STEEL CORD FOR REINFORCING RUBBER ARTICLES AND RUBBER CRAWLER AND TIRE USING SAME

Abstract

Provided is a steel cord for reinforcing rubber articles, which can prevent a reduction in the strength of the steel cord caused by twisting steel filaments, and a tire and a crawler using the steel cord. Provided is a steel cord 1 for reinforcing rubber articles formed by twisting a plurality of sheath strands 3 are twisted around a core strand 2, and the core strand 2 comprises: a core composed of two core filaments 2a aligned in parallel without being twisted; and at least one sheath composed of a plurality of sheath filaments 2b twisted around the core, and a diameter dc of the core filament 2a and a diameter ds of the sheath filament 2b satisfy the following expression (1):

dc<ds (1)

and the tensile strength T (MPa) of the core filament 2a satisfies the relationship represented by the following expression (2):

T<365017000(dc0.15).sup.2 (2).

Claims

1. A steel cord for reinforcing rubber articles formed by twisting a plurality of sheath strands in which a plurality of steel filaments are twisted around a core strand in which a plurality of steel filaments are twisted, characterized in that the core strand comprises: a core composed of two core filaments aligned in parallel without being twisted; and at least one sheath composed of a plurality of sheath filaments twisted around the core, and a diameter dc of the core filament and a diameter ds of the sheath filament satisfy the following expression (1):
dc<ds (1) and the tensile strength T (MPa) of the core filament satisfies the relationship represented by the following expression (2):
T<365017000(dc0.15).sup.2 (2).

2. The steel cord for reinforcing rubber articles according to claim 1, wherein a structure of the core strand is a structure comprising a core composed of two core filaments and a first sheath composed of m sheath filaments formed around the core, or a structure comprising a core composed of two core filaments, a first sheath composed of m sheath filaments formed around the core, and a second sheath composed of n sheath filaments formed around the first sheath, where m is from 5 to 7, and n is from 10 to 15.

3. The steel cord for reinforcing rubber articles according to claim 1, wherein the diameter dc of the core filament is from 0.15 to 0.40 mm.

4. The steel cord for reinforcing rubber articles according to claim 1, wherein the tensile strength T of the core filament is 2,500 MPa or more.

5. The steel cord for reinforcing rubber articles according to claim 1, wherein the diameter dc of the core strand and the diameter ds of the sheath filament satisfy the relationship represented by the following expression (3):
dc>0.5ds (3).

6. The steel cord for reinforcing rubber articles according to claim 2, wherein the diameter dc of the core filament is from 0.15 to 0.40 mm.

7. The steel cord for reinforcing rubber articles according to claim 2, wherein the tensile strength T of the core filament is 2,500 MPa or more.

8. The steel cord for reinforcing rubber articles according to claim 2, wherein the diameter dc of the core strand and the diameter ds of the sheath filament satisfy the relationship represented by the following expression (3):
dc>0.5ds (3).

9. The steel cord for reinforcing rubber articles according to claim 3, wherein the tensile strength T of the core filament is 2,500 MPa or more.

10. The steel cord for reinforcing rubber articles according to claim 3, wherein the diameter dc of the core strand and the diameter ds of the sheath filament satisfy the relationship represented by the following expression (3):
dc>0.5ds (3).

11. The steel cord for reinforcing rubber articles according to claim 4, wherein the diameter dc of the core strand and the diameter ds of the sheath filament satisfy the relationship represented by the following expression (3):
dc>0.5ds (3).

12. A rubber crawler, comprising: a reinforcing rubber article including the steel cord according to claim 1.

13. A rubber crawler, comprising: a reinforcing rubber article including the steel cord according to claim 2.

14. A rubber crawler, comprising: a reinforcing rubber article including the steel cord according to claim 3.

15. A rubber crawler, comprising: a reinforcing rubber article including the steel cord according to claim 4.

16. A rubber crawler, comprising: a reinforcing rubber article including the steel cord according to claim 5.

17. A tire, comprising: a reinforcing rubber article including the steel cord according to claim 1.

18. A tire, comprising: a reinforcing rubber article including the steel cord according to claim 2.

19. A tire, comprising: a reinforcing rubber article including the steel cord according to claim 3.

20. A tire, comprising: a reinforcing rubber article including the steel cord according to claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a cross-sectional view of a steel cord for reinforcing rubber articles according to one suitable embodiment of the present invention.

