JP2008025040A - Steel cord and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide steel cord capable of improving the flatness of a composite sheet, and to provide a method for producing the steel cord. <P>SOLUTION: The steel cord comprises two core wires 2 having substantially the same diameter composed of mutually and linearly contacted wires 2c arranged in parallel to each other along the wire axis 2a and two side wires 3 having substantially the same diameter as those of the core wires 2 laid so as to be wound around the core wires, wherein the core wires 2 are waved as desired before the side wires 3 are laid therearound. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel cord used for tire reinforcement and a method for manufacturing the same.

  A steel radial tire uses a sheet (hereinafter referred to as a composite sheet) in which a steel cord and rubber are combined and integrated into a part of a member. Recently, there are cases where the number of steel cords to be embedded is as few as 50 to 100 and the width of the composite sheet is narrower than before. If the linearity of the steel cord used in that case is poor, the flatness of the composite sheet immediately during the tire manufacturing process becomes poor, which becomes a factor that significantly impairs the workability of the manufacturing process. A part of the narrow composite sheet is manufactured using a composite sheet manufacturing apparatus manufactured by STEELASTIC. By using the composite sheet manufacturing device of STEELASTIC, the cord surface that passes through the die can be covered with rubber extruded with an extruder, etc., and a large number of coated cords can be aligned and brought into close contact. A composite sheet is produced.

  By the way, if a wire with poor straightness is used as the core wire of a steel cord having a 2 + 2 configuration, the straightness of the entire cord is also deteriorated due to the influence. Usually, as the variation in straightness of the core wire increases, the variation in straightness of the entire cord also increases. When such a core wire is embedded in the composite sheet, the flatness of the sheet deteriorates, the workability in the tire molding process deteriorates, and the quality of the tire becomes unstable. Thus, in the steel cord of the 2 + 2 structure type, there is a problem that the straightness of the two untwisted core wires greatly affects the straightness of the entire cord.

  Various proposals have conventionally been made regarding steel wires having a 2 + 2 structure. For example, Patent Document 1 and Patent Document 2 each propose a steel cord having a 2 + 2 structure for corrugating a core wire.

  In Patent Document 1, corrugation is applied to a core wire to increase the twist rate of the wire so that a load is evenly applied to all the constituent wires of the cord. We have proposed a technology that improves the fatigue resistance of steel cords by reducing the contact area and suppressing the occurrence of fretting wear between wires.

Patent Document 2 discloses a technique for improving the rigidity of the steel cord by corrugating the core wire so that the circumscribed circle of the cord becomes a substantially straight shape, so that the core wire has an appropriate spiral shape. is suggesting.
Japanese Patent Laid-Open No. 6-73672 Japanese Patent No. 3708379

  However, when the above-described conventional steel cord is embedded in a rubber sheet to produce a composite sheet, for example, as shown in FIG. 9, the corner portion 40 of the composite sheet RS warps and is deformed. Is not kept. This is thought to be because the straightness of the steel cord has an adverse effect on the flatness of the composite sheet.

  This invention is made | formed in order to solve said subject, and it aims at providing the steel cord which can improve the flatness of a composite sheet, and its manufacturing method.

  None of the above Patent Documents 1 and 2 specifically mentions how the straightness of the steel cord affects the flatness of the composite sheet, and suggests a correlation between the two. It has not been. Thus, as a result of intensive studies on how the straightness of the steel cord affects the flatness of the composite sheet, the present inventors have completed the present invention described below.

  The steel cord according to the present invention includes two core wires having substantially the same diameter, which are arranged so that mutual contact lines that come in linear contact with each other along the wire axis line, and substantially the same diameter as the core wire. Two side wires twisted to wrap around the core wire, the core wire being subjected to the desired undulation before the side wire is twisted around it It is characterized by.

  The steel cord manufacturing method according to the present invention is a steel cord manufacturing method for manufacturing a steel cord having a 2 + 2 structure, wherein (i) two core wires are fed to a stranding machine and twisted, (ii ) A desired corrugation is applied to the core wire using a corrugating device incorporated in the strand wire machine, and (iii) two core wires are wound around the two core wires corrugated in the step (ii). Twist the side wires in the direction opposite to the twisting direction of the step (i), thereby untwisting the core wire by substantially the same amount as the twisting amount of the step (i), and the two core wires Are arranged so that the mutual contact lines (2c) that come in linear contact with each other are along the wire axis (2a), and (iv) the two are arranged so that the mutual contact line (2c) is finally along the wire axis (2a). It is characterized by winding a steel cord with a 2 + 2 structure with the core wires aligned. That.

