Steel wire and tire

Abstract

A steel wire, wherein a cross section of the steel wire perpendicular to a long dimension direction has a flat shape, an outline of the cross section has a pair of opposing straight line portions (11) and a pair of opposing curved line portions (12) connecting between the straight line portions (11), the curved line portions (12) have a pair of first regions (131) located on the straight line portions (11) side and a second region (132) located between the pair of first regions (131), a radius of curvature R1 of the first regions (131) is 0.05 mm or more and less than 0.15 mm, a radius of curvature R2 of the second region (132) is 0.13 mm or more and 0.2 mm or less, and an angle between the straight line portions (11) and the curved line portions (12) is 165 degrees or more.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a steel wire and a tire.

[0002] This application claims priority based on International Application PCT / JP2020 / 039289 based on the Patent Cooperation Treaty, filed on October 19, 2020, and incorporates by reference the entire disclosure of the International Application. BACKGROUND

[0003] For example, in Patent Literature 1, an air radial tire provided with a sidewall reinforcing layer in which a plurality of single wire steel wires are laid and embedded in rubber in a region from a bead portion to a sidewall portion is disclosed, the air radial tire being characterized in that the single wire steel wires are in a flat shape, the flatness of the single wire steel wires is 40% to 70%, the length diameter of the single wire steel wires is 0.80 mm or less, the average interval of the single wire steel wires is 0.60 mm or more, and the product of the buckling load of each single wire steel wire and the mass of the steel wires per unit area of the sidewall reinforcing layer is 400 N·kg / m 2 or more.

[0004] Prior Art Documents

[0005] Patent Literature

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2015-178301 SUMMARY

[0007] The steel wire of the present disclosure has a flat shape in a cross section perpendicular to a long dimension direction, and an outline of the cross section has a pair of straight line portions and a pair of curved line portions connecting between the straight line portions, the curved line portions have a pair of first regions on the straight line portion side and a second region between the pair of first regions, a radius of curvature R1 of the first region is 0.05 mm or more and less than 0.15 mm, a radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less, and an angle between the straight line portion and the curved line portion is 165 degrees or more. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1A is a cross-sectional view at a surface perpendicular to a long dimension direction of a steel wire of one aspect of the present disclosure.

[0009] Figure 1B is a view that shows a vicinity of a point of intersection between a straight line portion and a curved line portion in a cross-sectional view at a surface perpendicular to a long dimension direction of a steel wire of one aspect of the present disclosure.

[0010] Figure 2 is an explanatory view of one configuration example of a rolling device that can be used when manufacturing a steel wire of one aspect of the present disclosure.

[0011] Figure 3 is a sectional view of a tire of one aspect of the present disclosure.

[0012] Figure 4 is a view schematically showing a belt.

[0013] Figure 5 is an explanatory view of a durability test in an experimental example.

[0014] Figure 6 is an explanatory view of a Charpy impact test device in an experimental example. DETAILED DESCRIPTION

[0015] [Problems to be Solved by the Present Disclosure]

[0016] With respect to a tire, for example, in addition to weight reduction for reduction in rolling resistance and the like, improvement in durability is required so that the frequency of replacement of the tire can be suppressed and the tire can be used for a longer period of time. Also, with respect to a steel wire used for a tire, a steel wire that can form a tire excellent in lightness and durability is required.

[0017] Therefore, an object of the present disclosure is to provide a steel wire that can form a tire excellent in lightness and durability.

[0018] [Effects of the Present Disclosure]

[0019] According to the present disclosure, a steel wire that can form a tire excellent in lightness and durability can be provided.

[0020] [Explanation of Embodiments of the Present Disclosure]

[0021] First, an embodiment of the present disclosure will be explained by citing. In the following explanation, the same reference numerals are attached to the same or corresponding elements, and the same explanation will not be repeated for them.

[0022] (1) The steel wire of one aspect of the present disclosure has a flat shape in a cross section perpendicular to a long dimension direction, the outer shape of the cross section has a pair of opposing straight line portions and a pair of opposing curved line portions connecting between the straight line portions, the curved line portions have a pair of first regions on the straight line portion side and a second region between the pair of first regions, the radius of curvature Rl of the first region is 0.05 mm or more and less than 0.15 mm, the radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less, and the angle between the straight line portion and the curved line portion is 165 degrees or more.