[0017] FIG. 2 is a cross-sectional view in the width direction of a rubber crawler according to one suitable embodiment of the present invention.

[0018] FIG. 3 is one side cross-sectional view of a tire according to one suitable embodiment of the present invention.

[0019] FIG. 4 is a graph illustrating an expression (2) and relationships between diameters dc and tensile strengths of core filaments of core strands of Examples and Comparative Examples, including prophetic Examples and prophetic Comparative Examples.

MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, a steel cord for reinforcing rubber articles of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a steel cord for reinforcing rubber articles according to one suitable embodiment of the present invention. A steel cord 1 of the present invention has a multi-twisted structure in which a plurality of sheath strands 3 in which a plurality of steel filaments are twisted are twisted around a core strand 2 in which a plurality of steel filaments are twisted. Although, in the illustrated example, six sheath strands 3 are twisted around one core strand 2, the structure of a steel cord of the present invention is not limited thereto, and for example, the number of sheath strands may be from 6 to 10.

[0021] In the steel cord 1 of the present invention, the core strand 2 comprises a core composed of two core filaments 2a aligned in parallel without being twisted and at least one sheath composed of a plurality of sheath filaments 2b twisted around the core. In the steel cord 1 of the present invention, the structure of the core strand 2 is preferably a structure composed of a core composed of two core filaments 2a and a first sheath composed of m sheath filaments 2b formed around the core, or a structure composed of a core composed of two core filaments 2a, a first sheath composed of m sheath filaments 2b formed around the core, and a second sheath composed of n sheath filaments 2b formed around the first sheath, where m is 5 to 7 and n is 10 to 15. That is, preferably, a 2+m structure or a 2+m+n structure, where m is from 5 to 7, and n is from 10 to 15, and in the illustrated steel cord 1, the core strand 2 has a 2+6 structure. When the structure of the core strand 2 has such a structure, productivity of a steel cord is not compromised and sufficient strength can be obtained.

[0022] In the steel cord of the present invention, the diameter dc of a core filament 2a of the core strand 2 and the diameter ds of a sheath filament 2b satisfy the following expression (1):

dc<ds (1),

or preferably, the following expression (4):

dc<0.92ds (4).

As the diameter of the core filament 2a of the core strand 2 is closer to the diameter of the sheath filament 2b of the core strand 2, the roundness of the final multi-twisted steel cord deteriorates and the cross section of the cord becomes elliptical. In cases in which such a steel cord having poor roundness is used to manufacture a product, when the steel cord passes through a complicated path in a processing step, the steel cord is twisted halfway and a molding operation of the product deteriorates.

[0023] Further, in the steel cord 1 of the present invention, the diameter dc of the core filament 2a of the core strand 2 and the diameter ds of the sheath filament 2b satisfy the following expression (3):

dc>0.5ds (3).

When the diameter of the core filament 2a becomes too small, the core becomes small, and therefore, a gap between the sheath filaments 2b becomes small and the rubber permeability of the core strand 2 may deteriorate.

[0024] Still further, in a steel cord 1 of the present invention, the tensile strength T (MPa) of the core filament 2a constituting the core strand 2 needs to satisfy a relationship represented by the following expression (2):

T<365017000(dc0.15).sup.2 (2).

By using the steel filament satisfying such requirements for the core filament 2a of the core strand 2, preceding breakage of the core filament 2a can be prevented.

[0025] When the diameter dc of the core filament 2a of the core strand 2 is large, in order to satisfy the relationship of the above expression (2), the tensile strength of the core filament 2a must be reduced, which increases the risk of preceding breakage of the core filament 2a and may increase the twisting loss. Accordingly, in the steel cord 1 of the present invention, the diameter dc of the core filament 2a of the core strand 2 is preferably in the range of from 0.15 to 0.40 mm, more preferably from 0.15 to 0.35 mm, and further preferably from 0.15 to 0.33 mm. When the diameter dc of the core filament 2a of the core strand 2 is in the above range, the effect of the present invention can be favorably obtained without deteriorating the productivity of the steel cord.

