JP3495164B2 - Pneumatic tire - Google Patents

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 for a vehicle using a steel cord for a carcass and a belt, and a breaker or a side ply for imparting cut resistance. The present invention relates to a pneumatic bias tire using a cord. In particular, it relates to a technology for improving the durability and reducing the weight of tires for large vehicles such as trucks and buses.

[0002]

2. Description of the Related Art A steel cord used as a reinforcing material for a radial tire is strongly required to have high strength in order to reduce the weight of the tire. However, when the strength of the steel wire constituting the steel cord is increased, the fatigue resistance is usually lowered, and there is a problem that the durability of the tire is lowered accordingly. In order to solve such a problem, some proposals have been made to improve the fatigue resistance of the steel cord.

For example, in the steel wire disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-71084, after a high carbon steel wire having a carbon content of 0.6% or more is plated, the approach angle is 8 degrees or less at the end of the wire drawing step. Residual stress on the wire surface was determined by X-ray diffractometry using a drawing die and was 45 on the tensile side in the axial direction.
Those having a Kg / mm ² or less have been proposed. Also,
The metal wire disclosed in JP-A-57-149578 is said to have excellent mechanical fatigue characteristics by compressing and uniformly dispersing the residual stress on the outer surface.

Furthermore, in order to obtain a steel cord having excellent corrosion fatigue resistance, an alloy steel wire rod to which an element imparting corrosion resistance is added to a raw material wire is used, or a steel cord is used.
It has been attempted to suppress the contact between the steel filament and moisture by invading the rubber inside the cord.

[0005]

However, in the method of reducing the residual tensile stress on the surface of the steel wire during wire drawing proposed in the above-mentioned Japanese Patent Application Laid-Open No. 5-71084, these steel wires are twisted together. Due to plastic deformation at the time, residual stress on the tensile side relatively occurs inside the spiral of the steel wire obtained by untwisting the steel cord, and corrosion fatigue resistance There is a problem that the effect cannot be obtained.

Further, in the method proposed in Japanese Patent Laid-Open No. 57-149578, as shown in FIG. 5, the treatment is performed so as to give a residual compressive stress mainly to the entire outer circumferential surface of the steel cord. Therefore, a residual compressive stress is mainly applied to the outer side of the spiral shape of the steel wire, and it is expected to improve the corrosion fatigue resistance inside the steel cord where rubber hardly penetrates. There is a problem that the effect is not so good. The reason for this is that by forming the steel wire in a spiral shape, a sufficient residual compressive stress is generated on the outside of the spiral for corrosion fatigue resistance, and further processing is unnecessary.

On the other hand, the method of adding an element for imparting corrosion resistance has the problems that the cost of the wire rod increases and the wire drawability decreases.

Further, the method of improving the corrosion resistance in which the steel cord penetrates the rubber into the inside to prevent the contact between the steel wire and the water cannot obtain the effect unless the rubber penetrates sufficiently, for example, the rubber penetration. However, if the adhesion is insufficient, there is a problem that voids are generated at the interface between the steel element wire and the rubber and the corrosion resistance is lowered.

[0009]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned drawbacks, in which a steel cord wire for rubber reinforcement having a carbon content of 0.70% by weight or more is drawn. With a diameter of 0.10 to 0.40 mm and a strength of 300
A steel cord of 0 N / mm ² or more, a plurality of the steel strands are twisted together to form a steel cord, and the spiral obtained by untwisting the steel cord Spiral radius of curvature R ₀ of a steel wire having a circular shape and the radius of curvature R of the helix when the surface layer in the spiral inner part of the steel wire is dissolved and removed.
₁ and the ratio of _{{(R 1 / R 0)} × 100}, excellent rubber reinforcing steel in corrosion resistance, which is a less than 100 -
The present invention relates to a pneumatic tire using a cord.

