EP2414582B1 - Method and device for the manufacture of a steel strand having a three-layer structure - Google Patents

Description

The present invention relates to processes and devices for manufacturing three-layer metal cables, in particular of M + N + P construction, which can be used in particular for reinforcing rubber articles such as 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 particular with a view to improving 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 central layer or core and one or more layers of concentric threads arranged around this core. The most used three-layer cables are essentially M + N + P construction cables, formed of a core 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 outer hoop thread wound helically around the outer layer. Such a cable is described in the application JP2007303044 . We know of the document JP2006283249 a corresponding manufacturing method of such a cable comprising a step of balancing the twists.

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 empty channels or capillaries are formed, along and inside the cables, and corrosive agents such as water or even oxygen in the air, likely to to enter the tires for example following 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, 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 an air permeability of the cable, along its axis, which is As low as possible, it has been necessary according to these prior art methods to use relatively large amounts of rubber during sheathing. Such quantities lead to a spurious overflow, more or less pronounced, of the raw rubber at the periphery of the finished cable manufacturing.

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

We also know of the document JP2008202196 a cable each wire of the inner layer is individually sheathed by passing through a bath of a liquid solution comprising a liquid rubber composition.

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 de gainage du noyau (C1) par une composition de caoutchouc dite « gomme de remplissage », à l'état non réticulé au moyen une tête d'extrusion unique_;
• une première étape d'assemblage par retordage des N fils de la deuxième couche (C2) autour du noyau (C1) ainsi gainé, pour formation en un point, dit « point d'assemblage » d'un câble intermédiaire dit « toron d'âme » (C1+C2) ;
• une seconde étape d'assemblage par retordage des P fils de la troisième couche (C3) autour du toron d'âme (C1+C2) ;
• une étape d'équilibrage final des torsions du câble comprenant la gomme de remplissage à l'état non réticulé ;

le câble obtenu présentant un débit d'air moyen inférieur à 2 cm³/min au test de perméabilité à l'air selon la norme ASTM D2692-98.Accordingly, a first object of the invention is a method of manufacturing a metal cable with three concentric layers (C1, C2, C3) of the type gummed in situ, comprising a first inner layer or core (C1) around which are surrounded together in a helix in a pitch p ₂ , in a second intermediate layer (C2), N son of diameter d ₂ , N varying from 3 to 12, second layer 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 ranging from 8 to 20, said method comprising the following steps:

• a cladding step of the core (C1) by a rubber composition called "filling rubber", in the uncrosslinked state by means of a single extrusion head;
• a first assembly step by twisting the N son of the second layer (C2) around the core (C1) and sheathed for formation at a point, called "assembly point" of an intermediate cable called "strand of soul "(C1 + C2);
• a second assembly step by twisting the P son of the third layer (C3) around the core strand (C1 + C2);
• a final balancing step of the twists of the cable comprising the filling rubber in the uncrosslinked state;

the cable obtained having an average air flow rate of less than 2 cm ³ / min in the air permeability test according to the ASTM D2692-98 standard.

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

• des moyens d'alimentation de la première couche ou noyau (C1) ;
• des moyens de gainage du noyau (C1) comprenant une tête d'extrusion unique ;
• des moyens d'alimentation et des premiers moyens d'assemblage par retordage des N fils de la deuxième couche (C2) autour du noyau (C1) gainé, en un point dit point d'assemblage, pour formation d'un câble intermédiaire dit « toron d'âme » (C1+C2) ;
• des moyens d'alimentation et des seconds moyens d'assemblage par retordage des P fils autour du toron d'âme, 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:

• feed means for the first layer or core (C1);
• core cladding means (C1) comprising a single extrusion head;
• supply means and first assembly means by twisting the N son of the second layer (C2) around the core (C1) sheathed, at a point called said point of assembly, for forming an intermediate cable said " core strand "(C1 + C2);
• supply means and second assembly means by twisting the P son around the core strand, for setting up 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 3 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 de gainage du noyau (C1) par une composition de caoutchouc dite « gomme de remplissage », à l'état cru (c'est-à-dire non réticulée ou non cuite) ;
• puis une première étape d'assemblage par retordage des N fils de la deuxième couche (C2) autour du noyau (C1) ainsi gainé, pour formation en un point, dit «point d'assemblage » d'un câble intermédiaire dit « toron d'âme » (C1+C2) ;
• puis une seconde étape d'assemblage par retordage des P fils de la troisième couche (C3) autour du toron d'âme ainsi formé ;
• enfin, 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 the type gummed in situ, comprising a first inner layer or core (C1) around which are surrounded together in a helix in a step p ₂ , in a second intermediate layer (C2), N son of diameter d ₂ , N varying from 3 to 12, second layer 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 preferably operated in line and continuously:

