JP3606475B2 - Steel cord for reinforcing rubber articles and pneumatic radial tire - Google Patents

Description

【００２２】
【表２】

【００２３】
上記表１および表２から明らかなように、本発明のスチールコードは、比較例に比べて大幅にコアフィラメントの破断寿命が延びていることが分かる。
【００２４】
【発明の効果】
以上説明してきたように本発明のスチールコードにおいては、ラップフィラメントを除去したことでシースフィラメントとラップフィラメントとのフレッティング摩耗がなくなり、かつコアフィラメントに型付けを施しその型付け率を所定の範囲に限定したことにより、その破断寿命が大幅に改善されるという効果が得られる。よって、かかるスチールコードを補強材として用いた空気入りタイヤの走行寿命は、ばらつきなく安定してかつ大幅に向上する。
【図面の簡単な説明】
【図１】（ア）は、コードの理想直径Ｄを表す説明図である。
（イ）は、コアフィラメントの振幅Ｈを表す説明図である。[0001]
[Industrial application fields]
The present invention relates to a steel cord for reinforcing rubber articles, and more particularly, to a steel cord for reinforcing rubber articles having an improved fracture life and a pneumatic radial tire using the cord as a carcass ply cord.
[0002]
[Prior art]
Conventionally, steel cords used for large tires for trucks and buses are well known to have a 3 + 9 + 1 structure composed of three core filaments, nine sheath filaments, and one wrap filament.
[0003]
[Problems to be solved by the invention]
In such a steel cord having a 3 + 9 + 1 structure, one wrap filament wound around the outer side of 12 filaments is removed, and the number of 9 sheath filaments is further reduced to 7 to 8 steel cords. The fretting wear between the wrap filament and the sheath filament during running is eliminated, and the number of sheath filaments is reduced, so that rubber can easily enter the inside of the cord and the contact between each filament is eased. Decline can be prevented.
[0004]
However, when a pneumatic tire using a steel cord having such a 3 + 7 structure or a 3 + 8 structure as a reinforcing material was actually run, there was a problem that the running life varied greatly.
[0005]
Accordingly, an object of the present invention is to investigate the cause of such variations in running life, to improve the breaking life of steel cords having a 3 + 7 structure or a 3 + 8 structure, and to stably extend the running life of a pneumatic tire without variation. is there.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor has conducted earnest research on the behavior of the reinforcing cord of a running tire, and has obtained the following knowledge.
[0007]
During running, an input such as pulling or bending is applied to the reinforcing steel cord of the tire, and at that time, repeated contact pressure is generated at the contact portion between the filaments in the cord. In the portion where the contact pressure is generated, material fatigue of the steel filament occurs, which becomes the core of fracture. Here, in a structure such as a 3 + 7 or 3 + 8 structure in which there is no wrap filament and a gap is provided between the sheaths so that rubber can easily enter the inside of the cord, the contact portion between the cores where the steel filaments are in direct contact It was found that the largest contact pressure was generated in the film, and that the tendency to become the core of fracture was high. In other words, the filaments that make up the steel cord are usually twisted after being bent into a corrugated shape, but if this molding rate is small, the force to return the twist increases, and the filament between the core and the core in contact with each other It has been found that the contact pressure increases and the progress of material fatigue increases.
[0008]
Therefore, as a result of further diligent research based on such knowledge, the present inventor performed mold forming on the core filament, and when the mold forming rate was limited to a predetermined range, the contact pressure at the contact portion between the core and core was It has been found that it can be lowered, and the present invention has been completed.
[0009]
That is, the present invention comprises a two-layer structure of a core in which three steel filaments are twisted together and a sheath in which 7 to 8 steel filaments are twisted at a different pitch from the core. In the steel cord for reinforcing rubber articles in which no wrap filament is wound around, all the filaments constituting the core are molded into a corrugated shape,
F = H / D
(Where H represents the amplitude of the core filament, D represents the ideal diameter of the cord excluding the sheath filament), and the filament forming rate F is 0.95 or more, and the filament diameter of each filament is 0. The present invention relates to a steel cord for reinforcing rubber articles characterized by being 20 to 0.24 mm.
[0010]
The present invention also relates to a pneumatic radial tire using the steel cord for reinforcing rubber articles as a ply cord.
[0011]
Here, the ideal diameter D of the cord excluding the sheath filament refers to the diameter of the circumscribed circle of the core filament layer in the cord cross section when it is assumed that the three core filaments are twisted together without any gap (see FIG. 1 (I)). The amplitude H of the core filament is the amplitude of the waveform when the filament is bent and twisted into a waveform (FIG. 1 (b)).
[0012]
[Action]
The steel cord of the present invention has a core filament molding rate F defined by the above formula of 0.95 or more, which is significantly better than the steel cord having a value less than 0.95. It becomes. Therefore, in the pneumatic tire using such a steel cord as a reinforcing material, variation in running life is reduced, and a longer life is achieved.
[0013]
In the present invention, by removing the wrap filaments, the contact pressure between the filaments is reduced, and the development of corrosion cracks generated from the contact portions between the filaments is suppressed.
[0014]
Further, in order to ensure good rubber penetration between the core and the sheath, the pitch of the core filament is made different from the pitch of the sheath filament. Preferably, the core pitch: sheath pitch is about 1: 2.
[0015]
In the present invention, it is preferable that all filaments have substantially the same wire diameter. This is because the manufacturing cost increases when a plurality of types of filament diameters are used in combination in the cord.
[0016]
Moreover, it is preferable that the twist direction of a core and a sheath is the same direction. This is because in a different direction, the contact angle at the contact portion between the core and the sheath increases, the contact pressure between the core and the sheath increases, and the fatigue resistance of the cord decreases.
[0017]
If the number of sheath filaments is 6 or less, the filament diameter must be increased in order to maintain the necessary cord strength, which causes a problem in the breaking life. As described above, it is difficult for rubber to enter the inside of the cord, which causes a problem in corrosion resistance.
[0018]
Furthermore, in the present invention, the filament diameter of each filament is preferably 0.20 to 0.24 mm. If this wire diameter is thinner than 0.20 mm, the strength per unit area of the tire side part, that is, the safety factor cannot be sufficiently maintained when used as a ply cord of a tire, and the side cut resistance is inferior. On the other hand, if the thickness is larger than 0.24 mm, it is difficult to improve the fracture life. More preferably, the filament diameter of each filament is 0.21 to 0.23 mm.
[0019]
【Example】
Next, the present invention will be specifically described with reference to examples and comparative examples.
Steel cords according to the following Table 1 and Table 2 were made as trial products.
Trial steel cords were applied to the carcass ply at a driving number of 30 / 5cm to produce radial tires for trucks and buses of size 10.00R20, and the core filaments of the tires after the actual running of 100,000 km were broken. The lifetime was obtained from the following formula and expressed as an index with Example 1 as 100. The smaller the value, the better the fatigue resistance of the core filament.
[0020]
Core filament breaking rate = {(total number of core filaments broken in cord taken out of tire / total number of core filaments in cord taken out of tire)} × 100
The obtained results are shown in Table 1 and Table 2 below.
[0021]
[Table 1]

