JP2001032183A - Steel wire for reinforcing rubber article, its correction and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reinforcing material excellent in fatigue resistance and suitable for a rubber article such as a pneumatic tire, etc., by producing a steel wire of which surface residual stress is in the compressed side and also its distribution is uniform both in circumferential and longitudinal directions. SOLUTION: This steel wire having 0.80-4.00 mm diameter, <=-1 mm compressed residual stress value obtained by covering the half circumferential part of the wire having 10 cm long with a lacquer in its longitudinal direction, subjecting it to an etching treatment, making the maximum bent amount of the wire as negative in the etched side and positive in the lacquer-coated side, 0.4×A range distribution width of the above stress values on setting the compressed residual stress values measured at least 8 evenly separated positions on circumference of the wire as A, and <=-2 mm absolute value of the difference of the maximum and minimum values of them, is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire for reinforcing a rubber article and having excellent fatigue resistance, a method for correcting the surface residual stress thereof, and a pneumatic tire.

[0002]

2. Description of the Related Art In a pneumatic tire, which is a typical example of a rubber article, since a large stress acts on the bead portion when the tire runs, a relatively thick steel wire is used for a bead core for reinforcing the bead portion. Have been. This steel wire is generally drawn to a target wire diameter by a drawing method using a die in order to enhance the reinforcing effect. However, in the processing by the drawing method, there is a disadvantage that the surface residual stress on the tensile side remains on the surface of the wire and the fatigue resistance of the wire is reduced.

It is known that in order to improve the fatigue resistance of this wire, it is sufficient to apply a compressive residual stress to the surface of the wire. For example, Japanese Patent Application Laid-Open No. 6-255325 discloses that There has been proposed a wire having a surface which is subjected to bending and has substantially no residual tensile stress.

[0004]

However, in a wire bent in one direction, the surface residual stress level becomes non-uniform in the circumferential direction of the wire. As a result, even if the surface residual stress is on the compression side in a certain direction. In the direction perpendicular to the direction, the surface residual stress of tension often occurs. Then, when a uniform force acts in the circumferential direction, the surface residual stress decreases the fatigue property from the tension side or the wire portion closest to the tension side, and becomes a starting point of fatigue fracture.

[0005] Here, among pneumatic tires, a pneumatic tire used for high-speed traveling under a high load, for example, an aircraft pneumatic tire, exerts a large stress on the bead portion during the traveling. It is necessary to install a bead core having a strength capable of withstanding such stress in the bead portion.

For this purpose, Japanese Patent Application Laid-Open No. 53-51804 discloses an arrangement in which a plurality of layers in which a plurality of metal side wires having a diameter smaller than the core wire are wound substantially spirally around one core wire. A so-called cable structure has been proposed. This cable structure is superior in strength as compared with a bead core having a square or hexagonal cross section.

However, in a pneumatic tire having a bead core of this type, there is a concern that fatigue breakage may occur with the long-term use of the pneumatic tire on the outside of the core wire of the bead core, particularly on the metal side wire constituting the innermost layer of the outermost layer. In this case, the durability of the bead portion may be reduced. That is, when a pneumatic tire is used at a high speed under a high load, a large external force acts on the bead core of the tire, and as a result of repeated torsion, a tensile deformation occurs on a metal side line constituting the outside of the core wire of the bead core. And the compression deformation is repeated, and plastic stress is generated from the surface of the metal side wire due to the repetitive stress accompanying the deformation, and ultimately fatigue fatigue failure occurs. Therefore, a steel wire applied to a bead core of this kind of tire is required to have extremely high fatigue resistance.

[0008] Since the deformation form and the magnitude of the deformation of the metal side line in the bead core vary depending on factors such as the design of the tire, the material or the structure of the bead, the point where the maximum input occurs in the circumferential direction of the side line is determined. It is possible to improve the fatigue resistance by identifying and keeping the residual stress at a high level. However, since bending and twisting are added to the side wire at the time of manufacturing the bead core, it is difficult to specify the maximum deformation portion of the metal side wire after manufacturing the bead core, for the wire serving as the metal side line before manufacturing the bead core.

Therefore, the present invention relates to a steel wire which does not lose its excellent fatigue resistance even at the stage of forming it into a bead core, and a method for straightening the wire for obtaining this steel wire, which has excellent bead portion durability. The purpose is to make proposals with pneumatic tires.

