EP2801659A1

EP2801659A1 - Metal cord with round and non-round filaments

Info

Publication number: EP2801659A1
Application number: EP13166603.4A
Authority: EP
Inventors: Roel DESPIEGELAERE; Jef Wilmots; Rik Mullebrouck
Original assignee: Bekaert NV SA
Current assignee: Bekaert NV SA
Priority date: 2013-05-06
Filing date: 2013-05-06
Publication date: 2014-11-12

Abstract

Metal cord (100, 200, 300, 510, 520, 530) for reinforcing elastomer products comprising n metal filaments (105, 210) twisted together in a cord twisting direction, all the metal filaments (105, 210) have the same cord twisting pitch, wherein at least one metal filament (210) has a cross section which deviates from a round cross section, e.g. a flat, oval or rectangular cross-section.

The metal cord (100, 200, 300, 510, 520, 530) has high rubber penetration, high strength and high fatigue resistance. Also, the use of the metal cord (100, 200, 300, 510, 520, 530) for reinforcing rubber product, e.g. a breaker layer of a tire, is disclosed.

Description

Technical Field

The invention relates to a metal cord for reinforcing elastomer product. The invention also relates to an elastomer product reinforced by the metal cord.

Background Art

A steel cord for reinforcing the rubber tire is always required to have a good rubber penetration. A good rubber penetration can help to prevent the moisture from penetrating into the steel cord and can help to reduce the friction between the steel filaments. Hence the corrosion of the steel cord is prevented and the abrasion of the filaments is reduced. The result is that the lifetime of the rubber tire is improved.
Normally, for a steel cord with a structure n×1, its rubber penetration is quite important but insufficient if no particular measures are taken. For example, one or more of the individual steel filaments may be subjected to a plastic deformation, either before or after the cord making, in order to create gaps between the filaments and to allow rubber to penetrate. This plastic deformation may be a helical preforming, a polygonal preforming or a crimping between a pair of toothed wheels. This plastic deformation requires an additional step in the whole manufacturing process.
JP5035889U discloses a steel cord with a structure of n×1, wherein at least one of the steel filament in the steel cord is the oval or flat steel filament, and the oval or flat steel filament has a smaller twisting pitch than the remainder steel filaments of the steel cord, the oval or flat filament has a twisting pitch is 0.3-0.7 times the twisting pitch of the steel cord. The rubber penetration of the steel cord is good, however, the cost of the steel cord is high, and the strength of the steel cord and the fatigue resistance of the steel cord are low and unacceptable.
It is required to find a steel cord with high rubber penetration, high fatigue resistance and high strength at an acceptable cost.

