JP2920422B2 - Steel cord and radial tire using this as reinforcement - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steel cord for rubber reinforcement, in particular, a high-strength steel cord of a single twist type and a radial tire using the same as a reinforcing material.

BACKGROUND ART In a radial tire, a reinforcing layer called a belt is provided between a tread and a carcass, and a steel cord is embedded in the reinforcing layer as a composite reinforcing material.

In such a steel cord, for example, a steel cord having a high elongation (High Elo
ngation Cord).

This high elongation steel cord is roughly classified into 3 × 7, 4
There are a multi-twist type represented by × 2 or 4 × 4, and a single-layer twist type of 1 × n type having 6 or less strands. However, the former multi-twist type has a problem that productivity is low because the number of twisting steps is two or more, and that the weight of the belt layer increases because of the large number of strands. Single layer twist types are generally advantageous.

The conventional single-layer twist type has, for example, a structure in which five strands are twisted in the same direction at a short twist pitch in a 1 × 5 structure. That is, by shortening the twist pitch and twisting the spring, the axial center (center) of the cord is made hollow to secure elongation.

However, in order to obtain a large elongation of, for example, 4% or more of the cutting load in this method, a method disclosed in Japanese Patent Application Laid-Open Publication No.
As described in Japanese Patent Publication No. 83, it is necessary to make the twist pitch very short, for example, 6.5 mm, or to make a double twist. For this reason, the productivity is reduced, and the twist reduction is large due to the short twist pitch, and the strength of the steel wire cannot be utilized efficiently. In addition, since a void is formed in the center of the cord where rubber does not penetrate, the tread is damaged and stays in the void when moisture enters from the wound, which causes corrosion fatigue of the steel cord or rubber and rubber. There is a problem that the adhesion is lowered to cause separation.

As a measure against such rubber penetration, Patent Application Publication No. 2-68337
No. 6 and Patent Application Publication No. 4-24296 disclose a high elongation steel with a single twist cord, a short twist pitch, and an open twist so as to loosen the twist and provide a gap between the wires. Code has also been proposed.

However, this prior art also has the problems of cost and strength reduction due to reduced twisting because the twisting pitch is short. further,
Since the twisting structure is unstable, the gap between the strands is liable to change, and when an external force is applied in the longitudinal direction of the cord during vulcanization of the rubber, the gap is reduced or the offset is generated. For this reason, fatigue breakage tends to occur due to stress concentration during buckling of the steam cord. Further, since the wires are loosely twisted and large gaps exist between the wires, there is a problem that the cord easily penetrates when a metal piece such as a nail is depressed, and the trauma resistance is reduced.

The present invention has been made in order to solve the above-described problems, and has an object to have a large elongation at break, a low twist reduction, a good rubber permeability, and a high resistance. An object of the present invention is to provide a single-layer twisted high elongation steel cord that can achieve cutability, good ride comfort and steering stability, and that can be easily and efficiently manufactured with a single twist. .

A second object of the present invention is to provide a radial tire having high cut resistance, good ride comfort and maneuverability, and in which a separation phenomenon does not easily occur.

DISCLOSURE OF THE INVENTION In order to achieve the above first object, the present invention provides a 1 × n wire in which three to six strands are twisted at a time in the same direction and at the same pitch.
A steel cord having a structure and an elongation at break of 5% or more, wherein the steel cord has a corrugated pitch L of 0.25 ≦ L / P ≦ 0.55 in relation to a twist pitch P of the cord;
Three to six strands that have been subjected to a spiral waving with a corrugation height H of 1.05 ≦ H / d ≦ 2.0 in relation to the strand diameter d have a cord outer diameter D and a cord twist pitch P of Having a helical composite structure twisted so that the ratio P / D is in the range of 8 to 15,
And 35 kgf / mm ² load elongation at 0.71 to 1.00%, is obtained by a structure in which 70 kgf / mm ² load at break is in a range of 1.18 to 1.57%.

The steel cord according to the present invention is provided with three to five wires on a plate or cylindrical rotating body on the strand introduction side of the buncher type twisting machine.
Using a device with a revolving preformer with pins attached, no means for fixing the twist of the wire is installed before and after the revolving preformer. The preformer is rotated in the direction opposite to the rotation direction of the buncher-type twisting machine, and the twist of the strand generated from the twisting machine body is positively guided to the revolving preformer 7 so that each strand has a helical habit. It is made by attaching and then twisting all the strands with a buncher type twisting machine.