[0010]

Means for Solving the Problems The inventors of the present invention have repeatedly conducted trial production of wires having various surface residual stresses, and as a result, have found that the distribution of residual stress on the wire surface can be suppressed.
The inventor has found that it is effective in solving the above problems, and has completed the present invention.

The gist of the present invention is as follows. (1) A steel wire having a diameter of 0.80 to 4.00 mm, wherein the surface residual stress is on the compression side, and the distribution of the compressive residual stress is uniform in a circumferential direction and a longitudinal direction. .

(2) In the above (1), a half-perimeter portion of a steel wire having a length of 10 cm is covered with a lacquer in the longitudinal direction, and then etched in a nitric acid aqueous solution. After the etching, the bending of the wire is maximized. The amount of bending in the bent state, the compressive residual stress value defined by the amount of bending when the wire is bent to the etched side is defined as a negative value and the case where the wire is bent to the lacquer coating side is defined as a positive value. But-
A steel wire having a diameter of 1 mm or less.

(3) In the above (1) or (2), when the average value of the compressive residual stress values measured at least at eight locations on the circumference of the steel wire is A, the measurement points at eight locations Wherein the distribution width of the compressive residual stress value is in the range of 0.4 × A.

(4) In the above (2) or (3), the absolute value of the difference between the maximum value and the minimum value in the compressive residual stress value measured at least at eight locations on the circumference of the steel wire is 2 mm.
A steel wire, characterized by:

(5) A steel wire is passed through a group of rollers arranged in a staggered manner, and the steel wire is sequentially brought into contact with each roller to apply a compressive residual stress to the surface of the steel wire. d
And a roller having a diameter R that satisfies the relationship of d / 2R <0.03 is used, and the center angle of each roller with respect to the arc formed by the contact area of the steel wire is set at 50 for at least two front roller groups from the entry side of the steel wire. ° or more, and in the at least five subsequent roller groups following the preceding roller group, the angle of the preceding roller group was gradually reduced to 3 ° or less. The processing of passing a steel wire through the roller group was performed on different sides of the steel wire. A method of straightening a steel wire, wherein the method is performed at least four times.

(6) In the above (5), the steel wire is passed through a group of rollers. Each time, the tension applied to the steel wire is controlled within a range of 1/8 or more of the tensile strength of the steel wire. Characteristic method of straightening steel wire.

(7) A bead core comprising at least three side wire layers in which a plurality of metal side wires smaller in diameter than the core wire are wound around the single core wire in a substantially spiral shape, and a bead core is embedded in the bead portion. In the pneumatic tire, at least one side layer of the bead core is formed by plating the peripheral surface of the steel wire according to any of the above (1) to (4) with Cu and Zn, Cu alone or Zn alone. A pneumatic tire characterized by being constituted by a metal side wire subjected to the following.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The fatigue resistance of a steel wire is improved by changing the tensile stress remaining on the wire surface after wire drawing to the compression side. If, for example, a cable bead is manufactured using this wire as a material and applied to a tire,
The fatigue resistance of the wire again decreases. To avoid this phenomenon, set the surface residual stress of the steel wire to the compression side,
It is important to make the distribution of the compressive residual stress uniform in the circumferential direction and the longitudinal direction.

That is, in applying a compressive residual stress to the surface of a steel wire, it is extremely effective to make the distribution of the compressive residual stress uniform not only in the longitudinal direction but also in the circumferential direction. Here, when the maximum input position in the wire can be specified when using the wire, by setting the residual stress at that position of the wire to the compression side, the fatigue property is improved. Since the wire has a complex input, it is difficult to specify the maximum input position on the wire. Therefore, if the distribution of compressive residual stress is made uniform in the circumferential and longitudinal directions so that the input may be applied to any part of the wire, the fatigue resistance of the wire will be higher and more stable. It can be improved.

In particular, it is preferable to apply a surface residual stress quantified by the following method to a steel wire. That is, the steel wire after wire drawing is 10 cm long
Then, the plating on the surface is removed with an aqueous solution of ammonium persulfate, and then, as shown in FIG. 1, a half-circumferential portion of each wire is covered with a lacquer in the longitudinal direction. %), And the amount of bending when the bending of the wire becomes maximum after this etching is defined as the surface residual stress value. In addition,
If the wire is bent before the etching, the difference in the amount of bending before and after the etching is determined and used as the surface residual stress value.