Disclosure of Invention

The primary object of the invention is to provide a metal cord, e.g. a steel cord with high rubber penetration, high fatigue resistance and high strength.
Another object of the invention is to provide an elastomer product with longer lifetime.
According a first aspect of the invention, a metal cord for reinforcing elastomer product is provided. The metal cord comprises n metal filaments twisted together in a cord twisting direction, all the metal filaments have the same cord twisting pitch, and at least one metal filament has a non-round cross-section.
Instead of the traditional metal cord consisting of the metal filaments with round cross-section, the invention metal cord comprises two kind of metal filaments, one is the metal filament with non-round cross-section and another is the metal filament with round cross-section. The inventor is surprized to find that, by combining the metal filament with non-round cross-section and the metal filament with round cross-section together, the rubber penetration of the steel cord is improved, while the strength of the steel cord and the fatigue resistance of the steel cord are still very high.
The metal cord of JP5035889U comprises round metal filament and non-round metal filament, and the non-round metal filament has a smaller twisting pitch than the cord twisting pitch, thereby more cavities among the steel filaments are created, as a result, the rubber penetration of the metal cord is improved. Although the metal cord of JP5035889U has high rubber penetration, the strength and fatigue resistance of the metal cord are quite poor. Different from JP5035889U , the present invention makes all the metal filaments have the same twisting pitch. In theory, the rubber penetration of the metal cord will turn bad if making the twisting pitch of the non-round metal filament being the same as the cord twisting pitch. It is surprized to find that the rubber penetration is almost kept without sufficient loss while the strength and the fatigue resistance are greatly improved compared with the metal cord of JP5035889U . Furthermore, the invention metal cord saves one step of manufacturing process - making the twisting pitch of non-round metal filament being smaller than the twisting pitch of round metal filament, so the invention metal cord saves a lot of cost.
In a preferable embodiment of the first aspect of the invention, at least the metal filament having a non-round cross-section does not show twist or rotation along its own axes along the metal cord. This creates more interspaces between the metal filament with non-round cross-section and the metal filament with round cross-section. The rubber penetration is much better, and the strength and the fatigue resistance are higher. Optionally, the remainder metal filaments do not show twist or rotation along its own axes along the metal cord or have a twist or rotation along its own axes along the metal cord.
In another preferable embodiment, each individual metal filament has a twist or rotation along its own axes along the metal cord, the twist or rotation is in the same direction as the cord twisting direction. Preferably, the number of the metal filament with non-round cross-section is more than one.
According to the present invention, n metal filaments are twisted together in a cord twisting direction, all the metal filaments have a same cord twisting pitch, this means that the metal cord is made by twisting n metal filaments in one single step (this structure is so-called n×1). Preferably, n ranges from 2 to 9. More preferably, n ranges from 3 to 6.
According to the present invention, all the metal filaments have the same cord twisting pitch. Preferably, the cord twisting pitch ranges from 4mm to 20mm.
Preferably, not more than 50% of the filaments have a non-round cross-section., Most preferably the remainder metal filaments of the metal cord, i.e. those with a round cross-section, are alternated with at least one metal filament with a non-round cross-section. Thereby, more interspaces between the metal filaments are created, and the rubber penetration of the metal cord is better.
According to the present invention, non-round cross-section may be flat, oval or rectangular cross-section. Preferably, the flat, oval or rectangular cross-section has a width W and a thickness T, wherein 1.05<W/≤T3. more preferably, 1.1<W/T≤3; most preferably, 1.2<W/T≤3.
According a second aspect of the invention, a use of the metal cord is as rubber reinforcement. The metal cord comprising n metal filaments twisted together in a cord twisting direction, wherein all the metal filaments have the same cord twisting pitch and at least one metal filament has a non-round cross-section, is for reinforcing rubber product. The rubber product may be a rubber tire or a rubber belt. In case of a tire, the metal cord of the present invention is particularly adapted to reinforce the breaker or belt ply or layer of a tire.

Brief Description of Figures in the Drawings

Figure 1 shows the cross-sectional view of a prior-art steel cord with a structure of 4x1.
Figure 2(a) to 2(b) shows the cross-sectional view of an invention steel cord with a structure of 4×1.
Figure 3(a) to 3(b) shows the cross-sectional view of another invention steel cord with a structure of 4×1.
Figure 4(a) to 4(c) shows the cross-sectional view of a flat, oval or rectangular steel filament.
Figure 5(a) to 5(c) shows the cross-sectional view of other invention steel cord.

