JP2016075003A - Steel cord and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fracture-proof steel cord with an elliptical cross section.SOLUTION: A steel cord has an elliptical cross section formed by twisting multiple filaments, and has a single stranded structure of 1×n (n=3 to 6) in which a hollow part exists at a center. The steel cord is used for a vehicle tire. An acute-angled part in a major axis side of an ellipse of the cross section of the steel cord has 0.35 or less of flexural stress index (σ) obtained from a following expression (1): σ=3704×d/(P×n×f) (expression 1), where d: diameter of filament constituting the steel cord (mm), P: steel cord twisting pitch (mm), n: steel cord twisting amount, f: steel cord flatness ratio (minor axis/major axis×100(%))SELECTED DRAWING: Figure 1

Description

  The present invention relates to a steel cord used for a vehicle tire and a manufacturing method thereof.

  A steel cord having an elliptical cross section is known from Patent Document 1 and Patent Document 2. In order to reduce the amount of rubber used and to improve the lateral rigidity as a dynamic characteristic of the tire, it is preferable to use a steel cord having an elliptical cross section as a reinforcement for a vehicle tire.

JP 2010-242278 A JP 2009-114583 A

  However, in such a steel cord, stress may concentrate on a pointed portion on the major axis side of the elliptical cross section, leading to breakage.

  Then, an object of this invention is to provide the steel cord of the cross-sectional ellipse shape which is hard to fracture | rupture, and its manufacturing method.

The steel cord used for the automobile tire of the present invention,
A steel cord having a 1 × n single twist structure (n = 3 to 6) in which a hollow portion exists in the center, in which a plurality of filaments are twisted to have an elliptical cross section,
The bending stress index (σ _i ) given by the following formula (1) is 0.35 or less for the pointed portion on the major axis side of the ellipse in the cross section of the steel cord.
σ _i = 3704 × d / (P × n × f) (Formula 1)
Where d: Diameter of the filament constituting the steel cord (mm)
P: Twist pitch of steel cord (mm)
n: Number of twisted steel cords f: Flatness ratio of steel cords (minor axis / major axis x 100 (%))

In addition, a method of manufacturing a steel cord used for an automobile tire according to the present invention,
A step of twisting a plurality of filaments to obtain a cord of 1 × n single twist structure (n = 3 to 6) having a hollow portion in the center;
The obtained cord is passed through a plurality of flattened rollers arranged in a staggered manner, and a 1 × n single twist structure (n = 3 to 6) cross-section elliptical steel cord having a hollow portion in the center is provided. And obtaining
The flattening roller satisfies the following (Formula 3).
33d ≦ R _d ≦ 55d (Formula 3)
R _d : Flattening roller outer diameter d: Filament diameter

  According to the present invention, a steel cord having an elliptical cross section that is difficult to break and a method for manufacturing the same are provided.

It is sectional drawing of the steel cord concerning this embodiment concerning the present invention. It is a side view of the steel cord concerning this embodiment concerning the present invention. It is a diagram for explaining an average layer Kokoro径D _s code. It is a figure for demonstrating the angle (alpha). It is a schematic diagram of the flattening roller used for manufacture of the steel cord concerning this embodiment concerning the present invention.

<Outline of Embodiment of the Present Invention>
First, an outline of an embodiment of the present invention will be described.
(1) One embodiment of the steel cord according to the present invention is:
A steel cord having a 1 × n single twist structure (n = 3 to 6) in which a hollow portion exists in the center, in which a plurality of filaments are twisted to have an elliptical cross section,
It is a steel cord used for an automobile tire in which the bending stress index (σ _i ) given by the following formula (1) is 0.35 or less with respect to the pointed portion on the major axis side of the ellipse in the cross section of the steel cord.
σ _i = 3704 × d / (P × n × f) (Formula 1)
Where d: Diameter of the filament constituting the steel cord (mm)
P: Twist pitch of steel cord (mm)
n: Number of twisted steel cords f: Flatness ratio of steel cords (minor axis / major axis x 100 (%))

  According to the configuration of (1), even when the steel cord is bent, the stress acting on the pointed portion on the long diameter side becomes a predetermined value or less, so that a steel cord that is not easily broken is obtained. For this reason, this steel cord can be used suitably as reinforcement of the breaker part of a tire.