[0022]
[Table 2]

[0023]
As is apparent from Tables 1 and 2 above, it can be seen that the steel cord of the present invention has a significantly longer core filament fracture life than the comparative example.
[0024]
【The invention's effect】
As described above, in the steel cord of the present invention, by removing the wrap filament, the fretting wear between the sheath filament and the wrap filament is eliminated, and the core filament is molded and its molding rate is limited to a predetermined range. By doing so, the effect that the fracture life is significantly improved can be obtained. Therefore, the running life of a pneumatic tire using such a steel cord as a reinforcing material is stable and greatly improved without variation.
[Brief description of the drawings]
FIG. 1A is an explanatory diagram showing an ideal diameter D of a cord.
(A) is explanatory drawing showing the amplitude H of a core filament.

Claims (2)

It consists of a two-layer structure consisting of a core in which three steel filaments are twisted and a sheath in which seven to eight steel filaments are twisted around the core at a different pitch from the core. In steel cords for reinforcing rubber articles that are not wound,
All the filaments that make up the core are molded into a waveform,
F = H / D
(Where H represents the amplitude of the core filament, D represents the ideal diameter of the cord excluding the sheath filament), and the filament forming rate F is 0.95 or more, and the filament diameter of each filament is 0. Steel cord for reinforcing rubber articles, characterized by being 20 to 0.24 mm . A pneumatic radial tire using the steel cord for reinforcing rubber articles according to claim 1 as a ply cord.

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