As shown in FIG. 2, the determination as to whether the surface residual stress is tensile or compressive is made when the wire is bent toward the etched side, and is determined when the wire is bent toward the lacquer-coated side. Then, in eight samples taken from the same wire, a lacquer coating of a half-circumferential portion was applied in a circumferential direction by 45 ° between each sample, the amount of bending was measured for each sample, and the average of the measured values was used. , The surface residual stress value.

It is advantageous to make the surface residual stress value of the wire thus determined to be -1 mm or less. Because
This is because, by clearly setting the surface residual stress of the wire to the compression side, the fatigue resistance particularly against repeated input can be improved.

Further, in order to make the distribution of the compressive residual stress of the steel wire uniform in the circumferential direction, when the average value of the residual stress measured at at least eight equally divided locations on the circumference of the steel wire is A, It is advantageous that the distribution width of the residual stress values at these eight measurement points is in the range of 0.4 × A. By setting the distribution width of the compressive residual stress value in the circumferential direction to the range of 0.4 × A, it is possible to provide substantially uniform fatigue resistance on the circumference of the wire. On the other hand, when the residual stress value is out of the above range, when a uniform strain is applied to the wire, a position where the residual stress value is relatively low serves as a starting point of fatigue fracture, resulting in a decrease in fatigue resistance.

For the same reason, it is advantageous to make the absolute value of the difference between the maximum value and the minimum value of the residual stress values measured at least eight places on the circumference of the steel wire equal to or less than 2 mm.

Next, the surface residual stress of the steel wire is calculated as follows:
A method of straightening a steel wire, which is a means for shifting from the tension side to the compression side and for making the residual stress distribution uniform, will be described in detail. That is, in FIG.
1 shows a straightening device A directly used in the method of the present invention. The straightening device A is installed between the final die of the wire drawing device and the winding device, and is used for straightening a steel wire. Correction device A
A first-stage roller group 1 composed of rollers 1a to 1c arranged in a staggered manner, and a second-stage roller group 2 composed of rollers 2a to 2g continuous with the first-stage roller group 1 and similarly arranged in a staggered manner.
After the compressive stress is applied by the first roller group 1, straightness is added by the second roller group 2.
The steel wire 3 is first introduced into the first roller group 1 and then the second roller group 2 through the guide roller 4 on the entry side, and has a V-shaped cross section formed on the peripheral surface of each roller of the first roller group 1 and the second roller group 2. It is guided by the groove and passes through the first roller group 1 and the second roller group 2 while being in contact with each roller, and is corrected.

Here, it is important that the diameter R of the roller satisfies the relationship d / 2R <0.03 ---- (1) with respect to the diameter d of the steel wire. Furthermore, it is important to set the arrangement of the rollers in a zigzag pattern based on the center angle (hereinafter referred to as the winding angle) α with respect to the arc formed by the contact area of the steel wire in each roller shown in FIG. That is, in the first roller group 1, the winding angle α is
While the arrangement of the rollers is set so as to be 50 ° or more, in the latter roller group 2, the winding angle α is set so as to gradually decrease toward the exit side of the wire. The winding angle α of the rollers 2a to 2g of the rear roller group 2 is
The angle is gradually reduced to 3 ° or less toward the exit side, but the width of the decrease may be an equal interval or an arbitrary interval.

The tensile stress mainly remaining on the surface layer of the steel wire after wire drawing is determined by the above-mentioned formula.
The problem can be solved by applying a compressive stress by passing the roller at a winding angle α of 50 ° or more through a pre-roller group including rollers having a diameter according to (1). That is, the steel wire is expressed by the above equation
By applying a winding angle α: 50 ° or more to a roller having a diameter in accordance with (1), a bending strain is applied to the surface of the steel wire up to the tensile plastic region, and then a compression strain is applied by releasing the steel wire to a natural state. obtain. Here, the winding angle is limited to 50 ° or more because, when the rigidity of the steel wire and the passing speed of the steel wire are very high, due to its inertia force, the roller diameter is less than 50 °. This is because it is impossible to give a bending strain proportional to.

