JP2001288685A - Steel cord - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve penetration of rubber into a steel cord. SOLUTION: This steel cord (2/5 steel cord) is made by twisting two core wires and five side wires to have an oval cross section. One wire (a) out of two core wires (a), b is excessively embossed and the core wires and the side wires are integrally twisted and processed to be flat and to have the oval cross section. The aforesaid one core wire (a) always lies between a pair of adjacent specific wires A, B. Thus, the oval cross section becomes uniform throughout the whole range of the steel cord and reduction of fatigue strength accompanied by generation of excess stress is prevented. A rubber is well penetrated into the steel cord during calendering. As the rubber is filled into the steel cord in a high filling rate, fretting is prevented and durability is improved. A steel radial tire uses the aforesaid steel cord.

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 twisted together. This is referred to as "2/5 steel code"), in which the short diameter and the long diameter of the cross section are substantially uniform over the entire length of the steel cord, and when the steel cord is 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 strands and a plurality of side strands are collectively twisted together has been conventionally used.
The steel cord must have the required strength and a certain degree of flexibility (flexibility). The strength, the number of core strands, the side strands, the wire diameter of the wire, the stiffness, etc. Flexibility is affected. If the number of core strands is three or more, a cavity is formed between the twisted core strands, and the larger the number, the larger the cavity becomes, making it difficult to fill the cavity with rubber. When the number is too large, the gap between the side strands becomes very small, and so it becomes difficult to make rubber sufficiently enter the steel cord. And
Various combinations of the number of two or more core strands and three or more side strands are known, and combinations with various wire diameters are known. Are also known. If the rubber inside the steel cord is not sufficiently filled, the durability of the steel cord decreases. Under the above-mentioned background, two core strands and five side strands, which have been preliminarily molded, are collectively twisted and flattened into an elliptical shape has been proposed (for example, Japanese Patent No. 29201010). This steel cord has two core strands, so that no void can be formed between the twisted core strands, and since there are five side strands, the steel cord has relatively low rubber penetration. It is easy to fill the inside of the steel cord with rubber. By the way, in a 2/5 steel cord in which two molded core strands and five side strands are twisted together and flattened to form an elliptical cross section, two molded core strands are used. Since the wires are twisted with each other, when flattened, the arrangement of the core strands and the side strands in a cross section of one twist pitch is, for example, as shown in FIGS. 2 (a) to 2 (d). ing. That is, focusing on the arrangement of the two core strands, the change is as follows. In FIG. 2 (a), which is a cross section at point 0, the core strands 1a, 1b are separated to the left and right, and in FIG. 2 (b), which is a cross section at a quarter pitch point, the core strands 1a, 1b are vertically shifted. In FIG. 2 (c), which is in close contact, the core strands 1a and 1b are separated to the right and left in FIG. 2 (c), and in FIG. The lines 1a and 1b are in close contact with the lower and upper sides. FIG. 2 (b)
In the position (d), the core strands 1a and 1b which are in close contact with each other on the elliptical minor axis serve as support for flattening, and as a result, are prevented from being crushed to a predetermined minor axis length. . Therefore, as compared with the shorter diameter of the elliptical shape of the steel cord at the positions of FIGS. 2 (a) and 2 (c), 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 strands 1a and 1b are vertically arranged as shown in FIGS. 2 (b) and 2 (d) to support the flattening process because the side strands 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 strands and the core strands are pre-typed, the combination of the side strands and the core strands is not regular, so that the above-mentioned FIG.
The arrangement of the core strands 1a and 1b as shown in (d) is irregularly scattered over the entire length of the steel code. In a cross section in which the arrangement of the core strands and the side strands is not as shown in FIGS. 2B and 2D, a predetermined flattening process is performed, so that the steel coil is formed.
Although the minor axes of the elliptical cross-sections are substantially equal, FIGS. 2 (b) and 2 (d)
In the case of, the minor axis of the elliptical cross section is large and the major axis is small. When so-called calendering is performed by arranging a large number of the above 2/5 steel cords in parallel, the surface of the rubber plate is locally thick at the positions 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 thick portion of the bending plane, that is, a portion where the minor axis of the steel cord is large (a portion where the major axis is small), as a result,
In this part, the fatigue strength decreases.