Further, in order to achieve the second object, the present invention is to use a high elongation steel cord having the above-described configuration, and to provide a radial tire partially reinforced even if the high elongation steel cord is not used.

The part reinforced by the steel cord is a belt, more preferably a belt close to a tread.

 The advantages and features of the present invention as described above will be described.

First, since the steel cord of the present invention has an elongation at break of 5% or more, a tire using the same has good cut resistance.

In addition, all the wires constituting the cord are given a helical wavy shape in which the helical shape is different from the helical shape due to the twisting of the cord, and specifically, in relation to the twist pitch P of the cord, it is 0.25. A spiral wavy shape having a wavy height H of 1.05 ≦ H / d ≦ 2.0 is obtained in relation to a wavy pitch L of ≦ L / P ≦ 0.55 and a strand diameter d. For this reason, a gap is formed between the strands while being twisted once in the same direction at a long twist pitch, so that rubber penetration is good, rubber penetrates to the center of the cord, preventing separation. Can be.

In addition, it has a helical composite structure that is twisted so that the ratio P / D of the cord outer diameter D to the cord twist pitch P is in the range of 8 to 15, and the cord twist pitch is long, so productivity is reduced. In addition, the strength utilization rate can be increased with a small twist reduction, and the cost can be reduced due to the long twist pitch and the single-layer twist.

Further, the steel cord according to the present invention has a compact cord form because the gap between the strands is obtained by the strands that have been previously helically corrugated.
Therefore, the gap is stable at the time of topping, and the displacement of the strand is unlikely to occur. Furthermore, since the bird's cage is less likely to be formed due to the axial compressive force, and an excessively large space is not formed as in a loosely twisted cord, it is difficult for foreign matter to penetrate the cord even when suffering a traumatic injury through the tread. Become.

Further, the code of the present invention, the elongation at 35 kgf / mm ² load
0.71 to 1.00%, for 70 kgf / mm ² load at break is in the range of 1.18 to 1.57%, it is possible to improve the balance between stiffness and elongation when used in the belt, good ride comfort and driving stability can do.

Further, since the stranding condition of the strand is set to 1.05 ≦ H / d ≦ 2.0 in relation to the stranding pitch L of 0.25 ≦ L / P ≦ 0.55 and the strand diameter d, it is strong. And good elongation can be realized without lowering the elongation.

Further, since the cords are twisted so that the ratio P / D of the cord outer diameter D to the cord twist pitch P is in the range of 8 to 15, the elongation at break of 5% or more can be realized with less twist reduction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway front view of a radial tire using a steel cord according to the present invention.

FIG. 2 is a partial sectional view of a fourth belt according to the present invention.

FIG. 3 is an enlarged side view showing an example of the steel cord according to the present invention.

 FIG. 4 is an enlarged sectional view of FIG.

FIG. 5 is a partial side view of a strand taken out of the cord shown in FIG.

FIG. 6 is an explanatory view illustrating a steel cord manufacturing apparatus according to the present invention.

FIG. 7 is a plan view of the revolution preformer in the apparatus of FIG.

 FIG. 8 is an enlarged side view of a steel cord of a comparative example.

 FIG. 9 is a side view of a conventional steel cord.

FIG. 10 is a cutting load-elongation curve diagram of the steel cord according to the present invention, the steel cord of the comparative example, and the steel cord of the conventional example.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a radial tire to which the present invention is applied. 11 is a carcass, 12 is a tread, and 13a, 13b, 13c, and 13d are a plurality of tires arranged between the carcass 11 and the tread 12 (four tires in this example). ) Belt.

As shown in FIG. 2, the belts 13a, 13b, 13c, and 13d are formed by topping rubber from both sides of a parallel-arranged steel cord 2 to form a rubber layer 14, and vulcanizing after forming the tire.

The rubber may be either natural rubber or synthetic rubber, but from the viewpoint of separation and cord durability, a 50% modulus is required.
It is preferably 10 to 40 kg / cm ² .

A feature of the present invention is that the steel cord 2 and the belt 13 d which is closest to the tread 12 using the steel cord 2 are used.
It was buried in.

3 and 4 show a high elongation steel cord having a 1 × 5 structure to which the present invention is applied, which has a collapsed pentagonal cross-sectional shape.

At least one pair of adjacent wires 1 and 1 constituting the cord 2 are in contact with each other.
At least one appears for each pitch.

