JPH08176977A - Rubber-reinforcing steel ford and radial tire using the same - Google Patents

Abstract

PURPOSE: To produce the subject steel cord improved in fatigue resistance and mechanical strength retention, and intended to improve the durability of a pneumatic tire by applying it to esp. the carcass ply of tire. CONSTITUTION: This rubber-reinforcing steel cord has a structure such that at least two coaxial layers 2, 3 each composed of many steel filaments stranded around the central basic structure 1 composed of 1 to 3 steel filaments. The steel cord has the following characteristics: the respective twist directions of the filaments are mutually same; for the filament arrangement. the central basic structure is the closest; for the coaxial layers, the respective diameters of the filaments are equal to one another and there are much number of wires so as to be mutually closed as possible along the circumscribed circle of the immediate inner layer or the central basic structure; for the outermost coaxial layer, there are a number of wires but one or two fewer than that of the above closest case along the circumscribed circle of the immediate inner layer; and there is no spiral wrapping filament 4 around the outermost coaxial layer (e.g. so-called non-spiral structure).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord having improved fatigue resistance and strength retention, which is particularly applied to a carcass ply of a heavy duty radial tire for trucks, buses and light trucks, It is a tire with improved durability.

[0002]

2. Description of the Related Art Generally, during tire running, in steel cords, fretting wear of filaments in the cords reduces the cross-sectional area of the filaments and the cord strength decreases. If the cross-sectional area of only some of the filaments in the cord is drastically reduced at that time, the filaments are likely to be subjected to impact tension and breakage during repeated bending. Once the filament breaks, the tensile stress of other filaments increases, and there is a problem that the fatigue fracture of the cord is promoted.

[0003]

In order to increase the durability of such a cord, it is necessary to prevent some filaments in the cord from prematurely prematurely breaking. It is desirable to be uniform.

The inventors of the present invention investigated the strength reduction of the carcass ply filament due to running of the tire for a cord which was stabilized by lapping the cord with a spiral wrap filament having a layer twist structure and found that the filament of the outermost coaxial layer It was found that the loss of strength was extremely large and that the main cause of the loss of strength was fretting wear with spiral wrap filaments.

Then, as a result of investigating a cord in which the spiral wrap filament, which is the main factor of the decrease in strength, is removed so that fretting due to this is not generated, the fretting by the spiral wrap filament is eliminated and the outermost coaxial layer The decrease in filament strength was less.

However, since the wrap filament has disappeared, the restraint of the cord is poor, and when the cord is bent excessively, the filament becomes disjointed, and an abnormal input occurs in a part of the filament and the filament breaks. Was seen about. In this case, the breaking life of the cord was significantly reduced compared to the cord stabilized by wrapping the cord with a spiral wrap filament. From this phenomenon, it became clear that the filament must be restrained in some form in order to prevent the shortening of the cord life due to an extreme bending input.

In the carcass ply cord having the layer-twisted structure as described above, the spiral wrap filament and the filament of the outermost coaxial layer are maintained while maintaining the filament constraint and suppressing the abnormal input to the filament at the time of large bending input of the cord. Reducing the fretting wear between them and preventing the strength of the outermost coaxial layer filaments from decreasing are left as problems to be urgently solved.

[0008]

The present invention provides (1) 1-3.
In a steel cord with a layer twist structure in which a central basic structure composed of two steel filaments and at least two coaxial layers composed of a large number of steel filaments arranged around this basic structure are twisted, All are twisted in the same direction, and the filament arrangement of the steel cords is the center. The basic structure is the closest arrangement. Within the coaxial layers arranged around the same, the wire diameter is the same. The number of strands that can be arranged on the circumscribed circle of is about 1 or 2 less than the number of strands that can be arranged on the circumscribed circle of the innermost layer of the outermost coaxial layer. A rubber supplement having a so-called non-spiral structure having a number of spiral wrap filaments that do not exist around the outermost coaxial layer. Use on the steel cord.

(2) In the above (1), preferably, the outermost coaxial layer and the one inner layer of the coaxial layers have different twist pitches, and a rubber-reinforcing steel cord.

(3) In (2) above, preferably, the filament diameter excluding the central basic structure of the steel cord is 0.
A steel cord for rubber reinforcement, which is 150 mm or more and 0.200 mm or less.

(4) The steel cord for rubber reinforcement in (3) above is preferably applied to a carcass ply of a pneumatic tire for heavy loads.