Mode(s) for Carrying Out the Invention

The metal cord of the present invention is a steel cord which comprises a number of steel filaments. The steel filament is made from a wire rod.
The wire rod is firstly cleaned by mechanical descaling and / or by chemical pickling in a H₂SO₄ or HCl solution in order to remove the oxides present on the surface. The wire rod is then rinsed in water and is dried. The dried wire rod is then subjected to a first series of dry drawing operations in order to reduce the diameter until a first intermediate diameter.
At this first intermediate diameter d1, e.g. at about 3.0 to 3.5 mm, the dry drawn steel wire is subjected to a first intermediate heat treatment, called patenting. Patenting means first austenitizing until a temperature of about 1000°C followed by a transformation phase from austenite to pearlite at a temperature of about 600°C - 650°C. After further cooling, the steel wire is then ready for further mechanical deformation.
Thereafter the steel wire is further dry drawn from the first intermediate diameter d1 until a second intermediate diameter d2 in a second number of diameter reduction steps. The second diameter d2 typically ranges from 1.0 mm to 2.5 mm.
At this second intermediate diameter d2, the steel wire is subjected to a second patenting treatment, i.e. austenitizing again at a temperature of about 1000°C and thereafter quenching at a temperature of 600°C to 650°C to allow for transformation to pearlite.
If the total reduction in the first and second dry drawing step is not too big, a direct drawing operation can be done from wire rod till diameter d2.
After this second patenting treatment the steel wire is usually provided with a brass coating: copper is plated on the steel wire and zinc is plated on the copper. A thermo-diffusion treatment is applied to form the brass coating.
The brass-coated steel wire is then subjected to a final series of cross-section reductions by means of wet drawing machines. The final product is a steel filament with a carbon content above 0.60 percent by weight, with a tensile strength typically above 2000 MPa and adapted for the reinforcement of elastomeric products.
Steel filaments adapted for the reinforcement of tyres typically have filaments with a final diameter ranging from 0.05 mm to 0.60 mm, e.g. from 0.10 mm to 0.40 mm. Examples of filament diameters are 0.10 mm, 0.12 mm, 0.15 mm, 0.175 mm, 0.18 mm, 0.20 mm, 0.22 mm, 0.245 mm, 0.28 mm, 0.30 mm, 0.32 mm, 0.35 mm, 0.38 mm, 0.40 mm.
Of course, the steel filaments may have big diameters like 4mm to 13mm for other applications such as belt for elevator.
The composition of steel filament has a minimum carbon content of 0.65% (even higher than 0.80%), a manganese content ranging from 0.40% to 0.70%, a silicon content ranging from 0.15% to 0.30%, a maximum sulphur content of 0.03%, a maximum phosphorus content of 0.30%, all percentages being percentages by weight. There are only traces of copper, nickel and / or chromium.
Then steel filaments are rolled by a pair of rollers to change the cross-section from round to non-round, i.e. flat, oval or rectangular. Thus non-round steel filaments are obtained. The flat wires have a pair of flat surfaces and a pair of round edges.
Figure 1 illustrates a prior art steel cord with a structure of 4×1. The steel cord 100 has four steel filaments 105 twisted together, all the steel filaments 105 have the same twisting pitch being 14mm.
Figure 2a to 2b illustrates an invention steel cord with a structure of 4×1. The steel cord 200 has three steel filaments 105 and one steel filament 210 twisted together. The steel filament 105 has a round cross-section and the steel filament 210 has a flat cross-section. The steel filaments 105 and the steel filament 210 have a same cord twisting pitch being 14mm. The steel filament 210 is made by rolling the steel filament 105, as a result, the steel filament 210 has a width W and thickness T as illustrated by Figure 4a, wherein W/T=1.9.
The steel cord 200 is made by a method called 'cabling', by means of a tubular twisting machine. Both Figure 2a and Figure 2b are the cross-sectional view of the steel cord 200, Figure 2b is the cross-sectional view after twisting the steel cord 200 in Figure 2a with 90°. So each individual steel filament 105 or 210 does not show twist or rotation along its own axes along the steel cord 200.
Figure 3a to 3b illustrates an invention steel cord with a structure of 4×1. The steel cord 300 has two steel filaments 105 and two steel filaments 210 twisted together. The steel filament 105 has a round cross-section and the steel filament 210 has a flat cross-section. The steel filaments 105 and the steel filament 210 have the same cord twisting pitch being 14mm. The steel filament 210 is made by rolling the steel filament 105, as a result, the steel filament 210 has a width W and thickness T, wherein W/T=1.9.
The steel cord 300 is made by a method called 'bunching', e.g. by means of a double-twisting machine. Both Figure 3a and Figure 3b are the cross-sectional view of the steel cord 300, Figure 3b is the cross-sectional view after twisting the steel cord 300 in Figure 2a with a degree of 90. The individual steel filament 105 or 210 has a twist or rotation along its own axes along the steel cord, the twist or rotation is in the same direction as the cord twisting direction.
Compared with the prior art steel cord 100 which is consisting of round steel filaments, the invention steel cords 200 and 300 provide an improved rubber penetration without losing the strength and the fatigue resistance too much. As the rubber penetration of the steel cord is greatly improved, the rubber tire reinforced by the invention steel cord has a longer lifetime. Compared with the prior art steel cord of JP5035889U , the strength and the fatigue resistance of the invention steel cord are much higher while the rubber penetration is almost the same. Thereby, the rubber tire reinforced by the invention steel cord has a longer lifetime. And furthermore, compared with the steel cord of JP5035889U which need an additional twisting process for making the flat filament having smaller twisting pitch than the cord twisting pitch, the invention steel cord saves such an additional twisting step, thereby saves the cost.
A rubber penetration test shows the advantage of the invention steel cord 200 and 300 compared with the prior art steel cord 100. The rubber penetration test is so-called air drop method, the lower the air%, the better the rubber penetration. Table 1 shows the test result. Table 1

