JP2569185Y2 - Steel cord for reinforcing rubber products - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord for reinforcing rubber products used as a reinforcing material for rubber products such as automobile tires and conveyor belts.

[0002]

2. Description of the Related Art In general, a steel cord of this type has a structure in which a plurality of strands are twisted, and a plurality of the steel cords are covered with a rubber material in a state of being aligned in parallel. Used as reinforcement for products. Therefore, the indispensable conditions for a steel cord are, of course, good mechanical strength, good chemical adhesion with rubber material, and good penetration of rubber material into the steel cord. That is. That is,
In order for a steel cord to sufficiently serve as a reinforcing material for a rubber product, it must be a complete composite with a rubber material.

[0003] Conventionally, a steel cord has a so-called closed twist structure in which four to five strands of a wire are closely adhered to each other and twisted. In this type of steel cord, since a hollow portion exists at the center of the cord, when a composite sheet is formed using a steel cord and two rubber sheets, the rubber material does not penetrate into the hollow portion. However, a complete composite with a rubber material cannot be formed simply by covering the outer periphery of the cord.

[0004] Therefore, in the case of rubber products using the above-mentioned steel cord, for example, automobile tires, the adhesion between the rubber material and the steel cord is not sufficient, and the rubber material and the steel cord are separated during running of the automobile, so-called separates. A phenomenon occurs that significantly impairs the function of the tire, and the moisture in the rubber material and the moisture penetrating from the tire cuts reach the inside of the cord and propagate in the longitudinal direction of the cord, corroding the steel cord. Therefore, the mechanical strength is greatly reduced.

For this reason, recently, a steel cord in which a rubber material penetrates into the inside of the steel cord and is adhered to the entire circumference of each strand has been considered. This steel cord has a so-called open twist structure in which wires are twisted while providing a gap between the wires.

However, in a steel cord having an open twist structure, in order for the rubber material to adhere to the entire circumference of each strand and to sufficiently penetrate into the cord, the gap between the strands must be rubber. It is necessary to make the gap sufficient for the material to enter, that is, 0.02 mm or more. However, if a sufficient gap is provided between the strands, the twisted structure tends to be unstable during the production of the steel cord, causing the strands to skew and the twist to be uneven in the longitudinal direction of the steel cord. Disadvantage.

Therefore, as shown in FIG. 3, two strands 8, 8 are closely attached to the center and twisted, and one strand 9, 9 is arranged on both sides thereof. A steel cord 10 has been proposed in which the strands have a small gap with each strand of the twisted strands and are twisted at the same pitch in the same direction. (Japanese Utility Model Publication No. 61-393) In this steel cord, the two strands 8 at the center are in contact with each other in the longitudinal direction of the cord, so that the twist is stable and the strands 9 on both sides are formed. , 9 are completely covered with rubber.

[0008]

However, the steel cord 10 is not only inferior in corrosion resistance but also in that the rubber material does not penetrate in the contact portion between the two central wires 8, 8, and the steel cord is repeatedly applied to the steel cord. When a compressive bending stress is applied, there is a problem that fretting wear easily occurs and the fatigue life is shortened.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the rubber material surely penetrates between the strands to form a complete composite. An object of the present invention is to provide a steel cord for reinforcing rubber products, which does not easily generate ting wear and has excellent fatigue properties.

[0010]

In order to achieve the above object, a steel cord according to the present invention is a steel cord formed by twisting four strands having the same wire diameter. Twist the wire in the center and place one on each side
Two strands are arranged, and each one strand has a small gap with each strand of the twisted wire, and in the same direction,
In a steel cord twisted at the same pitch, P
₁ is 0.7 P or less, and at least one of the strands twisted at the center is P ₁ = 6d to 30d, d ₁ = (d
+ 2 / 100mm) to (d + 2 / 10mm) (however, P
= Twist pitch, P ₁ = habit pitch, d ₁ = habit outer diameter, d
(Element wire diameter).

By the way, the numerical limitation in the above configuration is a result obtained by a number of experiments, respectively, for the following reason.

