JPH1053979A - Steel cord for reinforcing tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel cord for reinforcing a tire for a small-sized truck capable of holding an adequate carcass strength and a suitable cord interval simultaneously, reducing the weight of the tire and aiming at the maintenance and improvement of endurance thereof. SOLUTION: This steel cord for reinforcing a tire is obtained by twisting a filament having 320-400kgf/mm<2> tensile strength, 0.17-0.18mm filament diameter in a 3+9+1 structure and core filaments and sheath filaments in a same twisting direction but with different pitches, reverse twisting only spiral filaments against the sheath filaments, and using a filament having a same wire diameter as the core and sheath filaments. An interval of a cord plaiting at the crown center line part is made as <=2.1mm and that of at the folding back part of a bead is made as >=0.8mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel cord for reinforcing automobile tires. In particular, it relates to a steel cord for reinforcing a tire for a light truck.

[0002]

2. Description of the Related Art Conventionally, in steel cords used for large truck and bus tires, three core filaments at the center, nine sheath filaments spirally wound therearound, and one spiral filament at the outermost layer are used. It is well known that the so-called 3 + 9 + 1 structure has a filament tensile strength of 280 to 300 kgf / mm ² and a filament diameter of 0.22 to 0.23 mm. When such a cord having a 3 + 9 × 0.23 + 1 structure is applied to a tire for a small truck, in order to obtain an appropriate cord insertion interval, the carcass strength is excessive, the tire weight increases, and the rolling resistance increases. Fuel economy is also bad. On the other hand, if an attempt is made to obtain an appropriate carcass strength, the cord driving gap is widened, and the cord is raised on the inner surface of the tire due to the internal pressure, so that the adhesiveness is significantly reduced.
As described above, there is a problem that both the cord insertion interval and the carcass strength cannot be compatible.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel cord for reinforcing a tire for a small truck, which has both a proper carcass strength and a proper cord interval, thereby reducing tire weight and maintaining and improving durability. It is to realize.

[0004]

SUMMARY OF THE INVENTION The present invention provides a tensile strength 320.
~400kgf / mm ^2, filament diameter 0.17
The above problem was solved by using a filament having a diameter of 0.18 mm in a 3 + 9 + 1 structure. That is, a core filament obtained by twisting three filaments having a tensile strength of 320 to 400 kgf / mm ² and a filament diameter of 0.17 to 0.18 mm, nine sheath filaments wound spirally around the core filament and the outermost layer Consisting of one spiral filament,
The core filament and the sheath filament have the same twist direction and different pitches, and only the spiral filament is reverse-twisted with the sheath filament. As the core filament and the sheath filament, filaments having the same wire diameter are used.

[0005] In applying this tire reinforcing steel cord to a tire, the cord driving interval of the crown center line portion is set to 2.1 mm or less excluding the spiral, and the cord driving interval of the bead turning portion is set to 0.1 mm.
By adjusting the thickness to 8 mm or more, the tire weight, rolling resistance, and fuel economy suitable for a light truck tire can be obtained, and the adhesion and the bead portion durability (ply end separation property) can be maintained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a core filament and a sheath filament are twisted in the same direction and have different pitches. If the two filaments are twisted in different directions, the contact pressure between the two is high, and wear due to rubbing of each other, that is, fretting wear occurs, and the cord strength is significantly reduced. Even if the twist direction is the same, if the pitch is the same, the sheath filament falls into the gap between the cores, and the cord outer shape is polygonal (hexagonal).
And the contact with the spiral filament becomes non-uniform, which promotes fretting wear.

[0007] The core filament and the sheath filament have almost the same molding ratio in the range of 90 to 105%. 9
If it is 0% or less, the contact pressure between the core and the sheath is high, and the strength is significantly reduced. If it is 105% or more, the contact pressure between the sheath and the spiral is high, and the strength is significantly reduced.

[0008] The tensile strength of all the filaments is 320 to 400
between kgf / mm ^2, preferably to 330kgf / mm ² before and after. In the case of less than 320 kgf / mm ² , in order to maintain the same case strength, it is necessary to increase the number of shots or to increase the wire diameter, resulting in a decrease in tire durability or an increase in weight. Conversely, 400 kgf / mm ²
In the case of exceeding, the current steel cord manufacturing method frequently causes disconnection in a filament drawing process, which is not practical.

[0009] The filament diameter of the core filament and the sheath filament is between 0.170 and 0.180 mm, preferably around 0.175 mm. If it is less than 0.170 mm, in order to maintain the same case strength, a larger number of filaments must be twisted or the number of driven filaments must be increased, leading to a decrease in tire durability and an increase in manufacturing cost. Conversely, if it is more than 0.180 mm, the repetitive fatigue due to the side portion bending deformation during rolling of the tire is significantly reduced.