The surface layer is in a range from the surface of the steel wire to a depth from the surface corresponding to 5% of the diameter of the steel wire, and more preferably, the surface layer is from the surface of the steel wire to the steel. The present invention relates to a pneumatic tire using the above-mentioned rubber-reinforced steel cord in a range from the surface corresponding to 10% of the diameter of the strand.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has the above-mentioned constitution, and it is widely known that when the strength of the steel wire is increased, the corrosion fatigue resistance is lowered. The present inventors have found that in order to improve the corrosion fatigue resistance of the wire, it is sufficient to reduce the residual tensile stress on the inner surface of the spiral of the steel wire, and have reached the present invention.

In the present invention, the carbon content of the steel cord wire for a pneumatic tire is specified to be 0.7% by weight or more because the strength of the steel wire is 30 in order to reduce the weight of the tire.
This is because it is necessary to set it to 00 N / mm ² or more. Further, the reason for defining the diameter of the steel wire in the range of 0.10 mm to 0.40 mm is that the workability in the wire drawing process is deteriorated when it is less than 0.10 mm, and the machine of the steel wire is more than 0.40 mm. This is because the fatigue resistance is reduced.

When the twisted steel cord is untwisted, a plurality of helically shaped steel wires are obtained. This is a twisting process in which a straight steel wire is used as the steel cord. This is because the plastic deformation is applied to the steel wire in. Even if the surface residual tensile stress of the steel wire is reduced in the wire drawing process, the maximum residual tensile stress is generated inside the spiral of the steel wire in the twisting process,
The inside of the cord where the rubber hardly penetrates, that is, the inside of the spiral of the steel wire is exposed to a corrosive environment, and corrosion fatigue easily occurs.

The gist of the present invention is as described above.
The purpose is to reduce the residual tensile stress in the surface layer inside the spiral of the steel wire in the twisting process of the steel wire forming the cord, and from this, the wire drawing proposed in JP-A-5-71084. A method of reducing the residual tensile stress of the surface layer of the steel wire in the process can be used together.

When a tire is mounted on a vehicle and travels, the tire is repeatedly bent, and fretting occurs in which the steel wires forming the steel cord are frictionally worn with each other, which further facilitates corrosion. Therefore, it is preferable to reduce the residual tensile stress in the range from the surface of the steel wire to the depth of 5% of the diameter of the steel wire, and more preferably from the surface of the steel wire to the depth of 10% of the diameter of the steel wire. It is better to reduce the residual tensile stress of.

In order to reduce the tensile residual stress in the longitudinal direction inside the spiral of the steel wire obtained by untwisting the steel cord, the elastic limit stress of the steel wire is set to σ ₁ ,
Let σ ₂ be the stress that does not cause compressive plasticity in the entire cross section of the spirally shaped steel wire in the diametrical direction, and let σ ₃ be the maximum residual tensile stress inside the spiral. Σ ₃ + σ ₂
Process so as to satisfy the relationship of −σ ₁ > 0. By this process, plastic deformation is generated in the portion of the steel wire in the range of σ ₃ + σ ₂ −σ ₁ > 0. This will be described in more detail with reference to FIG.

FIG. 1 (a) schematically shows the residual stress associated with the twisted wire while ignoring the residual stress associated with the wire drawing in order to make the explanation easy to understand. The line is spirally shaped, indicating the maximum residual tensile stress at the inner surface layer of the spiral. 1 (a) shows
FIG. 7 is a stress distribution diagram when stress is applied to the steel wire in such a manner that compression plasticity is not generated in the entire cross section in the diametrical direction, and σ ₃ + σ ₂ −σ ₁ > 0 from the steel wire surface to the depth of L _1. The range is satisfied. In addition, FIG. 1C shows the residual stress when the stress σ ₂ is removed.

[0018]

EXAMPLES The present invention will be described in more detail with reference to examples. A steel wire having a diameter of 0.23 mm and a strength of 3800 N / mm ^{2 made of} carbon steel having a carbon content of 0.8% by weight is used as a core with three wire rods spirally shaped with a pitch of 6 mm. A steel cord with a (3 + 9 + 1) structure in which nine spirally shaped steel wires with a pitch of 12 mm are wound around a core, and one steel wire is further wound around the core is manufactured by a twisting machine. did. Further, the residual stress distribution inside the spiral in the spirally shaped steel element wire forming the steel cord was obtained by calculation. Then σ ₃ + σ ₂ −σ
By treating the steel cord with the apparatus shown in FIG. 2 so as to satisfy the relation of ₁ > 0, the maximum residual tensile stress of the spiral inner surface layer portion of the steel wire was reduced to the required depth.