When the habit pitch P ₁ is smaller than six times the strand diameter d for the spiral small habit shape of the strand,
The wire is easily broken due to undue plastic deformation applied to the wire at the time of hammering. On the other hand, if the wire is larger than 30 times, the tensile force due to the flow of the rubber material during molding of the rubber product or the ironing force applied to the cord surface As a result, the gap between the strands decreases, and the penetration of the rubber material becomes insufficient, so that P ₁ = 6d to 3
0d. The cord twist pitch P of the steel cord is preferably 8 to 12 mm from the viewpoint of twist stability and productivity, and P ₁ in this range is 0.3 P to 0.7 P for almost the same reason as described above. It is preferred that

Further, the habit outer diameter d ₁ is d + 2/100 mm
If it is smaller, the rubber material does not sufficiently penetrate into the cord during pressure vulcanization even if a rubber material having good fluidity is used, while d +
If it is larger than 2/10 mm, the stability of twisting will be poor,
Not only the fatigue property is reduced, but the cord elongation under extremely low load is increased, and the handling workability is poor, so that d ₁ = (d + 2)
/ 100 mm) to (d + 2/10 mm).

Here, the substantially spiral small habit means not only a precise spiral shape but also a substantially wavy shape, since substantially the same effect can be obtained.
By the way, if the wire diameter d of each strand is too small, the mechanical strength is inferior. On the other hand, if it is too large, the flexibility and the cord diameter increase, so that it is preferable to be in the range of 0.1 to 0.4 mm.

[0015]

When the steel cord for reinforcing a rubber product of the present invention having the above structure is pressed and vulcanized by being sandwiched between two rubber sheets, a substantially spiral shaped small wire between central strands is formed. The rubber material penetrates into the minute gap, and the periphery of each element wire is covered with the rubber material, so that the steel cord becomes a complete composite with the rubber material.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The steel cord for reinforcing rubber products of the present invention will be specifically described below with reference to embodiments. Example 1 In FIG. 1, a small spiral pitch P ₁ =
One strand 1 having a diameter of 7.0 mm and a habit outside diameter d _{1 of} 0.30 mm and one strand 2 which is substantially straight are twisted at the center (twist direction S twist, twist pitch P = 10 mm). One strand 3, 3 is arranged on both sides thereof, and each one strand has a small gap with each strand of the twisted wire, and has the same direction and the same pitch. The steel cord 4 is formed by twisting with each other. This embodiment is shown in Table 1 of the present invention 1.
Shown in Also, P ₁ = 2.0 mm and d ₁ = 0.42 mm
In the invention 3, P ₁ = 4.0 mm and d ₁ = 0.3
The case of 5 mm is shown in the present invention 5.

(Embodiment 2) In FIG. 2, a small spiral pitch P ₁ =
Two strands 5, 5 having a diameter of 7.0 mm and a habit outer diameter d _{1 of} 0.30 mm are twisted at the center in the same manner as in Example 1, and each strand having the same diameter on both sides thereof The steel cord 7 is formed by arranging one strand of each of the twisted wires with a slight clearance from each of the twisted wires and twisting them in the same direction and at the same pitch. This embodiment is shown in Table 2 of the present invention. P ₁ = 2.0 mm, d ₁ = 0.4
In the present invention, the case of 2 mm is defined as P ₁ = 4.0 mm and d ₁ =
The case of 0.35 mm is shown in the present invention 6. By the way, each wire diameter d of the wires 1, 2, 3, 5, and 6 of the first and second embodiments.
Is 0.25 mm. The outline of the manufacture of the steel cords 4 and 7 will be described. First, the two central wires are firstly twisted by a known twisting device, and then the wires on both sides are twisted with pins or the like. A steel cord is also manufactured.

As shown in Japanese Patent Publication No. 63-63293, a small spiraling habit is applied to the strands 1 and 5 by a hammering device which rotates with the supplied strand as an axis. A desired habit pitch P _{1 and a} desired habit outer diameter d ₁ are provided.

Next, in order to confirm the performance characteristics of the steel cord of the present invention, a comparative test was conducted between the steel cords of the present invention 1 to 6 described in the above embodiment and the conventional steel cord, and the penetration of the rubber material was examined. The elongation under a load of 5 kg, the fatigue property, the amount of fretting, and the workability were evaluated. The results shown in Table 1 below were obtained. In the table, N
S is the number of spiral small wires with a habit among the two wires at the center, d ₁ is the outer diameter of the habit, P ₁ is the habit pitch, RP is the permeability of rubber material, and SL is 5 kg load. Elongation, RF is fatigue, QF is fretting amount and HW
Indicates handling operability.

[0020]

[Table 1]

At the time of this evaluation, the permeability RP of the rubber material
(%) Is a rubber material having a 100% modulus of 35 kg / cm ² (normal rubber material used for a breaker of a tire in which a steel cord is embedded) under a tensile load of 5 kg applied to each cord. After vulcanization, take out the steel cord, disassemble the cord, observe the fixed length between each strand, and find the ratio of the length of the observed length that has contact with the rubber material as a percentage. , The average value was displayed. This value needs to be 60 or more.

