JPH10259582A - Tire-reinforcing steel cord - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high-elongation cord that has excellent fatigue resistance, secures traveling comfort and driving stability and shows excellent twisting efficiency. SOLUTION: Small spiral kinds are formed at a kink pitch of P1 in the apparent outer diameter of d1 all over the metal wires 2 with wire diameter of (d) and these wires are twisted in the twisting pitch of P to produce the objective tire-reinforcing steel cords so that their d, P, d1 and P1 may satisfy the following conditions (1), (2) and (3): (1) 0.01<=(d1 -d)/P1 <=0.03, (2) 1.2<=d1 /d<=2.5, (3) 40<=P/d<=90, and the cyclic elongation at break is >=4.5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire reinforcing steel cord which can be suitably used for reinforcing a belt portion of a tire of a heavy-duty vehicle such as a truck, a bus, a jeep or the like, or a vehicle traveling on a bad road. Hereinafter, simply referred to as “steel cord”).

[0002]

2. Description of the Related Art A large number of steel cords of this type are coated with a rubber material in a state of being aligned in parallel and used as a reinforcing material for automobile tires. The basic conditions when steel cord is used as a tire reinforcing material are that it has excellent mechanical strength, good chemical adhesion with rubber materials, good corrosion resistance, and a certain degree of flexibility. And the rubber has good penetration into the steel cord. In order for the steel cord to sufficiently fulfill the role of a reinforcing material for a rubber product, it must be a complete composite with a rubber material.

In particular, heavy-duty vehicles such as trucks, buses, and jeep vehicles and vehicles traveling on rough roads require excellent cut resistance in addition to the above conditions. The cut resistance is a performance that prevents a steel cord from breaking due to excessive deformation of a local portion of a tire when the tire steps on a stone or rides on a curb or the like. In order to improve the cut resistance, a steel cord having high elongation at the belt portion of the tire, that is, a so-called high elongation cord is used. The conventional high elongation cord has a twist configuration of 3 × 7 or 4 ×
This was a steel cord of the type in which the twist pitch was reduced by multi-layer twisting of No. 4. However, there is a problem that the productivity is low because the twisting step is required a plurality of times, and the manufacturing cost is increased.

[0004] In the conventional steel cord, when a tire is damaged while the automobile is running on a road surface, moisture penetrating from the wound reaches a gap in a central portion of the steel cord, and the steel cord is wound by a capillary phenomenon. A phenomenon of propagation in the longitudinal direction occurs. As a result, there is a problem that the steel cord is corroded and the fatigue resistance is greatly reduced. Moreover,
There was a problem that the adhesion between the steel cord and the rubber was reduced due to the corrosion of the steel cord, and when the steel cord was further advanced, the steel cord and the rubber were separated, so-called a separation phenomenon.

Therefore, in recent years, as a solution to the above-mentioned problem of the multilayer twisted high elongation code, a single layer open twisted structure high elongation code (hereinafter, referred to as a single layered high elongation code) has been used. . This is a single-layer twisted steel cord that is loosely twisted so as to provide a gap between the wires as disclosed in, for example, Japanese Patent Publication No. 6-57482 and Japanese Utility Model Publication No. 6-40623. And, by this, it is intended to improve rubber penetration while securing elongation.
That is, rubber invades from the gap between the strands during tire molding,
Since rubber is filled into the inside of the steel cord, even if the tire is damaged, moisture does not reach the inside of the steel cord and does not corrode.

[0006] The single layer structure high elongation code has an excessively large shaping (molding rate of 105 to 14) on each strand in advance.
0%) and then twisted with a twisting machine.
The term "molding ratio" as used herein is defined as "cord diameter when twisted with a gap between each strand / cord diameter when each strand is densely twisted" x 100 (%). And an excessively large pitch is equivalent to a twist pitch.
The twist pitch of this cord had to be considerably smaller than that of a normal steel cord in order to ensure a sufficient breaking elongation. For example, 6-4
No. 0623 discloses an example of “1 × 5 × 0.3
8, pitch 6 mm "steel cord is used. The pitch of 6 mm is considerably smaller than the pitch of the closed-type steel cord of the embodiment and the pitch of the conventional open-type steel cord. The conventional single-layered high elongation cord utilizes the general property that the length of each strand in the unit length of the cord is increased by reducing the pitch, thereby increasing the elongation allowance.