[0012]

The present invention will be described in detail below. The non-uniformity of the strength reduction of the filament of the layer twisted cord, especially the extreme reduction of the strength of the outermost coaxial layer filament during tire running, is that the spiral wrap filament is twisted in a direction different from the twisting direction of the outermost coaxial layer filament. This is due to the fact. In this case, since the contact area between the outermost coaxial layer filament and the spiral wrap filament is small, the contact pressure per unit area is large.

Further, when the tire rolls, a twist input is generated in the carcass ply cord of the ground contact portion of the tire in the longitudinal direction of the cord. If a twisting input occurs in the direction where the twist of the outermost coaxial layer is unraveled, if the spiral wrap filament is twisted in a direction different from the twisting direction of the outermost coaxial layer filament, the spiral wrap filament will be twisted. Twist input occurs in the filament, and relative movement occurs between both filaments. When the contact pressure is large and a large relative movement occurs, the spiral wrap filament causes the cross-sectional area of the outermost coaxial layer filament to decrease, and as a result, the strength of the outermost coaxial layer filament decreases.

Similarly, if twists are made in different directions between the coaxial layers of the cord, the contact pressure between the filaments between the layers in that portion increases, and the cross-sectional area of the filaments decreases, resulting in a reduction in the strength of the coaxial layer filaments. Occurs.

In addition, the surface treatment (plating) of the filament is exposed in the portion where the cross-sectional area is reduced (fretting portion), the filament is easily corroded, and the corrosive fatigue of the cord is also adversely affected.

Therefore, in the cord in which the spiral wrap filament for wrapping the layer-twisted cord in which all the coaxial layers are twisted in the same direction is removed, the strength of the filament is not lowered, but the filaments in each layer are arranged in the closest packing. In the cord, when a large bending input is generated as described above, the filaments are separated, an abnormal input occurs in a part of the filaments, the filaments are broken, and the breaking life of the cord is shortened.

On the other hand, in a cord in which the number of strands in the outermost layer is one or two less than the number of strands that can be arranged on the circumscribed circle of the coaxial layer inside the outermost layer, between the strands in the outermost layer. By containing the coating rubber, the outermost layer filament is constrained, an effect equivalent to that of a spiral is obtained, and it is possible to suppress the reduction in the strength of the filament and also to suppress the reduction in the cord breaking life at the time of large bending input.

Further, even in the cord having the above countermeasures, if the diameter of the strand becomes large, the strand breaks when an excessive bending input is applied to the cord. To avoid that,
It is effective to reduce the surface strain of the wire. Generally, the surface strain ε of the wire is approximated by ε = D / 2R (D: wire diameter, R: radius of curvature when the cord is bent). That is, in order to reduce the surface strain ε of the wire under a constant bending input R, it is effective to make the wire diameter D as thin as possible.

Here, the wire diameter for preventing the wire from breaking due to the extreme bending input applied to the carcass ply of the heavy-duty radial tire is the wire diameter that does not break, except for the central basic structure in the cord in which the above effects are taken into consideration. It has been confirmed by experiments by the applicant that the thickness of 0.20 mm or less is particularly preferable. That is, the filament diameter is 0.15 mm
If it is smaller than 0.20 mm, the cord cannot have sufficient strength, and if it is larger than 0.20 mm, the surface strain becomes large, which is not preferable.

Further, in order to make the wire diameter as thin as possible and to secure the necessary cord strength, it is necessary to have three or more coaxial layers, and further, the strength per unit cross-sectional area of the wire ( It is preferable to use a so-called high strength steel material having a tensile strength of 330 kg / cm ² or more.

[0021]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Tire size: 10,00R20 16PR (Radial tire for truck bus) Number of driving: 22.0 drums / 5cm Drum running condition: Speed 60km / h Internal pressure 8 kgf / cm ² (normal) 1 kgf / cm ² (when large bending input) Load JIS 100% load (normal time) JIS 40% load (when large bending input) were conducted under the same test conditions.

As a non-spiral rubber penecord having three layers of unidirectional twist according to the present invention, 1 + 6 + 11 structure (Example 1: ∞ / S / S twist), 1 + 6 + 1 with a thinner wire diameter.
1 structure (Example 2: ∞ / S / S twist) and 3 + 9 + 13 structure (Example 3: S / S / S twist) were compared, and each cord represented by an index with 100 as the cord strength when new Experiments were conducted on the cord strength retention after normal running, the filament breakage rate after large bending input running, and the fretting depth.

