CN118056037A

CN118056037A - Method for producing metal wire for reinforcing rubber products

Info

Publication number: CN118056037A
Application number: CN202280067244.4A
Authority: CN
Inventors: G·库西内; X·德帕里斯; P·莫里索
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2021-10-25
Filing date: 2022-10-25
Publication date: 2024-05-17
Also published as: FR3128389A1; EP4423324A1; WO2023072902A1; FR3128389B1

Abstract

The invention relates to a method for producing steel wires that can be used to reinforce rubber products, comprising at least one of the following steps: the metal wire with diameter d1 is electropolished by passing it continuously through a bath of deep eutectic solvent with a current density between 10A/dm ² and 50A/dm ² and a residence time of the wire in the bath of deep eutectic solvent between 10 seconds and 3 minutes.

Description

Method for producing metal wire for reinforcing rubber products

Technical Field

The present invention relates to the field of processes for the preparation of metal wires useful for reinforcing rubber articles, and to the use of such metal wires.

Background

Rubber articles such as pneumatic tire casings, tracks or conveyor belts are reinforced with a reinforcing ply composed of metal reinforcements arranged parallel to each other side by side. Each of these metal reinforcements may consist of a single metal wire or an assembly of metal wires. Such reinforcements, in the case of pneumatic tire casings, for example but not limited to metal wires, can range in diameter from 0.15 mm to 0.5mm, or in the case of light vehicles, for example, assemblies of two or more metal wires, the assembly of two metal wires having a diameter of 0.30 mm ("2.30" assembly).

These metal wires are prepared by drawing in a manner known to the person skilled in the art. The drawing process generally comprises a first step of dry drawing, in which a wire, typically 4.5 to 6.5 mm in diameter, coming from a steelworks is drawn in a gaseous environment (for example air) through a series of dies to a diameter typically ranging from 0.6 to 3.0 mm. The resulting wire may then be heat treated to adjust the microstructure of the steel and may be coated with a metal coating (e.g., brass) and then wet drawn to a final diameter that may range from 0.06 millimeters to 0.4 millimeters.

These wires are required to have sufficient mechanical strength to properly reinforce the rubber article and to have a sufficiently uniform surface finish to limit wear of the wire drawing die and avoid breakage problems, among other characteristics.

The benefit of improving the surface condition of the wire prior to coating the wire with an adhesion promoting alloy has been demonstrated. Document JP 07268787 thus describes a yarn with a maximum valley height of 15 micrometers measured in the radial direction of the yarn, the effect of which is to improve the fatigue strength of the yarn. However, this document does not disclose any means other than the special attention that is required to draw the wire to achieve such a surface condition.

There are various methods of reducing the surface roughness of metal elements. For example, a shot blasting operation may be performed, with the risk of introducing foreign matter into the treated component, to shorten the service time of the die, or dry wire drawing may be performed without using a lubricant, although this may result in a corresponding increase in wire drawing costs due to more frequent die replacement.

Document US 4 859 289 also attempts to improve the surface condition of the filaments before they are coated by electropolishing them in sulfuric and phosphoric acid baths, in particular in order to limit the separation between coating and filaments. The roughness Ra of the treated filaments in the examples was 0.9 microns. The disadvantage of this treatment is the use of acids, which can cause problems for handling and reprocessing. Furthermore, acid bath electropolishing applied to filaments useful for reinforcing rubber articles cannot achieve very low levels of roughness.

In conducting research, the applicant has found that electropolishing methods carried out under specific conditions enable to increase the productivity of the drawing step, while at the same time increasing the durability of the metal wires that can be used to reinforce rubber articles.

Disclosure of Invention

The invention relates to a method for preparing a steel metal wire for reinforcing rubber products, which at least comprises the following steps:

a. A step of electropolishing the metal wire of diameter d1, wherein the metal wire is continuously passed through a bath of deep eutectic solvent while being subjected to an anodic current having a current density between 10A/dm ² and 50A/dm ², the residence time of the wire in the bath of deep eutectic solvent being between 10 seconds and 3 minutes;

b. and drawing the metal wire to a diameter d 2.