[0023] The steel wire can be provided, for example, to a belt layer of a tire. The belt layer has a steel wire and rubber, and the steel wire is embedded in the rubber. The belt layer can be selected in thickness in such a manner that the steel wire is embedded in the rubber, and thus, by making the shape of a cross section of the steel wire perpendicular to the longitudinal direction (hereinafter, also simply referred to as "cross section") flat, the thickness of the steel wire can be suppressed, and the thickness of the belt layer can also be suppressed. Thus, by using the steel wire having the shape of the cross section flat, compared to a case where, for example, a round steel wire having the same cross-sectional area is used, the amount of rubber included in the belt layer can be suppressed. Thus, by using the steel wire having the shape of the cross section flat, the belt layer can be made lightweight, and a tire including the belt layer can also be made lightweight.

[0024] However, according to the research by the inventors of the present application and others, in the conventional steel wire having the cross section flat, the outer shape of the cross section includes a linear portion and a curved portion, and at a boundary portion between the linear portion and the curved portion, the slope changes greatly. Note that the slope refers to the slope of a tangent line of the outer shape in the cross section of the steel wire perpendicular to the longitudinal direction (hereinafter, also simply referred to as "slope"). Also, in a case where the conventional steel wire having the flat shape is applied to a tire, a crack occurs in the rubber from the boundary portion between the linear portion and the curved portion as a starting point, and this becomes a cause of a decrease in durability of the tire.

[0025] Thus, the inventors of the present application and others conducted further research. According to this research, by forming a first region and a second region in the curved portion, and making the respective radii of curvature be in the above-described range, the change in the slope at the boundary portion between the linear portion and the curved portion can be suppressed. Thus, it was found that, in a case where the steel wire of one aspect of the present disclosure satisfying the regulation is applied to a tire, a crack in the rubber can be suppressed, and the durability of the tire can be improved.

[0026] By making the radius of curvature R1 of the first region be 0.05 mm or more as described above, the change in the slope at the boundary portion between the linear portion and the curved portion can be suppressed. Thus, in a case where this steel wire is applied to a tire, a crack in the rubber can be suppressed, and the durability of the tire can be improved. By making the radius of curvature R1 of the first region be less than 0.15 mm, the length of the linear portion can be ensured, and the cornering stability of a tire using this steel wire can be improved.

[0027] By making the radius of curvature R2 of the second region be 0.13 mm or more, the amount of processing when manufacturing the steel wire can be suppressed, and the strength of the steel wire can be improved. By making the radius of curvature R2 of the second region be 0.2 mm or less, the force applied in the direction of the thickness T of the steel wire can be dispersed, and the durability of the steel wire, and a tire including the steel wire can be improved.

[0028] The steel wire can be processed into a prescribed shape by pressing and rolling a pre-processed steel wire having a cross section perpendicular to the long dimension direction in a circular shape, for example, using a pair of rolling rolls. Therefore, the aforementioned processing amount refers to the processing amount, i.e., the deformation amount, from the pre-processed steel wire to the point at which the prescribed shape is obtained.

[0029] By making the angle between the linear portion and the curved portion 165 degrees or greater in addition to making the radii of curvature of the first region and the second region of the curved portion the aforementioned ranges, the change in the slope at the boundary portion between the linear portion and the curved portion can be particularly suppressed. Therefore, the generation of cracks in the rubber starting from the boundary portion between the linear portion and the curved portion can be prevented, and the durability of the tire can be improved.

[0030] (2) The radius of curvature R1 can be different from the radius of curvature R2.

[0031] By making the radius of curvature R1 different from the radius of curvature R2, i.e., in the relationship R1≠R2, the change in the slope at the boundary portion between the linear portion and the curved portion can be particularly suppressed. Therefore, in the case in which this steel wire is applied to a tire, the generation of cracks in the rubber can be particularly suppressed, and the durability of the tire can be further improved.

