JPH0931876A - Steel cord and steel radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To producel cords which has a desired strength at breakage, high penetrativity of rubber and is useful for molded rubber products by preparing the strand by intertwisting the core wire and the side wires under specific conditions and making its cross section flat. SOLUTION: Two core wires 3 and five side wires 4 are twisted together into a strand. The strand is pressed with the flat peripheral face of the leveling roller to give a strand 2 having a flat cross section. The diameter of the side wire 4 D2 is larger than that of the core wire 3 D1 and the ratio of D2/D1 is preferably 1.60-2.12 and the flat ratio of the strands (LD/SD) is preferably 1.201.40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel radial tire and a steel cord used for a rubber molded product such as a conveyor belt and a steel radial tire using the same.

[0002]

2. Description of the Related Art Steel cords are used as reinforcing materials for rubber molded products such as steel radial tires and conveyor belts. As a typical example of the steel cord, a two-layer twist (3
+6) There is a steel cord with a structure. This (3 + 6) steel cord is formed by first twisting three steel wires to form a core strand, and then further twisting six steel wires around the outer circumference to form side strands. Such a two-layer twisted steel cord further has a different direction twist (SZ twist) type in which the twist of the core strand and the twist of the side strand are reversed, and the twist of the core strand and the twist of the side strand are made forward. Same direction twist (SS
Twisted) type.

[0003]

However, since the conventional (3 + 6) steel cord requires two twisting wire steps, the productivity is low and the manufacturing cost is high. Especially when using a buncher (double twister), in the twisted type, since the twist of the core strand is restored during the cross twist process, it is possible to pretwist at a pitch shorter than the pitch of the final cord. Therefore, productivity is low.

Further, in the (3 + 6) steel cord, rubber hardly penetrates to the center of the three-strand core strand, and a void is likely to occur in the center of the core. Having a void in the center of the core facilitates internal corrosion and fretting wear, which considerably shortens the life of the steel cord.

Further, in steel radial tires, it is necessary that the steel cord has a breaking strength above a certain level. However, if the cross-sectional area of the steel cords is increased to obtain the desired breaking strength, the laying pitch interval in the calendering process becomes too large, and the number of laying and laying on the rubber sheet cannot be increased.

An object of the present invention is to provide a steel cord having high productivity, a desired breaking strength and excellent rubber permeability. Another object of the present invention is to provide a long-life steel radial tire reinforced with a steel cord that is resistant to internal corrosion and fretting wear.

[0007]

The steel cord according to the present invention has two core wires and a diameter larger than the diameter of the core wires, and the core wires are bundled together around the core wires together with the core wires. And 5 side wires, and the cross section of the strand composed of these 5 side wires and 2 core wires is flat.

In this case, the cross section of the strand consisting of the five side wires and the two core wires is formed into an ellipse,
The ratio of the major axis to the minor axis of this ellipse (flatness ratio) is 1.1.
It is desirable to set it in the range of 0 to 2.00, and it is most preferable to set the aspect ratio in the range of 1.20 to 1.40.

If the aspect ratio is less than 1.10, the rubber permeability is lowered and the core wire is easily pulled out. On the other hand, if the aspect ratio is greater than 2.00,
This is because the major axis is increased and the number of lines to be laid out on the rubber sheet is reduced, and the desired number of lines to be laid out can be secured especially when the aspect ratio is 1.40, so that the strength level of the rubber molded product can be increased. Because.

The core wires have substantially the same diameter, the side wires have substantially the same diameter, and the ratio of the diameter of the side wire to the diameter of the core wire (wire diameter ratio) is 1.45.
The range of 2.25 is preferable, and the wire diameter ratio is most preferably 1.60 to 2.12.

This is because if the wire diameter ratio is smaller than 1.45, the mutual gap between the side wires becomes too wide and twisting failure occurs. On the other hand, if the wire diameter ratio is larger than 2.25, the mutual gap between the side wires becomes too narrow, and the rubber permeability decreases. Also, the effective cross-sectional area of the cord is reduced and the breaking load becomes insufficient.