(2) In the steel cord described above, it is preferable that the twist angle α determined by the following formula (2) from the twist pitch P and the average layer core diameter D _s is 4.8 ° or more.
α = tan ⁻¹ (π × D _s / P) (Formula 2)
α: Steel cord twist angle (°)
D _s : Average diameter of steel cord core layer (mm)
P: Twist pitch of steel cord (mm)

  A small twist angle has the effect of lowering the bending stress index, but it contributes to lowering the flattening efficiency. When pressing with a flattening roller for flattening, if the twist angle is small, the filament is likely to escape, resulting in poor flattening efficiency. For this reason, it is preferable that a twist angle shall be 4.8 degrees or more.

  (3) In the steel cord described above, it is preferable that at least one of the filaments has a larger combing shape than the other filaments.

  According to the configuration of (3), only a minimum number of filaments necessary for rubber penetration into the center of the cross section of the steel cord are given a relatively large habit, and other filaments are easily flattened. The minimum necessary habit is given. This makes it possible to obtain an ideal steel cord that is easily flattened and has little elongation in a low load range.

(4) One embodiment of a method for manufacturing a cable bead according to the present invention includes:
A step of twisting a plurality of filaments to obtain a cord of 1 × n single twist structure (n = 3 to 6) having a hollow portion in the center;
The obtained cord is passed through a plurality of flattened rollers arranged in a staggered manner, and a 1 × n single twist structure (n = 3 to 6) cross-section elliptical steel cord having a hollow portion in the center is provided. And obtaining
The flattening roller is a method of manufacturing a steel cord used for an automobile tire that satisfies the following (Equation 3).
33d ≦ R _d ≦ 55d (Formula 3)
R _d : Flattening roller outer diameter d: Filament diameter

As the outer diameter R _d of flattening rollers is less easily flattened steel cord, since the outer diameter R _d of flattening rollers is too large hardly flattened steel cord 1, the outer diameter R _d of flattening rollers 22 filaments The diameter d is preferably 55 times or less.
Further, the outer diameter R _d of flattening rollers is too small load is increased which acts when to flattening the steel cord, the life of the flattening rollers is shortened. Therefore, the outer diameter R _d of flattening rollers 22 is preferably at least 33 times the filament.

(5) In the above steel cord manufacturing method,
Before twisting a plurality of the filaments,
At least one filament is provided with a habit for facilitating the entry of rubber satisfying the following formula (4):
0.11P ≦ p ₁ ≦ 0.59P, 0.40d ≦ h ₁ ≦ 4.5d (Formula 4)
The remaining filaments are preferably provided with a habit for facilitating flattening that satisfies the following formula (5).
0.11P ≦ p ₂ ≦ 0.50P, 0.10d ≦ h ₂ ≦ 2.5d (Formula 5)
p ₁ : Pitch pitch h ₁ for facilitating rubber intrusion p ₁ : Spike wave height for facilitating rubber penetration p ₂ : Pitch pitch h ₂ for facilitating flattening The height of the habit to make

According to the structure of (5), only a minimum number of filaments necessary for the penetration of rubber into the center of the cross section of the steel cord is given a relatively large weed (p ₁ , h ₁ ), and other filaments Is given the minimum necessary small habit (p ₂ , h ₂ ) for facilitating flattening. This makes it possible to obtain an ideal steel cord that is easily flattened and has little elongation in a low load range.

<Details of Embodiment of the Present Invention>
Hereinafter, embodiments of a steel cord according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

  The steel cord according to the present embodiment has a 1 × n single twist structure (n = 3 to 6) in which a plurality of filaments are twisted to have an elliptical cross section and a hollow portion exists in the center.

  The steel cord of the present embodiment will be described in detail with reference to FIGS. First, a steel cord having a 1 × 4 structure (n = 4) will be described as an example of an embodiment of a 1 × n (n = 3 to 6) single twist structure. FIG. 1 is a cross-sectional view of a steel cord 1. FIG. 2 is a side view of the steel cord 1.