[0026] In the steel cord 1 of the present invention, the tensile strength T of the core filament 2a of the core strand 2 is preferably 2,500 MPa or more. This is because when the tensile strength T of the core filament 2a of the core strand 2 is less than 2,500 MPa, a strength of the finally obtained steel cord is not sufficient in some cases. The tensile strength T of the steel filament can be adjusted by changing the wire drawing conditions. For example, when processing distortion of a steel filament at a time of wire drawing is reduced, a steel filament with a small tensile strength T can be obtained.

[0027] It is important for the steel cord 1 of the present invention to satisfy the above requirements, and there is no other particular limitations on the steel cord 1. For example, the twist pitch and twist direction of the sheath filaments 2b constituting the core strand 2 can be appropriately selected according to a conventional method. Although in the illustrated example, a sheath strand 3 has a 1+6 structure in which six sheath filaments 3b are twisted around one core filament 3a, in the steel cord 1 of the present invention, the structure of the sheath strand 3 is not particularly limited. A 3+9, 3+9+15, 1+6+12 structure or the like other than the 1+6 structure may be employed.

[0028] The diameter of the core filament 3a and the diameter of the sheath filament 3b constituting the sheath strand 3 may be the same or different, and further, the twist pitch and twist direction of the sheath filaments 3b constituting the sheath strand 3 can also be appropriately selected according to a conventional method. Still further, the twist direction, the twist pitch and the like of the strand are also not particularly limited, and can be appropriately selected according to a conventional method.

[0029] Next, a rubber crawler of the present invention will be described.

[0030] A rubber crawler of the present invention is a rubber crawler using a steel cord for reinforcing rubber articles of the present invention. FIG. 2 is a cross-sectional view in the width direction of a rubber crawler according to one suitable embodiment of the present invention. In the illustrated rubber crawler 10, a steel cord 1 of the present invention which is a reinforcing material is coated with a treat rubber 11, and some of a metal core 14 having a detachment prevention protrusion 12 and a wing portion 13 on the inner peripheral surface side is embedded in a rubber member 16 formed with a lug 15 on an installation surface side.

[0031] In the rubber crawler 10 of the present invention, as long as the steel cord 1 of the present invention is used as a tensile body, for other structures and the material of each member, those commonly used may be appropriately adopted, and they should not be particularly limited. For example, the same rubber composition as that of a treat rubber 11 may be adopted as a rubber composition forming a rubber member 16, and in this case, the thickness of the treat rubber 11 may be appropriately selected to arrange the rubber member 16 while considering a thickness formed by the rubber member 16.

[0032] Next, a tire according to the present invention will be described.

[0033] A tire of the present invention is a tire using a steel cord for reinforcing rubber articles of the present invention. For example, the steel cord of the present invention can be used as a reinforcing material for a carcass ply or a belt. Since the steel cord of the present invention has a multi-twisted structure and the core strand is excellent in rubber permeability, the steel cord can be suitably used for large tires or the like for off-road use such as tires for construction vehicles traveling on a wasteland.

[0034] FIG. 3 is one side cross-sectional view of a tire according to one suitable embodiment of the present invention. The illustrated tire 20 is a construction vehicle tire comprising: a carcass 22 composed of a ply extending in the radial direction between a pair of bead cores 21; a belt 23 composed of at least two (six in the illustrated example) belt layers arranged on the outer side in the tire radial direction of a crown portion of the carcass 22; and a tread 24 arranged on the outer side in the tire radial direction of the belt 23. In the tire 20 of the present invention, as long as the steel cord 1 of the present invention is used as a reinforcing member, for other tire structures and the material of each member, those commonly used may be appropriately adopted, and they are not particularly limited.

EXAMPLES

[0035] Hereinafter, the present invention will be described in more detail by way of Examples. Examples 3 and 4 and Comparative Examples 3, 4 and 5 are prophetic examples and prophetic comparative examples, respectively.

Examples 1 to 5 and Comparative Examples 1 to 5

[0036] Steel cords having the structures listed on Tables 1 to 3 were prepared. The strengths of the steel cords and the tensile strength of a steel filament constituting the steel cord are as listed on the same tables, and FIG. 4 is a graph illustrating an expression (2) and relationships between diameters dc and tensile strengths of core filaments of core strands of Examples and Comparative Examples. Measurement of the strength of the steel cords and measurement of the tensile strength of the steel filaments constituting the steel cords were carried out in accordance with JIS G 3510. The tensile strength T of the steel filaments was adjusted by controlling the wire drawing conditions. For each prepared steel cord, the twisting loss and presence or absence of a preceding breakage of a core filament of a core strand were evaluated. A calculation expression of the twisting loss is as follows.