The range of the wire diameter ratio is based on the case where two core wires of the same diameter and five wires of the same diameter side are tightly twisted together (oblateness ratio 1.0). For example, when the side wire diameter is D (= 0.370 mm), the diameter d of the core wire is obtained by using the following equation (1), and the obtained d (= 0.130) is obtained.
mm), the range of wire diameter ratio can be set. This corresponds to a tight twisted state, so that the actual core wire diameter D ₁ is larger than d.

D = (D / 2) × [1 / {sin (360 ° / 10)}] − (D / 2) (1) Further, the constituent wires have a tensile strength of 300 to 360 k.
It is desirable to use high-strength steel wire of gf / mm ² . This is because the tensile strength of the wire must be 300 kgf / mm ² or more in order for the steel cord to obtain the desired breaking strength. On the other hand, the tensile strength of the wire is 360 kgf /
This is because if it exceeds mm ² , the wire becomes brittle and is likely to be broken. In this case, the tensile strength is 33
It is preferable to use a high-strength steel wire in the range of 0 to 340 kgf / mm ² .

Further, it is preferable that the side wire has a shaping ratio different from that of the core wire before the side wire and the core wire are twisted together. When the side wire and the core wire having different patterning ratios are twisted together as described above, the side wire does not come into line contact with the core wire, and the permeability of rubber to the core is improved.

The present inventor has conducted earnest research on a so-called bunched type steel cord in which a plurality of wires are collectively twisted in order to solve the above-mentioned drawbacks of the two-layer twisted steel cord. As a result of various studies, the following was found.

In the bunched type steel cord, since the core strand and the side strand are in line contact with each other, the core strand is likely to come off. Further, since the adjacent wires are in close contact with each other, it is difficult for the rubber to sufficiently penetrate into the inside of the core strand. Furthermore, in the bunched type steel cord, the balance between the torque of the core strand and the torque of the side strand is not good, and the residual rotational torque of the core strand is extremely large.Therefore, the warping of the sheet near or far from the cut surface of the rubber sheet Cause

Based on these findings, the present inventors have made various flat steel cords having two core wires, five side wires and various side wire shaping ratios (corrugation ratios). I examined it repeatedly. As a result, it is possible to obtain a bunched type steel cord with a low wire contact rate by selecting an appropriate side wire shaping rate, and it is possible to realize uniform bundle twisting,
In addition, since the number of core wires is two, it is easy to flatten the rubber and rubber permeability is significantly improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, a core wire supply unit 12 and a side wire supply unit 14 are provided on the upstream side of the steel cord manufacturing line. The core wire supply unit 12 includes two bobbins 12a and 12b, and the side wire supply unit 14 includes five bobbins 14a to 14b.
e. 0.20 for each bobbin 12a, 12b
Each of the alloy-plated steel wires 3 having a diameter of mm is wound. An alloy-plated steel wire 4 having a diameter of 0.37 mm is wound around each bobbin 14a to 14e. In addition, each steel wire 3,
4 is Japanese Patent Laid-Open No. 3-28396 and Japanese Patent Laid-Open No. 2-26.
Alloy plating is performed by the method described in Japanese Patent No. 7257.

A tension equalizer is provided immediately downstream of the core wire supply unit 12. The tension equalizer includes a powder brake 16 and a drive motor 18. When the powder brake 16 applies an appropriate frictional resistance force to the wire 3 while the drive motor 18 pulls the wire 3, excessive feeding of the wire 3 is prevented. The tension equalizer includes a movable pulley 36 having a sensor 37, a detector 37a, and a swing arm 36a as shown in FIGS.
Is attached, and the tension applied to the wire 3 is feedback-controlled with high precision. The arm 36a is swingably supported by a shaft 36b.

Further, the two wires 3 are sent from the tension equalizer through the guide rollers 20 and 22 to the preformer 24, and as shown in FIG.
Each of them is preformed (corrugated) into a waveform.

