JPH0564850A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve tire durability by using a solid wire steel cord having its surface residual stress in the solid wire axial direction less than the specified value as a reinforcing material. CONSTITUTION:A carcass layer 2 is wound from inside toward outside around a bead core 1 of a pneumatic radial tire, while a two-layer belt layer composed of an outer belt layer 4u and an inner side belt layer 4d are disposed in the ring shape all over the periphery of a tire in the tire peripheral direction in the form of a ring outside the carcass layer 2 at a tread 3. A solid wire steel cord having 45kg/mm<2> or less surface residual stress in the solid wire axial direction is used as a cord 6 constituting respective belt layers of the outside belt layer 4a and a inside belt layer 4d. When the surface residual stress in the solid wire axial direction is beyond 45kg/mm<2>, the fatigue durability of steel cord is lowered and its use as the solid wire is difficult.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having improved durability and reduced weight.

[0002]

2. Description of the Related Art Conventionally, a steel cord has been used as a reinforcing material for a belt layer, a bead portion reinforcing layer and the like of a tire. This steel cord is in the form of a stranded cord formed by twisting a plurality of strands. For this reason, when this steel cord is used as a reinforcing material, it is fretting on the steel cord (wear due to contact between wires).
However, there are problems such as the occurrence of rust and the generation of rust due to the permeation of water in the gap between the wires.

Therefore, in order to solve this problem, it has been proposed to use a single wire steel cord as a reinforcing material for the belt layer (Japanese Patent Laid-Open No. 1-229704). However, the single-strand steel cord has a drawback that, unlike the twisted-strand steel cord, the cord is less likely to be broken because the elongation in the longitudinal direction and the width direction is small, resulting in poor fatigue durability. Therefore, the tire using the single-wire steel cord has a problem in durability.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic radial tire that uses a single wire steel cord, but has improved durability and weight reduction.

[0005]

The pneumatic radial tire of the present invention is characterized in that a single wire steel cord having a surface residual stress in the axial direction of the single wire of 45 kg / mm ² or less is used as a reinforcing material. As described above, in the present invention, the surface residual stress in the direction of the single wire is 45 kg / mm ² or less.By using the steel cord of the single wire, the fatigue durability which is a problem when the steel cord of the single wire is used is improved. It enables the application of single-wire steel cords to tires. In addition, since there is no useless space such as a gap between strands of a single-strand steel cord unlike a stranded steel cord, the diameter may be smaller than that of a stranded steel cord. Since the amount of the object (coat rubber) used can be reduced, the weight of the tire can be reduced.

The structure of the present invention will be described in detail below. FIG. 1 is a half-section explanatory view in the tire meridian direction showing an example of the pneumatic radial tire of the present invention. In FIG. 1, a carcass layer 2 is wound up from the inside of the tire to the outside around a bead core 1, and in the tread 3,
On the outside of the carcass layer 2, two belt layers including an outer belt layer 4u and an inner belt layer 4d are annularly arranged in the tire circumferential direction over the entire circumference of the tire. 5 is a carcass layer 2
Is a bead portion reinforcing layer (chafer) arranged on the outer side of the winding end portion of.

In FIG. 1, as the cords 6 constituting the respective belt layers of the outer belt layer 4u and the inner belt layer 4d, a single wire steel cord having a surface residual stress of 45 kg / mm ² or less in the axial direction of the single wire is used. There is. If the surface residual stress in the axial direction of the single wire exceeds 45 kg / mm ² , the fatigue resistance of the steel cord will be low, making it difficult to use in the single wire. The diameter of the steel cord is preferably 0.25 mm to 0.60 mm. 0.
If it is less than 25 mm, it is too thin and the belt layer buckles and the cord is easily broken. If it is more than 0.60 mm, it is too thick and separation occurs easily at the end of the belt layer.
In addition, as the cord of the bead portion reinforcing layer 5, or as all the cords of the belt layer and the bead portion reinforcing layer, the single wire steel cord having a surface residual stress of 45 kg / mm ² or less may be used.