  Here, “corrugation” refers to forming a wire into a two-dimensional or three-dimensional shape by applying a stress exceeding the elastic limit to the wire. Further, “two-dimensional corrugation” refers to forming a wire into a shape along a curve belonging to the same plane. Curves belonging to the same plane include two-dimensional curves such as sine curves, arc curves, cycloids, and cardioids. “Crimping undulation” means forming a wire into a two-dimensional shape that repeats the same wave in one plane. As a typical example of this crimp corrugation, there is a gear crimp corrugation process in which a wire is inserted between a pair of gears to form. The crimp corrugation includes a process of crushing a three-dimensional spiral wire from the side to form a two-dimensional shape.

  ADVANTAGE OF THE INVENTION According to this invention, the steel cord which can improve the flatness of a composite sheet, and its manufacturing method are provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram schematically showing an apparatus used in the steel cord manufacturing method of the present invention.

  The steel cord manufacturing apparatus 1 includes two feeding reels 5, an external guide roller 6, an In-Out type buncher twisting machine 10, a capstan 11, and a winding drum 12 in order from the upstream side of the pass line. The first feeding reel 5 is arranged in front of the (a) side entrance of the strand wire machine 10 so that one core wire 2 is drawn out from each reel 5 one by one. The external guide roller 6 bundles and aligns the two core wires 2 passing on the main path line, and the core wires 2 are twisted along the main path line so that they are aligned in parallel and lean against each other. It has a role of guiding to smoothly enter the wire machine 10. The buncher stranded wire machine 10 includes a plurality of turn rollers 7a to 7d, a corrugating device 8 and two feeding reels 9 in a cradle type housing.

  The turn rollers 7a to 7d have a function of revolving around the axis of the stranding machine 10 together with the cradle housing (moving along the track), thereby adding a twist of a desired direction and pitch to the wires 2 and 3. Yes.

  In the housing 81 of the corrugating device 8, a pair of upper and lower large rollers 82a and 82b are housed as shown in FIGS. The housing 81 includes an inlet guide 85 and an outlet guide 86. The wire 2 is introduced into the housing 81 through the inlet guide 85, passes between the large rollers 82 a and 82 b, and is sent out from the housing 81 through the outlet guide 86.

  As shown in FIG. 4, holders 87a and 87b are provided at equal pitch intervals on the outer periphery of the large rollers 82a and 82b, and small diameter pin rolls 83a and 83b are attached to the holders 87a and 87b, respectively. The pin rolls 83a (83b) and 83a (83b) adjacent to each other are attached so that there is almost no gap between them. The upper roller 82a is connected coaxially with the gear 84a, and the lower roller 82b is connected coaxially with the gear 84b. The upper and lower gears 84a and 84b mesh with each other. The upper and lower rollers 82a and 82b are surely synchronously rotated without slippage between the upper and lower rollers 82a and 82b by the both gears 84a and 84b.

  When the wire 2 is caught between the large rollers 82a and 82b, the wire 2 is bent by the upper and lower pin rolls 83a and 83b and is waved into a smoothly continuous two-dimensional shape. In this case, the diameter DR of the pin rolls 83a and 83b needs to be sufficiently larger than the wire diameter dW. The diameter DR of the pin rolls 83a and 83b is preferably in the range of 5 to 50 times the wire diameter dW. Note that the wire 2 may be two-dimensionally crimped using a gear crimping machine disclosed in Japanese Patent Laid-Open No. 10-25680 instead of the pin roll type corrugating apparatus 8 described above.

  The capstan 11 and the winding drum 12 are arranged in front of the (d) side outlet of the strand wire machine 10. The capstan 11 has a function of picking up the steel cord 4 coming out of the stranded wire machine 10 at a constant speed. The winding drum 12 has a role of winding the steel cord 4 as a final product.