Next, a tension equalizer for controlling the wire tension will be described with reference to FIGS. 2 (A) to 2 (C). A tension equalizer is provided immediately downstream of the side wire supply unit 14. The tension equalizer includes a powder brake 32, a drive motor 34, a moving pulley 36, a swing arm 36a, a detector 37a, and a sensor 37.

As shown in FIG. 2A, the wire 4 is wound around the drum of the powder brake 32 and the drum of the drive motor 34 so as to reciprocate a plurality of times. The powder brake 32 is provided with a dedicated braking mechanism, and rotational braking of the drum is controlled independently of the braking mechanism (bobbin brake) of the bobbins 14a to 14e.

The movable pulley 36 and the magnetic sensor 37 are the motor 3
4 is attached immediately downstream of the wire 4 so as to control the feeding speed of each wire 4. A weight (not shown) is attached to the movable pulley 36 so that a desired tension is applied to each wire 4. Arm 36a of movable pulley 36
An attitude detector 37a is attached to one end of the. The detector 37a faces the magnetic sensor 37. The detection end of the detector 37a is formed so as to form a cycloid curved surface.

The magnetic sensor 37 has a magnetic field forming circuit. The sensor 37 and the detector 37a are connected to the input side of a controller (not shown). When the swing arm 36a tilts with respect to the horizontal plane, the magnetic flux density of the magnetic field formed between the sensor 37 and the detector 37a changes, and a detection signal is sent to the controller. When the movable pulley 36 is at the reference position and the swing arm 36a is in the horizontal posture, no signal is sent from the sensor 37 and the detector 37a to the controller.

As shown in FIG. 2B, when the movable pulley 36 moves upward from the reference position and the arm 36a tilts with respect to the horizontal plane, a detection signal is sent from the sensor 37 and the detector 37a to the controller. The controller drives the motor 34 based on this detection signal to speed up the feeding of the wire 4. At this time, the force acting on the wire 4 is mainly due to the rotational driving force of the motor 34, and the powder brake 32 and the bobbin brake are lightly applied so that the wire 4 is evenly stretched. As a result, the movable pulley 36 descends to the reference position, and the arm 36a returns to the horizontal posture.

As shown in FIG. 2C, when the movable pulley 36 moves downward from the reference position and the arm 36a tilts with respect to the horizontal plane, a detection signal is sent from the sensor 37 and the detector 37a to the controller. The controller decelerates the rotation speed of the motor 34 based on this detection signal and delays the feeding speed of the wire 4. As a result, the movable pulley 36 rises to the reference position, and the arm 36a returns to the horizontal posture. In this way, the tension applied to the wire 4 is controlled so as to always have a constant level.

Further, guide rollers 38 and 39 are provided on the downstream side of the movable pulley 36, and each wire 4 is guided toward the preformer 24 of the horizontal portion 40. As shown in FIG. 4, the plate 2 of the preformer 24
The wire 4a is provided with a plurality of wire guide pins 25. When the wires 3 and 4 pass through the wire guide pin 25 one after another, the wires 3 and 4 are shaped in a desired waveform.

A preformer 24, a first end plate 26, a second end plate 28, and a voice 30 are arranged in this order on the horizontal portion 40. The first end plate 26, the second end plate 28, and the voice 30 are fixed to the base so as not to move. Further, a double twister type buncher (twisting wire machine) 50 is provided on the downstream side of the voice 30. First, when the two wires 3 pass through the second end plate 28, they are fed horizontally toward the voice 30, and when the two wires 3 and the five wires 4 pass through the voice 30, the buncher 50 twists them. Then, (2/5) strand 2a is formed. This (2/5) (or (1 × 7)) strand 2a
Is a substantially perfect circle having a diameter D ₀ as shown in FIG.

The double twister type buncher 50 has a cradle 100, and capstans 56a and 56b, a leveling roll portion 60, and a winding bobbin 69 are provided in the cradle 100. The first and second turn rolls 52a and 52b are arranged on the same axis and are revolved around the axis. The body frame of the buncher 50 is rotatably supported by the frame by a pair of hollow spindles. A loop is laid between the pair of spindles. A first turn roll 52a is provided on one spindle, and a second turn roll 52b is provided on the other spindle. The pair of spindles allows the first and second
The turn rolls 52a, 52b are revolved around the axis. The strand 2a is fed from the first turn roll 52a toward the second turn roll 52b so as to draw an arc.

