer (C3), for example twelve in number, delivered by means power supply (170). The final cable (C1 + C2 + C3) thus formed is finally collected on the rotary reception (19), after passing through the torsion balancing means (18) 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 (different pitch p ₂ and p ₃ and / or different direction of torsion of the layers C2 and C3), we use a device comprising two rotating organs (feeding or receiving), and not just one as described above ( Fig. 3 ) for exemple.

The figure 2 schematically, in section perpendicular to the axis of the cable (assumed rectilinear and at rest), an example of a preferred cable 1 + 6 + 12 gummed in situ, obtainable using the method according to the previously described invention.

This cable (noted C-1) is of the compact type, that is to say that its second and third layers (respectively C2 and C3) are wound in the same direction (S / S or Z / Z according to a recognized nomenclature ) and moreover at the same step (p ₂ = p ₃ ). This type of construction has the consequence that the wires (21, 22) of these second and third layers (C2, C3) form around the core (20) or first layer (C1) two substantially concentric layers which each have a contour (E ) (shown in dashed lines) which is substantially polygonal (more precisely hexagonal) and non-cylindrical as in the case of cables with so-called cylindrical layers.

This cable C-1 can be described as cable gummed in situ: each of the capillaries or interstices (voids in the absence of filling rubber) formed by the adjacent wires, taken three by three, of its three layers C1, C2 and C3, is filled, at least in part (continuously or not along the axis of the cable), by the filling rubber in such a way that for any cable length of 2 cm, each capillary comprises at least one rubber stopper.

More specifically, the filling rubber (23) fills each capillary (24) (symbolized by a triangle) formed by the adjacent wires (taken three to three) of the various layers (C1, C2, C3) of the cable, by discarding them very slightly. We see that these capillaries or interstices are naturally formed either by the core wire (20) and the son (21) of the second layer (C2) surrounding it, or by two son (21) of the second layer (C2) and a wire (23) of the third layer (C3) which is immediately adjacent thereto, or else by each wire (21) of the second layer (C2) and the two wires (22) of the third layer (C3) which are immediately adjacent; a total of 24 capillaries or interstices (24) are thus present in this cable 1 + 6 + 12.

According to a preferred embodiment, in this cable M + N + P, the filling rubber extends in a continuous manner around the second layer (C2) which it covers.

For comparison, the figure 3 recalls the section of a cable 1 + 6 + 12 (noted C-2) conventional (ie, not gummed in situ), also of the compact type. The absence of filling rubber makes practically all the son (30, 31, 32) are in contact with each other, which leads to a particularly compact structure, moreover very difficult to penetrate (not to say impenetrable) from the outside by rubber. The characteristic of this type of cable is that the various wires form three to three of the channels or capillaries (34) which for a large number of them remain closed and empty and thus conducive, by "wicking" effect, to the propagation corrosive environments such as water.

By way of preferred examples, the process of the invention is used for the manufacture of construction cables 1 + 6 + 11 and 1 + 6 + 12, in particular, among these, those consisting of wires having substantially the same diameter of the second layer (C2) at the third layer (C3) (in this case d ₂ = d ₃ ).

II. EXAMPLES OF CARRYING OUT THE INVENTION

The following tests demonstrate the ability of the method of the invention to provide three-layer cables which, compared to the prior art in situ three-layered cords, have the significant advantage of having a reduced amount of gum. filling, which guarantees them 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.

II-1. Measurements and tests used II-1-A. Dynamometric measurements

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

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

II-1-B. Air permeability test

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

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

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

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

The test is carried out on 2 cm of cable length, thus coated by its surrounding rubber composition (or coating gum) in the fired state, as follows: air is sent to the cable inlet at 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; a leakproofness test of the seal is made using a solid rubber specimen, ie without cable.

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

II-1-C. 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 minutes 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 this 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 yarns thus devoid of any trace of gum are removed from the beaker, dried under a stream of nitrogen or air, and finally weighed.

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

II-2. Cable manufacturing and testing

In the following tests, 1 + 6 + 12 layered wires made of brass-coated carbon steel thin wires are manufactured.

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. <b> Table 1 </ b> Steel φ (mm) Fm (N) Rm (MPa) NT 0.18 68 2820 NT 0.20 82 2620

These wires are then assembled in the form of 1 + 6 + 12 layer cables, the construction of which is in accordance with the representation of the figure 1 and whose mechanical properties are given in Table 2. <b> Table 2 </ b> Cable p ₂ (mm) p ₃ (mm) Fm (daN) Rm (MPa) At (%) C-1 10 10 125 2650 2.4

The example (C-1) of cable 1 + 6 + 12 prepared according to the method of the invention, as schematized in FIG. Fig. 1 , is therefore formed of 19 son in total, a core wire of diameter 0.20 mm and 18 son around, all of diameter 0.18 mm, which were wound in two concentric layers at the same pitch (p ₂ = p ₃ = 10.0 mm) and in the same direction of twist (S) to obtain a cable of the compact type. The level of filling rubber, measured according to the method indicated previously in paragraph II-1-C, is equal to about 17 mg per g of cable. This filling rubber is present in each of the 24 capillaries formed by the various son taken three to three, that is to say that it fills all or at least partly each of these capillaries in such a way that it exists at least, on any length of cable of length equal to 2 cm, a rubber stopper in each capillary.