The invention also relates to the use of the metal wire obtained by the preparation method according to the invention in rubber articles selected from the group consisting of pneumatic tire casings, non-pneumatic tire casings, tracks and conveyor belts.

Definition of the definition

The carbon-containing compounds referred to in this specification may be of fossil origin or bio-based compounds. In the latter case, they may be partially or wholly produced from biomass, or may be obtained from renewable raw materials produced from biomass. This relates in particular to polymers, plasticizers, fillers, etc.

For the purposes of the present invention, the expression "parts by weight per 100 parts by weight of elastomer" (or phr) is understood to mean parts by mass per 100 parts by mass of elastomer.

In the present invention, all percentages (%) shown are mass percentages (%), unless explicitly indicated otherwise.

Furthermore, any numerical interval represented by the expression "between a and b" represents a range of values extending from greater than a to less than b (i.e., the endpoints a and b are excluded), while any numerical interval represented by the expression "a to b" means a range of values extending from a up to b (i.e., the strict endpoints a and b are included).

Drawings

Fig. 1 depicts a diagram of a method of making a metal wire according to the present invention.

Detailed Description

Step a) -electropolishing

The preparation method of the metal wire comprises the following steps: a) A step of electropolishing the metal wire of diameter d1, wherein the metal wire is continuously passed through a deep eutectic solvent bath, wherein an anodic current is subjected, the current density being present in the range of 10A/dm ² to 50A/dm ², the residence time of the wire in the deep eutectic solvent bath being between 10 seconds and 3 minutes.

The current density in the bath is expressed as amperes per dm ² of surface area of the wire immersed in the bath. The current density ranges from 10A/dm ² to 50A/dm ², preferably between 15A/dm ² and 30A/dm ².

The electropolishing step allows dissolution of the coarse peaks of the metal wire, thereby reducing its overall roughness. The residence time of the wire in the eutectic solvent bath needs to be long enough for electropolishing to proceed satisfactorily, but not so long that the dimensions of the bath are compatible with typical travel speeds in industrial drawing processes. Preferably, the residence time of the filaments in the deep eutectic solvent bath is from 10 seconds to 3 minutes, preferably from 20 seconds to 150 seconds.

Preferably, the diameter d1 ranges from 0.6 mm to 3.0 mm.

The deep eutectic solvent is formed by mixing two or more compounds in a precise ratio corresponding to the eutectic point. This mixture behaves like a pure body.

Preferably, the deep eutectic solvent is selected from the group consisting of a eutectic mixture of choline chloride and ethylene glycol and a eutectic mixture of choline chloride and glycerol. Such a mixture presents little Health and Safety (HSE) risk. Therefore, in addition to better surface conditions obtained at the end of the electropolishing step, the handling of the solvent is easier than with the use of an acid. The preferred deep eutectic solvents are capable of reducing in a particularly effective manner the surface defects of steel wires intended for reinforcing rubber articles, in particular pneumatic tire casings.

The deep eutectic solvent is prepared by simply mixing its constituent compounds in the correct proportions at a temperature sufficient to bring all the components into the liquid phase. For example, a deep eutectic solvent consisting of choline chloride and ethylene glycol is prepared by diluting powdered choline chloride in ethylene glycol at a temperature of about 105 ℃ and then cooling the resulting mixture. The solvent obtained has a composition corresponding to the eutectic point, i.e. a molar ratio ethylene glycol/choline chloride equal to 2:1.

Preferably, the temperature of the deep eutectic solvent bath ranges from 50 ℃ to 100 ℃, preferably from 50 ℃ to 80 ℃. Below 50 c, the conductivity of the solvent is low and the current density required to perform the electropolishing process in a satisfactory time frame becomes excessive. By limiting the temperature of the bath, the solvent is allowed to remain below the eutectic point while minimizing energy costs and operational risks such as combustion.

Preferably, at the end of step a), the surface of the metal wire exhibits an arithmetic average roughness Ra of less than or equal to 0.3 microns, ra measured according to standard ISO 4287 in 2009.