First and second turn rolls 52a, 52
In b, each rotation axis is inclined at a predetermined angle with respect to the horizontal plane. The take-up bobbin 69 includes the first and second bobbins.
It is provided so as to maintain a constant posture regardless of the revolution of the turn rolls 52a and 52b.

First and second turn rolls 52a, 52
Overtwisters 54a and 54b, capstans 56a and 56b, a guide roll 58, a leveling roll group 60, and a take-up bobbin 69 are arranged between each other. The over twisters 54a and 54b are for applying excessive twist to the strand 2a to further plastically deform the corrugated wires 3 and 4.

As shown in FIG. 3, when the strand (wire bundle) 2a passes through the second turn roll 52b, it is overtwisted by the over twisters 54a and 54b, and the first
It reciprocates between the capstan 56a and the second capstan 56b, enters the leveling roll section 60, further reciprocates between the first capstan 56a and the second capstan 56b, and winds via the traverser 68. It is wound around the take-up bobbin 69.

Next, the leveling roll unit 60 will be described with reference to FIGS. As shown in FIG. 5, the leveling roll unit 60 includes two upper and lower roller units 61 and 62. The lower roller unit 62 is fixed, and the upper roller unit 61 is supported by a pressurizer (not shown) so as to be able to move up and down. The lower roller unit 62 includes two guide rollers 64 and many leveling rollers 66,
The upper roller unit 61 includes a large number of leveling rollers 66. The upper and lower rollers 64 and 66 are arranged in a staggered manner so as to be staggered. The zigzag arrangement pitch of the leveling rollers 66 is preferably in the range of 0.7 to 2.3 times the roller diameter. In this embodiment, the guide roller 64 and the leveling roller 66 have a diameter of 16 mm.
It is. The diameter of these rollers 64, 66 is preferably in the range of 10 to 20 mm.

As shown in FIG. 6, a V groove 64a is formed on the peripheral surface of the guide roller 64. The strand 2a is guided in the V groove 64a. The guide rollers 64 are provided on the entrance side and the exit side of the strand 2a, respectively.

As shown in FIG. 7, the peripheral surface 66a of the leveling roller 66 is flat. When the upper roller unit 61 is lowered, the flat peripheral surface 66a of the leveling roller 66 is pressed against the strand 2a to form the flat strand 2. That is, the strand 2a having a substantially perfect circular cross section as shown in FIG. 8 is crushed, and becomes a strand 2 having an elliptical cross section as shown in FIGS. When the strand 2a is crushed, the two core wires 3 do not project outside the five side wires 4. The reason why the core wire 3 does not protrude outward is that the side wire 4 is corrugated by the preformer 24 and an appropriate tension is applied to the core wire 3. Incidentally, in this embodiment, the maximum corrugation height of the core wire 3 (diameter 0.20 mm) is 0.54 mm, and the side wire 4 (diameter 0.37 mm).
The maximum peak height of corrugation is 1.371 mm. On the other hand, if the side wire 4 that is not corrugated at all is sent to the leveling roll portion 60, the core wire 3 jumps out of the side wire 4. Therefore, the higher the maximum corrugation height of the side wire 4 is, and the greater the tension of the core wire 3 is, the more the core wire 3 does not protrude to the outside of the side wire 4.

Next, the steel cords of Examples 1 and 2 and their evaluation will be described with reference to FIGS. 9 to 21. (Example 1) FIG. 9 to FIG. 14 using a cradle-type stranding machine described in Japanese Patent Laid-Open No. 5-302283.
The steel cord 2 having the (1 × 7) structure shown in FIG.
FIG. 9 shows a cross section of the cord at the reference point, and FIG. 10 shows a cross section of the cord at a position shifted by 1/4 pitch from the reference point.
FIG. 11 shows a cross section of the cord at a position shifted by ½ pitch from the reference point, and FIG. 12 shows a cross section of the cord at a position shifted by 3/4 pitch from the reference point. The production conditions and product size of Example 1 are shown below.