[0032] (3) In the cross section, in the case in which a center line located at an equal distance from the pair of opposing linear portions and the two intersection points of the pair of opposing curved portions are set as a first end portion and a second end portion, and in the case in which two points on the center line that are separated from the first end portion and the second end portion by 0.1 mm are set as surface-side measurement points, and a point on the center line that is located at an equal distance from the first end portion and the second end portion is set as a center measurement point, the difference between the Vickers hardness at the two surface-side measurement points, i.e., HV1, and the Vickers hardness at the center measurement point, i.e., HV2, i.e., HV1-HV2 is -60 HV0.1 or greater and -10 HV0.1 or less.

[0033] In the case in which HV1-HV2 is -10 HV0.1 or less, the hardness of the center portion including the center measurement point is higher than the hardness of the surface side including the surface-side measurement points. In this way, by making the hardness of the center portion of the steel wire higher than the hardness of the surface side, the impact received by the linear portion can be uniformly received by the entire surface including the aforementioned linear portion. In the case of a flattened steel wire, the impact resistance can sometimes decrease, but by using a steel wire having the aforementioned hardness distribution, the impact resistance can be improved.

[0034] However, in order to make HV1-HV2 less than -60 HV0.1, the hardness of the center portion needs to be particularly increased. Therefore, when flattening is performed in order to manufacture the steel wire, excessive pressure needs to be applied, and the material of the steel wire can become brittle or the like. Therefore, as described above, HV1-HV2 is preferably -60 HV0.1 or greater.

[0035] (4) Also, the surface can have a brass plating film containing copper and zinc.

[0036] Note that, hereinafter, copper is also sometimes denoted by the chemical symbol Cu, and zinc is also sometimes denoted by the chemical symbol Zn.

[0037] The steel wire of one aspect of the present disclosure has a brass plating film containing Cu and Zn on the surface, whereby, in the case where the steel wire is covered with rubber and vulcanized to produce a tire, a Cu2S-containing adhesive layer can be formed on the rubber side from the interface between the steel wire and the rubber. Note that Zn has an effect of promoting the generation of Cu2S. By forming this adhesive layer, the adhesion between the steel wire and the rubber can be improved, and a tire with particularly excellent durability can be produced.

[0038] (5) Also, the brass plating film described above can further contain one or more elements selected from cobalt, nickel, iron, tin, and bismuth.

[0039] Note that, hereinafter, cobalt is also sometimes denoted by the chemical symbol Co, nickel is also sometimes denoted by the chemical symbol Ni, iron is also sometimes denoted by the chemical symbol Fe, tin is also sometimes denoted by the chemical symbol Sn, and bismuth is also sometimes denoted by the chemical symbol Bi.

[0040] The ionization tendency of Co, Ni, Fe, Sn, and Bi is greater than that of Zn. Therefore, by further containing one or more elements selected from Co, Ni, Fe, Sn, and Bi in the brass plating film, one or more elements selected from the group of the above-described elements such as Co can function in the form of sacrificing corrosion resistance, or the combined potential of Cu and Zn can be made higher, thereby improving the corrosion resistance of the brass plating film. As a result, the adhesion between the steel wire and the rubber can be further improved, and the durability of the tire can be further improved.

[0041] (6) A tire can be produced that contains the steel wire described in any one of (1) to (5).

[0042] The tire according to one aspect of the present disclosure can suppress the thickness of the belt layer containing the aforementioned steel wire, and can make the belt layer lightweight. Therefore, the tire according to one aspect of the present disclosure including the belt layer can also be made lightweight, and the rolling resistance of the tire can be suppressed.

[0043] In addition, the tire according to one aspect of the present disclosure uses the aforementioned steel wire, and therefore has excellent durability.

[0044] [Details of Embodiments of the Present Disclosure]

[0045] Hereinafter, a specific example of a steel wire, a tire of one embodiment (hereinafter, referred to as "this embodiment") of the present disclosure will be described with reference to drawings. Note that the present disclosure is not limited to these examples, but is illustrated by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0046] 〔Steel wire〕

[0047] Hereinafter, based on the above-mentioned findings, the steel wire of this embodiment will be described. Figure 1A , Figure 1B The steel wire of this embodiment will be described.

[0048] (1) Regarding the cross-sectional shape

[0049] Figure 1A is a cross-sectional view at a surface of the steel wire 10 of this embodiment perpendicular to the longitudinal direction.