• first, a cladding step of the core (C1) by a rubber compound called "gum filling", in the green state (that is to say uncrosslinked or uncured);
• then a first assembly step by twisting the N son of the second layer (C2) around the core (C1) and sheathed, for formation at a point, called "assembly point" of an intermediate cable said "strand d 'soul' (C1 + C2);
• then a second assembly step by twisting the P son of the third layer (C3) around the core strand so formed;
• finally, 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 (C3) around the second layer (C2).

The diameter d ₀ (or total overall diameter) of the core (C1) is preferably in a range of 0.08 to 0.50 mm, this core may consist of a single wire or several son previously assembled between them by any known means, for example by cabling or more preferably by twisting. Preferably, the number denoted "M" of yarn (s) of the core is within a range of 1 to 4. More preferably, the core consists of a single unitary wire (M equal to 1) whose diameter d ₁ is itself more preferably within a range of 0.08 to 0.50 mm.

According to the invention, this core (C1) is first sheathed by uncrosslinked filling rubber (in the green state), provided by an extrusion screw at an appropriate temperature. The filling rubber can thus be delivered at a fixed point, unique and compact, by means of a single extrusion head.

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 sheathed core, connected to the extruder, as well as means for controlling the centering of the core in the extrusion head. 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 20 mg per g of cable.

Typically, at the outlet of the extrusion head, the core of the cable, at every point of its periphery, is covered with a minimum thickness of filling compound which is preferably greater than 20 μm, more preferably greater than 30 μm, especially between 40 and 80 μm.

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, the various isoprene copolymers, and mixtures Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), whether the latter are prepared by emulsion polymerization (ESBR) or in solution (SSBR), the isoprene copolymers -butadiene (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. But the invention also applies to cases where the filling gum is free of sulfur and even of any other crosslinking system, it being understood that it could be sufficient, for its own crosslinking or vulcanization, the crosslinking or vulcanization system already present in the matrix of rubber that the cable of the invention is intended to strengthen, and likely to migrate by contact of said surrounding matrix to the filling rubber.

The filling rubber may also comprise all or part of the usual additives intended for tire rubber matrices, 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 the second step, the N wires of the second layer (C2) are twisted together (direction S or Z) around the core (C1) sheathed to form the strand of soul (C1 + C2), in a manner known per se; 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 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.

During this twisting, the N son come to rely on the filling rubber, to become embedded in the gum sheath covering the core (C1). This filling rubber, in sufficient quantity, then naturally fills the capillaries that form between the core (C1) and the second layer (C2).

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

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

At this stage of the process, the cable of the invention is not yet complete: the above capillaries delimited by the N wires of the second layer (C2) and the P wires of the third layer (C3) are not 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 pass the cable, thus provided with its filling rubber in the green state, 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 or rollers through which circulates the cable in a single plane or preferably in at least two different planes.

It is assumed a posteriori that, during the passage through the various balancing means above, the latter generate, on the N and P son of the second and third layers (C2 and C3), a torsion and radial pressure which are sufficient for redistributing the filling gum in the uncured (ie, uncrosslinked, uncured) state, still hot and relatively fluid, by transferring it in part, capillaries formed by the core (C1) and the N son of the second layer (C2), towards the inside of the capillaries formed by the N son of the second layer (C2) and the P son of the third layer (C3), finally offering the cable of the invention the excellent impermeability property to the air that characterizes it. The dressing function, provided by the use of a trainer tool, would also have the advantage that the contact of the rollers of the trainer with the son of the outer layer (C3) will exert an additional radial pressure on the filling rubber promoting again its optimal distribution in the capillaries present between the second layer (C2) and the third layer (C3) of the cable.

In other words, the method of the invention described above exploits the torsion of the son and the radial pressure exerted on them at the final stage of manufacture of the cable, to radially distribute the filling rubber inside. cable, while perfectly controlling the amount of filling compound provided. The person skilled in the art will in particular be able to adjust the arrangement, the diameter of the pulleys and / or rollers of the torsion balancing means in order to modify the intensity of the radial pressure exerted on the threads.