Wire tensile strength: 335 ± 5 kgf / mm ² Core wire diameter D ₁ ; 0.175 mm side wire diameter D ₂ ; 0.370 mm twist pitch; 16 mm twist direction; S twist core wire type ratio; 131 .3% side wire type ratio; 110.4% flatness ratio; 1.30 average major axis LD; 1.29 mm average minor axis SD; 0.99 mm cord breaking load; 185.7 kgf / mm ² Fig. 9 As shown in FIGS. 13 and 14, a flat steel cord 2 having a long diameter LD and a short diameter SD was obtained. In the steel cord 2 of this Example 1, when the average major diameter LD was the same, the average minor diameter SD was considerably smaller than that of the steel cord of the (1 × 9) structure of the comparative example.

Incidentally, the steel cord of the (1 × 9) structure of the comparative example is a flat shape in which three core wires and six side wires described in JP-A-5-302283 are bundled together. Corresponds to a cross section. (Example 2) Using the same cradle type stranding machine as in Example 1 above, a steel cord 2A having a (1x7) structure shown in Figs. 15 to 18 was manufactured. 15 shows a code cross section at a reference point, FIG. 16 shows a code cross section at a position displaced by 1/4 pitch from the reference point, and FIG. 17 shows a code at a position displaced by 1/2 pitch from the reference point. FIG. 18 shows a cross section of the cord at a position displaced by 3/4 pitch from the reference point.

The manufacturing conditions and product size of Example 2 are shown below. Wire tensile strength: 335 ± 5 kgf / mm ² Core wire diameter D ₄ ; 0.175 mm side wire diameter D ₅ ; 0.370 mm twist pitch; 16 mm twist direction; S twist core wire type ratio; 132.2% Side wire type ratio; 125.0% Flatness ratio; 1.33 Cord average major axis LD; 1.42 mm Cord average minor axis SD; 1.07 mm Cord breaking load; 185.2 kgf / mm ² (Example 3) Using the same cradle type stranding machine as in Examples 1 and 2, a steel cord (not shown) of Example 3 having a (1 × 7) structure was manufactured.

The manufacturing conditions and product size of Example 3 are shown below. Wire tensile strength: 335 ± 5 kgf / mm ² Core wire diameter d; 0.200 mm side wire diameter D; 0.370 mm Twisting pitch: 16 mm Twisting direction: S Twisted core wire type ratio: 135.0% Side wire Type ratio; 112.8% Flatness ratio; 1.34 Average major axis LD of cord; 1.38 mm Average minor axis SD of cord; 1.03 mm Cord breaking load; 186.5 kgf / mm ² rubber permeability; 100% [ Evaluation of rubber permeability] The steel cords 2 and 2A of Examples 1 to 3 were evaluated for rubber permeability as compared with the conventional product and the comparative product. A steel cord of (3 + 6) structure was used for the conventional product. Further, as a comparative example, Japanese Patent Laid-Open No. 5-302
The steel cord having the flat cross section (1 × 9) structure described in Japanese Patent No. 283 was used.

The rubber permeability was evaluated as follows. First, a steel cord having a length of 20 pitches is prepared for each of the example, the conventional example, and the comparative example. The side wire of each cord is stripped off, and a total of 40 rubber penetration states are visually inspected visually with the naked eye.

A point system was adopted for visual inspection. If the point where the rubber is completely penetrated is 5 points, the point where the rubber is about half penetrated is 2.5 points, and the point where the rubber is not penetrated is 0 point, the total number out of 100 points in the table is Dot or back 100
The total number of points was examined. Further, these scores were totaled and divided by 2 to obtain an average score, which was expressed as a percentage to evaluate the rubber permeability. Those having a rubber permeability of 90% or more were judged to be acceptable.