When the steel cord is incorporated into a tire, the cord insertion interval at the crown center portion is set to 2.1 mm or less. This code insertion interval is set to 2.
If it is more than 1 mm, the rubber gauge covering the shoulder cord becomes thinner due to the tire internal pressure, causing a phenomenon (wash bullet) in which the cord is extruded in a rib shape and the adhesion between the cord and the rubber is remarkably reduced, resulting in separation. Failures are more likely to occur. The cord insertion interval at the bead turn-back portion is 0.8 mm or more. When the cord insertion interval is less than 0.8 mm, the cord interval at the ply end portion becomes narrow, and a crack generated by shear strain during rolling of the tire is likely to be connected, so that the separation resistance of the bead portion deteriorates.

As described above, the present invention provides a tensile strength of 320 to 40.
0 kgf / mm ² , filament diameter 0.17 to 0.18
By using filaments in the range of mm in a 3 + 9 + 1 structure, appropriate carcass strength and cord spacing are maintained, tire weight is reduced, and durability is improved. Further, in the application of this cord, there is a concern that the fretting wear resistance may be reduced due to an increase in tension due to the internal pressure applied per unit cross-sectional area of the filament. The application of this code is realized by optimizing.

[0012]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. 7.50 inch tire width, rim diameter 1
The present invention is applied to a carcass ply of a 6-inch radial tire (7.50R16), and the fretting amount, ply end separation property, and wash bullet property (W / B property) of the resulting tire are measured by the following measurement methods. And evaluated.

(1) A carcass cord was taken out from a tire after running on the ground with a fretting amount of 100,000 km, and the cord was sealed in a thermosetting resin and cured to prepare a sample. 1mm
Buffing with a grinder every time, photographing 35 cord cross-sectional photographs, measuring the fretting depth of each sheath filament from the photograph, calculating the average value of the maximum fretting depth of each sheath filament, The fretting amount of the cord was used. It was indicated by an index with Comparative Example 1 being 100. The smaller the value, the better the fretting wear resistance.

(2) Separation of ply end The tire is dissected after traveling 100,000 km on a good road in the actual field, and the ply end is taken out. At four places on the tire circumference, 80 places at both ends of 10 cords are examined. Among them, the ratio of the number of connected cracks is determined as a crack connection ratio, and this value is indicated by an index with Comparative Example 1 being 100.

(3) W / B property A test sample is cut out from a tire after 100,000 km running on the ground, and a steel cord is pulled up to perform a peeling test. Are fixed between the upper and lower chucks, respectively, and the tensile speed is 50 with an Instron or Tensilon type tensile tester.
Peeling was performed under the conditions of ± 5 mm / min, and the amount of rubber adhering on the cord was evaluated. A 90% or more Rubber adhesion B 75 to 90% {C 50 to 75%} D 25 to 50% {E 0 to 25%}

Table 1 shows the characteristics of the tire reinforcing steel cord of each tire, and the evaluation results of the fretting amount, the ply end separation property, and the W / B property.

[0017]

[Table 1]

[0018]

The steel cord of the present invention has reduced fretting wear, less ply end separation,
Low generation of wash bullets (W / B) and high adhesion between cord and rubber. Therefore, a proper carcass strength and a proper cord interval can be maintained at the same time, the tire weight is reduced, and the durability is maintained and improved.

Claims (6)

[Claims] 1. A tire reinforcing steel cord comprising three twisted core filaments, nine sheath filaments wound around the core filaments and one spiral filament of the outermost layer, and a core filament. A steel cord for tire reinforcement in which the sheath filaments have the same twist direction and different pitches, and only the spiral filament is reverse-twisted with the sheath filament. 2. The tire reinforcing steel cord according to claim 1, wherein the core filament and the sheath filament have the same diameter. 3. The steel cord for reinforcing a tire according to claim 1, wherein a tensile strength of the filament, excluding the spiral filament, is in a range of 320 to 400 kgf / mm ² . 4. The tire reinforcing steel cord according to claim 1, wherein the diameters of the core filament and the sheath filament are in a range of 0.170 mm to 0.180 mm. 5. A carcass ply in which a cord driving interval of a crown center line portion is set to 2.1 mm or less excluding a spiral and a cord driving interval of a bead turning portion is set to 0.8 mm or more excluding a spiral. 3. A steel cord for reinforcing a tire for a light truck according to any one of the above items. 6. The molding rates of the core filament and the sheath filament are both in the range of 90 to 105%, and the molding rates of the core and the sheath are substantially equal. A steel cord for reinforcing tires according to any one of the above.