(Twisting Loss)

[0037] The twisting loss (%) was calculated according to the following expression.

twisting loss (%)=(sum of filament strength (N)measured value of cord strength (N))/sum of filament strength (N)100

Here, the sum of filament strength is a total value of strengths of filaments constituting the steel cord, each filament not being twisted.

TABLE-US-00001 TABLE 1 Comparative Example 1 Example 1 Comparative Example 2 Example 2 Structure [00001] [00002] 2 0.28 + 6 0.36 + 2 0.30 + 6 0.36 + 6 (0.36 + 6 0.33) 6 (0.36 + 6 0.33) Twist Core strand /S18 /S18 pitch Sheath strand /S18 /S18 Cord /S32.4 /S32.4 Strength Cord strength 11809 13120 12841 13209 (N) Sum of filament 14324 14302 14366 14282 strength (N) Filament 0.185 strength (mm) (N) 0.225 (mm) 0.26 (mm) 0.28 214 203 (mm) 0.30 235 193 (mm) 0.33 279 279 279 279 (mm) 0.36 321 321 321 321 (mm) Twisting loss (%) 18 8 11 8 Presence or absence of present absent present absent preceding breakage dc (mm) 0.28 0.28 0.30 0.30 3650 17000 (dc 0.15).sup.2 3363 3363 3268 3268 Tensile strength of 3475 3297 3325 2730 core filament (MPa)

TABLE-US-00002 TABLE 2 Comparative Example 3 Example 3 Comparative Example 4 Example 4 Structure [00003] [00004] 2 0.225 + 6 0.28 + 2 0.185 + (6 + 11) 0.26 + 6 (0.28 + 6 0.26) 6 (0.36 + 6 0.33) Twist Core strand /S14 /S11/Z18 pitch Sheath strand /S14 /S18 Cord /S25 /S32.4 Strength Cord strength (N) 8045 8645 13552 14090 Sum of filament 9408 9392 15264 15246 strength (N) Filament 0.185 100 91 strength (mm) (N) 0.225 144 136 (mm) 0.26 182 182 182 182 (mm) 0.28 214 214 (mm) 0.3 (mm) 0.33 279 279 (mm) 0.36 321 321 (mm) Twisting loss (%) 15 8 11 8 Presence or absence of present absent present absent preceding breakage dc (mm) 0.225 0.225 0.185 0.185 3650 17000 (dc 0.15).sup.2 3554 3554 3629 3629 Tensile strength of 3622 3420 3720 3385 core filament (MPa)

TABLE-US-00003 TABLE 3 Comparative Example 5 Example 5 Structure [00005] 2 0.30 + 6 0.36 + 6 (0.36 + 6 0.33) Twist Core strand /S18 pitch Sheath strand /S18 Cord /S26.5 Strength Cord strength (N) 12552 12912 Sum of filament 14366 14282 strength (N) Filament 0.185 (mm) strength 0.225 (mm) (N) 0.26 (mm) 0.28 (mm) 0.30 (mm) 235 193 0.33 (mm) 279 279 0.36 (mm) 321 321 Twisting loss (%) 13 10 Presence or absence of present absent preceding breakage dc (mm) 0.30 0.30 3650 17000 (dc 0.15).sup.2 3268 3268 Tensile strength of 3325 2730 core filament (MPa)

[0038] It is found from Tables 1 to 3 that in the steel cord of the present invention, the core filament of the core strand did not experience a preceding breakage and the twisting loss was small.

DESCRIPTION OF SYMBOLS

[0039] 1 steel cord

[0040] 2 core strand

[0041] 2a core filament

[0042] 2b sheath filament

[0043] 3 sheath strand

[0044] 3a core filament

[0045] 3b sheath filament

[0046] 10 rubber crawler

[0047] 11 treat rubber

[0048] 12 detachment prevention protrusion

[0049] 13 wing portion

[0050] 14 metal core

[0051] 15 lug

[0052] 16 rubber member

[0053] 20 construction vehicle tire

[0054] 21 bead core

[0055] 22 carcass

[0056] 23 belt

[0057] 24 tread