The results of the examples, comparative examples and conventional products are shown below. Rubber permeability (%) of the side of the core Rubber permeability (%) Example (1 × 7) Configuration code 90-100 90-100 Comparative example (1 × 9) Configuration code 80-90 85-100 Conventional product (3 + 6) Configuration code 30 to 50 80 to 95 Next, effects of the embodiment will be described with reference to FIGS. 19 and 20.

FIG. 19 is a graph plotting the results of examining the relationship between the two in each example, with the major axis (mm) on the horizontal axis and the rubber permeability (%) on the vertical axis. FIG. 20 is a graph chart in which the abscissa represents the aspect ratio and the ordinate represents the rubber permeability (%), and the results of examining the relationship between the two in each example are plotted.

In each figure, the circle (curve A) shows the result when the side wire has a patterning rate of 110.4%, and the square (curve B) shows the result when the side wire has a patterning rate of 125.0%. , And the triangle (curve C) shows the result of setting the side wire patterning rate to 137.0%. The core wire diameter is 0.175m
m, side wire diameter 0.370 mm, cord twist pitch 1
It was 6 mm.

As is clear from FIGS. 19 and 20, the rubber penetrability is improved as the molding rate of the side wire is increased. It was also found that, with the same molding rate, the larger the major axis and the larger the flatness ratio, the more the rubber permeability is improved.

Next, a case of manufacturing a steel radial tire for a truck or a bus using the above steel cord will be described with reference to FIGS. As shown in FIG. 21, first, another steel cord 2B is arranged so as to be substantially straight and at equal intervals, and raw rubber plates 73 are attached so as to sandwich the steel cord 2B from above and below. A carcass plate is produced by such calendering. The carcass plate is cut along the cutting line 91 into predetermined lengths. The cutting line 91 is orthogonal to the steel cord 2B. The uncut end surfaces of the obtained cut sheet are joined together and used as a tire carcass 72. The carcass 72 is wound around the drum of the tire building machine. Sidewall 8
4 is integrally molded with the side ply 76 and the bead filler 78. On the other hand, a bead 80 is manufactured by molding a steel wire into a ring shape. Drums on sidewall 8
4 is wound and this is united with the carcass 72. Remove the tire assembly from the drum and set it on the drum of the molding machine. Then, the beads 80 are fitted into both sides of the tire assembly, and both ends of the carcass 72 are wound around the beads 80. Pressurized air is supplied into the tire assembly to inflate it.

As shown in FIG. 22, the steel cord 2
(2A) are arranged so as to be substantially straight and at equal intervals, and raw rubber plates 75 are attached so as to sandwich the steel cord 2 (2A) from above and below. A belt plate is produced by such calendering. The belt plate is cut into various sizes along the cutting line 93. The cutting line 93 is oblique to the steel cord 2 (2A). The obtained cut sheets are belts 74a-7
4d used respectively. The belts 74a to 74d are successively laminated on the carcass of the tire assembly.

Extruding synthetic rubber from the tread extractor,
This is cooled and cut into a predetermined length, and the tread 82
Is prepared. The tread 82 is attached to the outer peripheral surface of the tire assembly. While the tire assembly is being pressurized and expanded, it is heated to produce a raw tire having a predetermined shape. The raw tire is vulcanized in a vulcanizer to cure the raw rubber. Further, after undergoing the final inspection, a steel radial tire 70 as shown in FIG. 23 was obtained.

[0050]

According to the steel radial tire of the present invention,
Fretting does not occur because the core of the steel cord is fully filled with rubber. Further, since the steel cord of the present invention has a flattened cross section, the shape retention of the cord is enhanced, and twisting of the core strand and the side wire is less likely to occur. Therefore, the warp of the sheet does not substantially occur near the cut surface of the rubber sheet or far from the cut surface.

Further, since the steel cord of the present invention has two core wires and has a structure in which no void is formed in the core portion, it has excellent rubber permeability, and the core portion is sufficiently filled with rubber.

Further, the steel cord of the present invention can sufficiently secure the laying pitch interval in the calendering process without impairing the breaking strength, and can lay many rubber sheets on the rubber sheet.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram showing a steel cord manufacturing line.

2 (A), 2 (B), and 2 (C) are schematic views showing a wire tension control device.