  As shown in FIG. 1, the steel cord 1 has four filaments 11, 12, 13, and 14 having the same diameter d [mm]. The steel cord 1 is configured by twisting four filaments 11 to 14 with a spiral tang by twisting so that a hollow portion exists in the center of the cross section. Further, at least two filaments 12 and 14 out of these have a habit smaller than the twist pitch after twisting.

  In FIG. 1, the outline outer peripheral surface of the steel cord 1 which the four filaments 11-14 make with a broken line is shown. The substantially outer peripheral surface is a virtual surface obtained by connecting the outermost peripheral portions of the filaments 11 to 14 over the entire circumference of the steel cord 1. The general outer peripheral surface is an elliptical shape.

In such a steel cord 1, the bending stress index (σ _i ) given by the following expression (1) is set to 0.35 or less with respect to the pointed portion 15 on the major axis side of the ellipse in the cross section shown in FIG. .
σ _i = 3704 × d / (P × n × f) (Formula 1)
Where d: Diameter of the filament constituting the steel cord 1 (mm)
P: Twist pitch of steel cord 1 (mm)
n: Number of twists of steel cord 1 f: Flatness ratio of steel cord 1 (minor axis / major axis x 100 (%))

The flatness of the steel cord 1 is a ratio f = a / b between the shortest dimension a [mm] and the longest dimension b [mm] of the substantially outer peripheral surface as shown in FIG.
Moreover, the twist pitch P of the steel cord 1 means the length of the period in which one filament 11 appears as seen from the side as shown in FIG.

Generally, when a wire rope is bent to a certain curvature, the maximum bending stress generated in the filament is expressed as follows.
σ = E _b / D × d
D: Sheave diameter E _b : Bending stress elastic modulus of wire rope d: Filament diameter

  The present inventors considered the above formula by replacing it with a steel cord having an elliptical cross section. When bending is applied to a steel cord having an elliptical cross section, stress concentrates on the sharp part of the major axis of the elliptical cross section. Thus, if the steel cord is designed so that the maximum bending stress generated in the sharp part of the major axis of the cross-sectional ellipse becomes a certain value or less, it can be suitably used for an automobile tire while ensuring fatigue strength.

At this time, the maximum bending stress of the steel cord having an elliptical cross section is inversely proportional to the twist pitch p of the filament, the number of twists n of the filament, and the flatness f (minor axis / major axis × 100 (%)). They found out. Therefore, the present invention has been completed by considering that the maximum bending stress index of the steel cord having an elliptical cross section is expressed by the above (formula 1).
In deriving the above (Equation 1), the sheave diameter D = 540 (13-inch tire rim diameter + tyre height) calculated from the assumed tire rim diameter and tire thickness (flatness) to which the steel cord is applied. × 2) and the longitudinal elastic modulus E (20000) determined from the physical properties of the steel, the value of E _b / D = 20000/540 = 3704 was used.

  By setting the bending stress index represented by the above (formula 1) to 0.35 or less, even when the steel cord is bent, only a bending stress of a predetermined size or less is applied to the sharp part on the major axis side of the cross-sectional ellipse. Since it does not act, a steel cord that is difficult to break and can be suitably used as a reinforcement for the breaker portion of the tire is obtained.

The steel cord of this embodiment is obtained by twisting filaments to obtain a cord having a circular cross section, and then performing a flattening process. The flattening efficiency during production depends on the number n of twists. Specifically, the flattening efficiency increases as the area of the hollow portion surrounded by each filament at the center of the cross section of the steel cord before flattening increases. If this hollow portion is large, it means that the filament is easily moved by an external force and is easily flattened.
If the number of twists is 2, there is no hollow part in the cross section, and flattening cannot be achieved. Even in the case where the number of twists is two, the long diameter apparently increases by making the filaments non-contact with each other, so that the cross section can be formed into an elliptical shape, but this is not realistic because the elongation of the steel cord increases. For this reason, the twist number n is 3 or more.
When the number of twists is three, a hollow portion is present at the center of the cross section and can be flattened. However, since the cross sectional area of the hollow portion is relatively small, flattening is difficult. When the number of twists is 4 or more, the area of the hollow portion becomes relatively large, and flattening can be performed more efficiently. When the number of twists is 5 or 6, the area of the hollow portion is further increased, and flattening can be efficiently performed, and a steel cord having a flatness ratio of 70 or less can be produced.