By setting the winding angle α to 50 ° or more, more preferably 60 ° or more, a large compressive stress can be applied. However, even if the winding angle α exceeds 70 °, the compressive stress does not increase. In addition, at least two rollers are required in order to expect the above-mentioned effects. However, even if more than five rollers are used, the effect cannot be expected to increase, and large equipment is required. It is preferable that Further compressive stress can be applied by reducing the roller diameter.However, when the roller diameter is extremely small, the rotation speed of the roller is increased and the roller life is shortened.
When treating a 0.80 to 4.00 mm steel wire, the roller diameter is preferably in the range of 26.7 to 133.3 mm.

Next, when the steel wire is passed through the subsequent roller group, a high straightness is imparted by gradually reducing the winding angle α of each roller to 3 ° or less toward the exit side. That is, after bending the steel wires having different straightnesses with a large curvature at the entrance rollers of the first roller group 1 and the second roller group 2, the winding angles of the second roller group 2 around the plurality of rollers are gradually reduced. By gradually reducing the bending strain, the correction that gives high straightness can be divided and gradually performed.

In order to expect the above effect, at least 5
Although more than seven rollers are required, more preferably about ten rollers are advantageous in terms of achieving both straightness and durability of the rollers. If the winding angle α of the final roller exceeds 3 °, the desired straightness cannot be obtained by the final bending, so that the angle is set to 3 ° or less.

The winding angle α can be adjusted by the positional relationship between the adjacent rollers. Specifically, as shown in FIG. 5, the distance P between the center axes of the adjacent rollers in the steel wire passing direction can be adjusted. What is necessary is just to adjust the distance H between the center axes of the adjacent rollers in the direction perpendicular to the passing direction.

In the illustrated example, the number of rollers in the first-stage roller group 1 is three and the number of rollers in the second-stage roller group 2 is seven. However, the type of steel wire, the desired residual stress value, straightness, etc. Can be increased or decreased according to

Using at least four sets of the above-mentioned straightening devices A, as shown in FIG.
By applying at least four times to the different surfaces of the steel wire, a uniform compressive stress having a circumferential distribution can be applied to the wire. In particular, when the correction is performed four times, as shown in FIG. 7, it is preferable to make contact with the roller group at positions separated from each other by 45 °, that is, at eight equally divided locations on the wire circumference.

Here, when the steel wire 3 is passed through the roller group four or more times, it is advantageous to order the surfaces of the steel wire 3 that come into contact with each roller group.
For example, in FIG. 7, when the steel wire 3 is passed through the roller group four times, the order is I → II → III → IV, the separation angle θ ₁ between the contact surface I and the contact surface II is 90 °, and The separation angle θ ₂ between each of planes I and II and III is 45
°, and a separation angle theta ₃ between each the same IV contact surfaces I and II and 45 °. That is, when selecting a contact surface, a surface having a maximum separation angle with all the already corrected contact surfaces may be selected.

Further, in order to apply a uniform compressive stress in the circumferential direction of the steel wire, it is important to control the tension at the time of bending the wire. In the present invention,
One wire must be bent at least four times, and at this time, the tension applied to the wire needs to be made as small as possible in each time. Therefore, as shown in FIG. 8, for example, the steel wire 3 that has passed through the final die 5 is immediately guided to the straightening device A and passed therethrough, then wound around the capstan 6, and the drawing force from the die 5 is given by the capstan 6. Thus, the pulling force can be directly used as the tension of the steel wire in the straightening device A. The pulling force can be controlled in the range from 0 to the tensile strength by adjusting the processing area reduction rate in the final die. Reference numeral 7 in FIG. 8 is a guide roller. Then, the steps from the capstan 6 to the guide roller 7 shown in FIG. 8 are similarly reproduced in the subsequent three sets of straightening devices, whereby four bending operations can be performed under the same tension.

The tension applied to the steel wire is as follows:
Preferably, the tensile strength is at least 1/8 of the tensile strength of the wire. Because, in order to impart compressive residual stress, it is necessary to plastically deform the wire, and if less than 1/8 of the tensile strength, the plastic deformation required to adjust the residual stress does not occur.
This is because there is a fear.