Prior art steel cord 100 Invention steel cord 200 Invention steel cord 300

Air% 100 0 10
Figure 4a to 4c illustrate some steel filaments with non-round cross-section. Figure 4a illustrates a steel filament 210 with a flat cross-section, steel filaments 210 has a width W and a thickness, wherein W/T=1.4. Figure 4b illustrates a steel filament 410 with an oval cross-section, W/T=1.6. Figure 4c illustrates a steel filament 415 with a rectangular cross-section, W/T=1.8. All these steel filaments with non-round cross-section may be made by rolling the round steel filaments.
Figure 5a to 5c illustrate some embodiments of the invention. Figure 5a illustrates a steel cord 510 with a structure of 3x1, wherein one of three steel filaments is flat steel filament, the one flat steel filament does not show twist or rotation along its own axes along the steel cord, and the other two round steel filaments have a twist or rotation along its own axes along the steel cord. Figure 5b illustrates a steel cord 520 with a structure of 5×1, wherein one of five steel filaments is flat steel filament. Figure 5c illustrates a steel cord 530 with a structure of 6×1, wherein three of six steel filaments are flat steel filaments, and the three round filaments are alternated with the three flat steel filaments.
As the invention steel cord has high rubber penetration, high strength and high fatigue resistance, the steel cord can be used for reinforcing elastomer product, i.e. rubber tire or rubber belt.

Claims

A metal cord for reinforcing elastomer product, said metal cord comprising an number n metal filaments twisted together in a cord twisting direction, all said metal filaments having the same cord twisting pitch, characterized in that at least one said metal filament has a non-round cross-section.
A metal cord as claimed in claim 1, characterized in that at least said metal filament having a non-round cross-section does not show twist or rotation along its own axis along said metal cord.
A metal cord as claimed in claim 1, characterized in that each of said metal filaments has a twist or rotation along its own axis along said metal cord, said twist or rotation is in the same direction as said cord twisting direction.
A metal cord as claimed in any one of claims 1 to 3, characterized in that said number n ranges from 2 to 9.
A metal cord as claimed in claim 4, characterized in that said number n ranges from 3 to 6.
A metal cord as claimed in any one of claims 1 to 5, characterized in that not more than 50 % of said n metal filaments have a non-round cross-section.
A metal cord as claimed in claim 6, wherein metal filaments with a round cross-section are alternated with metal filaments with a non-round cross-section.
A metal cord as claimed in any one of claims 1 to 7, characterized in that said non-round cross-section is flat, oval or rectangular cross-section.
A metal cord as claimed in claim 8, characterized in that said flat, oval or rectangular cross-section has a width W and a thickness T, wherein 1.05<W/T≤3.
A metal cord as claimed in claim 9, wherein 1.1<W/T≤3.
A metal cord as claimed in any one of claims 1 to 10, characterized in that said cord twisting pitch ranges from 4mm to 20mm.
Use of a metal cord as claimed in any one of claims 1 to 11 as rubber reinforcement.
Use as claimed in claim 12, wherein said reinforced rubber is a tire.
Use as claimed in claim 13, wherein a belt or breaker layer of said tire is reinforced.