  In Patent Document 1, examples with an aspect ratio of 30 to 40 are listed. If such an extremely flat steel cord is used, the lateral rigidity of the tire can be increased. However, the bending stress index of such a flat steel cord is a considerably large value, which is twice the bending stress index of a steel cord having a flatness ratio of 70%. For this reason, it is necessary to lower the bending stress index by using a filament having a small diameter, increasing the number of twisted filaments, or increasing the twist pitch. As a result, manufacturing becomes difficult and costs increase, which is not realistic. In addition to these problems, it is not easy to flatten the steel cord so that the flatness ratio is 30 to 40%, and it is difficult to manufacture.

<Relationship between twist pitch and average layer core diameter>
Further, the steel cord according to the present embodiment, it is preferable twist angle α obtained by the following formula and a twist pitch P average layer Kokoro径D _s (2) is 4.8 ° or more.
α = tan ⁻¹ (π × D _s / P) (Formula 2)
α: Twist angle (°)
D _s : Cord average layer core diameter (mm)
P: Cord twist pitch (mm)

The average layer core diameter (mm) of the cord is a diameter of a circle formed by connecting the centers of individual filaments before flattening as shown in FIG. When the cord is composed of four filaments 11 to 14 as in the illustrated example, the distance D _S1 between the filament centers 11a and 13a of the two filaments 11 and 13 facing each other and facing each other in the cross section. The average distance D _S2 between the filament centers 12a and 14a of the two filaments 12 and 14 can be calculated as D _S = (D _S1 + D _S2 ) / 2. For convenience, after measuring the cord outer diameter at two points (vertical and horizontal), the average value of the filament diameters may be subtracted from the average value of the cord outer diameters at the two points.

As shown in FIG. 4, the twist angle α in the code schematic representation of the outer diameter Dc, the angle of the tangent of a right triangle the length of two sides perpendicular consists P and [pi] D _S, that is, determined as the expansion angle.

A small twist angle has the effect of lowering the bending stress index, but it contributes to lowering the flattening efficiency. When pressing with a flattening roller (details will be described later) for flattening, if the twist angle is small, the filament will easily escape and flattening efficiency will deteriorate. For this reason, it is preferable that a twist angle shall be 4.8 degrees or more.
However, if the twist angle becomes too large, the twist pitch becomes small, which increases the cost and increases the bending stress index. For these reasons, the twist angle is preferably 11 ° or less.

<Size of habit shape>
Moreover, it is preferable that at least one filament has a larger crease shape than other filaments even after being pressed by a roller for flattening. A large wrinkle shape means that the wrinkle height is large, for example.

More specifically, before twisting a plurality of filaments, at least one filament is given a habit to facilitate the intrusion of rubber satisfying the following formula (4), and the remaining filaments are given the following formula It is preferable to provide a habit for facilitating flattening that satisfies (5).
0.11P ≦ p ₁ ≦ 0.59P, 0.40d ≦ h ₁ ≦ 4.5d (Formula 4)
0.11P ≦ p ₂ ≦ 0.50P, 0.10d ≦ h ₂ ≦ 2.5d (Formula 5)

Generally, a closed cord in which a plurality of filaments are in close contact and twisted together is not easily flattened, and an open cord in which a plurality of filaments are twisted together with a gap between each other is easily flattened. However, open cords are not easy to use because the cords themselves are unstable, such as large elongation in low load areas.
Therefore, in the cord described in Patent Document 1, as an intermediate plan between the closed cord and the open cord, a fine spiral comb is attached to each filament separately from the twist pitch, and the cross-sectional shape is elliptic before twisting. It has been proposed to obtain a flat cord by twisting together after processing into a shape.
However, although it is not as much as open cords to give all filaments a relatively large habit for the purpose of improving rubber penetration into the central portion, the elongation in the low load region is increased and it tends to be difficult to handle.
Therefore, in the steel cord according to the present embodiment, a relatively large number of creases are given to the minimum number necessary for rubber penetration into the central portion in the cross section, and the other filaments are at least necessary to facilitate flattening. A small habit is given. As a result, the wrinkles are reduced to an inconspicuous extent after pressing with a roller for flattening, and an ideal steel cord with less elongation in a low load region can be obtained.