Preferably, the diameter of the metal wire at the end of step a) is from 5 to 25 microns smaller than the diameter of the wire at the entry into step a). This reduction in diameter is associated with electropolishing, which eliminates the roughness of the wire.

The dissolved portion of the wire precipitates to the bottom of the bath, enabling the bath to maintain its effectiveness during long treatment periods.

As is well known to those skilled in the art, the electropolishing step may be incorporated into the drawing process without the need to alter other steps of the process. Therefore, it is very simple to implement in an industrial environment.

Step b) -drawing of the wire

The method according to the invention comprises the step of drawing the wire to a diameter d 2. This step is well known to those skilled in the art and is commonly referred to as "wet drawing".

The step of drawing the wire to a diameter d2 is performed by passing the wire continuously through a plurality of dies of progressively decreasing diameter of the outlet. The number of dies and thus the number of successive diameter reductions depends on the ductility of the wire and the diameter d2 to be achieved. The smaller the diameter, the more the number of dies may be.

A device for pulling the wire, such as a stepped capstan, downstream of each die, allows a pulling force to be applied sufficient to pull the wire through each die. The drawing device and the die are immersed in a liquid bath of drawing lubricant, for example as described in document WO 2008/113481.

Wet drawing is understood to mean that the metal wire is circulated in a liquid environment, for example an aqueous solution. Preferably, the drawing lubricant during wet drawing is in liquid form. During wet drawing, the pulling device (e.g., capstan) is exposed to a liquid environment, such as an aqueous solution.

Thus, the wire is subjected to 1 to m drawing operations (m varies, for example, from 8 to 23) in order to reduce the diameter of the wire from the intermediate diameter d1 (or slightly smaller than d1, since the electropolishing step may result in a slight reduction in the diameter of the wire) to the final diameter d2 and to increase the maximum tensile strength of the wire.

Preferably, the diameter d2 ranges from 0.06 mm to 0.4 mm. Such filaments may be used to reinforce rubber articles, such as rubber articles selected from the group consisting of pneumatic tire casings, non-pneumatic tire casings, tracks, and conveyor belts. A non-pneumatic tire casing refers to a casing whose shape is maintained by means other than a gas (e.g., air) under pressure. For example, such non-pneumatic tire casings can be held in shape using semi-rigid struts. For such use, such filaments may be used as such or in the form of an assembly of a plurality of filaments. The assembly may be implemented by any method known to those skilled in the art (e.g., wiring, twisting, etc.). Among such components, there may be mentioned conventionally used components, such as a 2.30 component (two wires of 0.30 in size) or a 19.18 component (3-layer cord comprising a core wire, a second layer 6 wires and a third layer 12 wires).

Preferably, the drawing operation forms an uninterrupted series of wet drawing operations that draw the wire from the intermediate diameter d1 to the final diameter d 2. Each operation from 1 to m times is a wet drawing operation in which the metal wire is passed through a die having a diameter smaller than the diameter of the wire upstream of the die. Thus, the diameter of the wire downstream of the die is smaller than the diameter upstream of the die. Each downstream die has a diameter smaller than the diameter of the die located upstream. For an uninterrupted series of operations of wet drawing a metal wire from a median diameter d1 to a final diameter d2, the true strain is defined as ε' =2.ln (d 1/d 2).

An uninterrupted series of drawing operations is understood to mean that the metal wire passes successively in series through a plurality of drawing dies, each pass corresponding to one drawing operation. Except for the last pass, each pass is directly followed by the next die. In an uninterrupted series of drawing operations, the metal wire does not undergo any operations other than the drawing operation, in particular any heat treatment or coating operations. In other words, the metal wire does not undergo any operation, in particular any heat treatment operation or coating operation, between two directly successive drawing operations of the series.

Step ab) -formation of a metallic coating

Preferably, the method of producing a metal wire according to the present invention comprises a step ab) between an electropolishing step a) and a drawing step b), which forms a metal coating on the surface of the metal wire obtained from step a), said metal coating being selected from the group consisting of copper, zinc, nickel, cobalt, tin, iron, aluminum, manganese, alloys of two of these metals and alloys of three of these metals, preferably from the group consisting of alloys of copper and zinc, alloys of copper and tin and ternary alloys of copper, zinc and metals selected from the group consisting of nickel, cobalt, tin and iron.