[0007]

However, the conventional single-layer open structure high elongation code has the following problems. First, since the twist pitch is small, the twist efficiency is extremely deteriorated. That is, for example, when the rotation speed of the twisting machine is constant, the twist pitch is １ ／.
As a result, the twisting efficiency is reduced by half, which leads to an increase in cost, which is a fatal problem in these days when cost competition is intense. Secondly, since the pitch is short, the restoring force when receiving an excessive tensile load is poor. That is, since the twist pitch is short, the cord itself is in a state of a kind of spring, and the initial breaking elongation is large, but when repeatedly receiving an excessive tensile load, the state becomes `` the spring is fully extended ''. turn into. For this reason, when embedded and used in rubber, the cord and rubber no longer work together, causing local stress to act inside the tire, reducing ride comfort and steering stability. In this case, the steel cord and rubber are partially separated from each other, so that the fatigue resistance of the steel cord is greatly reduced, the life of the tire is extremely reduced, and the safety is also reduced.

There are various means for individually solving the various problems of the prior art. For example, to improve the twisting efficiency, the twisting pitch may be increased, and to improve the cut resistance, the twisting pitch may be reduced to increase the elongation. However, a steel cord satisfying both twisting efficiency and cut resistance was impossible with the conventional cord configuration. The present invention solves the above-mentioned problems of the conventional single-layer open structure high elongation cord, and has good twisting efficiency, excellent fatigue resistance, and good ride comfort and steering when used in a tire belt. An object is to ensure stability.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a small spiral habit different from a twisted habit is provided on all of the cord constituting wires, and the apparent outer diameter d _{1 of} the small spiral habit is reduced. By appropriately controlling the interrelationship between the pitch P ₁ , the twist pitch P of the steel cord, and the strand diameter d, the conflicting properties of twist efficiency and cut resistance can be satisfied at the same time. That is, the steel cord for tire reinforcement according to the present invention has the same strand diameter d (d = 0.2
In a steel cord having a 1 × n structure in which n (n = 4 to 6) metal wires of 5 mm to 0.40 mm) are twisted at a twist pitch P, the conditions of the following expressions (1) to (3) are satisfied. It is limited to satisfy all conditions, and the elongation at break is 4.5% or more. (1) 0.01 ≦ (d ₁ −d) / P ₁ ≦ 0.03 (2) 1.2 ≦ d ₁ /d≦2.5 (3) 40 ≦ P / d ≦ 90 Here, repeated fracture The elongation is, as described later, a length obtained by using an Instron tensile tester and applying a tensile load of 60% of the breaking load at the time of the initial breaking of the steel cord, repeating the loading and removing as one set 10 times, Thereafter, a tensile load was applied to measure the length when at least one strand was broken. If the repeated elongation at break is 4.5% or more, the fatigue resistance and cut resistance required for the high elongation cord can be sufficiently secured. Is preferably 5% or more.

In the formula (1), when (d ₁ -d) / P ₁ is less than 0.01, a gap between the steel cord strands cannot be sufficiently secured, and the rubber penetration property is reduced. Also, 0.0
If it exceeds 3, the rubber and the steel cord will not work together, and the fatigue resistance will decrease and the ride comfort will deteriorate. In addition, in the formula (2), when d ₁ / d is less than 1.2, a sufficient gap cannot be secured between the strands, so that the rubber infiltration property is deteriorated and sufficient elongation cannot be obtained. Also,
If it exceeds 2.5, the gap becomes too large, the cord stability is deteriorated, and the fatigue resistance is reduced. Further, equation (3)
When P / d exceeds 90, it is difficult to secure elongation, and when it is less than 40, the twisting efficiency cannot be sufficiently increased as compared with the conventional single-layered high elongation cord. It should be noted that satisfying all the conditions of each expression provides a synergistically effective effect as a high elongation code, and if any of the conditions is not satisfied, some problem as described above occurs. Things.