Normally, flattening of the steel cord can be performed efficiently when the steel cord is flattened under a low tension. Therefore, it is possible to obtain a steel cord having a flatness ratio of 50% or less. However, when a steel cord is manufactured using a buncher machine in an out-in type, the tension after twisting the filament tends to increase. To cover this increase in tension, in addition to providing a relatively large habit to at least one strand to facilitate rubber penetration before twisting, all other filaments have a small wave height. To do. As a result, when pressing for flattening, the warp imparted to all the filaments is stretched by a certain amount and the tension is lowered, so that flattening can be achieved efficiently.
It is more preferable that the wrinkles provided for facilitating flattening have disappeared in the steel cord after flattening, but a slight amount of wrinkles may remain. If the residual amount of the habit is large, the steel cord is stretched with a low load, so that the handling is deteriorated in the tire manufacturing process.

<Method of manufacturing steel cord>
Next, a method for manufacturing the steel cord described above will be described.

The steel cord of this embodiment is twisted into a 1 × n single twist structure (n = 3 to 6) having a hollow portion at the center.
For example, at least one filament is given a habit for facilitating the penetration of rubber satisfying the following formula (4), and the remaining filament is given a habit for facilitating flattening satisfying the following formula (5). It is preferable to give.
0.11P ≦ p ₁ ≦ 0.59P, 0.40d ≦ h ₁ ≦ 4.5d (Formula 4)
0.11P ≦ p ₂ ≦ 0.50P, 0.10d ≦ h ₂ ≦ 2.5d (Formula 5)
p ₁ is a habit pitch for facilitating the penetration of rubber, and h ₁ is a habit wave height for facilitating the penetration of rubber. p ₂ is a habit pitch for facilitating flattening, and h ₂ is a habit wave height for facilitating flattening.
In addition, it is preferable that the habit for facilitating flattening represented by Formula 5 does not stand out even if it does not disappear after flattening.
Further, all the filaments may be crushed in accordance with the twist pitch so as to have a 1 × n single twist structure in which a hollow portion exists in the center. That is, you may give two types of habits, the habit corresponding to the twist pitch P, and the habit satisfying the following formula (4) or (5) to each of the filaments before being twisted together.

  Next, a plurality of filaments are twisted to obtain a 1 × n single-stranded structure (n = 3 to 6) cord having a hollow portion at the center.

  Further, the obtained cord is passed through a plurality of flattening rollers arranged in a staggered manner, and a steel of 1 × n single twist structure (n = 3 to 6) having an oval cross section in which a hollow portion exists in the center. The code is obtained.

Here, the flattening roller is set to satisfy the following (Formula 3).
33d ≦ R _d ≦ 55d (Formula 3)
R _d : Flattening roller outer diameter d: Filament diameter

FIG. 5 is a schematic diagram showing a flattening device 20 that performs flattening processing.
As shown in FIG. 5, the flattening device 20 has a base 21 and a plurality of flattening rollers 22 provided on the base. A rotating shaft 23 of the flattening roller 22 extends in a direction perpendicular to the base 21.
The flattening roller 22 includes a movable roller 22a in which the rotation shaft 23a is provided so as to be movable in the passage direction 24, and a fixed roller 22b in which the rotation shaft 23b is fixed so as not to move. The rotating shaft 23a of the movable roller 22a is provided integrally with the bolt 25. The bolt 25 is attached to the movable side base 26 so as to be able to advance and retreat in a direction orthogonal to the line direction 24.
The plurality of flattening rollers 22 are provided in a zigzag manner along the direction of line 24. Filaments are stretched around the plurality of flattening rollers 22. By moving the movable roller 22a by moving the bolt 25 back and forth, the degree of bending of the staggered filaments can be adjusted.
It is preferable that the outer diameter R _d of the flattening rollers 22 arranged in a staggered pattern and the diameter d of the filament satisfy the following relational expression (3).
33d ≦ R _d ≦ 55d (Formula 3)