This step is well known to the person skilled in the art, and can be performed by a continuous operation of depositing copper, depositing zinc and then causing thermal diffusion, for example when the coating is made of brass.

Step pa) -diameter reduction of the wire

The method according to the invention preferably comprises, before step a), a step pa) of reducing the diameter of the metal wire from the diameter d to the diameter d 1.

The diameter d preferably ranges from 4.5 mm to 6.5 mm.

This step may be performed using any method known to those skilled in the art. For example, this step may be performed by rolling, by passing the wire through successive pairs of rollers, each pair of rollers being oriented at an angle relative to, for example perpendicular to, the preceding pair of rollers.

In a preferred embodiment, this step is performed using wiredrawing. This drawing step is well known to those skilled in the art and is commonly referred to as "dry drawing". It generally includes a plurality of operations.

In a first unwinding step, a metal wire, preferably made of steel and having a maximum tensile strength between 300 mpa and 700 mpa, with an initial diameter d in the range of 4.5 mm to 6.5 mm, is unwound. The wire, known as wire, is stored in the form of a coil on an unwinder from which the wire is unwound using an automatic unwinding device (e.g., an unwinder). The microstructure of the steel is ferrite-pearlite at this time.

Next, in the step of removing the scale from the wire, the wire is passed over a plurality of continuous pulleys and over two straighteners each formed of a plurality of pulleys, the pulley of each straightener being rotatably mounted about an axis perpendicular to the rotation axis of the pulley of the other straightener. Thereby removing an iron oxide layer called scale (scale) present on the surface of the wire rod.

Next, the wire is covered with a layer of wire drawing lubricant, n being variable from 6 to 12, for example, before drawing is actually started with n wire drawing operations.

The purpose of the n wire drawing operations is to reduce the diameter of the metal wire from the initial diameter d to the intermediate diameter d1.

The drawing operation preferably forms an uninterrupted series of dry drawing operations that draw the wire from the initial diameter d to the intermediate diameter d 1. Each drawing operation is a dry drawing operation in which a metal wire is passed through a die having a diameter smaller than the diameter of the wire upstream of the die. Thus, the diameter of the wire downstream of the die is smaller than the diameter upstream of the die. Each die has a diameter smaller than the diameter of the die located upstream. For an uninterrupted series of steps of dry drawing the wire from the initial diameter d to the intermediate diameter d1, the true strain is defined as epsilon=2.ln (d/d 1).

Means for pulling the wire, such as a capstan, downstream of each die, allow a pulling force to be applied sufficient to pull the wire through each die. The drawing lubricant is used in powder form.

Dry drawing is understood to mean the circulation of a metal wire in a gaseous environment, for example ambient air. The drawing lubricant during dry drawing is in powder form. During dry drawing, the pulling device (e.g., capstan) is exposed to a gaseous environment, such as ambient air.

An uninterrupted series of drawing steps is understood to mean that the metal wire passes successively in series through a plurality of drawing dies, each pass corresponding to one drawing operation. Except for the last pass, each pass is directly followed by the next die. In an uninterrupted series of drawing operations, the metal wire does not undergo any operations other than the drawing operation, in particular any heat treatment or coating operations. In other words, the metal wire does not undergo any operation, in particular any heat treatment operation or coating operation, between two directly successive drawing operations of the series.

At the end of the dry drawing operation, the wire may be wound onto a reel during the winding operation before being treated in a subsequent step of the method according to the invention. Winding onto reels can be used for temporary storage of the wire or for transporting the wire to a place where further steps of the method according to the invention are carried out. The metal wire is then uncoiled in an uncoiling operation before being fed into the next step of the method according to the invention.

Preferably, the metal wire is subjected to a heat treatment operation. If the winding operation is performed at the end of the dry drawing operation, the heat treatment operation is performed after the unwinding operation.