The elongation SL (%) at a load of 5 kg indicates the elongation of each cord, and is 0.4 in terms of handling workability and twist stability.
It needs to be 0% or less.

For the fatigue RF, a plurality of steel cords are used.
A 100% modulus is embedded in a rubber material of 35 kg / cm ² to form a composite sheet. Using this sheet, the cord breaks through fretting wear, buckling, etc. using a three-point pulley bending fatigue tester. The number of repetitions up to this point was determined, and the result was represented by an index with the code of Conventional Example 1 as 100.

The amount of fretting QF (μ) is calculated by disassembling the cord of the three-point pulley bending fatigue tester, taking a micrograph of the fracture surface of each wire, and determining the maximum wear of the fretting-occurring portion of the fracture surface. The depth was measured. Then, the average value of each strand was calculated and displayed.

The handling workability HW is an evaluation of the complexity of the work and the handling of the cord during the production of the steel cord and the formation of the composite sheet. ×, very inferior compared to
A little inferior was evaluated as △, and a no difference was evaluated as ○.

In Table 1, Conventional Example 1 is 1 × 4 × 0.2
5 Closed twisted steel cord, very stable twist, elongation at 5 kg load, good handling workability, but poor rubber material infiltration.

Conventional example 2 has an average shaping ratio (cord diameter when twisted with a gap between each strand / cord diameter when each strand is densely twisted × 100) of 1% of 130% 4x
It is a steel cord with a 0.25 open twist structure and has excellent penetration and fatigue properties of rubber material, but has large elongation under a load of 5 kg and is inferior in handling workability.

Conventional example 3 is a steel cord having a 2 + 1 + 1 structure composed of only substantially straight wires, has a small elongation under a load of 5 kg, has good handling workability, but has two strands twisted in the center. The penetration of the rubber material between the strands is still insufficient, the amount of fretting wear is large, and the fatigue properties are poor.

Comparative Examples 1 to 3 are steel cords having a 2 + 1 + 1 structure using a spiral wire having a small habit. However, the habit shape is different from that of the present invention, and all the evaluation items cannot be satisfied.

On the other hand, the steel cords of the present inventions 1 to 6 have rubber infiltration properties, elongation under 5 kg load, fatigue properties,
It was found that both the amount of fretting and the workability were satisfactory and that it was optimal as a reinforcing material for rubber products.

[0031]

[Effect of the Invention] The steel cord for reinforcing rubber products of the present invention has no hollow portion inside the cord over almost the entire area in the longitudinal direction of the cord, and has a small cord elongation under extremely low load.
The handling workability is also good. In addition, when the steel cord is covered with rubber material, the rubber material surely spreads between the wires constituting the steel cord, so that it becomes a complete composite with rubber material, preventing corrosion of the cord and rubber material. The separation phenomenon between the cord and the cord can be prevented, and the fatigue life of the rubber product can be extended. Moreover, even if repeated bending stress is applied, buckling does not easily occur, and the amount of wear due to the fretting phenomenon is small, so that excellent fatigue properties are obtained. further,
If the cord elongation under extremely low load is large, there are problems such as the puncture of the reel when winding the steel cord on the reel and the waving of the sheet when forming the composite sheet. It has the effect.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a steel cord according to a first embodiment.

FIG. 2 is a sectional view showing a steel cord according to a second embodiment.

FIG. 3 is a sectional view showing a conventional steel cord having a 2 + 1 + 1 structure.

[Explanation of symbols]

 1, 5: wire having a substantially spiral small habit 2, 3, 6: wire 4, 7, ... steel cord

Claims (1)

(57) [Scope of request for utility model registration] 1. A steel cord formed by twisting four strands having the same wire diameter, wherein two strands are twisted in the center, and one strand at each side. I arranged to have a respective wire and small unto gap of each one line which strands twisted mentioned above and in the same direction, steel cords twisted at the same pitch, P ₁ is 0.7P or more
At least one strand is P ₁ = 6d~30d the combined strands twisted under, and in the _{center, d 1 = (d + 2} / 100m
m) to (d + 2/10 mm) (where P = twist pitch,
A steel cord for reinforcing rubber products, which has a substantially spiral small habit satisfying P ₁ = habit pitch, d ₁ = habit outer diameter, d = element diameter.