Reference numerals A1 and A2 in FIG. 2 are tension load devices for applying tension to the steel cord, and have a mechanism in which the tension load can be freely set. B is a bending device for bending the steel cord, in which a plurality of rollers are arranged in a zigzag manner, and the bending amount of the steel cord can be freely changed. C is a steel cord winding device. The tension of the steel cord between A1 and A2 can be freely adjusted by A1, and B is the steel cord.
When tension is not applied to the rucor, the roll diameter and biting depth are adjusted so that plastic deformation does not occur so that bending is applied only in the elastic region. This adjustment of the aforementioned σ1, σ2, relationship .sigma.3, i.e. σ ₃ + σ ₂ -σ
Steel as residual stress up to a desired depth by _1> 0 can be reduced - Turkey - 1000 N / mm ² with respect to de (Example 1), 1300N / mm ² (Example 2), 1500 N
A tension of / mm ² (Example 3) was applied.

As a comparative example, after the wire drawing, the residual tensile stress of the surface layer of the steel wire was reduced by repeated bending work and then twisted (Comparative Example 1). Further, after the steel cord was made into a steel cord, the residual tensile stress was set to A1 and the tension of the steel cord of A2 was set to 50 N / mm ^2, and the circumference of the steel cord was adjusted by adjusting the bending process with a roller. The entire surface was treated to give residual compressive stress (Comparative Example 2).

The steels of the above-mentioned Example 3 and Comparative Example 2
Carcass plies were made by using rucors, and these carcass plies (the number of cords to be driven: 30.28 /
Five types of pneumatic radial tires (tire size 11R22.5, 14PR) using 5 cm) were prototyped.

The steel cord produced in this manner is untwisted and decomposed into a steel wire having a spiral shape,
About the steel wires that form the inner sheath of these steel wires 10
After cutting it to a length of 0 mm and applying enamel to the longitudinal direction of the steel wire and to the semicircle, soak it in a 50% aqueous solution of nitric acid, and make the semicircular side without enamel a prescribed thickness. Was melted, and the continuous movement of the steel wire at that time was measured. The measurement was performed for both the movement of the radius of curvature when the inside of the spiral of the steel wire melts and the movement for the entire 100 mm steel wire. The former measurement is as shown in FIG. 3, where R ₀ is the spiral curvature radius (mm) before the spiral inner surface layer is removed, and R ₁ is the spiral curvature radius (mm) after the spiral inner surface layer is removed. . Further, the measurement in the latter is as shown in FIG. 4, and the case of moving to the P side is −, and the case of moving to the Q side is +.

Corrosion fatigue resistance was evaluated on the basis of 100 tires.
A steel cord cut into a length of mm is dipped in a neutral aqueous solution containing a small amount of nitrate ion and sulfate ion, and 1 minute per minute.
The number of rotations until the steel wire was broken was recorded by repeatedly applying a bending stress of 300 N / mm ² at a speed of 000 rotations. The results are shown in Table 1. In Table 1, the number of revolutions until the fracture in Comparative Example 1 is set to 100 and is indexed, and the larger the number, the better the corrosion fatigue resistance.

The evaluation of the corrosion fatigue resistance of tires is carried out by disposing a tube inside the inner liner of the tire at the time of assembling the rim of these test tires, and between the inner liner and the tube. Each of the test tires was filled with 300 ml of water and evaluated by the life (driving distance) until a cord break (CBU) failure in the drum test. The results are shown in Table 1. In Table 1, the traveling distance of Comparative Example 1 is set to 100 and is indexed, and the larger the number, the better the corrosion fatigue resistance. In addition, these test tires had an internal pressure of 8K.
g / cm ² , and a JIS 100% load was applied. The running speed is 60 km / h.

