JP3511132B2 - Steel cord for tire reinforcement - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire reinforcing steel cord (hereinafter simply referred to as "cord") used for automobile tires.

[0002]

2. Description of the Related Art For automobile tires, a cord having a 1 × n structure in which n strands are twisted together, or b strands are further twisted on the outer side in which a core strands are twisted Codes of a + b structure are commonly used. A plurality of the above cords are covered with rubber and used in a state where a plurality of cords are aligned in parallel.

By the way, an essential requirement for a tire reinforcing material is to have excellent fatigue resistance. That is, if the cord is excellent in strength and is a complete composite with rubber and has excellent fatigue resistance, the life of the tire can be greatly extended and the safety is improved. Can fully fulfill the role of. If the rubber does not penetrate into the cord and only the outer circumference of the cord is covered, the adhesion between the rubber and the cord will not be sufficient, causing a so-called separation phenomenon in which the cord and rubber are separated when the vehicle is running, or Moisture and water that has penetrated from the cuts in the tire corrode the cord, causing a decrease in mechanical strength. Further, since the wires are in direct contact with each other, a so-called fretting phenomenon occurs in which the wires rub against each other due to vibration during traveling of the automobile and wear. These are factors that significantly reduce the fatigue resistance of the tire.

Therefore, in the steel cord having the above-mentioned 1 × n structure or a + b structure, there is a so-called open cord in which the strands are sweetly twisted together to provide a gap between the strands in order to improve rubber penetration.

However, the open cord has a large free space in which each strand can move, and the twisted structure tends to be unstable during the production of the cord, which causes the strands to be biased or unevenly twisted. . Moreover, in this cord, the gap between the strands is reduced due to the tension of the extremely low load, and the rubber does not penetrate into the cord. Therefore, it does not become a complete composite with the rubber, which causes the above-mentioned harmful effects. Become.

Moreover, the code of 1 × n structure has a structure of 6
There is a problem that the strands of a book are twisted together, and it cannot be used for a tire that requires high strength. Further, since the a + b structure cord has more strands than the 1 × n structure cord, there is an advantage that the strength of the cord can be increased, but the step of forming the core layer and forming the outer layer around the core layer are advantageous. Since it requires two steps, the productivity is low and the manufacturing cost is high.

As a means for solving the decrease in productivity of the above cords, cords of a / b structure have recently been used. This cord is obtained by twisting a plurality of core wires and a plurality of side wires at the same pitch at once, and since it is once twisted, the productivity does not decrease. However, even in this code, the problem of making an open structure has not been solved.

The inventors of the present invention have developed a cord having a flat cross-section, which has been a spotlight in recent years because it has the a / b structure capable of coping with high strength without lowering the productivity and is capable of reducing the weight of the tire. As a result of intensive research on factors that improve fatigue resistance by a large number of experiments, the inventors have found that there is a close relationship between the vibration damping characteristic value of the cord and the fatigue property, and completed the present invention. The vibration damping characteristic value is a value determined by giving the vibration energy to the cord and stopping the vibration, and the number of strands and the wire diameter. It changes depending on the distance and contact between the strands in the direction, that is, the degree of adhesion.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a cord having excellent fatigue resistance while maintaining productivity.

[0010]

That is, in the cord of the present invention, two to three strands are used as core strands and four to seven strands are used as side strands and twisted at once in the same direction. In a steel cord having a flat cross section, the vibration damping characteristic value A represented by the following formula is 1200 to 5500.
Is characterized in that. A = (n ₁ / d ₁ ² + n ₂ / d ₂ ² ) × NA A: Vibration damping characteristic value n ₁ : Number of core wires (pieces) n ₂ : Number of side wires (pieces) d ₁ : Core wire Diameter (mm) d ₂ : Side wire diameter (mm) N: Vibration damping frequency (times)

In the above structure, the number of core strands is set to 2 to 3 because one strand has a straight line shape, so that an appropriate elongation required for a cord cannot be obtained and flexibility is high. This is because the diameter formed by the core wire group increases and the cord diameter increases when the number of core wires is 4 or more.

The reason why the number of side strands is 4 to 7 is
When the number is 3 or less, the gap between the side strands becomes too large, and the twist becomes unstable. When the number is 8 or more, the gap between the strands becomes too small, and the rubber infiltration property deteriorates.

The relational expression in the above configuration is a relational expression derived from various experimental data, and it changes depending on the number of strands constituting the cord, the strand diameter, and the degree of adhesion (openness) of the strands in the major axis direction of the cord. Is. When this value is in the range of 1200 to 5500, the fatigue resistance of the cord is remarkably improved.