The rotational speed of the winding drum 12 is adjusted according to the winding amount of the steel cord 4 wound around the drum so that the winding tension of the steel cord 4 is constant. Further, a desired tension is applied to the wires 2 and 3 by applying an appropriate braking force to the first and second feed reels 5 and 9.

(Manufacture of steel cord)
Next, the case where a steel cord having a 2 + 2 configuration in which the twisting direction is S and the twisting pitch is P will be described in detail using the above manufacturing apparatus.

  When the core wire 2 is fed from each reel 5 to the stranding machine 10, the two core wires 2 are twisted in the Z direction in the section from the guide roller 6 to the turn roller 7a on the (a) side, and the twist pitch 2P. (Z direction) and then twisted in the same direction in the section from the turn roller 7b on the (b) side to the corrugating device 8 to become the twist pitch P (Z direction) (second twist) ). Subsequently, the core wire 2 is twisted in the reverse direction in the section from the corrugating device 8 to the turn roller 7c on the (c) side to become a twist pitch 2P (Z direction) (first twist back), (d) side In the section from the turn roller 7d to the capstan 11, it is further twisted in the opposite direction and finally returns to the state where no twist is entered (second twist back).

  In this way, the two core wires 2 are twisted back by the same amount as twisted, so that the mutual contact line 2c (including the mutual separation line 2n where the wires are partly separated from each other) becomes the wire axis 2a. To be aligned along. The mutual contact line 2c is twisted and twisted, but is not twisted with respect to the wire axis 2a, and is along the wire axis 2a as shown in FIG. 6B. That is, the mutual contact line 2c extends substantially parallel to both the wire axes 2a, and the two core wires 2 are arranged so that the wire axes 2a are substantially parallel.

  By the way, in the section from the corrugating device 8 to the turn roller 7c on the (c) side, the side wires 3 are fed from each reel 9 to the pass line, and two side wires are provided around the corrugated core wire 2A. 3 is twisted in the S direction. The core wire 2 is untwisted in parallel with the twisting of the side wires 3.

  Further, between the corrugating device 8 which is the first untwisting section and the turn roller 7c on the (c) side, the corrugating device is provided before the side wire 3 is twisted around the core wire 2. The desired corrugation is applied to the core wire 2 by 8. The corrugated shape of the corrugated wire 2A needs to be a two-dimensional shape such as a sine curve, an arc curve, a cycloid, or a cardioid in the same plane. The reason for this is that if the corrugated shape of the core wire is made into a three-dimensional shape such as a spiral curve or a spiral curve, the corrugating device becomes larger in size with a complicated structure than the two-dimensional shape, and the stranded wire This is because it becomes difficult to arrange the machine 10 inside.

  The minimum corrugated height is preferably 0.04 mm. This is because, in order to reduce the arc height H to within 30 mm (acceptance determination), corrugation with a height of 0.04 mm is required at the minimum.

  Further, the corrugation pitch P1 is desirably 2 to 20 mm. This is because a practical corrugation pitch is within this range.

  When the steel cord 4 having the 2 + 2 structure integrated in this way comes out of the stranding machine 10, the steel cord 4 is taken up at a constant speed by the capstan 11 and then taken up on the take-up drum 12.

(Manufacture of composite sheet)
A calendar device is generally used for manufacturing the composite sheet. The steel cord is arranged in a comb shape, sandwiched between two thin rubber sheets, and then rolled and integrated with a roll to obtain a composite sheet.

  The manufacturing process of the composite sheet having the narrow width described above will be described with reference to FIG. The rubber coating apparatus 20 for producing the composite sheet includes a rubber extruder (extruder) and a cord drawing machine (not shown). The rubber extruder continuously supplies molten liquid rubber to the die 23. The cord drawing machine draws a plurality of steel cords 4 from the holes of the die 23 at the same time and pulls the solidified composite sheet from the die 23.

  The molten rubber R is extruded from the outlet 22 of the pressure vessel 21 of the rubber extruder, enters the die 23 through the tapered diameter reduction inlet 24, and adheres to the periphery of the steel cord 4 while passing through the die 23. The shape is extruded so as to be a sheet. Thereby, a composite sheet in which the rubber R and the steel cord 4 are closely integrated is formed. In the composite sheet, the steel cord 4 is completely buried in the rubber R. The pitch interval between adjacent cords 4 is, for example, 1.0 to 2.0 mm.