A single wire steel cord having a surface residual stress of 45 kg / mm ² or less in the axial direction of the single wire is, for example, a die drawing process in which a plurality of dies are sequentially drawn to gradually reduce the cross section of the cord. In the step of manufacturing a single wire steel cord by (drawing), it can be obtained by setting the die inlet angle at the final die drawing, that is, the die approach angle to 8 ° or less. FIG. 2 shows an example of a cross section of the die when the die is drawn out for the final time. In FIG. 2, the die 10 is an iron case 11
And the nib 12 inside it. 13 is a code entrance and 14 is a code exit. Dice approach angle is code entrance
In FIG. 13, the inner slope of the left nib 12 and the right nib 12
Is an angle 2θ between the inner surface and the inclined surface. The dice approach angle 2θ is set to 8 ° or less (2θ ≦ 8 °). θ
Corresponds to the angle formed by the inclined surface of the inner surface of the left nib 12 and the die center line M, and the angle formed by the inclined surface of the inner surface of the right nib 12 and the die center line M, respectively.

The surface residual stress may be measured by determining the 200 crystal plane spacing of αFe of the steel cord by the X-ray diffraction method.

[0010]

【Example】

Example 1 A 1.70 mm diameter steel cord made of high-carbon steel containing 0.82% carbon was plated with copper and zinc by a diffusion plating method, and then heat treated to alloy it, and a plating adhesion amount of 4.0.
It was set to g / kg (Cu = 63.5%, Zn = 36.5%). This steel cord is drawn into a small diameter one by one using a die,
A single-wire steel cord with a diameter of 30 mm was used. At this time, the die approach angle 2θ in the final die is 2 °
It was ~ 16 °. The case of 2θ = 12 ° is the conventional steel cord.

The surface residual stress in the direction of the single wire axis of the obtained single wire steel cord having a diameter of 0.30 mm was measured by the X-ray diffraction method. The results are shown in Table 1 below. Further, in order to examine the fatigue durability of this steel cord, a rotating bending fatigue test was conducted by a conventional method and the number of times until breakage under the same stress was measured. The results are shown in Table 1 in percentage. From Table 1, it can be seen that the fatigue durability is excellent when the surface residual stress in the direction of the single wire is 45 kg / mm ² or less.

Example 2 Wire drawing was carried out in the same manner as in Example 1 to obtain 0.50 m
A steel cord with a diameter of m was prepared. At this time, the die approach angle 2θ in the final die is 2
The angle was 8 °, 12 ° and 16 °. The obtained single-wire steel cord was embedded in coated rubber to form a belt layer having a tire structure shown in Fig. 1 with a rubber thickness of 1.2 mm and an end number of 40/50 mm, and a pneumatic radial tire of tire size 165SR 13 was obtained. Manufactured.

This tire was mounted on a domestic passenger car (1600 cc), and the number of steel cord breakages in the belt layer was measured after traveling 50,000 km on an ordinary road at an air pressure of 2.0 kg / cm ² . Based on this result, the number of steel cord breakages of the tire using the conventional steel cord (when 2θ = 12 °) was 100.
Is shown in Table 2 below as an index. The smaller the number, the better. As is clear from Table 2, the surface residual stress in the single-axis direction is
It can be seen that the pneumatic radial tire using the single-layer steel cord of 45 kg / mm ² or less as the reinforcing material for the belt layer has excellent durability because the number of steel cord breakages in the belt layer is small.

[0014]

As described above, according to the present invention, the conventional single wire steel cord is used because the single wire steel cord having the surface residual stress in the axial direction of the single wire of 45 kg / mm ² or less is used as the reinforcing material. The tire durability can be improved more than the tire. Further, according to the present invention, the weight of the tire can be reduced as compared with the case where the twisted steel cord is used because the single wire steel cord is used.

[Brief description of drawings]

FIG. 1 is a tire meridian direction half-section explanatory view showing an example of a pneumatic radial tire of the present invention.

FIG. 2 is a cross-sectional view of an example of a die at the time of final drawing of the die.

[Explanation of symbols]

1 bead core, 2 carcass layer, 3 tread, 4u outer belt layer, 4d inner belt layer, 5 bead reinforcement layer, 6 cords, 10 dies, 11 iron case, 12 nibs, 13 cord inlets, 14 cord inlets.

Claims (1)

[Claims] 1. The surface residual stress in the direction of the single wire is 45 kg / mm ²
A pneumatic radial tire that uses the following single-wire steel cord as a reinforcing material.