The wire 1 has a diameter d of 0.15 to 0.45 mm, similarly to a known wire.
Brass plating or zinc plating is applied to the surface of the steel wire within the range. Before the cords are twisted, the strands 1 and 1 are given a wave so that waves having a predetermined pitch and height are continuously repeated. In this state, the strands 1 and 1 are twisted at once at the same pitch and in the same direction at a predetermined twist pitch P larger than the corrugated pitch. FIG. 5 shows a wave form of one strand 1 when the twisted cord is disassembled, and 10 is a wave.

The steel cord 2 according to the present invention will be described in detail.
The upper limit of the number of strands 1 in the present invention is six. This is because, when the number of strands is 7 or more, the cord becomes a multi-layered cored form by twisting, so that good elongation characteristics cannot be obtained. Therefore, the present invention does not include 1 × 7 structure, 1 × 8 structure, 1 × 9 structure, 1 × 10 structure, 1 × 11 structure, 1 × 12 structure, and the like. However, the present invention is not limited to the 1 × 5 structure as shown,
Includes × 4 structure and 1 × 6 structure. In addition, in these, a single wire having the same diameter or a moderately thin wire is spirally wrapped on the outer periphery.

The present invention is based on the fact that such a steel cord having a 1 × 3 structure to a 1 × 6 structure has a high elongation characteristic with an elongation at break of 5% or more. This is because it is indispensable for improving the cut resistance of the tire.

The present invention aims at achieving such an elongation at break of 5% or more with a single twist without shortening the cord twist pitch, and at the same time, improving the rubber permeability.

Therefore, according to the present invention, the wire 1 is given a spiral wavy shape in advance, and the wires 1, 1 are twisted to give a spiral shape different from the spiral shape previously attached. Thus, the twisted element wire 1 is given a helical composite shape so that the element wire can be twisted at a design twist rate or more.

The corrugated pitch L of the strands 1 increases the elongation if shortened, but the breaking load decreases. The shorter the cord twist pitch P, the greater the elongation, but the lower the twist, the lower the breaking load. Therefore, in the present invention, the corrugated pitch L and the cord twist pitch P are set within predetermined optimum ranges.

First, the corrugated pitch L of the strand 1 is smaller than the cord twist pitch P, and the L / P is preferably in the range of 0.25 to 0.55. The reason is that making the corrugated pitch L smaller than 0.25 is effective for improving the elongation, but the shape becomes uneven, the load is not uniformly applied to each strand, and the cord cutting load is reduced. That's why. However, if the corrugation pitch L is larger than 0.55 in L / P, the length of the strand twisted beyond the design twist rate becomes insufficient, and the elongation of the cord decreases, which is not appropriate.

The corrugated height H is 1.05 in relation to the wire diameter d.
The range of ≦ H / d ≦ 2.0 is preferred. The reason is that H / d is 1.05
If it is smaller than this, the elongation will be insufficient, and if H / d is more than 2.0, a uniform load will not be applied to the strand, and the elongation will also be insufficient.

On the other hand, the cord twist pitch P is represented by the ratio (P / D) to the cord outer diameter D as described above. Here, the “cord outer diameter D” refers to X in FIG.
It is calculated by averaging the element diameters measured in the -X direction and the Y-Y direction, and the present invention sets the P / D to 8 to 15, most preferably 10 to 14.

If the P / D is less than 8, the productivity is still low, the reduction in twist is large, and the strength of the strand cannot be efficiently utilized, and the twist is not uniform, which is not suitable. Making the P / D larger than 15 is effective in terms of cord productivity and twist reduction, but cannot achieve elongation at break of 5% or more and is not appropriate. .

By setting the corrugated pitch L in the range of 0.25 ≦ L / P ≦ 0.55 and the cord twist pitch P in 10/14 by P / D, it is possible to achieve a good balance between elongation characteristics, productivity and rubber permeability. .

Further, the steel cord 2 according to the present invention has an elongation at break of 5% or more as described above, and in addition to 35 kgf / mm
The elongation at ² loading from 0.71 to 1.00%, the elongation at 70 kgf / mm ² load 1.
The range is 18 to 1.57%.

The reason for this is that if the elongation at break is merely specified, suitable elongation characteristics cannot be realized when actually used for a belt, and the practicability is poor.

35 kgf / mm ² load elongation is elongation at 1/6 load of the cutting load. 35 kgf / mm ² load elongation is not well follow the code the motion of 0.71% smaller than rubber, undesirably deteriorating the riding comfort. However, if it is increased so as to exceed 1.00%, the rigidity is poor and too soft, so that the controllability of the steering deteriorates.