Thus, unexpectedly, it has been found possible to make the filling rubber penetrate into the very core of the cable of the invention and into all of its capillaries, by depositing the rubber upstream 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 according to the method of the invention, gummed in situ by its filling rubber in the green state, is completed.

Preferably, in this completed cable, the thickness of filling rubber between two adjacent wires of the cable, whatever they are, is greater than 1 micron, preferably between 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.

According to another preferred embodiment of the invention, the following relationship is satisfied (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: $$\mathrm{5}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}\right)<{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{2}}\le {\mathrm{p}}_{\mathrm{3}}<\mathrm{5}\mathrm{\pi }\left({\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{1}}+\mathrm{2}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{2}}+{\mathrm{d}}_{\mathrm{3}}\right)\mathrm{.}$$

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 amount of adhesion promoter, typically by example of 5 to 15 phr of a metal salt such as a salt of cobalt, nickel or a lanthanide salt such as neodymium (see, in particular, application WO 2005/113666 ), and advantageously reducing the amount of said promoter (or even removing it completely) in the surrounding rubber matrix. Of course, it will also be possible to adjust the formulation of the filling compound in order to optimize its viscosity and thus its penetration inside the cable during manufacture of the latter.

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

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 core (C1) consists of a unitary wire whose diameter d ₁ is within a range of 0.08 to 0.50 mm.

If the core the first layer (C1) consists of several son (ie, M is different from 1), then the M son are preferably assembled together in an assembly pitch which is preferably between 4 and 15 mm, especially between 5 and 10 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 even more preferred embodiment, the first layer (C1) comprises a single wire, the second layer (C2) has 6 wires (N equal to 6) and the third layer (C3) has 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 cable prepared according to the invention, like any layer cable, can be of two types, namely of the compact layer type or the type with cylindrical layers.

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 which is generally 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).

Thus prepared, the cable manufactured according to the invention can be described as airtight in the fired state: in the air permeability test described in paragraph II-1-B which follows, it is characterized by a 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.

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, with the naked eye and at a distance of three meters or more, between a cable reel according to the invention and a conventional cable reel not gummed in situ.

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 (which 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 de la première couche ou noyau (C1) ;
• des moyens de gainage du noyau (C1) ;
• des moyens d'alimentation et des premiers moyens d'assemblage par retordage des N fils de la deuxième couche (C2) autour du noyau (C1) gainé, en un point dit point d'assemblage, pour formation d'un câble intermédiaire dit « toron d'âme » de construction C1+C2 ;
• des moyens d'alimentation et des seconds moyens d'assemblage par retordage des P fils autour du toron d'âme, 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:

• feed means for the first layer or core (C1);
• cladding means of the core (C1);
• supply means and first assembly means by twisting the N son of the second layer (C2) around the core (C1) sheathed, at a point called said point of assembly, for forming an intermediate cable said " core strand of C1 + C2 construction;
• supply means and second assembly means by twisting the P son around the core strand, for setting up 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 type and rotating receiving, used for the manufacture of a cable with three layers, of M + N + P construction, of the compact type (p ₂ = p ₃ and same direction of torsion of the layers C2 and C3) as illustrated for example in the figure 2 commented later.

In this device (10), a single core wire (C1) first passes through a cladding zone consisting for example of a single extrusion head (11). Feeding means (120) then deliver, around the core wire (C1) and sheathed (for example consisting of a unitary wire), N son (12) through a grid (13) distribution (axisymmetric splitter), coupled or not with a grain of assembly (14), beyond which converge the N (for example six) son of the second layer at an assembly point (15), for formation of the core strand (C1 + C2) of M + N construction (for example 1 + 6). The distance between the sheathing point (11) and the convergence point (15) is for example between 1 and 5 meters.

Around the core strand (C1 + C2) thus formed (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 feeding means (170). The final cable (C1 + C2 + C3) is finally collected on the rotary reception (19), after crossing 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. 1 ) 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 (empty spaces 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 such 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 wires (21) of the second layer (C2) surrounding it, or by two wires (21) of the second layer (C2) and a wire (23) of the third layer (C3) which is immediately adjacent to them, or else by each wire (21) of the second layer (C2) and the two son (22) of the third layer (C3) which are immediately adjacent thereto; a total of 24 capillaries or interstices (24) are thus present in this cable 1 + 6 + 12.

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 cord to make it impervious to air; it has been described for example in ASTM D2692-98.