The above-described method of shifting the surface residual stress of the steel wire to the compression side is effective mainly for a wire obtained through a normal drawing process. That is, the normal wire drawing process is performed through a plurality of dies after the heat treatment, and the area reduction rate in each of the dies is about 15 to 20%, and the residual stress on the surface of the obtained wire is around the circumference. Will have large variations. Therefore, to eliminate this variation,
The above-described correction by the rollers from multiple directions works effectively.

On the other hand, when the wire is drawn through a plurality of dies, the compressive stress is uniformly applied to the wire surface by setting the area reduction rate in the final die to several percent, preferably 1 to 5%. It is possible to apply. That is,
When the reduction in area during wire drawing is reduced, only the wire surface is drawn, and a compressive stress is applied to the wire surface. However, if the final area reduction rate exceeds 5%, the effect is reduced. On the other hand, if the final area reduction rate is less than 1%, the pressure applied to the dies increases, so that stable drawing becomes difficult. Therefore, it is desirable that the area reduction rate in the final die is in the range of 1 to 5%.

The above-mentioned steel wire has, on its peripheral surface,
After plating with Cu and Zn, Cu alone or Zn alone in order to secure adhesion to rubber, it is used as a metal side wire of a bead core of a pneumatic tire, particularly a side wire layer of a bead core of a cable structure. Here, as the tire, for example, an aircraft tire shown in FIG. 9 is advantageously adapted.

That is, in FIG. 9, reference numeral 11 denotes a pair of bead cores, and a carcass 12 extending in a toroidal shape between the bead cores 11 has a skeleton. And tread 14
Is arranged. In the tread 14, a plurality of circumferential grooves extending along the equatorial plane O of the tire and lateral grooves extending in a direction crossing these circumferential grooves are appropriately arranged.

The carcass 12 has a plurality of carcass plies, each of which is composed of a large number of textile cords, extending in a direction substantially perpendicular to the equatorial plane O of the tire. And a turn-up ply 12a wound around the tire from the inside to the outside, and a down ply 12b extended to the bead core 11 along the outside of the folded portion.

The belt 13 is composed of a plurality of plies in which a number of textile cords extending at an angle with respect to the equatorial plane O of the tire and arranged in parallel with each other are covered with rubber.
Either a structure in which the cords are overlapped with each other between the laminated plies, or a structure in which a plurality of plies, in which a plurality of textile cords extending along the equatorial plane O of the tire are covered with rubber, are overlapped. It is composed of the above structure or a combination structure of both.

As shown in FIGS. 2 and 3, the bead core 11 includes a core wire 15 made of one ring-shaped steel wire,
Around the core wire 15, at least three side wire layers, in the illustrated example, four side wire layers 17 A to 17 D are arranged, in which a plurality of side wires 16 made of a steel wire having a diameter smaller than the core wire 15 are spirally wound. Consisting of At least one combination of these side line layers 17A to 17D in which the winding directions are reversed between the layers is sufficient. In other words, if the winding directions are reversed between the two layers, even if the winding directions between the remaining layers are the same. Preferably, the winding directions are all reversed between the layers. This is because, if the winding directions between the layers are reversed, the cross-sectional shape of the bead core becomes closer to a perfect circle, and the carcass is easily wound around the bead core during tire production.

Here, it is important that at least one side layer of the bead core 11 is formed of the side wire 16 obtained by plating the steel wire according to the present invention with a predetermined plating. This is because, when the surface residual stress of the side wire is on the tensile side, tensile strain is applied to the surface of the side wire particularly when the surface is subjected to tensile deformation, so that fatigue fracture easily proceeds. That is, when the pneumatic tire is rolled under high load,
Since repeated stress due to large tensile and compressive deformation is added to the side line of the bead core of the tire, especially the inner side line of the outermost layer, a crack is generated from the surface by plastic deformation on each side line due to this stress, especially in the surface of the side line When the residual stress on the side wire surface is on the tensile side,
The cracks grow faster and eventually the side lines break. Therefore, the resistance to fatigue fracture of the bead core, the so-called fatigue fracture resistance, is that at least one layer of the bead core, preferably the inner layer of the outermost layer, is formed on the side line where the surface residual stress is on the compression side. It is much better. Of course, the fatigue fracture resistance is further improved by configuring all the side line layers with the side lines whose surface residual stress is on the compression side.