[0050] Figure 1B is a view that shows the vicinity of the intersection point of the straight portion 11 and the curved portion 12 in the cross-sectional view at the surface of the steel wire 10 of this embodiment perpendicular to the longitudinal direction.

[0051] The steel wire 10 of this embodiment is a wire, that is, a single wire, and can also be referred to as a single wire steel wire. Furthermore, the steel wire 10 of this embodiment is preferably not subjected to twist processing in the longitudinal direction, and is preferably a straight steel wire.

[0052] As shown in FIG. 1A, the steel wire 10 of this embodiment can have a flat shape in a cross section perpendicular to the longitudinal direction. The flat shape referred to here means, for example, a shape in which the thickness is shorter than the width and is flat. Figure 1A The steel wire can be provided in a belt layer of a tire, for example. As described later in the description of the tire, the belt layer has a steel wire and rubber, and the steel wire is embedded in the rubber. The belt layer can be selected in terms of thickness in such a manner that the steel wire is embedded in the rubber, and thus by making the shape of the cross section of the steel wire a flat shape, the thickness of the steel wire can be suppressed, and the thickness of the belt layer can also be suppressed. Thus, by using a steel wire whose cross-sectional shape is a flat shape, the amount of rubber included in the belt layer can be suppressed as compared to the case where a circular steel wire having the same cross-sectional area is used. Thus, by using a steel wire whose cross-sectional shape is a flat shape, the belt layer can be made lightweight, and a tire including the belt layer can also be made lightweight.

[0053] However, according to the research by the inventors of the present disclosure and the like, in the case where a steel wire whose cross-sectional shape is a flat shape is embedded in rubber, a crack in the rubber sometimes occurs from the vicinity of the boundary between the straight portion and the curved portion of the steel wire, and the adhesion of the steel wire to the rubber can be decreased.

[0054]

[0055] ​Accordingly, the inventors of the present application have further studied a steel wire that can achieve both lightness and durability of a tire in the case of use in a tire. As a result, it has been found that by making the shape of the cross section of the steel wire a prescribed flat shape, it is possible to improve the lightness and durability of a tire using the steel wire.

[0056] As shown in Figure 1A , the outer shape of the cross section of the steel wire 10 of the present embodiment has a pair of opposing straight portions 11 and a pair of opposing curved portions 12 that connect between the straight portions 11.

[0057] The straight portions 11 can have a first straight portion 111 and a second straight portion 112.

[0058] The curved portions 12 can have a first curved portion 121 and a second curved portion 122.

[0059] The curved portions 12 can be arranged so as to connect between the pair of straight portions 11.

[0060] It is preferable that the first straight portion 111 and the second straight portion 112 be parallel as shown in Figure 1A . Note that the parallel here does not mean strict parallel, but means that the two straight portions are arranged side by side.

[0061] The first curved portion 121 and the second curved portion 122 are arranged so as to be opposite. The first curved portion 121 and the second curved portion 122 can each be arranged so as to connect between the end portion of the first straight portion 111 and the end portion of the second straight portion 112. For example, as shown in Figure 1A , the first curved portion 121 and the second curved portion 122 can each adopt a curved shape that protrudes to the outside of the steel wire 10.

[0062] The curved portions 12 can have a pair of first regions 131 on the side of the straight portions 11, that is, on the side of both end portions of the curved portions 12, and a second region 132 between the pair of first regions 131.

[0063] Also, the radius of curvature R1 of the first region 131 is preferably 0.05 mm or more and less than 0.15 mm, and more preferably 0.05 mm or more and 0.1 mm or less.

[0064] Further, the radius of curvature R2 of the second region 132 is preferably 0.13 mm or more and 0.2 mm or less, and more preferably 0.14 mm or more and 0.2 mm or less.

[0065] According to the research of the inventors of the present invention, in conventional steel wires with a flat cross-section, the shape of the cross-section includes a straight portion and a curved portion, and the slope changes significantly at the boundary between the straight portion and the curved portion. Furthermore, when conventional steel wires with a flat shape are applied to tires, cracks are generated in the rubber starting from the boundary between the straight portion and the curved portion, which is a cause of decreased tire durability.