  Such a composite sheet was wound around a reel of a winder, this reel was attached to the supply side of the cutting line, and the composite sheet was cut into a predetermined length by a cutting machine (not shown).

(Tire manufacturing)
The composite sheet is cut so that the embedded cords 4 cross each other at a predetermined angle inside the tire. A plurality of cut sheets and a member such as a tread are respectively incorporated at appropriate positions on a raw rubber tire (green tire) on a tire molding machine and molded into a predetermined shape. When the rubber molded product thus assembled is heated to a predetermined vulcanization temperature to cure the rubber, a desired tire product can be obtained.

(Example)
Next, referring to Table 1, each sample code of the example, the comparative example, and the conventional example will be described in comparison.

(Example 1)
As Example 1, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. As a raw material wire, a piano wire (high-tensile steel wire) specified in JIS G3502 is drawn to a desired wire diameter, subjected to an appropriate heat treatment, and then a brass-plated wire is drawn to obtain a 0.25 mm wire. What was used was used. As manufacturing conditions, the corrugated height was 0.041 mm, the free coil diameter of the raw material wire was 614.8 mm, the cord outer diameter was 0.63 mm, and the twisting pitch of the side wire was 15.3 mm. The cutting load of the cord was 571N.

(Example 2)
As Example 2, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.093 mm, the free coil diameter of the raw material wire was 415.3 mm, the cord outer diameter was 0.65 mm, and the twisting pitch of the side wire was 14.5 mm. The cutting load of the cord was 586N.

(Example 3)
As Example 3, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.041 mm, the free coil diameter of the raw material wire was 418.1 mm, the cord outer diameter was 0.65 mm, and the twisting pitch of the side wire was 14.9 mm. The cutting load of the cord was 575N.

Example 4
As Example 4, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.093 mm, the free coil diameter of the raw material wire was 763.5 mm, the cord outer diameter was 0.65 mm, and the twisting pitch of the side wire was 14.9 mm. The cutting load of the cord was 588N.

(Example 5)
As Example 5, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.041 mm, the free coil diameter of the raw material wire was 266.0 mm, the cord outer diameter was 0.65 mm, and the twisting pitch of the side wire was 14.7 mm. The cutting load of the cord was 581N.

(Example 6)
As Example 6, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.093 mm, the free coil diameter of the raw material wire was 244.0 mm, the cord outer diameter was 0.64 mm, and the twisting pitch of the side wire was 15.1 mm. The cutting load of the cord was 588N.

(Comparative Example 1)
As Comparative Example 1, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.223 mm, the free coil diameter of the raw material wire was 186.0 mm, the cord outer diameter was 0.64 mm, and the twisting pitch of the side wires was 14.8 mm. The cutting load of the cord was 576N.

(Comparative Example 2)
As Comparative Example 2, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.223 mm, the free coil diameter of the raw material wire was 198.2 mm, the cord outer diameter was 0.64 mm, and the twisting pitch of the side wire was 14.8 mm. The cutting load of the cord was 584N.

(Comparative Example 3)
As Comparative Example 3, a steel cord having a 2 + 2 structure was manufactured using the apparatus 1 shown in FIG. The same raw material wire as above was used. As manufacturing conditions, the corrugated height was 0.223 mm, the free coil diameter of the raw material wire was 143.0 mm, the cord outer diameter was 0.65 mm, and the twisting pitch of the side wire was 14.8 mm. The cutting load of the cord was 580N.

(Conventional example 1)
As Conventional Example 1, a steel cord having a 2 + 2 structure was manufactured using the apparatus 100 of FIG. The same raw material wire as above was used. The apparatus 100 has substantially the same configuration as that of the apparatus 1 in FIG. 1 except that it does not include a corrugating apparatus. The apparatus 100 sequentially includes two feeding reels 105, an external guide roller 106, and an In- An Out type buncher stranded wire machine 110, a capstan 111, and a winding drum 112 are provided.