The heat treatment operation makes it possible to modify the metallurgical structure of the metal wire of intermediate diameter d1, thus regenerating the structure of the wire. Those skilled in the art know how to find the individual parameters for this step, for example by looking at "LES PRINCIPES DE base du Traitement thermique DES ACIERS [ basic principle of heat treatment of steel ]", andr e Constant and Guy Henry, ISBN 2-85330-083-8.

During this operation, the metal wire of intermediate diameter d1 is heated to a temperature greater than or equal to the austenitizing temperature of the steel, in this case greater than or equal to 850 ℃. Based on the chemical composition of the steel, the person skilled in the art knows what austenitizing temperature needs to be reached, in particular as described in "Prencis de m talurgie [ metallurgical profile ]" of ISBN 2-12-260121-6. Therefore, if austenitization is insufficient, no recrystallized band remains, and the obtained austenite is not uniform, which hinders the subsequent wire drawing. If austenitizing is excessive, the microstructure obtained by subsequent cooling is acicular ferrite (known as) Rather than a ferrite-pearlite structure.

The metal wire of intermediate diameter d1 is then cooled to give the steel a pearlitic or ferrite-pearlitic microstructure. As is well known to those skilled in the art, the metal wire is cooled to avoid forming microstructures other than pearlitic, ferritic or ferrite-pearlitic structures. Too high a cooling rate may result in acicular ferrite, bainite or martensite microstructures. By using the materials described in particular in literature Atlas des courbes de transformation DES ACIERS DE[ Deformation Curve atlas of Steel manufactured in France ] "(IRDIS, 1974), a person skilled in the art knows how to determine the cooling rate from the chemical composition of the steel and from the austenitizing temperature.

Metal wire

"Wire" refers to an object that is very long compared to its cross-section, which is viewed in a plane perpendicular to the maximum length of the wire. The shape of the cross-section of the wire may be circular, oval or polygonal, for example square or rectangular, in which case the corners may be circular. The shape of the cross-section of the wire is partly imparted during the step pa) of reducing the diameter when this step is carried out and partly imparted during the step b) of drawing the metal wire. Preferably, the cross-section of the wire is circular, oval or rectangular in shape. "diameter of a wire" refers to the maximum length of the wire cross-section.

Preferably, the metal wire is a steel wire. Any steel that can be used to reinforce rubber articles selected from the group consisting of pneumatic tire casings, non-pneumatic tire casings, tracks, and conveyor belts is suitable as the steel. Such steels are particularly required to be able to be drawn to diameters in the range of 0.6 mm to 2.5 mm, in particular for use as "bead wires", or even to be able to be drawn to diameters in the range of 0.06 mm to 0.4 mm, in order to be used alone or as an assembly as reinforcing elements in rubber articles, such as carcass plies or crown plies.

According to a preferred embodiment, when carbon steel is used, its carbon content (in weight% of the steel) is in the range of 0.1% to 1.1%, its silicon content (in weight% of the steel) is in the range of 0% to 1%, its chromium content (in weight% of the steel) is in the range of 0% to 1%, the contents of elements Mn, cu, mo, al, P and S are both below 1% (in weight% of the steel), the remaining components of the steel being iron and unavoidable impurities.

The invention is particularly applicable to steels of the normal tensile ("NT"), high tensile ("HT"), super tensile ("ST") or extreme tensile ("UT") steel cord type, NT, HT, ST and UT being defined according to the standard ISO 17832:2018-05. Once drawn, the total elongation At break (At), i.e. the sum of the elastic elongation and the plastic elongation, of the wire is preferably greater than 2.0%.

Examples

Example 1 reduction of valley depth

The valley depth of a tire reinforcing carbon steel wire having a diameter of 1.75 mm, a carbon content of 0.86 wt% and a mechanical strength of 1300 mpa was measured. Valley depth measurements Sv were performed according to standard ISO 25178 of 2015. The mechanical strength is measured according to standard ASTM D4975-14.

A wire having a diameter of 1.75 mm was obtained by dry-drawing a wire having a diameter of 5.5 mm using 12 continuous dies to gradually reduce the diameter of the wire.

The following table lists the results obtained for wires obtained by conventional wire drawing (dry drawing) and wires treated by electropolishing.

