JP3464960B2 - Steel cord - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord for reinforcing a rubber material such as a tire, in particular, a steel cord having an elliptical cross section in which two core strands and five side strands are bundled together. This is referred to as "2/5 steel cord"), and the minor axis length and major axis length of the cross section of the entire length of the steel cord are substantially uniform, and when embedded in the rubber material of the tire. It is possible to improve the penetration of rubber into the steel cord.

[0002]

2. Description of the Related Art A steel cord in which a plurality of core wires and a plurality of side wires are collectively twisted together has been conventionally used.
The steel cord is required to have a required strength and a predetermined flexibility (flexibility). Depending on the number of core wires, side wires, wire diameter, twist hardness, etc., the above strength, Flexibility is affected. When the number of core wires is 3 or more, cavities are formed between the twisted core wires, and the larger the number, the larger the cavities, and it becomes difficult to fill the cavities with rubber. If the number of wires increases, the gap between the side strands becomes very small, which makes it difficult to sufficiently infiltrate the rubber into the steel cord. And
Various combinations of the number of core wires of 2 or more and the number of side wires of 3 or more and various wire diameters are known, and the ratio of the major and minor diameters of the elliptical shape is known. Various ones are known. If the inside of the steel cord is not fully filled with rubber, the durability of the steel cord will decrease. Under the above-mentioned background, it has been proposed that two pre-shaped core element wires and five side element wires are collectively twisted and flattened into an elliptical shape (for example, Japanese Patent No. 2920110). In this steel cord, since there are two core wires, no cavity can be formed between the twisted core wires, and since there are five side wires, it is relatively rubber-penetrating. Since it is good, it is easy to fill the steel cord with rubber. By the way, in a 2/5 steel cord in which two shaped core element wires and five side element wires are twisted together and flattened into an elliptical cross section, the two shaped core elements are Since the wires are twisted with each other, when flattened, the arrangement of the core wires and the side wires in the cross section between 1 pitch of twist is as shown in, for example, FIGS. 2 (a) to 2 (d). ing. That is, focusing on the arrangement of the two core wires, the changes are as follows. In FIG. 2 (a), which is a cross section at 0 point, the core strands 1a and 1b are separated from each other in the left and right, and in FIG. In FIG. 2 (c), which are in close contact with each other and have 2/4 pitch points, the core wires 1a and 1b are separated from each other on the right and left, and in FIG. 2 (d), which is a cross section at 3/4 pitch points, The lines 1a and 1b are in intimate contact with the bottom and top. 2 (b),
At the position (d), the core wires 1a and 1b that are in close contact with each other on the short diameter of the ellipse serve as a support for flattening, and as a result, are prevented from being crushed to a predetermined short diameter. . Therefore, compared with the elliptical minor axis of the steel cord at the positions shown in FIGS. 2 (a) and 2 (c), as shown in FIG.
The minor axis of (d) is large (that is, the major axis Ds of FIG. 2B is smaller than the major axis Dc of FIG. 2A. Also, FIG. 2D).
Is also small). The two core wires 1a and 1b are arranged vertically as shown in FIGS. 2 (b) and 2 (d) to support flattening. The side wires are symmetrical about the minor axis of the ellipse. And the core wires 1a and 1b are arranged on the minor axis. However, since the side element wires and the core element wires are pre-shaped, the combination of the arrangement of the side element wires and the arrangement of the core element wires is not regular. Therefore, as shown in FIG.
The arrangement of the core wires 1a and 1b as shown in (d) is irregularly scattered over the entire length of the steel cord. In the cross section where the arrangement of the core wire and the side wire is not as shown in FIGS. 2 (b) and 2 (d), a predetermined flattening process is performed, so the steel coil
2 (b) and 2 (d), although the minor axis of the elliptical cross section of the
In the case of, the short diameter of the elliptical cross section is large and the long diameter is small. When a large number of the above 2/5 steel cords are arranged in parallel and subjected to so-called calendering, the surface of the rubber plate is locally thick at the position of the arrangement shown in FIGS. become. When an in-plane bending force is applied to a plate having an uneven thickness in this way, bending stress concentrates on a portion where the thickness is large on the bending plane, that is, a portion where the short diameter of the steel cord is large (the portion where the long diameter is small). as a result,
Fatigue strength is reduced in this portion.

[0003]

SUMMARY OF THE INVENTION The present invention is based on the recognition of the above problems, and relates to a steel cord obtained by twisting two core wires and five side wires together and flattening them. The problem is to devise a structure so that the core wire is prevented from being arranged in close contact with each other in the vertical direction and the short diameter of the steel cord is substantially equal over its entire length. is there.