The diameter of the core wire 11 is preferably 1.3 times or more the diameter of the side wire 16. That is, the diameter of the core wire 11 is
If the diameter is less than 1.3 times the diameter of 16, the number of side wires 16 wound around the core wire 11 is too small, and in order to give the required strength to the bead core, the number of side wire layers must be increased. As a result, the bead core diameter increases and the weight increases.
The disadvantage is the increase in tire weight.

On the other hand, the side line preferably has a diameter of 0.80 to 4.00 mm. That is, if the diameter of the side wire is less than 0.80 mm,
The number of windings at the time of manufacturing the bead core increases, and the operation takes time, resulting in a decrease in productivity. On the other hand, if the diameter of the side wire exceeds 4.00 mm, it becomes difficult to mold the side line at the time of manufacturing the bead core, which also causes a decrease in the productivity of the bead core.

[0047]

EXAMPLE 1 Using a straightening device shown in FIG. 3, a treatment for applying a compressive stress to a steel wire (C: 0.72 wt%) drawn to a diameter of 2.1 mm through a plurality of dies after heat treatment was performed. Was.
The first roller group 1 and 7 with three rollers
The roller diameter of the latter roller group 2 with two rollers is 40
mm, the winding angle α in the first roller group 1 was set to 60 °, and the winding angle α in the second roller group 2 was set to gradually decrease from 20 °, and the final winding angle was set to 2 °. The additional tension of the wire was adjusted to an appropriate value of 1/8 or more of the tensile strength, and the wire passing speed was 10 m / min.

The above treatment was applied to the surface of the wire according to the three conditions shown in Table 1 to give a residual stress. The surface residual stress in Table 1 was obtained by cutting eight wires of 10 cm in length and measuring 0 °, 45 °, 90 °, 135 °, 180 °,
Samples were prepared for measuring residual stresses in eight directions, distinguished by rotating the ends in the same direction by rotating them at 225 °, 270 °, and 315 °.
The surface residual stress was measured in accordance with and. In addition, 8
The individual residual stress values measured from the directions were averaged to determine an average surface residual stress amount. In addition, as the distribution width of the residual stress, the difference between the maximum value and the minimum value in the residual stress values measured from eight directions was shown as an absolute value.

Next, each wire was subjected to a twist test to evaluate fatigue resistance. That is, after removing the plating on the surface of the wire with an aqueous solution of ammonium persulfate, a right-handed twist is given to each wire once, then a left-handed twist is given two times, and then a right-handed twist is given once. The process of giving and returning to the original state was defined as one cycle, and how many cycles were required until breaking was measured, and the result was expressed as an index by the following equation. The larger the index is, the larger the improvement in fatigue resistance is, and the more excellent the fatigue resistance is. Table 1 also shows the test results. (Fatigue resistance index) = (number of break cycles in invention wire) / (number of break cycles in comparative wire) x 100

[0050]

[Table 1]

From Table 1, the comparative wire is a case where the average value of residual stress is -1.75 mm and the distribution width is 3 mm when the roller treatment is performed from one direction, and the distribution width of the invention wires 1 and 2 is small. And 1 mm, the fatigue resistance is inferior. That is, the inventive wire is superior in fatigue resistance as compared with the conventional wire that has been subjected to roller treatment from one direction,
Further, it can be seen that the fatigue resistance is improved as the distribution width of the circumferential residual stress is reduced.

Next, as a bead core of the tire shown in FIG. 9, a bead core having a structure shown in FIGS. 10 and 11 was applied under the specifications shown in Table 2, and a radial tire for aircraft having a size of 46 × 17R20 / 30PR was used. Prototype made. Each tire thus obtained was examined for fatigue resistance. Table 2 shows the results of these surveys.

For the surface residual stress, eight side lines of 10 cm in length were cut off before manufacturing the bead core of the cable structure, and the circumferential direction was 0 °, 45 °, 90 °, 135 °, 180 °, 225 °, 270 °, respectively.
、 And 315 ° rotation, bending the ends, and preparing samples for measuring the residual stress in eight directions.
The surface residual stress was measured in accordance with and. In addition, 8
The individual residual stress values measured from the directions were averaged to determine an average surface residual stress amount.