More easily flattened steel cord 1 the outer diameter R _d of flattening rollers 22 is small, since the outer diameter R _d of flattening rollers 22 is too large hardly flattened steel cord 1, the outer diameter R of the flattening rollers 22 _d is preferably at most 55 times the diameter d of the filament.
Further, the load is increased which acts when to flattening the steel cord 1 the outer diameter R _d is too small flattened roller 22, the life of the flattening rollers 22 is shortened. Therefore, the outer diameter R _d of flattening rollers 22 is preferably at least 33 times the filament.

The influence of the outer diameter of the flattening roller 22 on the flattening efficiency of the steel cord 1 is great. In order to achieve flattening without excessively pressing the filaments 11 to 14 by the flattening rollers 22 arranged in a staggered manner, the steel cord is in a relationship with the diameter d of the filaments 11 to 14 constituting the steel cord 1. It has been found that it is important to select the optimum outer diameter R _d of the flattening roller 22 according to the diameter d of the filaments 11 to 14 constituting 1.
However, if the flattening roller 22 having an extremely small outer diameter is selected just because the flattening is effective, the strength of the flattening roller 22 is insufficient and the life is shortened, or the bearing of the flattening roller 22 is used. May burn and become unrotatable and may damage the steel cord 1. Therefore, as shown in (Equation 3), flattening roller 22 is preferably selected to have an outer diameter R _d 55 times the 33-fold or more the diameter d of the filament 11 to 14.

<Examples and Reference Examples>
The steel cords according to Examples 1 to 5, 11 to 16, 21 to 27, and 31 to 36 flattened so as to satisfy the above formula (1) according to the present embodiment as described above, the above formula (1) The flattened steel cords according to comparative examples 1, 11, 21, 31 that were not satisfied and the steel cords according to conventional examples 1, 11, 21, 31 that were not flattened were produced and evaluated. The results are shown in Tables 1-5.

Table 1 shows Examples 1 to 5, Comparative Example 1, and Conventional Example 1 in which the number of twists is three steel cords.
Using a steel cord wire of φ5.5 mm containing 0.82% by mass of C, patenting and drawing are repeated, and then the surface is subjected to brass plating. By final drawing, a filament for stranded wire of φ0.480 mm is obtained. Various steel cords were produced using this filament.

(Twist angle)
In Tables 1 and 2, the twist angle indicates a calculated value calculated from the actually measured number of twists, twist pitch, and filament diameter.

(Filament pitch and height)
In a buncher type stranded wire machine, a filament before a twisting opening for giving a habit before twisting was sampled, and the filament was enlarged with a universal projector, and the pitch and height of the wrinkle were measured.

(Outer diameter of flattening roller)
The diameter of the roller part in contact with the filament was defined as the outer diameter of the flattening roller. When a circumferential U-shaped groove was provided on the outer periphery of the roller, the diameter of the groove bottom was defined as the outer diameter of the flattening roller.

(Flat rate)
The major and minor diameters of the steel cord were measured at three locations with a micrometer, and the average value was adopted.

(Rubber penetration)
A rectangular parallelepiped where steel cords are lined up on a rubber sheet for tires at equal intervals (twice the diameter) and then covered with a rubber sheet, resulting in a total thickness of 5 times the diameter of the steel cord. The steel cord is taken out from the steel cord / rubber composite with a cutter knife after being naturally cooled by pressure vulcanization (150 ° × 30 minutes).
Among the filaments constituting the steel cord, one or two filaments were removed by untwisting using a cutter knife, and the rubber intrusion area inside the steel cord was displayed as a percentage.

