JP2000017587A - Steel cord for reinforcing rubber articles and pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain steel cords for reinforcing rubber articles that are applicable to radial tires with increased durability in moor lands by twisting the sheath strands that are prepared by twisting together a plurality of steel filaments around the core strand that are prepared by twisting together a plurality of steel filaments. SOLUTION: The objective steel cord for reinforcing rubber articles is produced by twisting 5-8 sheath strands that are prepared by twisting a plurality of steel filaments 3 in which the filaments 3 constituting the outermost layer has a flat cross sections inscribing to the ellipses and satisfies the relation of 0.8<=aT/[c(2b+c)]1/2<=1.15 where T=tan(n-2)π/2n (n is the sheath strand count; c is the diameter of the core strand; a is the major axis of the ellipse of the sheath strand; b is the minor axis of the same ellipse) around the core strand 1 so that the shaft axis of the core strand 1 may come on the extension line of the minor axis of the ellipse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel cord used as a reinforcing material for rubber articles such as pneumatic tires and industrial belts, and a pneumatic radial tire in which a carcass is reinforced by a belt made of the steel cord.

[0002]

2. Description of the Related Art Pneumatic tires, which are well known as rubber articles reinforced with steel cords, especially construction vehicle tires, are used when traveling on rough roads or rough roads such as rough terrain.
When the tire rides on a large protrusion, rock, or the like, a portion of the tire that hits the protrusion, rock, or the like is locally deformed significantly, so that a large input is particularly applied to a belt cord, which may result in cord breakage.

[0003] Therefore, (3+), which is generally used as a belt cord, is used for a belt of a tire for construction vehicles.
9) A multi-twisted cord exemplified in FIGS. 1 and 2 is used, which has a larger diameter than the steel cord having the +1 structure or the (3 + 9 + 15) +1 structure and has a larger load to break, that is, a larger cutting load.

When these cords are used, the strength of the belt is certainly improved, but the cords may still break depending on the shape of the road surface protrusion or the load applied to the tire, which may shorten the life of the tire. I was

Here, as a means for avoiding cord breakage, it is effective to increase the number of cords driven into the belt, that is, the number of steel cords present per unit width of the belt treat. However, as the distance between cords becomes narrower, the distance between cord end faces that are not bonded to rubber naturally becomes smaller, and as a result, the peeled surface with the cord is easily connected at the belt end, and the separation from this point develops. There's a problem.

Further, by increasing the thickness of each filament constituting the cord, it is possible to increase the cord strength by increasing the thickness of the cord. However, when the diameter of the cord is increased, the interval between the cords is reduced, so that the separation starting from the belt end is caused.In addition, the thickness of the treat is increased and the amount of rubber is increased. The amount also increases, and the belt durability deteriorates.

[0007]

That is, in the case of a tire of this type, particularly in a belt, it is disadvantageous to reduce the gap between the cords and increase the thickness of the treat. It is important to increase the power of the.

Here, as a cord structure having enhanced cord strength, a so-called New Orrington structure in which a thin strand is twisted into a gap between strands in a multi-twist structure is known. Since the strands need to be twisted in advance, there is a disadvantage that productivity is greatly deteriorated.

The multi-twisted cord proposed in Japanese Patent Application Laid-Open No. HEI 8-81889, in which flat strands are twisted, has the advantage that the treat can be made thinner, but the arrangement of filaments in the cord is restricted. Because of this, we cannot expect a significant improvement in code strength.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cord having improved durability against breakage caused by large bending deformation without increasing the cord diameter. An object of the present invention is to provide a tire with improved performance.

[0011]

The gist of the present invention is as follows.
It is as follows. (1) A steel cord formed by twisting 5 to 8 sheath strands in which a plurality of steel filaments are twisted around a core strand in which a plurality of steel filaments are twisted, wherein each sheath strand is The filament constituting the outermost layer is inscribed in an ellipse, has a flat cross-sectional shape, and is arranged in a direction in which a core strand is positioned on the extension of the minor axis of the ellipse, and the number of sheath strands is n. A steel cord for reinforcing rubber articles, wherein the following formula is satisfied, where C is the diameter of the core strand, and a is the major axis of the ellipse of the sheath strand and b is the minor axis. Record

(Equation 2)

(2) The steel cord for reinforcing rubber articles according to the above (1), wherein the sheath strand has the axis of the cord substantially on the extension of the minor axis of the ellipse.