[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 strands and five side strands together and flattening them. It is an object of the present invention to devise a structure so as to prevent the occurrence of a portion where the core strands are closely arranged vertically and to make the short diameter of the steel cord substantially uniform over its entire length. is there.

[0004]

Means taken to solve the above problem is to twist two core strands and five side strands at once and flatten them to form an elliptical cross section. When one of the two core strands is excessively shaped and the core strands and side strands are twisted together at once, and this is flattened to form an elliptical cross section, The above-mentioned one core strand is always interposed between a specific pair of side strands adjacent to each other.

[0005]

The operation will be described with reference to FIGS. 1 (a) to 1 (d). Of the two core strands, one of the core strands a is overmolded, so the two core strands a and b and the five side strands are twisted together. , Two core strands a, b
Are not twisted with each other, but one overmolded core strand a is twisted around the other core strand b. Therefore, two core strands a, b
Does not adhere. Further, since the one core strand a is excessively shaped, its twist amplitude is large and its twist pitch is equal to the twist pitch of the side strands, so that a specific pair of adjacent strands A, B Are always interposed between them. Therefore, the two core strands a and b are not arranged in close contact with each other up and down, and the pair of side strands A and B are arranged symmetrically about the elliptical minor axis. Even if two core strands a and b are vertically arranged at the position shown in FIG. 1 (b, d), the two core strands a and b adhere to each other in this arrangement as described above. However, one core strand is always interposed between adjacent specific strands A and B. Therefore, the minor 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 amplitude of the overmolded one of the core strands is set to 1.5 to 7.5 times the wire diameter of the core strand.

[0007]

An embodiment will be described with reference to FIG.
Example 1 has a core element wire a having a wire diameter of 0.175 mm and a wire diameter of 0.3.
70 mm side strands A, B ...
The ratio D / d of the minor axis d and the major axis D, which are collectively twisted, is 1.
3 is an elliptical steel cord. The reason why the side strands A, B,... Were excessively shaped in advance is that if the side strands are tightly twisted, it is difficult to crush and flatten the steel cord. Then, the steel cord is loosely twisted, crushed and flattened. This is common practice when flattening steel cords. The diameter of the core strand b is the same as the diameter of the core strand a. The twist pitch of the steel cord is 18 mm, and the amplitude of the core strand a is 2.5 times the wire diameter of the core strand. As a result of measuring the major axis and minor axis of the elliptical cross section of the steel cord of this example in a range of 100 m in length, 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
5 mm. 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 difference between the maximum and minimum of the major axis was 0.11 mm, and the difference of the maximum and minimum of the minor axis was 0.08 mm in the same measurement results as in the above conventional example. In the above embodiment, the core element wire diameter is in the range of 0.17 to 0.22 mm, and the ratio of the side element wire diameter to the core element wire diameter is 1.5 to
This is approximately applicable to the range of 2.0.

[0008]

As described above, according to the present invention, two core strands and five side strands are collectively twisted and flattened to obtain an elliptical cross-section of the steel cord. The length of the major axis and the minor axis of the elliptical cross section can be stably made substantially constant. Therefore, local excessive stress due to in-plane bending force due to the unevenness of the elliptical cross section is prevented from occurring, and a decrease in fatigue strength due to the generation of the excessive stress is prevented. In addition, since one of the core strands is always interposed between a specific pair of side strands adjacent to each other, rubber penetration into the steel cord at the time of calendering is good, and therefore, rubber can enter the inside of the steel cord. The filling rate is high, so fretting is prevented and its durability is improved.

[Brief description of the 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 strand A, B ... side strand

Claims (3)

[Claims] 1. A steel cord in which two core strands and five side strands are twisted together and flattened to form an elliptical cross section, one of the two core strands When the core wire and side wire are twisted collectively and flattened to form an elliptical cross section, the overmolded one of the core wires and the specific pair adjacent to each other Steel cord that is always interposed between the side strands. 2. The steel cord according to claim 1, wherein the amplitude of the overmolded one of the core strands is 1.5 to 7.5 times the wire diameter of the core strand. 3. A steel radial tire in which a large number of the steel cords according to claim 1 or 2 are arranged in parallel and embedded.