70 kgf / mm ² load elongation is the elongation at 1/4 load of the cutting load. Similarly, if it is less than 1.18%, the ride comfort will decrease, and if it is more than 1.57%, the maneuverability will decrease. . Within the above range, not only the cut resistance is good, but also the riding comfort and maneuverability are good, and ideal cord elongation characteristics can be realized.

Accordingly, the present invention provides a single-layer twist type elongation at break of 5%.
In spite of the high elongation steel cord described above, the twist pitch is long and a large elongation is obtained by once twisting, so that the twist reduction is small and the strength of the material can be used efficiently.

Furthermore, a plurality of twisted strands with a helical wavy pattern at a pitch shorter than the cord twist pitch are twisted at the same time at a long twist pitch. . For this reason,
Although it is a so-called compact cord, a gap leading to the center of the cord is formed everywhere, so that the rubber has good permeability and excellent corrosion fatigue resistance.

As a result, even if an external injury is caused, foreign matter does not penetrate, and the separation of the belt can be effectively prevented while having good cut resistance. Also, since the balance between rigidity and elongation is good, riding comfort is good and maneuverability is good. And a radial tire with good durability can be obtained.

The steel cord 2 according to the present invention is manufactured in one step by a double twist type buncher type twisting machine 5 schematically shown in FIGS.

That is, the buncher type twisting machine 5 has a main body (cradle) 52 and hollow shafts 51 and 51 'driven and rotated by a prime mover 50, and a bow coaxially rotating with the hollow shafts 51 and 51' on the main body 52. 53,53 are installed. A winding bobbin 56 and a capstan 55 upstream of the winding bobbin 56 are provided on the main body 52, and an overtwisting machine 54 is further upstream of the winding bobbin 56. A voice 6 is provided on the hollow shaft 51 on the inlet side, and a plurality of revolution preformers 7 are arranged upstream of the voice 6.

Each of the revolution preformers 7 has three to five pins 70, 71, 72 attached to a plate-shaped or cylindrical rotating body 74, respectively. A plurality of supply bobbins 8 are provided upstream of the revolving preformer 7, and the wires 1 are led out of the supply bobbins 8 and collected by the voice 6 through the pins 70, 71, 72, respectively. I have.

In addition, no rolls or the like for fixing the twist of the strand are installed before and after the revolving preformer 7, and the twist of the strand generated from the twisting machine body is positively reduced.
Should be guided to

Power from the buncher-type twisting machine 5 is guided to each of the rotating bodies 74 via a clutch or a transmission (not shown).
The rotating bodies 74 are revolved at the same time by linking the 74 with each other by gears or the like. The revolution is adjusted in a direction opposite to that of the bow 53 and at a predetermined rotation ratio.

Therefore, in producing the cord, the wires 1 are guided from the supply bobbins 8 to the voices 6 via the revolving preformers 7, respectively. Then, the wire 1 is guided through the hollow shaft 51 through the guide roll 57 through the bow 53, from the other guide roll 58 through the hollow shaft 51 ′ to the overtwisting machine 54, and is wound up through the capstan 55. Lead to 56.

In this state, the hollow shafts 51, 51 'are driven to rotate the bow 53, and the revolving preformers 7, 7 revolve at a required ratio with the rotation of the bow 53. In this way, the strand 1 is given a continuous wavy shape while passing through the pins 70, 71, 72 of the revolution preformer 7. In addition, since the preformer 7 itself rotates around the wire passing line, the wire becomes spiral, and in this state, the voice 6 is continuously sent to be bundled.

Then, in this state, each of the strands 1 and 1 enters the hollow shaft 51, and the first twist is inserted in the process of reaching the guide roll 57. Further, in the process from the guide roll 58 to the hollow shaft 51 ', a second twist is inserted, and the steel cord 2 is thereby twisted.
Then, while passing through the overtwisting machine 54, the twist is adjusted and the bobbin 56 winds the twist.

The pitches of the first and second twists are larger than the corrugated pitch by the revolving preformer 7, and the twist pitch is longer than 10 times the cord diameter (16 to 30 times for one time). Therefore, the steel cord 2 as illustrated in FIGS. 3 and 4 can be efficiently produced.