The electropolished filaments differ from the control filaments only in that the electropolishing treatment is performed after the same drawing as the control filaments. The electropolishing process was performed as follows: the filaments were continuously transferred at a temperature of 70 ℃ in the presence of a current density of 20.7A/dm ² into a bath of deep eutectic solvent, which is a mixture of ethylene glycol and choline chloride in a 2:1 molar ratio, with a residence time of the filaments in the bath of 60 seconds.

Eddy current measurements, which are well known in the metallurgical arts for analyzing surface defects, are used to measure the number of surface defects. For this purpose, the wire passes through an electromagnetic coil to which an electric current is applied. Defects are detected as changes in the amplitude and phase of the generated eddy currents.

TABLE 1

Silk thread	Sv (micrometers) according to ISO25178	Number of surface defects
			0.86% C control yarn	14.48 Micrometers	30
0.86% C electropolished filaments	4.02 Micrometers	17

The treatment according to the invention results in a significant reduction in the depth of surface defects and in the number of surface defects.

Example 2-reduction of die wear in wet drawing

The control filaments and electropolished filaments from example 1 were drawn into filaments by passing through 19 consecutive dies in a wet drawing step.

The wear is determined by measuring the change in diameter of the wire leaving the last die over time. The more the die wears, the more the diameter increases. When the control wire reached the tolerance limit, the test was stopped. The diameter variation of the control yarn and of the yarn obtained by the method according to the invention is shown in figure 2. It can be seen that the diameter of the wire obtained by the method according to the invention varies slower than the diameter of the control wire, allowing for prolonged use of the mould.

Example 3 improvement of rotational bending Strength

The wires from the prior art and the wires obtained according to the method of the invention are compared during a rotational bending test carried out in a humid environment (at least 60% relative humidity). The test can measure the maximum rotational bending endurance stress (SigmaD and SigmaD, respectively) of each tested wire in a dry or wet environment (60% relative humidity).

The rotational bending test ("Hunter fatigue test") is a known fatigue test; this is described in patent US-se:Sup>A-2 435 772 and is used in, for example, patent application EP-se:Sup>A-220 766 to test the fatigue corrosion strength of metal wires intended for reinforcing the casing of pneumatic tires.

The test principle is as follows: and respectively clamping two ends of a sample with a determined length of the silk thread to be tested in two parallel jaws. In one of the jaws, the wire is free to rotate, while in the second jaw (which is itself motorized), the wire remains fixed. The bending applied to the wire will exert a given bending stress σ on this wire, the strength of which varies with the radius of curvature applied, which itself depends on the working length of the specimen (for example from 70 to 250 mm) and the distance between the two jaws (for example from 30 to 115 mm).

To test the durability of the wire preloaded in this way, the wire is subjected to a number of rotation cycles about its own axis by actuating the motorized jaw, alternately exerting a tensile stress and a compressive stress (+σ; - σ) on each point on the circumference of the wire cross-section.

In practice, the test was performed as follows: the first stress sigma was chosen and a maximum of 10 ⁵ cycles of fatigue testing was started at a rate of 3000 revolutions per minute. Depending on the results obtained, i.e. whether the cord breaks after these up to 10 ⁵ cycles, a new stress σ (which is lower or higher than the previous stress, respectively) is applied to the new specimen, which is changed according to the so-called staircase method described in the journal of the american society of statistics (43, 1948, 109-126) by Dixon & Mood. A total of 17 iterations were therefore performed, the endurance limit, expressed as σ _d, corresponding to a breaking probability of 50% of the wire after 10 ⁵ fatigue cycles, being determined by statistical treatment of the test defined by the staircase method.

The test uses a Bekaert rotary bender, typically RBT model, equipped with a power down detector. The breaking of the cord as referred to herein means breaking of at least one strand of filaments constituting the cord.

The stress σ is calculated as follows:

Where E is the young's modulus of the material (in mpa), For the diameter of the broken wire (in mm), C is the distance between the two jaws (in mm) (c=lo/2.19; where Lo is the working length of the specimen).