As a comparative example, a twist structure 1 + 6 + 12 + 1 which is a cord with a three-layer twist spiral (comparative example 1: control, ∞ / S / S / Z twist), and a twist structure 1 + 6 + 12 which is a three-layer twist non-spiral cord (comparative example 2) :
∞ / S / S twist), 1 + 6 + 12 (Comparative Example 3: ∞ / S /
Z twist) 3 + 9 + 15 + 1 twist structure, which is a cord with three-layer twist spiral (Comparative Example 4: S / S / Z / S twist), three-twist non-spiral twist structure 3+
9 + 15 (Comparative Example 5: S / S / Z twist), 3 + 9 + 15
An experiment was performed on (Comparative Example 6: S / S / S twist).
The results are summarized in Table 1 and Table 2. The diameter of the spiral filament of steel cord in Comparative Examples 1 and 2 is 0.15 mm.

Evaluation method (1) Chord strength retention rate The cord strength retention rate was obtained by measuring the breaking strength at ten carcass cords taken from a drum running tire under normal conditions and measuring the breaking strength at an Instron type tensile tester. To
The value obtained by dividing the average strength of breaking strength of 10 cords pulled out from a new tire is the cord strength retention rate,

[Equation 1] It was expressed by.

(2) Fretting Depth Two wires of each layer of a carcass cord taken out from a drum running tire under normal conditions are taken out two by two, and due to fretting wear in the range of 13 cm ± 2 cm from the center of the tire to both sides. The decrease in wire diameter was measured and the maximum values were compared.

(3) Filament breakage rate at the time of large bending input Ten carcass cords of a tire which was run on a drum of 10,000 km under a large bending input condition were taken out, the number of broken filaments was counted, and the number of broken filaments was calculated. What was divided by the total number of filaments and expressed as a percentage was taken as the filament breakage rate. The lower the filament breakage rate, the better.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As described above, according to the steel cord of the present invention, the fretting wear of the outermost coaxial layer filament due to the spiral wrap filament is reduced, and the strength reduction of the filament in the cord is suppressed. Therefore, the life of the cord is improved. Further, a pneumatic tire using the same also has an effect of improving tire durability.

[0030]

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention, 1 + 6 + 11.
It is sectional drawing of the layer twisted cord of a structure.

FIG. 2 is an embodiment of the present invention, 3 + 9 + 13.
It is sectional drawing of the layer twisted cord of a structure.

FIG. 3 is a comparative example of the present invention, 1 + 6 + 12.
It is sectional drawing of the layer twisted cord of +1 structure.

FIG. 4 is a comparative example of the present invention, 3 + 9 + 15.
It is sectional drawing of the layer twisted cord of +1 structure.

FIG. 5 represents the amplitude of the filament.

FIG. 6 depicts fretting depth.

[Explanation of Codes] 1 ... Core filament 2 ... First sheath filament 3 ... Second sheath filament 4 ... Spiral wrap filament H ... Amplitude of filament Df ... Fretting depth

Claims (4)

[Claims] 1. A layer-twisted structure steel in which a central basic structure composed of one to three steel filaments and at least two coaxial layers composed of a large number of steel filaments arranged around this basic structure are twisted together. In the cord, all the filaments are twisted in the same direction, the filaments of the steel cord are arranged in the center, and the basic structure is the closest packing. In the coaxial layer arranged around the filaments, the wires having the same diameter are arranged. , The number of strands that can be arranged on the circumscribed circle of the inner layer of one layer or the central basic structure, and the number of strands of wire that can be arranged on the circumscribed circle of the inner layer of one layer for the outermost coaxial layer It has a so-called non-spiral structure in which the number of strands is one or two less and the spiral wrap filament does not exist around the outermost coaxial layer. Steel cord for rubber reinforcement characterized by 2. A steel cord for rubber reinforcement, wherein the outermost coaxial layer of the steel cord according to claim 1 and the coaxial layer of one inner layer thereof have different twist pitches. 3. A steel cord for rubber reinforcement, wherein the filament diameter excluding the central basic structure of the steel cord in claim 1 is 0.150 mm or more and 0.200 mm or less. 4. A heavy-duty radial tire in which the steel cord for rubber reinforcement according to any one of claims 1 to 3 is applied to a carcass ply.