For the manufacture of this cable, we used a device as described previously and schematized in the figure 1 . The filling gum 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-1 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 module E10 of the composition is about 6 MPa. This composition was extruded at a temperature of about 65 ° C. through a 0.580 mm calibration die.

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

On the other hand, control gummed in situ cables, of the same construction as the C-1 compact cables above, were prepared according to the method described in the application WO 2005/071557 mentioned above, in several discontinuous steps, by sheathing via an extrusion head of the intermediate core strand 1 + 6, then in a second step by wiring the remaining 12 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 ³ / min, in other words that no 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 M + N + P 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, in particular without the difficulties associated with overflowing of rubber during their manufacture.

Claims (15)

1. Method of manufacturing a metal cord with three concentric layers (C1, C2, C3) of M+N+P construction, comprising a first, internal, layer (C1) consisting of M wires of diameter d₁, M varying from 1 to 4, around which there are wound together in a helix, at a pitch p₂, in a second, intermediate, layer (C2), N wires of diameter d₂, N varying from 3 to 12, around which there are wound together as a helix at a pitch p₃, in a third, outer, layer (C3), P wires of diameter d₃, P varying from 8 to 20, the said method comprising the following steps which are performed in line:

   - an assembling step by twisting the N wires around the first layer (C1) in order to form, at a point named the "assembling point", an intermediate cord named "core strand" of M+N construction;

   - downstream of the assembling point, a sheathing step in which the M+N core strand is sheathed with a rubber composition named "filling rubber", in the uncrosslinked state;

   - an assembling step in which the P wires of the first layer (C3) are twisted around the core strand thus sheathed;

   - a final twist-balancing step.
2. Method according to Claim 1, in which the diameter d₂ is comprised in a range from 0.08 to 0.45 mm and the twisting pitch p₂ is comprised in a range from 5 to 30 mm.
3. Method according to Claim 1 or 2, in which the tensile stress applied to the core strand, downstream of the assembling point, is comprised between 10 and 25% of its breaking strength.
4. Method according to any one of Claims 1 to 3, in which the rubber of the filling rubber is a diene elastomer.
5. Method according to Claim 4, in which the diene elastomer is chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and blends of these elastomers.
6. Method according to Claim 5, in which the diene elastomer is an isoprene elastomer, preferably natural rubber.
7. Method according to any one of Claims 1 to 6, in which the extrusion temperature for the filling rubber is comprised between 50°C and 120°C.
8. Method according to any one of Claims 1 to 7, in which the quantity of filling rubber delivered during the sheathing step is comprised between 5 and 40 mg per gram of final cord, preferably between 5 and 30 mg per gram of final cord.
9. Method according to any one of Claims 1 to 8, in which the core strand, after sheathing, is covered with a minimum thickness of filling rubber that exceeds 5 µm.
10. Method according to any one of Claims 1 to 9, in which the diameter d₃ is comprised in a range from 0.08 to 0.45 mm and the pitch p₃ is greater than or equal to p₂.
11. Method according to any one of Claims 1 to 10, in which the wires of the third layer (C3) are wound in a helix at the same pitch and in the same direction of twisting as the wires of the second layer (C2).
12. In-line rubberizing and assembling device that can be used for implementing a method according to any one of Claims 1 to 11, the said device comprising, from upstream to downstream in the direction of travel of the cord as it is being formed:

    - feed means, for, on the one hand, feeding the M wires of the first layer (C1) and on the other hand feeding the N wires of the second layer (C2);

    - first assembling means which by twisting assemble the N wires to apply the second layer (C2) around the first layer (C1) at a point named the assembling point, to form an intermediate cord named "core strand" of M+N construction;

    - downstream of the said assembling point, means of sheathing the M+N core strand;

    - at the exit from the sheathing means, second assembling means which by twisting assemble the P wires around the core strand thus sheathed, in order to apply the third layer (C3);

    - at the exit from the second assembling means, twist balancing means.
13. Device according to Claim 12, comprising a stationary feed and a rotating receiver.
14. Device according to Claim 12 or 13, in which the sheathing means consist of a single extrusion head comprising at least one sizing die.
15. Device according to any one of Claims 12 to 14, in which the twist balancing means comprise at least one tool chosen from straighteners, twisters or twister-straighteners.

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