[0025]

[Table 1]

As is apparent from Table 1 above, Comparative Example 1
Since the residual tensile stress of the steel wire surface layer was reduced by repeated bending after wire drawing and then twisted, the effect of reducing the residual tensile stress was weakened by the twisted wire. Comparative Example 2 is A
Since the tension between 1 and A2 is insufficient, the wire 100 mm
Although the residual stress in the entire movement has a compressive action, the residual tensile stress inside the spiral shaped in the steel wire is not reduced. In addition, the same result was obtained for the change of the spiral curvature radius when the core and the sheath were melted inside the spiral, and the movement of the entire length of the steel wire of 100 mm. As described above, it is clear that the durability of the pneumatic tire using the steel cord of the present invention is excellent.

FIG. 6 is a cross-sectional view showing the outline of a pneumatic tire, in which a (carcass) is a code layer responsible for the skeleton of the tire, and b (belt) reinforces the crown of the tire. The code layer, c (bead), is a reinforcing material for the bead portion. In the embodiment of the present invention, the cover of a pneumatic radial tire is used.
As described in the example used for the dregs a, the belt b, the belt protection layer, the side protection plies of the pneumatic radial tire, the reinforcement c of the bead portion, and the pneumatic bias tire have the brace. It is obvious that the durability of the tire can be improved by using it as a car or a side reinforcing layer.

[0028]

The residual tensile stress of the spiral inner surface layer of the steel wire constituting the pneumatic tire reinforcing steel cord is reduced, so that the corrosion resistance of the steel cord is improved and It is a useful invention in which the durability of a filled tire is significantly improved, and since the steel cord applied to the present invention has high strength, it is possible to reduce the weight of the tire and also improve the durability. It is a useful invention.

[Brief description of drawings]

FIG. 1 is a schematic view showing a stress distribution in a diametrical cross section of a steel wire constituting a steel cord.

FIG. 2 is a partial view for manufacturing the steel cord of the present invention.

FIG. 3 is a diagram showing a change in a radius of curvature of a spirally-formed steel element wire inside a spiral.

FIG. 4 is a diagram showing the amount of movement of the tip of the steel cord of 100 mm.

FIG. 5 is a diagram showing a portion where residual stress is reduced by repeatedly adjusting a steel cord and adjusting a bending main body.

FIG. 6 is a cross-sectional view showing an outline of a pneumatic tire.

[Explanation of symbols]

A1, A2 ... Tension load device for applying tension to the steel cord, B ... Bending device for bending the steel cord, C ... Steel cord winding device, R ₀・ ・ ・ Helix radius of curvature before removal of the inner surface of the spiral, R ₁・ ・ ・ Radius of spiral curvature after removal of the inner surface of the spiral, S ・ ・ ・ Outer surface of the circumference (outer side of the spiral), a ・ ・ ・ Carcass of the tire, b ・ ・ ・Tire belt, c ... Tire bead.

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Claims (3)

(57) [Claims] 1. A rubber-reinforced steel cord wire having a carbon content of 0.70% by weight or more, which is drawn to have a diameter of 0.10 to 0.40 mm and a strength of 3000 N / m.
A steel cord of m ² or more, wherein a plurality of the steel strands are twisted together to form a steel cord, which is obtained by untwisting the steel cord. Ratio between the spiral curvature radius R _{0 of the} steel wire having a pattern and the radius of curvature R ₁ of the spiral when the surface layer in the spiral inner part of the steel wire is removed by dissolution {(R ₁ / R ₀ ) × 100} Is less than 100, and a rubber-reinforced steel cord having excellent corrosion resistance is used as at least a part of the cord reinforcing member. 2. The pneumatic tire according to claim 1, wherein the surface layer is in a range from the surface of the steel wire to a depth from the surface corresponding to 5% of the diameter of the steel wire. . 3. The pneumatic tire according to claim 1, wherein the surface layer has a range from the surface of the steel wire to a depth from the surface corresponding to 10% of the diameter of the steel wire. .