(3) In a pneumatic radial tire having a carcass extending in a toroidal shape between a pair of bead portions and having at least one layer of belt on the carcass, the belt described in (1) or ( A pneumatic radial tire characterized by applying the steel cord according to 2).

[0014]

FIG. 3 shows a cross section of a steel cord applied to a tire belt or the like in accordance with the present invention, with respect to a twisted structure (3 + 9) + 6 × (2 + 8). The steel cord is obtained by twisting nine steel filaments around three steel filaments, and twisting eight steel filaments around two core filaments around the core strand 1. In addition, six sheath strands 2 are twisted.

As the structure of the sheath strand, 3 + 10, 1 × 5, 3 + 10 + 15, and 2 + 8 + 13 structures are suitable, but the structure is not particularly limited and can be appropriately selected. On the other hand, 1+
A 6,3 + 9, 3 + 9 + 15 or 1 + 6 + 12 structure is suitable.

Here, each sheath strand 2 has a flat cross-sectional shape in which the filament 3 constituting the outermost layer is inscribed in an ellipse, and the core strand 1 is positioned on the extension of the minor axis of the ellipse. It is important to place them in the correct orientation. That is, as shown in FIG. 4, when the major axis of the ellipse in the sheath strand 2 is a and the minor axis is b, the extension line L of the minor axis b shown in FIG. Including contact with
It is sufficient that the extension line L is within the circumcircle of the core strand 1 as shown in FIGS. In particular, FIG.
It is recommended that the sheath strand 2 be disposed such that the extension line L of the short axis b substantially passes through the axis of the cord, in the illustrated example, the axis of the core strand 1 as shown in FIG.

Because the sheath strand 2 is flattened and the short axis of the ellipse is arranged toward the core strand, the gap X between the strands in the conventional cord shown in FIGS. 1 and 2 is obtained. And Y etc. are reduced, and more filaments are efficiently arranged per unit area of the cord, resulting in high cord strength. Further, by making the sheath strand 2 flat, the number of contact points with the core strand increases, and local stress concentration is avoided, so that the strength is also improved. On the other hand, the number and the twist structure of the sheath strands may be those according to the related art, so that productivity is not hindered.

Furthermore, around the core strand, 5-8
When twisting n sheath strands selected from the following, it is important that the major axis a and the minor axis b of the ellipse in the sheath strand and the diameter C of the core strand satisfy the following equation. is there.

(Equation 3)

Because,

(Equation 4) If the ratio is less than 0.8, the gap between the sheath strands becomes large, and it is difficult to achieve the desired object of the present invention, in which the gap is reduced to improve the strength.
on the other hand,

(Equation 5) Exceeds 1.15, the gap into which the sheath strand enters is narrowed, and as shown in FIG. 5, it becomes difficult to manufacture a cord even when the filaments between adjacent sheath strands are taken into consideration.

The number n of sheath strands is 5 to 8
The reason is that if n is 4 or less, it becomes difficult to reduce the gaps X and Y shown in FIGS.
This is because code productivity is impaired in the above case.

By the way,

(Equation 6) Is 1, the circumscribed ellipses of the sheath strands are in contact with each other around the core strand, as shown in FIG.

The major axis a and the minor axis b of the sheath strand
It is advantageous that the ratio b / a, that is, the so-called oblateness, is in the range of 0.5 to 0.95. That is, if b / a is less than 0.5, excessive molding of the filament is required, which is disadvantageous in production. On the other hand, if b / a exceeds 0.95, the cross-sectional shape of the sheath strand becomes close to a circle. , It is difficult to obtain the desired effect.

In the cord according to the present invention, the flattened sheath strand is wound around the core strand so that its short axis always extends toward the core strand, or a sheath having an ordinary circular cross section is used. After the strand is loosely twisted and formed, the sheath strand is wound around the core strand, and then the entire cord is crushed to flatten the sheath strand. At that time, spirally wrap the wrap filament around the sheath strand 2,
It is also possible to strengthen the cord bundle.