(Fatigue resistance)
A rubber sheet for a tire is stretched on a drum having a diameter of 500 mm, and the rubber sheet is laminated until the thickness becomes 3 mm. The steel cord is turned around the laminated rubber sheet at equal intervals (twice the diameter of the steel cord) 10 times to cut the steel cord. Thereafter, a rubber sheet for tire is laminated on the steel cord, similarly to the lower side, until the thickness becomes 3 mm to produce a simple belt. Then, this belt is vulcanized and molded together with the drum (150 ° × 30 minutes) and allowed to cool naturally. The fatigue characteristics were evaluated by applying this to a belt tester having a pulley diameter of φ250 mm with 5% of the cord breaking strength applied to the belt.
The fatigue characteristics of the examples and comparative examples when the fatigue strength of the steel cord of the conventional example is set to 100 are shown in the table as indexes. In addition, about each Example, the comparative example, and the prior art example, fatigue characteristics were evaluated twice and the average was shown to the table | surface.

(Comprehensive evaluation)
The evaluation was carried out with the following three items (1) to (3). A case where all satisfactory results were obtained was indicated as ◯, and a case where even one unsatisfactory result was indicated as ×.
(1) Flattening: An evaluation was made based on whether the flattening efficiency at the time of manufacturing the steel cord was good or bad.
(2) Rubber penetration rate: 90% or more was evaluated as good, and less than 90% was evaluated as impossible.
(3) Fatigue resistance test: Evaluated by the time at which the filament of the major diameter portion of the steel cord cross-section was broken.

Each of Examples 1 to 5 is a steel cord having three twists and a bending stress index given by (Equation 1) of 0.35 or less.
Comparative Example 1 is a steel cord having a bending stress index of 0.40.
Conventional Example 1 is a steel cord having a circular cross section that has not been flattened as a reference cord.
In Example 4, the twist angle is 4.5 ° which is smaller than 4.8 °. For this reason, when flattening the steel cord of Example 4, the filament easily escaped and was difficult to manufacture. As a result, the flatness ratio was higher than those of Examples 1 to 3, but the rubber penetration and fatigue resistance were inferior to those of Examples 1 to 3.
In Example 5, the roller outer diameter / filament diameter is 58 which is larger than 55. For this reason, when flattening the steel cord of Example 5, the flattening roller diameter was larger than the filament diameter, and the flattening efficiency was not good. As a result, the flattening rate was as high as in Example 4, but the rubber penetration and fatigue resistance were comparable to those in Examples 1 to 3.

Each of Examples 11 to 16 is a steel cord having four twists and a bending stress index given by (Equation 1) of 0.35 or less.
Conventional Example 11 is a steel cord having a circular cross section that has not been flattened as a reference cord.
Comparative Example 11 is a steel cord having a bending stress index of 0.38 that is greater than 0.35. The rubber penetration was 90%, but the fatigue resistance was below 90.
In Example 15, the twist angle is 4.6 ° which is smaller than 4.8 °. For this reason, when flattening the steel cord of Example 15, the filament easily escaped and was difficult to manufacture. As a result, the flattening rate was higher than those of Examples 11 to 14, but the rubber penetration and fatigue resistance were inferior to those of Examples 11 to 14.
In Example 16, the roller outer diameter / filament diameter is 58 which is larger than 55. For this reason, when flattening the steel cord of Example 16, the flattening roller diameter was larger than the filament diameter, and the flattening efficiency was not good. As a result, the flattening rate was a high value as in Example 15, but the rubber penetration and fatigue resistance were inferior to those in Examples 11-14.

Examples 21 to 27 are all steel cords having five twists and a bending stress index given by (Equation 1) of 0.35 or less.
Conventional Example 21 is a steel cord having a circular cross section that has not been flattened as a reference cord.
Comparative Example 21 is a steel cord having a bending stress index of 0.36 greater than 0.35. The fatigue resistance was below 90.
In Example 26, the twist angle is 4.6 ° which is smaller than 4.8 °. For this reason, when flattening the steel cord of Example 26, the filament easily escaped and was difficult to manufacture. As a result, the flattening rate was higher than those of other Examples 21 to 25, but the rubber penetration and fatigue resistance were inferior to those of Examples 21 to 25.
In Example 27, the roller outer diameter / filament diameter is 57 larger than 55. For this reason, when flattening the steel cord of Example 27, the flattening roller was large with respect to the filament diameter, and the flattening efficiency was not good. As a result, the flattening rate was as high as that of Example 26, but the rubber penetration and fatigue resistance were comparable to those of Examples 21 to 25.