If the rotation directions of the revolving preformers 7, 7 and the bow 53 are the same, the corrugated pitch becomes substantially longer. In contrast, the revolution by the rotation direction in the opposite direction of the preformer 7,7 and bow 53, the actual corrugation pitch L is, the corrugation pitch L ₀ by the revolution preformer reciprocal code twist pitches P The reciprocal of the sum of the reciprocals, ie, [L =
(L ₀ × P) / (L ₀ × P)], and the short corrugated pitch L
Can be obtained.

Example Next, an example of the present invention will be described.

1) First, the steel cord of the present invention was made, and the results of the property test were shown in Table 1 together with Comparative Examples 1 to 7 and the conventional example.
Shown in

The manufactured steel cord had a strand diameter of 0.35 mm and a 1 × 5 structure, and the manufacturing apparatus shown in FIGS. 6 and 7 was used. The main body rotation speed was 2500 rpm, and the revolution preformer used was a cylindrical three-pin type. In the conventional example, a cord was manufactured by removing the preformer.

FIG. 8 shows the cord shape of Comparative Example 1, and FIG. 9 shows the cord shape of the conventional example. In Table 1, D is the cord outer diameter, P
Is the twist pitch of the cord, L is the corrugated pitch, H is the corrugated height, and d is the strand diameter. The corrugated pitched corrugated height in Table 1 is a value obtained by taking out a strand of a manufactured cord and taking out an actual wire. In Comparative Examples 1 and 2, the fact that the corrugated pitch L and the corrugated height H could not be measured means that the corrugated pitch height was too low to measure with the projector.

In the property test, "Elongation at break" was performed in accordance with ASTM, and "Rubber permeability" was obtained by vulcanizing a steel cord under a tension of 100 g, then dividing it into two parts, and visually checking the wire surface inside the steel cord. It is the result of observing and expressing the area covered with rubber in percentage.

"Bending rigidity" is a value obtained by applying a predetermined bending to a cord sample having a length of 70 mm and measuring the magnitude of a moment required for the bending.

"Durability" is a vulcanized test specimen in which the cord sample is embedded in the same rubber as the rubber used for the belt and vulcanized.
The number of times until the cord was broken by repeatedly bending it by using a testing machine provided with three rolls having a diameter of 33 mm was measured.

As is clear from Table 1, in the present inventions 1 and 2, since the relationship between the corrugated pitch of the strands, the wave height and the cord twist pitch is appropriate, the cutting load is high despite the large breaking elongation. Also, elongation at 35 kgf / mm ² load at break and 70 kgf / mm ² load is good. Further, since a gap leading to the center of the cord is formed by a wave pitch shorter than the cord twist pitch, rubber permeability is also good.

In Comparative Example 1, sufficient characteristics were not obtained due to a short cord twist pitch, and productivity was poor. In Comparative Example 2, P / D was too small, resulting in poor productivity and insufficient characteristics. Comparative Example 3 is P / D
Is too large to obtain sufficient elongation. In Comparative Example 4, the cutting load was low because L / P was too small.
In Comparative Example 5, elongation and rubber permeability were insufficient because L / P was too large. In Comparative Example 6, the elongation was insufficient because H / d was off the lower limit, and in Comparative Example 7, the shape as a stranded wire could not be maintained because H / d was slightly off the upper limit, and the elongation was insufficient. It has become.

Although conventional example elongation at break are clear, poor rubber penetration, 35 kgf / mm ^2, not even as good at the time of elongation and 70 kgf / mm ² load load, also the productivity poor.

FIG. 10 shows the relationship between the cutting load and elongation of the products 1 and 2 of the present invention (shown as these), Comparative Example 1 (shown as this), and the conventional example (shown as this). Is shown. The product of the present invention does not extend sharply changes with respect to the load, 35 kgf / mm ² load at -70kgf / mm ² load when - until breaking load, it can be seen that the smooth and large elongation is obtained.

2) Next, the cord of the present invention is used as a reinforcing cord of the fourth belt 13d closest to the tread of FIG.
A radial tire with a tire of 1000R20 was created.

The rubber had the following composition (parts by weight) and was vulcanized under the conditions of 150 ° C. × 25 min.

Natural rubber: 100 HAF: 50 Stearic acid: 1 ZnO: 5 3C: 3
Sulfur: 2 Vulcanization accelerator: 1.5 Antioxidant: 0.5 Belt thickness was 2.1 mm, cord spacing was 2.2 mm, and cord angle was 20 degrees. The first belt has a 3 + 6 structure cord, rising 65 degrees to the right, and the second belt has a 3 + 6 structure, rising to the left.
At 20 degrees, the third belt has a 3 + 6 structure, rising 20 degrees to the right.
The carcass has a normal steel cord (3 + 9 + 15 × 0.17
5 + 1) were arranged at an angle of 90 degrees at a density of 13 lines / 2.54 cm.