The fatigue resistance of the tire was 17.1 kgf / cm ²
After filling the internal pressure of the drum and mounting it on the rim (45 x 16-20) of the drum testing machine, apply a load of 16700 kgf and drive at 64 km / h for 1 hour.
After running repeatedly for 10 minutes 800 times, a side line in an inner side layer of the outermost layer was taken out from the tire after the test and a new tire by about 30 cm, and evaluated by a twisting test. This is similar to the above, in which the wire is given a right-handed twist one turn, then a left-handed twist two times, and then a right-handed twist one turn, and the process of returning to the original state is one cycle. The number of cycles required to break was indicated by an index using the following equation.
The number of break cycles of a conventional one-way wire is indexed to 100.
It indicates that the larger the value is, the better the fatigue property is and the more excellent the fatigue resistance is. (Fatigue resistance index) = (number of fracture cycles in test wire) / (number of fracture cycles in comparative wire) x 100

The productivity of a bead core is compared with that of a conventional product by comparing the production time with that of a conventional product. did.

[0056]

[Table 2]

From Table 2, Comparative Example 1 is a case where a wire having a mean value of residual stress of -1.75 mm and a distribution width of 3 mm using a conventional roller-treated roller in one direction is used. Fatigue resistance is inferior to the case of 0 and 1 mm where the distribution width is small. That is, the invention example is superior in fatigue resistance as compared with the case of using a conventional wire that has been subjected to a roller treatment from one direction, and the fatigue resistance increases as the distribution width of the residual stress in the circumferential direction decreases. It can be seen that it has been improved. Inventive Examples 4 and 5 have wire diameters of 0.8 and 3.
9 mm, and the wire diameters of Comparative Examples 2 and 3 were 0.6 and 4.2 m.
As compared to m, the number of windings is smaller and the diameter is smaller,
The productivity of the bead core having the cable structure is not hindered.

Example 2 When a steel wire (C: 0.72 wt%) was produced by wire drawing through a plurality of dies to a diameter of 2.3 mm after heat treatment, the area reduction rate in the final die was changed to the three conditions shown in Table 3. Then, wire drawing was performed. About the wire thus obtained, 8 pieces of 10 cm in length were cut from each wire,
0 °, 45 °, 90 °, 135 °, 180 °, 225
Samples were prepared for measuring residual stress in eight directions, distinguished by rotating the ends in the same direction by rotating them at an angle of 270 °, 315 °, and the residual stress was measured according to FIGS. 1 and 2 for each. . Further, individual residual stress values measured from eight directions were averaged to obtain an average surface residual stress amount. Also, as the distribution width of the residual stress,
The difference between the maximum value and the minimum value in the residual stress values measured from eight directions is shown as an absolute value.

Next, each wire was subjected to the same torsion test as in Example 1 to evaluate the fatigue resistance.
Table 3 also shows the evaluation results.

[0060]

[Table 3]

From Table 3, the comparative wire was obtained when the reduction rate of the final die was 15%, the average value of the residual stress was −2 mm, and the distribution width was 3 mm. The fatigue resistance is inferior to that of the small 0 and 1 mm cases. In other words, it can be seen that the inventive wire has better fatigue resistance than the conventional wire drawn by ordinary drawing.

Further, as the bead core of the tire shown in FIG. 9, a bead core having the structure shown in FIGS.
A prototype of a radial tire for aircraft of size 46 × 17R20 / 30PR was applied under the following specifications. The tires thus obtained were examined for fatigue resistance and bead core productivity in the same manner as in Example 1 described above. Table 4 shows the results of these surveys.

For the surface residual stress, eight side lines each of which is 10 cm long were cut out before manufacturing the bead core of the cable structure, and the circumferential direction was 0 °, 45 °, 90 °, 135 °, 180 °, 225 °, 270 °, respectively.
、 And 315 ° rotation, bending the ends, and preparing samples for measuring the residual stress in eight directions.
The surface residual stress was measured in accordance with and. In addition, 8
The individual residual stress values measured from the directions were averaged to determine an average surface residual stress amount.

[0064]

[Table 4]

From Table 4, it can be seen that Comparative Example 1 uses a conventional wire having a mean value of residual stress of -2.0 mm due to normal drawing and a distribution width of 3 mm. And 1 mm, the fatigue resistance is inferior. That is, it can be seen that the invention example is superior in fatigue resistance as compared with the case where the conventional wire drawn by normal drawing is used.
Inventive examples 3 and 4 have wire diameters of 0.8 and 3.9 mm.
Since the number of windings is small or the diameter is small as compared with the wire diameters of 0.6 and 4.2 mm in Comparative Examples 2 and 3, the productivity of the bead core having the cable structure is not hindered.