[0004]

[Means for Solving the Problems] Means taken for solving the above-mentioned problems are as follows. Two core wires and five side wires are twisted together and flattened into an elliptical cross section. In the steel cord described above, when one of the two core wires is excessively shaped, the core wire and the side wire are twisted together and flattened into an elliptical cross section, 2 Book
The core wires of are not overwhelmed with each other
One core wire that has been stripped is centered on the other core wire.
That is, one of the above-mentioned core wires twisted around and shaped excessively always intervenes between a specific pair of adjacent side wires.

[0005]

The operation will be described with reference to FIGS. 1 (a) to 1 (d). When one core wire a of the two core wires is oversized, when two core wires a and b and five side wires are twisted together Two core wires a and b
Are not twisted with each other, but one over-shaped core wire a is twisted around the other core wire b. Therefore, the two core wires a and b
Will never come into close contact with each other. Further, since the one core wire a is overshaped, the twisting amplitude is large, and the twisting pitch is equal to the twisting pitch of the side wires. Therefore, a specific pair of adjacent side wires A and B are provided. It is twisted together with these always intervening. Therefore, the two core wires a and b are not vertically arranged in close contact with each other, and the pair of side wires A and B are arranged symmetrically with respect to the short diameter of the elliptical shape. At this position, even if the two core wires a and b are vertically arranged [FIG. 1 (b, d)], both core wires a and b are closely attached in this arrangement as described above. None, and one core wire is always interposed between the adjacent specific side wires A and B. Therefore, the short diameter of the elliptical shape of the steel cord does not locally increase. Therefore, the elliptical cross section of the steel cord is uniform over its entire length.

[0006]

[Embodiment 1] The overmolded one of the core wires has an amplitude of 1.5 to 7.5 times the diameter of the core wire.

[0007]

EXAMPLES Examples will be described with reference to FIG.
Example 1 has a core wire a having a wire diameter of 0.175 mm and a wire diameter of 0.3.
70mm side strands A, B ... are over-shaped in advance,
Ratio D / d = 1.
3 is a steel cord having an elliptical cross section. It should be noted that the side strands A, B, ... are over-shaped in advance because it is difficult to flatten the steel cord by crushing the steel cord if the side strands are densely twisted. Then, the steel cord is twisted loosely and crushed and flattened. This is normally done when flattening a steel cord. The core wire b has the same diameter as the core wire a. The twist pitch of the steel cord is 18 mm, and the amplitude of the core wire a is 2.5 times the wire diameter of the core wire. With respect to the steel cord of this example, the major axis and the minor axis of the elliptical cross section were measured in the range of 100 m in length, and the maximum major axis was 1.33 m.
m, the minimum is 1.28 mm, and the difference between the minimum and maximum is 0.0
It was 5 mm. Moreover, the maximum of the minor axis is 1.02 mm, the minimum is 0.99 mm, and the difference between the maximum and the minimum is 0.03 mm.
Met. Incidentally, the maximum and minimum difference in major axis and the maximum and minimum difference in minor axis in the same measurement results for the above-mentioned conventional example were 0.18 mm and 0.08 mm, respectively. In the above examples, the diameter of the core wire is in the range of 0.17 to 0.22 mm, and the ratio of the wire diameter of the side wire to the wire diameter of the core wire is 1.5 to.
It almost fits in the range of 2.0.

[0008]

As described above, according to the present invention, two core wires and five side wires are bundled together and flattened to have an elliptical cross section. The major axis and minor axis of the elliptical cross section can be stably made substantially constant. Therefore, it is possible to prevent the local overstress from being generated due to the in-plane bending force due to the nonuniformity of the elliptical cross-section, and to prevent the fatigue strength from being lowered due to the occurrence of the overstress. In addition, since one of the core wires is always present between the specific pair of adjacent side wires, rubber penetration into the steel cord is good at the time of calendering. The filling rate is high, which prevents fretting and improves its durability.

[Brief description of drawings]

FIG. 1 is a sectional view of a steel cord according to an embodiment.

FIG. 2 is a sectional view of a conventional steel cord.

[Explanation of symbols]

a, b, 1a, 1b ... Core wire A, B ... Side wires

Claims (3)

(57) [Claims] 1. A steel cord in which two core wires and five side wires are twisted together and flattened to have an elliptical cross section, one of the two core wires When the core wire and the side wire are twisted together and flattened into an elliptical cross section, the two core wires are twisted together.
Without being overmolded, one overstranded core wire
A steel cord twisted around one core wire around the other core wire so that the one oversized one of the core wires is always present between a specific pair of adjacent side wires. 2. The steel cord according to claim 1, wherein the over-shaped one core wire has a molding amplitude of 1.5 to 7.5 times the wire diameter of the core wire. 3. A steel radial tire in which a large number of steel cords according to claim 1 or 2 are arranged in parallel and embedded.