Examples 31 to 36 are all steel cords having six twists and a bending stress index given by (Equation 1) of 0.35 or less.
Conventional Example 31 is a steel cord having a circular cross section that has not been flattened as a reference cord.
Comparative Example 31 is a steel cord having a bending stress index of 0.36 greater than 0.35. The fatigue resistance was below 90.
In Example 35, the twist angle is 4.7 ° which is smaller than 4.8 °. For this reason, when flattening the steel cord of Example 35, the filament easily escaped and was difficult to manufacture. As a result, the flattening rate was higher than those of Examples 31 to 34, but the rubber penetration and fatigue resistance were inferior to those of Examples 31 to 34.
In Example 36, the roller outer diameter / filament diameter is 59 which is larger than 55. For this reason, when flattening the steel cord of Example 36, the flattening roller was large with respect to the filament diameter, and the flattening efficiency was not good. As a result, the flattening rate was as high as that of Example 35, but the rubber penetration and fatigue resistance were comparable to those of other Examples 31 to 34.

  The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1: Steel cord 11, 12, 13: Filament 14: Pointed portion on the long diameter side 20: Flattening device 21: Base 22: Flattening roller 23: Rotating shaft 24: Direction of wire

Claims (5)

A steel cord having a 1 × n single twist structure (n = 3 to 6) in which a hollow portion exists in the center, in which a plurality of filaments are twisted to have an elliptical cross section,
The steel cord used for the tire for motor vehicles whose bending stress index ((sigma) _i ) given by the following Formula (1) is 0.35 or less about the pointed part by the side of the major axis of the ellipse in the section of the steel cord.
σ _i = 3704 × d / (P × n × f) (Formula 1)
Where d: Diameter of the filament constituting the steel cord (mm)
P: Twist pitch of steel cord (mm)
n: Number of twisted steel cords f: Flatness ratio of steel cords (minor axis / major axis x 100 (%)) Twist pitch P and the average layer Kokoro径D _s angle twist obtained by the following formula (2) from α is 4.8 ° or more, a steel cord for vehicle tires according to claim 1.
α = tan ⁻¹ (π × D _s / P) (Formula 2)
α: Steel cord twist angle (°)
D _s : Average diameter of steel cord core layer (mm)
P: Twist pitch of steel cord (mm)   The steel cord used for the automobile tire according to claim 1 or 2, wherein at least one of the filaments has a larger crease shape than the other filaments. A step of twisting a plurality of filaments to obtain a cord of 1 × n single twist structure (n = 3 to 6) having a hollow portion in the center;
The obtained cord is flattened by passing through a plurality of flattening rollers arranged in a staggered manner, and a 1 × n single-stranded structure (n = 3 to 6) having an elliptical cross section having a hollow portion at the center. Obtaining a code, and
The flattening roller is a method of manufacturing a steel cord used for an automobile tire that satisfies the following (Equation 3).
33d ≦ R _d ≦ 55d (Formula 3)
R _d : Flattening roller outer diameter d: Filament diameter Before twisting a plurality of the filaments,
At least one filament is provided with a habit for facilitating the entry of rubber satisfying the following formula (4):
0.11P ≦ p ₁ ≦ 0.59P, 0.40d ≦ h ₁ ≦ 4.5d (Formula 4)
The manufacturing method of the steel cord of Claim 4 which gives the habit for facilitating the flattening which satisfy | fills following Formula (5) to the said remaining filament.
0.11P ≦ p ₂ ≦ 0.50P, 0.10d ≦ h ₂ ≦ 2.5d (Formula 5)
p ₁ : Pitch pitch h ₁ for facilitating rubber intrusion p ₁ : Spike wave height for facilitating rubber penetration p ₂ : Pitch pitch h ₂ for facilitating flattening The height of the habit to make

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