  The production conditions were as follows: no corrugation, the raw wire free coil diameter was 360.0 mm, the cord outer diameter was 0.65 mm, and the side wire twist pitch was 14.9 mm. The cutting load of the cord was 606N.

(Conventional example 2)
As Conventional Example 2, a steel cord having a 2 + 2 structure was manufactured using the apparatus 100 of FIG. The same raw material wire as above was used. The manufacturing conditions were as follows: no corrugation, the raw wire free coil diameter was 227.0 mm, the cord outer diameter was 0.65 mm, and the side wire twist pitch was 14.9 mm. The cutting load of the cord was 614N.

(Conventional example 3)
As Conventional Example 3, a steel cord having a 2 + 2 structure was manufactured using the apparatus 100 of FIG. The same raw material wire as above was used. The production conditions were as follows: no corrugation, the free coil diameter of the raw material wire was 82.0 mm, the cord outer diameter was 0.64 mm, and the twisting pitch of the side wire was 15.0 mm. The cutting load of the cord was 617N.

(Evaluation of code straightness)
“Arc height” is a characteristic used for evaluating the performance of steel cords used in tire belt portions and tire carcass portions. The “arc height” is used for evaluating the linearity of the steel cord, and is important as a means for evaluating the linearity of the cord in an unconstrained state. If the arc height is too large, in the composite sheet cutting process of the tire manufacturing process, defects such as twisting and rising will occur in the cut composite sheet, not only significantly reducing workability, but also the tire quality is uniform. This is because the tire performance may be adversely affected. In the process using the narrow composite sheet as described above, the same problem occurs when the arc height is large. Rather, since the width of the composite sheet is narrow, there is a tendency that the influence when the rising edge of the sheet occurs is increased.

  As shown in FIG. 7A, a cord 4 cut to a length L2 (for example, 400 mm) is used for measuring the arc height. As shown in FIG. 7B, the arc height is the arc height AH formed by the cord 4 with both ends of the cord 4 being in contact with the flat base 19. Usually, it is satisfactory if the arc height AH is 30 mm or less, and it can be said that the cord has no practical problem. On the other hand, when the arc height AH exceeds 30 mm, it is not good, and the composite sheet using the cord has a large jump at the end portion, which tends to cause trouble in the final tire product.

  As shown in Table 1, in the cords of Examples 1, 2, 3, 4, 5, and 6, the arc height (linearity) was 18.9 mm, 16.7 mm, 15.0 mm, 18.3 mm, 20. Good results were obtained with 8 mm and 16.1 mm. On the other hand, in the cords of Comparative Examples 1, 2, and 3, the arc height was as large as 33.1 mm, 31.9 mm, and 33.2 mm, respectively, and all exceeded the acceptance standard (30 mm). In the cords of the conventional examples 1, 2, and 3, the arc heights were 13.6 mm, 16.9 mm, and 34.5 mm, respectively.

(Evaluation of sheet flatness)
With reference to FIG.8 and FIG.9, the evaluation method of the flatness of a composite sheet is demonstrated.

  First, a method for measuring the flatness of the composite sheet will be described. A rubber sheet R having a thickness of 0.5 mm × width of 100 mm × length of 1000 mm is wound around the outer periphery of the drum 30 shown in FIG. 8A, and one cord 4 is wound thereon as shown in FIG. 8B. Wrap it at a predetermined interval. Furthermore, as shown in FIG. 8 (c), the rubber sheet R of the same size is stacked thereon, and this is pressed from above to be pressure-bonded. The sheet RS is cut in the width direction so as to cross the wound cord 4 to obtain a composite sheet RS having a size of width 100 mm × length 1000 mm.

  After the obtained composite sheet RS is left on the flat base 19 for a sufficiently long time as shown in FIG. 9, the rising amounts W1 and W2 of the sheet end portion 40 from the surface of the base 19 are measured. To do. The measured rise amounts W1 and W2 serve as indexes for evaluating the flatness of the composite sheet RS. Usually, it is good if the average measured value of the rising amount at the end is 5 mm or less, and it can be said that the composite sheet has no practical problem. On the other hand, if the average measured value of the rising amount at the end exceeds 5 mm, it is defective.