The internal pressure of 7.5 kg /
The drum test was performed at a speed of 40 km / h by filling a cm ³ and applying a JIS standard load.

For comparison, a radial tire (Comparative Tire 1) in which a conventional product was embedded in a belt under the above conditions, a radial tire (Comparative Tire 2) in which Comparative Example 4 was embedded in a belt under the above conditions, and Comparative Example 6 a belt under the above conditions. A running test was also performed on the radial tire (Comparative Tire 2) embedded in the tire.

When a running time equivalent to a running distance of 25,000 km was reached, the tire was disassembled, and the steel cord in each belt layer was broken and the cord edge separation was inspected. As a result, in the tire of the present invention, the breakage of the steel cord and the separation at the cord edge were 0. On the other hand, the comparative tire 1 had a cord breakage of 20% and a cord edge separation of 15%.
%, Comparative tire 2 had a cord breakage of 15% and cord edge separation of 10%, and Comparative tire 3 had a cord breakage of 25% and a cord edge separation of 20%.

From these results, it can be seen that the radial tire according to the present invention has good fatigue resistance due to the cord following the expansion and contraction of the belt rubber, whereas the tire belt layer of each of the comparative tires 1 to 3 is damaged. Is evident.

Industrial applicability The steel cord of the present invention can be used in addition to radial tires.
It can be used as a reinforcing material for various rubber products such as conveyor belts and high pressure hoses.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D07B 1/06 B60C 9/00

Claims (8)

(57) [Claims] 1. A 1 × n structure in which three to six strands are twisted at a time in the same direction and at the same pitch, and the elongation at break is 5%.
The single-layer twisted steel cord described above, wherein the steel cord has a relation of 0.25 ≦
The relationship between the corrugated pitch L of L / P ≦ 0.55 and the wire diameter d is 1.0
3 to 6 strands having a helical wavy shape having a corrugation height H of 5 ≦ H / d ≦ 2.0, and a ratio P / D of a cord outer diameter D to a cord twist pitch P of 8 to 15 It has a composite structure of twisted helical shapes as in the range of, and 35 kgf / mm ² load elongation at 0.71~1.00%, 70kgf / mm ² load at break is from 1.18 to 1.5
Steel cord characterized in the range of 7%. 2. The steel cord according to claim 1, wherein each strand has a diameter of 0.15 to 0.45 mm. 3. A cross section perpendicular to the longitudinal direction, wherein at least two adjacent strands are in contact with each other, and at least one strand appears at every one pitch of the cord. Steel cord described in. 4. A revolving machine in which a revolving preformer in which three or five pins are mounted on a plate-like or cylindrical rotating body is arranged on the side of the buncher-type stranding machine where the strands are introduced. No means for fixing the twist of the wire before and after the former is installed, and the revolving preformer is rotated in the direction opposite to the rotation direction of the buncher-type twisting machine with the wire passing through the pin, The twisting of the strands generated from the stranding machine body is positively guided to the revolving preformer 7 to give a spiral curl to each strand, and then all the strands are twisted by a buncher type twisting machine. The steel cord according to any one of claims 1 to 3, wherein the steel cord is made by joining together. 5. A 1 × n structure in which three to six strands are twisted at a time in the same direction and at the same pitch, and the elongation at break is 5%.
A radial tire at least partially reinforced with the above single-layer stranded steel cord, wherein the steel cord is
0.25 ≦ L / P ≦ 0.5 in relation to the cord twist pitch P
1.05 ≦ H / d ≦ in relation to the corrugated pitch L of 5 and the wire diameter d
Spiral wavy with a wavy height H of 2.0 3 ~
The ratio of the cord outer diameter D to the cord twist pitch P of six strands
Has a helical composite structure twisted so that P / D is in the range of 8 to 15, and 35 kgf / mm ² elongation under load of 0.7
1 to 1.00%, a radial tire 70 kgf / mm ² load at break is equal to or in the range of 1.18 to 1.57%. 6. The radial tire according to claim 5, wherein each element wire has a diameter of 0.15 to 0.45 mm. 7. The radial tire according to claim 5, wherein the partially reinforced portion is a belt. 8. The radial tire according to claim 5, wherein the belt is a belt close to a tread.