FIG. 3 is a schematic perspective view showing an arrangement relationship of respective parts of the double twister.

FIG. 4 is a schematic view showing a preformer for shaping a wire.

FIG. 5 is a schematic view showing a leveling roll portion in a double twister.

FIG. 6 is a diagram showing guide rollers provided on the entrance side and the exit side of the leveling roll unit.

FIG. 7 is a diagram showing an intermediate roller of a leveling roll unit.

FIG. 8 is a cross-sectional view showing a steel cord (round strand) before flattening.

FIG. 9 is a cross-sectional view showing a steel cord according to the first embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a steel cord according to the first embodiment of the present invention.

FIG. 11 is a cross-sectional view showing a steel cord according to the first embodiment of the present invention.

FIG. 12 is a cross-sectional view showing a steel cord according to the first embodiment of the present invention.

FIG. 13 is an external view showing a part of the steel cord of the first embodiment as seen from the direction orthogonal to the major axis.

FIG. 14 is an external view showing a part of the steel cord of the first embodiment as seen from the direction orthogonal to the short axis.

FIG. 15 is a cross sectional view showing a steel cord according to a second embodiment of the present invention.

FIG. 16 is a cross-sectional view showing a steel cord according to the second embodiment of the present invention.

FIG. 17 is a cross-sectional view showing a steel cord according to the second embodiment of the present invention.

FIG. 18 is a cross-sectional view showing a steel cord according to the second embodiment of the present invention.

FIG. 19 is a graph showing the relationship between the major axis and rubber permeability of each example.

FIG. 20 is a graph showing the relationship between the flatness ratio and rubber permeability of each example.

FIG. 21 is a plan view showing a calendar sheet before cutting.

FIG. 22 is a plan view showing a calendar sheet before cutting.

FIG. 23 is a cross section of a steel radial tire.

[Explanation of symbols]

 2, 2A ... Steel cord 3, 3A ... Core wire 4, 4A ... Side wire

Claims (10)

[Claims] 1. A steel cord which is embedded in a rubber molded body and reinforces the rubber molded body, comprising two core wires and a diameter larger than the diameter of the core wires. And a side wire which is twisted together with the core wire at a time, and a cross section of a strand composed of these five side wires and two core wires is flat. . 2. A cross section of a strand composed of five side wires and two core wires is formed into an ellipse, and the ratio of the major axis to the minor axis of the ellipse is set to a range of 1.10 to 2.00. The steel cord according to claim 1, wherein 3. The two core wires have substantially the same diameter, the five side wires have substantially the same diameter, and the ratio of the diameter of the side wire to the diameter of the core wire is 1.45. ~
The steel cord according to claim 1, wherein the steel cord has a range of 2.25. 4. The steel cord according to claim 1, wherein a steel wire having a tensile strength of 300 to 360 kgf / mm ² is used for the core wire and the side wire. 5. The steel cord according to claim 1, wherein a shaping ratio of the side wire is made different from a shaping ratio of the core wire before the side wires are twisted together with the core wire at a time. 6. A radial steel tire reinforced with a steel cord, wherein the steel cord has two core wires, and the diameter of the core wires is larger than the diameter of the core wires. A radial steel tire comprising: and five side wires that are twisted together in a lump, wherein a cross section of a strand composed of these five side wires and two core wires is flat. 7. The cross section of a strand composed of five side wires and two core wires is formed into an ellipse, and the ratio of the major axis to the minor axis of this ellipse is set to a range of 1.10 to 2.00. The radial steel tire according to claim 6, wherein 8. The two core wires have substantially the same diameter, the five side wires have substantially the same diameter, and the ratio of the diameter of the side wire to the diameter of the core wire is 1.45. ~
The radial steel tire according to claim 6, wherein the range is 2.25. 9. The radial steel tire according to claim 6, wherein a steel wire having a tensile strength of 300 to 360 kgf / mm ² is used for the core wire and the side wire. 10. The steel cord according to claim 6, wherein the side wire has a molding rate different from that of the core wire before the side wire and the core wire are twisted together.