In the above structure, the core wire diameter d ₁ is preferably smaller than the side wire diameter d ₂ . This is because when the core wire diameter is equal to or larger than the side wire diameter, the core wire interrupts between the outer layer wires and prevents rubber from entering.

Further, since the cord of the present invention has a flat cross section, the belt layer can be thinned by arranging the cord so that the minor axis side thereof matches the thickness side of the tire belt layer. it can. The flat shape preferably has a major axis / minor axis = 1.1 to 2.0. This is 1.
If it is less than 1, the cross-sectional shape of the cord will be close to a circular shape, and the effect of flattening it cannot be expected. If it exceeds 2.0, the major axis will increase and the number of laid lines per unit area of the rubber sheet will decrease. This is because the strength of rubber products decreases.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing one embodiment of the cord of the present invention. This cord 1 has a core wire diameter of 2/5 structure in which two core wires 2 are arranged on the core and five side wires 3 are arranged on the side, and these are twisted at once at the same pitch. Is a cord smaller than the diameter of the side strand. The sectional shape is a flat structure, and the vibration damping characteristic value A which is the configuration of the present invention is in the range of 1200 to 5500.

In this embodiment, the two core wires are in contact with each other, but the present invention is not limited to this, and an open structure is also possible.

The strand diameter is generally 0.15 to 0.40 mm for tire reinforcement.

[0020]

EXAMPLES Examples of the present invention will be specifically described below.

A diameter of 0.2 is obtained by repeating the patenting and drawing process of a wire having a diameter of 5.5φ and brass-plating the surface.
~ 0.38 mm of several kinds of strands are manufactured, these strands are combined and twisted at once, and various a based on the present invention are obtained.
A cord having a / b structure (a: 2 to 3, b: 4 to 7) was manufactured by changing the open degree.

All the above cords are twisted,
These cords were pressed through the rollers arranged in a zigzag pattern to form a flat cross section.

Then, the fatigue resistances of the above codes were compared. The results are shown in Table 1.

[0024]

[Table 1]

In the above evaluation, the fatigue resistance was evaluated by embedding a plurality of the above cords in a rubber sheet and using this sheet with a three-point pulley bending fatigue tester. The result is the experiment No. The value was indexed with 1 being 100. Eventually, fretting wear, buckling, etc. lead to breakage, etc., but the number of repetitions until this state was evaluated.

Further, as for the vibration damping number N, as shown in FIG.
The number of times until the vibration stops when one end A is fixed to 0 mm and the opposite open end B is bent toward the minor axis of the cord by θ = 30 ° and then opened and vibrated. Is. The value obtained by substituting this numerical value, the number of strands, and the diameter of the strand into the above equation is the vibration damping characteristic value A.

The graph of FIG. 2 shows the relationship between the vibration damping characteristic value A and the fatigue value in Table 1 above.

In FIG. 2, it can be seen that the vibration damping characteristic value and the fatigue value have a great relationship. From the fatigue limit line (lower limit) Y required for the cord, the vibration damping characteristic value is 1
It can be seen that the fatigue resistance of the cord is improved when the number is 200 to 5,500.

[0029]

Since the steel cord of the present invention has the above-mentioned structure, it has excellent fatigue resistance. Moreover, since it is twisted once, the productivity is not reduced and a cord having high strength can be obtained. Further, when used for a tire, the thickness of the tire can be reduced and the weight of the tire can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a steel cord of the present invention.

FIG. 2 is a graph showing a relationship between a vibration characteristic value and a fatigue value.

FIG. 3 is a schematic diagram for explaining a method of measuring the number of vibration dampings.

[Explanation of symbols]

1 steel cord 2 core wire 3 side wires 4 Fixing jig W Steel cord cut sample L Examiner θ Bending angle A fixed end B open end

Claims (3)

(57) [Claims] 1. Two to three strands are core strands and 4 to 7 strands are side strands, which are twisted together in the same direction at a time.
In a steel cord having a flat cross-sectional shape, the vibration damping characteristic value A represented by the following formula is 1200 to
A steel cord for tire reinforcement, which is 5500. A = (n ₁ / d ₁ ² + n ₂ / d ₂ ² ) × NA A: Vibration damping characteristic value n ₁ : Number of core wires (pieces) n ₂ : Number of side wires (pieces) d ₁ : Core wire Diameter (mm) d ₂ : Side wire diameter (mm) N: Vibration damping frequency (times) 2. The steel cord for tire reinforcement according to claim 1, wherein the core wire diameter d ₁ is smaller than the side wire diameter d ₂ . 3. The flat shape has a major axis / minor axis = 1.1 to 2.0.
The steel cord for tire reinforcement according to claim 1 or 2.