In the high elongation cord, it is preferable that the difference between the initial elongation at break and the repeated elongation at break is small. Also, a small spiral pitch P
₁ is preferably in the range of P ₁ = 0.2P~0.8P. This is because, if P ₁ is less than 0.2P, can not increase the habit outer diameter d ₁ habit pitch is too small, smaller gaps between the strands, the rubber intrusion ratio decreases, also the elongation of the steel cord It is not enough. When P ₁ conversely exceeds 0.8P, because the action of the small spiral habit is rapidly lost, rubber penetration property and elongation at break is lowered. Further, a more preferable range is P ₁ = 0.3P
~ 0.6P.

The steel cord of the present invention has sufficient elongation at break, has a sufficient restoring force even when repeatedly receiving an excessive load, has excellent cut resistance, and has sufficient rubber penetration. And the twisting efficiency can be greatly improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a steel cord according to the present invention,
(A) is a side view, and (B) is a cross-sectional view. In FIG. 1, a steel cord 1 has a small spiral habit having an apparent outer diameter d ₁ and a habit pitch P ₁ , and all the metal wires 2 provided regularly are simultaneously formed in the same direction as the spiral direction of the spiral habit. It is configured by twisting. This steel cord 1 has the same strand diameter (0.25 to 0.40 mm)
(N = 4 to 6) of the metal strands 2 is previously provided with a small spiral habit, and then each strand is twisted by a stranding machine. As a means for applying a small spiral habit to each strand, as shown in JP-B-63-63293, a hammering device that rotates with the supplied strand as an axis may be used. As another means, it is conceivable that the wire is bitten into a gear or the like and subjected to planar corrugation, and then the wire is twisted into a substantially spiral shape.
This method is not preferable because stress concentrates at the bending point and fatigue resistance deteriorates. In the present invention, since each element wire has a small spiral habit smoothly and regularly, stress concentration hardly occurs, which effectively acts on fatigue resistance. This small spiral shape is important in high elongation codes

The steel cord according to the present invention can use either a buncher type or a tubular type twisting machine.
A "hard twist" structure that can be manufactured by densely twisting each strand in the same direction as the helical direction of the small spiral habit, and completely different from the loose twist of the conventional single-layered hieronation cord And has good shape stability and excellent fatigue resistance. It should be noted that the degree of twisting rigidity of the steel cord can be adjusted by adjusting the strand feeding tension and the cord winding tension during twisting. Thus, the elongation at break of the steel cord can be adjusted to some extent.

[0016]

EXAMPLES Examples of the present invention will be specifically described below in comparison with conventional examples and comparative examples.

Tables 1 to 3 show the results of trial production of steel cords of various configurations in which a wire rod equivalent to SWRS77A was drawn, and then a plurality of brass-coated wires were twisted with a buncher twister. It is shown. Table 1 is 1 ×
Table 2 shows a steel cord having a 1 × 5 structure, and Table 3 shows a steel cord having a 1 × 6 structure. And change the twist pitch, the number of twisted wires, the shape of the twist,
Example cords satisfying the conditions of the present invention, comparative examples deviating from the conditions of the present invention, and prototype cords of the conventional example, which is a conventional single-layered high-elongation cord, were manufactured, and each steel cord was evaluated. In addition, the experiment No. in each table | surface.
Thirteen steel cords are conventional single-layered high elongation cords, and the embossing rate was set to 120%.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