  As shown in Table 1, with the cords of Examples 1, 2, 3, 4, 5, and 6, the average measured rise amount was 3 mm, 2 mm, 1 mm, 2 mm, 3 mm, and 2 mm, respectively, and good results were obtained. It was. On the other hand, in the cords of Comparative Examples 1, 2, and 3, the average measured values of the rising amount were as large as 21 mm, 25 mm, and 24 mm, respectively, and all exceeded the acceptance standard (5 mm). In the cords of the conventional examples 1, 2, and 3, the average measured values of the rising amount were 2 mm, 2 mm, and 27 mm, respectively.

  The present invention can be used for manufacturing a steel cord for reinforcing tires of passenger cars, trucks, buses and the like. In particular, the cord of the present invention is effective for reinforcing the tire belt portion.

The schematic block diagram which shows typically the apparatus used for the manufacturing method of the steel cord of this invention. The front view which shows the outline | summary of a corrugation apparatus (pin roll processing machine). The side view which shows the outline | summary of a corrugation apparatus (pin roll processing machine). The elements on larger scale which show the principal part of a corrugated apparatus (pin roll processing machine). The cross-sectional schematic diagram for demonstrating the preparation methods of the composite sheet which coat | covers rubber | gum on a steel cord. (A) is a schematic cross-sectional view showing the wire position for each 1/4 pitch of the cord of the present invention, (b) is a perspective view schematically showing the appearance of the cord of the present invention, and (c) is a 1/4 pitch of the conventional cord. The cross-sectional schematic diagram which shows each wire position, (d) is a perspective view which shows typically the external appearance of the conventional cord. (A) is a figure which shows the steel cord cut | disconnected by predetermined length, (b) is a schematic diagram for demonstrating the arc height measuring method of a steel cord. (A)-(c) is a schematic diagram for demonstrating the procedure which produces the test piece of the composite sheet used for flatness measurement. The schematic diagram for demonstrating the method to measure the flatness of a composite sheet. The schematic block diagram which shows typically the apparatus used for the manufacturing method of the conventional steel cord.

Explanation of symbols

1 ... Steel cord manufacturing equipment,
2, 3 ... wire, 2A ... corrugated wire, 4 ... steel cord,
5 ... Feed reel,
6 ... External guide roller,
7a-7d ... Turn roller,
8 ... Crimping device (pin roll wave processing machine), 81 ... Housing,
82a, 82b ... large rollers, 83a, 83b ... pin rolls,
85 ... Inlet guide, 86 ... Outlet guide, 87a, 87b ... Holder,
9 ... feed reel,
10 ... Stranding machine, 11 ... Capstan, 12 ... Winding bobbin,
19 ... the base,
20 ... rubber coating device,
21 ... Pressure chamber of the extruder, 22 ... Outlet,
23 ... Voice,
24 ... Taper inlet, 25 ... Taper outlet,
30 ... drum,
40: sheet edge,
R ... Rubber, RS ... Composite sheet.

Claims (4)

Two core wires having substantially the same diameter, which are arranged so that mutual contact lines in linear contact are aligned with the wire axis;
Two side wires that are substantially the same diameter as the core wire and twisted to wrap around the core wire;
The steel cord is characterized in that a desired corrugation is applied to the core wire before the side wire is twisted around the core wire.   The steel cord according to claim 1, wherein the corrugation of the core wire is a two-dimensional corrugation formed while the core wire passes through a stranding machine. In the steel cord manufacturing method for manufacturing the steel cord of 2 + 2 structure,
(i) Two core wires are fed to a twisting machine and twisted,
(ii) applying a desired corrugation to the core wire using a corrugating device incorporated in the stranding machine;
(iii) Two side wires are twisted around the two core wires corrugated in the step (ii) in the direction opposite to the twist direction in the step (i), and thereby the core wires are Twist back by substantially the same amount as the twisted amount in step (i), and align the mutual contact lines that linearly contact the two core wires along the wire axis.
(iv) A method of manufacturing a steel cord, comprising winding up a steel cord having a 2 + 2 structure in a state where the two core wires are aligned so that the mutual contact line is finally along the wire axis.   4. The method according to claim 3, wherein the corrugation in the step (ii) is a two-dimensional corrugation performed while the two core wires pass through a stranding machine.

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