The test is here carried out either on cables extracted from tires or rubber sheets which they reinforce, thus already coated from the outside by rubber in the fired state, or on raw manufacturing cables, which have been coated and subsequent cooking.

In the second case, the raw cables must be previously embedded, coated from the outside by a so-called coating gum. For this, a series of 10 cables arranged in parallel (inter-cable distance: 20 mm) is placed between two skims (two rectangles of 80 x 200 mm) of a rubber composition in the raw state, each skim having a thickness 3.5 mm; the whole is then locked in a mold, each of the cables being kept under a sufficient tension (for example 2 daN) to ensure its straightness during the establishment in the mold, using clamping modules; then the vulcanization (baking) is carried out for 40 min at a temperature of 140 ° C and a pressure of 15 bar (rectangular piston 80 x 200 mm). After 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 under a pressure of 1 bar, and the volume of air is measured at output, 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 used.

The carbon steel wires are prepared in a known manner, for example starting from machine wires (diameter 5 to 6 mm) which are first cold-rolled, by rolling and / or drawing, to a neighboring intermediate diameter. of 1 mm. The steel used is a known carbon steel (USA AISI 1069 standard) with a carbon content of 0.70%. The intermediate diameter son undergo a degreasing treatment and / or pickling, before further processing. After deposition of a brass coating on these intermediate son, is carried on each wire a so-called "final" work hardening (ie, after the last patenting heat treatment), by cold drawing in a moist medium with a drawing lubricant which is for example in the form of an emulsion or an aqueous dispersion. The brass coating that surrounds the son has a very small thickness, significantly less than one micrometer, for example of the order of 0.15 to 0.30 microns, which is negligible compared to the diameter of the steel son. The steel wires thus drawn have the diameter and the mechanical properties indicated in Table 1 below. <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 10 126 2645 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 rate of filling rubber, measured according to the method indicated previously in paragraph II-1-C, is equal to about 16 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 of such that there is 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 85 ° C. through a 0.400 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 paragraph I-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 gummed cables in situ which, thanks to an optimal penetration rate by rubber, on the one hand have a high endurance in carcass reinforcement of the tires, on the other hand can be implemented efficiently under industrial conditions, in particular without the difficulties associated with overflowing of rubber during their manufacture.

Claims (14)

1. Method of manufacturing a metal cord with three concentric layers (C1, C2, C3) of the type rubberized in situ, comprising a first, internal, layer or core (C1), 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 second layer 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, characterized in that said method comprises the following steps:

   - a sheathing step in which the internal layer or the core (C1) is sheathed with a rubber composition named a "filling rubber", in the uncrosslinked state;

   - a first assembling step by twisting the N wires of the second layer (C2) around the internal layer or the core (C1) thus sheathed in order to form, at a point named the "assembling point", an intermediate cord named "core strand" of M+N construction;

   - a second assembling step in which the P wires of the third layer (C3) are twisted around the core strand;

   - a final twist-balancing step;

   the obtained metal cord exhibiting an average flow rate less than 2 cm³/min according to the air permeability test of ASTM D2692-98 standard.
2. Method according to Claim 1, in which the extrusion temperature for the filling rubber is comprised between 50°C and 120°C.
3. Method according to Claim 1 or 2, in which the quantity of filling rubber delivered during the sheathing step is comprised between 5 and 40 mg per gram of final cord.
4. Method according to any one of Claims 1 to 3, in which the internal layer or the core (C1), after sheathing, is covered with a minimum thickness of filling rubber that exceeds 20 µm.
5. Method according to any one of Claims 1 to 4, in which the rubber of the filling rubber is a diene elastomer.
6. Method according to Claim 5, 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.
7. Method according to Claim 6, in which the diene elastomer is an isoprene elastomer, preferably natural rubber.
8. Method according to any one of Claims 1 to 7, 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.
9. Method according to any one of Claims 1 to 8, in which the core consists of a single individual wire, the diameter d₁ of which is comprised in a range from 0.08 to 0.50 mm.
10. Method according to any one of Claims 1 to 9, 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).
11. Method according to any one of Claims 1 to 10, in which N varies from 5 to 7.
12. Assembling device, characterized in that it also forms an in-line rubberizing device and in 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 feeding the first layer or the core (C1);

    - sheathing means for sheathing the internal layer or the core (C1);

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

    - feed means and second assembling means which by twisting assemble the P wires around the core strand, 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 twist balancing means comprise at least one tool chosen from straighteners, twisters or twister-straighteners.

Images