The above-mentioned cord is used for reinforcing a carcass by applying a ply formed by embedding a plurality of the cords in parallel to each other and burying the rubber sheet in a rubber belt to provide a reinforcement for a carcass. May be in accordance with conventional pneumatic tires for construction vehicles, for example the belt structure shown in FIG. 6 is advantageously adapted. In this figure, reference numeral 4 denotes a bead core, 5 denotes a carcass wound around the bead core 4 from the inside to the outside of the tire, and 6 denotes a 4- to 6-layer structure arranged on the carcass 5. Belts and 7 are treads located on this belt.

[0025]

EXAMPLE After loosely twisting and forming a sheath strand having a circular cross section, the sheath strand was wound around a core strand, and then the entire cord was crushed to flatten the sheath strand. Were prepared, and the cutting load was measured for each cord in accordance with JIS G3510. The cord has a C content of 0.80 to 0.85.
Using steel filament of the same steel material of wt%,
The twist angle of the sheath strand is 80.5 ° for all cords
And The cord diameter is 1.8 m as shown in Table 1.
m, similarly, 2.5 mm in Table 2 and 3.7 mm in Table 3. As shown in Tables 1 to 3, the measurement results of the cutting load show that, in the cords of the present invention, the cutting load is increased even in the same cord diameter, and the cord strength is greatly improved. Understand.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

Next, on the belt of the construction vehicle tire having the size of 36.00 R51 shown in FIG. 6, the invention code is applied to the first and second belts in order from the carcass side at 10.2 cords / 50 mm. The tires were prototyped by applying the invention cords to the 3 and 4 belts at a driving number of 6.5 / 50 mm. In addition, a high extensibility cord was used for the fifth and sixth belts in order to suppress the progress of corrosion when the belts were cut.

For comparison, similar tires were compared with 10.2 comparative codes / first and second belts.
A prototype tire was also manufactured in which the comparative code 3 was applied to the third and fourth belts at a driving number of 6.5 mm / 50 mm at a driving number of 50 mm. This comparative tire also has the fifth and sixth belts,
A high elongation cord was used to suppress the progress of corrosion when receiving a cut.

After the tire thus obtained is incorporated into a standard rim, and adjusted to an air pressure corresponding to the maximum added capacity,
Attached to a dump running at 40km / h in the same mine,
After running for about 1000 hours, the tire was removed, the tire was dissected, and the number of locations broken by cutting the cord was measured. Table 4 shows the results. Naturally, it is better to reduce the number of cuts.

[0032]

[Table 4]

Based on the results shown in Table 4, the invention codes are shown as Nos.
It is clear that the durability is improved when the belt is used for the fourth belt, and the invention cord is used for the first and second belts or the third and fourth belts.
It can be seen that a sufficient effect is obtained even when used only for the belt.

[0034]

According to the present invention, the rupture resistance of the cord can be improved without increasing the cord diameter. Therefore, by applying this cord to a tire belt, it is possible to improve the durability especially in a wasteland. It is possible to provide an improved tire suitable for a construction vehicle tire.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a conventional cord.

FIG. 2 is a sectional view showing a conventional cord.

FIG. 3 is a sectional view showing a cord according to the present invention.

FIG. 4 is a sectional view showing an arrangement of sheath strands in the cord according to the present invention.

FIG. 5 is a diagram showing behavior of a sheath strand during cord production.

FIG. 6 is a sectional view showing a tire structure suitable for the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core strand 2 Sheath strand 3 Filament 4 Bead core 5 Carcass 6 Belt 7 Tread

Claims (3)

[Claims] A steel cord comprising a core strand in which a plurality of steel filaments are twisted, and 5 to 8 sheath strands in which a plurality of steel filaments are twisted, twisted around a core strand. The strand has a flat cross-sectional shape in which the filament constituting the outermost layer is inscribed in an ellipse, and is oriented in such a manner that the core strand is located on an extension of the minor axis of the ellipse. Where n is the diameter of the core strand, C is the diameter of the core strand, and a is the major axis of the ellipse of the sheath strand and b is the minor axis thereof. Note 2. The steel cord for reinforcing a rubber article according to claim 1, wherein the sheath strand has the axis of the cord located substantially on the extension of the minor axis of the ellipse. 3. A carcass extending in a toroidal shape between a pair of bead portions, and at least one carcass is provided on the carcass.
A pneumatic radial tire having a layer belt, wherein the steel cord according to claim 1 or 2 is applied to the belt.