Control filaments were obtained in a conventional manner. The yarn obtained by the method according to the invention differs from the control yarn only in that it has undergone an electropolishing treatment prior to the wet drawing step.

For each wire, its tensile strength Rm after aging at 150 ℃ for 60 minutes, rm expressed in megapascals and measured according to standard ASTM D4975; and the amplitude of the drop corresponding to the loss of strength of the wire and calculated as:

Decrease (%) = (Sigma-Sigma 2)/Sigma x 100

The results are shown in the following table.

TABLE 2

	Rm	Decrease in amplitude
			Control filaments 0.86% C0.32 mm diameter	3416	41.18％
Electropolishing filaments 0.86% C0.32 mm diameter	3338	33.23％
			Control filaments 0.55% C0.18 mm diameter	3050	55.61％
Electropolishing filaments 0.55% C0.18 mm diameter	3003	48.56％
			Control filaments 1% C0.38 mm diameter	3476	43.99％
Electropolishing filaments 1% C0.38 mm diameter	3471	38.13％
			Control filaments 1% C0.35 mm diameter	3603	42.00％
Electropolishing filaments 1% C0.35 mm diameter	3579	34.11％

The filaments obtained according to the method of the invention provide a significantly smaller drop amplitude for all diameters and carbon contents tested, while having a similar tensile strength as the control filaments.

Claims

1. A method for preparing a steel wire for reinforcing rubber articles, comprising at least the steps of:

a. a step of electropolishing a metal wire of diameter d1, wherein the metal wire is continuously passed through a bath of a deep eutectic solvent selected from the group consisting of a eutectic mixture of choline chloride and ethylene glycol and a eutectic mixture of choline chloride and glycerol while being subjected to an anodic current, the current having a density between 10A/dm ² and 50A/dm ², the residence time of the wire in the bath of deep eutectic solvent being between 10 seconds and 3 minutes;

b. and drawing the metal wire to a diameter d 2.

2. The method for producing a metal wire according to the preceding claim, wherein the diameter d1 ranges from 0.6 to 3.0 mm.

3. A method of producing a metal wire according to any one of the preceding claims, wherein the temperature of the deep eutectic solvent bath is in the range 50 ℃ to 100 ℃, preferably 50 ℃ to 80 ℃.

4. The method of manufacturing a metal wire according to any one of the preceding claims, wherein at the end of step a) the surface of the metal wire exhibits an arithmetic average roughness Ra of less than or equal to 0.3 microns, measured according to standard ISO 4287 in 2009.

5. The method of any one of the preceding claims, wherein the diameter of the wire at the end of step a) is from 5 to 25 microns smaller than the diameter of the wire at the entry into step a).

6. The method of manufacturing a metal wire according to any of the preceding claims, wherein the diameter d2 ranges from 0.06 to 0.4 mm.

7. A method of producing a metal wire according to any one of the preceding claims, comprising a step ab) between electropolishing step a) and drawing step b), forming a metal coating on the surface of the metal wire resulting from step a), said metal coating being selected from the group consisting of copper, zinc, nickel, cobalt, tin, iron, aluminum, manganese, alloys of two of these metals and alloys of three of these metals, preferably from the group consisting of alloys of copper and zinc, alloys of copper and tin and ternary alloys of copper, zinc and metals selected from the group consisting of nickel, cobalt, tin and iron.

8. The method for preparing a metal wire according to any one of the preceding claims, comprising a step pa) of reducing the diameter of the metal wire from a diameter d to a diameter d1 before step a).

9. The method for producing a metal wire according to the preceding claim, wherein the diameter d ranges from 4.5 to 6.5 mm.

10. The method for preparing a metal wire according to any one of the preceding claims, wherein the step pa of reducing the diameter is performed by wire drawing.

11. The method of any of the preceding claims, wherein the metal wire can be used to reinforce a rubber article selected from the group consisting of a pneumatic tire casing, a non-pneumatic tire casing, a track, and a conveyor belt.

12. Use of a metal wire obtained from the preparation process according to any one of the preceding claims in a rubber article selected from the group consisting of pneumatic tire casings, non-pneumatic tire casings, tracks and conveyor belts.