Next, each evaluation item in the table will be described. Initial breaking elongation (%) A steel cord before embedding in rubber is cut into a fixed length (length L) to form a test piece, which is pulled up and down by an Instron tensile tester, and when at least one strand breaks. The length L1 of the steel cord was measured and calculated by the following equation. Initial elongation at break (%) = (L1-L) / L × 100 Repeated elongation at break (%) Using the same test machine as above, the breaking load at the time of initial breaking obtained by using a steel cord before embedding in rubber A test piece (length L2) is obtained by repeating the load and removal as one set 10 times at a tensile load of 60%. A tensile test similar to the above was performed, and the length L3 of the steel cord when at least one strand was broken was measured and calculated by the following equation. Elongation at break (%) = (L3-L2) / L2 × 100 Rubber penetration rate Each cord is embedded in a rubber material with a tensile load of 5 kg applied, vulcanized and pressed, then the cord is taken out and the cord is disassembled. Then, a certain length was observed, and the ratio of the length having a trace of contact with the rubber material to the observed length was expressed as a percentage. Fatigue resistance A steel cord is sandwiched between two rubber sheets with a tensile load of 5 kg applied, and after vulcanization and pressurization, the rubber sheet is cut into narrow and narrow pieces at a fixed width, and one steel cord is rubberized. Create a rubber belt including the center and use it as a test piece. Next, the test piece was placed over a group of pulleys of a three-point pulley fatigue tester used as a belt fatigue tester, and the test piece was reciprocated in the longitudinal direction with a constant load applied. The number of reciprocations until the sample was broken was measured. 13 for the conventional example is 100
Exponential notation. Greater fatigue resistance is better. Twisting efficiency The productivity of each cord in the state where the rotation speed of the twisting machine was kept constant was measured in Experiment Nos. The case of 13 is expressed as an index with 100 as the index, and the higher the twisting efficiency, the better.

As is clear from Tables 1, 2, and 3, the conventional single-layered hierogation code (experimental N
o. 13) Although the initial elongation at break is large, the repeated elongation at break is low, the fatigue resistance is considerably poor, and the twist pitch is small, so that the production cost is required. (Each Table Experiment Nos. 1 to 7)
Has a repeated elongation at break of 4.5% or more, a small difference between the initial elongation at break and the repeated elongation at break, a high rubber penetration rate, high fatigue resistance, and high elongation. The code turned out to be very good. Further, since the twisting efficiency is several times higher than that of the conventional example, it was confirmed that the steel cord can be manufactured at low cost.

On the other hand, the comparative examples which did not satisfy any of the conditions of the present invention had the following problems. (D ₁ −
d) / P is less than 0.01 (Experiment No. 1 in each table)
In 2), the elongation at break was small, and the fatigue resistance and the rubber penetration were lower than those of the conventional example. (D ₁ -d) / P is 0.
Those over 0.3 (Experiment No. 11 in each table) slightly improved the fatigue resistance as compared with the conventional example, but were not sufficient. Those whose d ₁ / d is less than 1.2 (Experiment No.
In 9), the rubber penetration rate was extremely poor and the fatigue resistance was poor. When the ratio d ₁ / d was more than 2.5 (Experiment No. 10 in each table), the rubber penetration rate was slightly lowered, and the fatigue resistance was not sufficient. Those having a P / d of more than 90 (Experiment No. 8 in each table) had low elongation at break, low rubber penetration rate, poor fatigue resistance, and were not effective as high elongation cords.

[0024]

The steel cord of the present invention is provided with a spiral habit smaller than the twist pitch on all the strands, and
The relationship among the habit outer diameter d ₁ , the habit pitch P ₁ , the strand diameter d and the twist pitch P is appropriately limited, and since the repetition breaking elongation is large, the cut resistance is excellent and the high rubber penetration can be secured. Also, compared to the conventional single-layer open structure high elongation cord, the difference between the initial elongation at break and the repeated elongation at break is small, so it is excellent in fatigue resistance, and the twisting efficiency is improved several times. It has excellent effects such as production.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a steel cord of the present invention,
(A) is a side view, and (B) is a cross-sectional view.

[Explanation of symbols]

 1 Steel cord 2 Metal wire

Claims (1)

[Claims] (1) The same strand diameter d (d = 0.25 mm to 0.4)
0 mm) in a 1 × n steel cord in which n (n = 4 to 6) metal strands are twisted with each other at a twist pitch P, all of the metal strands have an apparent outer diameter d ₁ and a habit pitch. provided habit of small spiral is P _1, and d, P, d ₁ and P ₁ satisfies the following conditions (1) to (3), and, in repeated breaking elongation of 4.5% or more A steel cord for reinforcing a tire, wherein (1) 0.01 ≦ (d ₁ −d) / P ₁ ≦ 0.03 (2) 1.2 ≦ d ₁ /d≦2.5 (3) 40 ≦ P / d ≦ 90