[0066]

As described above, the steel wire of the present invention has a very small reduction in fatigue even after being processed, for example, in connection with the manufacture of a bead core. Therefore, the steel wire of the present invention is most suitable for a reinforcing material for a rubber article, particularly a reinforcing material for a tire bead core. Material can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a procedure for measuring a surface residual stress of a wire.

FIG. 2 is a schematic view showing a procedure for measuring a surface residual stress of a wire.

FIG. 3 is a schematic view showing a straightening device used in the present invention.

FIG. 4 is a diagram illustrating winding of a steel wire around a roller group.

FIG. 5 is a diagram showing an arrangement of rollers.

FIG. 6 is a schematic diagram illustrating a combination of correction devices.

FIG. 7 is a view showing a contact surface of a steel wire with a roller group.

FIG. 8 is a diagram showing a means for applying tension to a steel wire.

FIG. 9 is a diagram showing a tire according to the present invention.

FIG. 10 is a diagram showing a structure of a bead core according to the present invention.

FIG. 11 is a diagram showing a structure of a bead core according to the present invention.

[Explanation of symbols]

 1 Front Roller Group 1a Roller 1b Roller 1c Roller 2 Rear Roller Group 2a Roller 2b Roller 2c Roller 2d Roller 2e Roller 2f Roller 2g Roller 3 Steel Wire 4 Guide Roller 5 Final Die 6 Capstan 7 Guide Roller 11 Bead Core 12 Carcass 13 Belt 14 Tread 15 core wire 16 side wire

Claims (7)

[Claims] 1. A steel wire having a diameter of 0.80 to 4.00 mm, characterized in that the surface residual stress is on the compression side and the distribution of the compressive residual stress is uniform in the circumferential direction and the longitudinal direction. Steel wire. 2. The steel wire according to claim 1, wherein a half-perimeter portion of the steel wire having a length of 10 cm is covered with a lacquer in the longitudinal direction, and then etched in a nitric acid aqueous solution. After the etching, the bending of the wire is maximized. The amount of bending in the state, when the wire is bent to the etched side is a negative value and when the wire is bent to the lacquer coating side is a positive value, the compressive residual stress value, defined by the amount of bending, −
A steel wire having a diameter of 1 mm or less. 3. The compressive residual stress at eight measurement points according to claim 1 or 2, wherein A is the average value of the compressive residual stress values measured at least at eight locations on the circumference of the steel wire. A steel wire having a value distribution range of 0.4 × A. 4. The method according to claim 2, wherein the absolute value of the difference between the maximum value and the minimum value in the compressive residual stress value measured at least at eight locations on the circumference of the steel wire is 2 mm or less. And steel wire. 5. A steel wire is passed through a group of rollers arranged in a staggered manner, and the steel wire is sequentially brought into contact with each roller to apply a compressive residual stress to the surface of the steel wire. And a roller having a diameter R that satisfies the relationship of d / 2R <0.03 is used, and the center angle of each roller with respect to the arc formed by the contact area of the steel wire is set at 50 for at least two front roller groups from the entry side of the steel wire. ° or more, in the at least five subsequent roller groups following the former roller group, gradually decreased from the angle of the former roller group to 3 ° or less,
A method of straightening a steel wire, wherein a process of passing a steel wire through a roller group is performed at least four times on different surfaces of the steel wire. 6. The steel wire according to claim 5, wherein the tension applied to the steel wire is controlled within a range of 1/8 or more of the tensile strength of the steel wire each time the steel wire is passed through the roller group. Steel wire straightening method. 7. A bead core comprising at least three side wire layers in which a plurality of metal side wires having a smaller diameter than the core wire are wound around the single core wire in a substantially helical manner is embedded in the bead portion. In the pneumatic tire, at least one side layer of the bead core is a metal obtained by plating a peripheral surface of the steel wire according to any one of claims 1 to 4 with plating composed of Cu and Zn, Cu alone or Zn alone. A pneumatic tire comprising a side line.