[0066] Therefore, the inventors of the present invention conducted further research. According to this research, by forming a first region 131 and a second region 132 in the curved portion 12, and setting their respective radii of curvature to the aforementioned range, changes in the slope at the boundary between the straight portion 11 and the curved portion 12 can be suppressed. Therefore, it was discovered that when the steel wire of this embodiment, satisfying this requirement, is applied to a tire, cracking in the rubber can be suppressed, improving tire durability.

[0067] As described above, the first region 131 can be configured such that it is located on the side of the straight section 11 within the curved section 12. Therefore, as... Figure 1A As shown, for example, the first curved portion 121 may have a first region 131 on the side of the first straight portion 111 and the side of the second straight portion 112. Figure 1A As shown, the first region 131 may also be provided in a manner that is directly connected to the first straight section 111 and the second straight section 112, which are straight sections 11, but it is not limited to this manner. For example, a transition region in which the radius of curvature of the straight section 11 changes from the straight line to the first region 131 may also be provided between the straight section 11 and the first region 131.

[0068] The second region 132 can be disposed between a pair of first regions 131. The second region 132 can, for example, be disposed at the center of the curved portion 12 in the longitudinal direction. It should be noted that the curved portion 12 is disposed along the thickness T of the wire 10; therefore, the center of the curved portion 12 in the longitudinal direction can also be referred to as the center of the thickness T direction. Figure 1A As shown, the first region 131 and the second region 132 may also be continuously provided on the curved portion 12, but are not limited to this method. For example, a transition region where the radius of curvature of the first region 131 changes to the radius of curvature of the second region 132 may be provided between the first region 131 and the second region 132.

[0069] exist Figure 1A In the diagram, the first region 131 and the second region 132 are shown only on the side of the first curved section 121, but the second curved section 122 may also have the first region and the second region.

[0070] Furthermore, by making the radius of curvature R1 of the first region 131 0.05 mm or more as described above, the change in slope at the boundary between the straight section 11 and the curved section 12 can be suppressed. Therefore, when this steel wire is applied to a tire, cracking in the rubber can be suppressed, improving tire durability. By making the radius of curvature R1 of the first region 131 less than 0.15 mm, the length of the straight section 11 can be ensured, improving the steering stability of the tire using this steel wire. It should be noted that steering stability refers to the tire's ability to follow the steering wheel's movements when the steering wheel of the vehicle is turned. Higher steering stability means higher tire following the steering wheel's movements.

[0071] By making the radius of curvature R2 of the second region 132 0.13 mm or more, the amount of processing during the manufacture of the steel wire can be suppressed, thereby increasing the strength of the steel wire. By making the radius of curvature R2 of the second region 132 0.2 mm or less, the force applied along the thickness T of the steel wire can be dispersed, thereby improving the durability of the steel wire and the tire containing the steel wire.

[0072] The radius of curvature R1 of the first region 131 and the radius of curvature R2 of the second region 132 in the curved section 12 can each satisfy the aforementioned range. Therefore, the radius of curvature R1 of the first region and the radius of curvature R2 of the second region can be the same or different. However, it is preferable that the radius of curvature R1 and the radius of curvature R2 are different. By making the radius of curvature R1 and the radius of curvature R2 different, that is, in a relationship of R1≠R2, the change in slope at the boundary between the straight section and the curved section can be particularly suppressed. Therefore, when this steel wire is applied to a tire, cracking in the rubber can be particularly suppressed, further improving the tire's durability.

[0073] Furthermore, according to the research of the inventors of the present invention, it is preferable that the radius of curvature R1 of the first region 131 located on the straight section 11 side of the curved section 12 and the radius of curvature R2 of the second region 132 satisfy the relationship R2 > R1. This is because, by making R2 > R1, the steering stability of the tire using the steel wire can be improved.

[0074] And, as Figure 1B As shown, the angle θ between the straight section 11 and the curved section 12 is preferably 165 degrees or more, and preferably 170 degrees or more.

[0075] By not only setting the radii of curvature of the first region 131 and the second region 132 of the curved portion 12 to the aforementioned range, but also setting the angle θ between the straight portion 11 and the curved portion 12 to 165 degrees or more, significant changes in slope at the boundary between the straight portion 11 and the curved portion 12 can be effectively suppressed. Therefore, cracks in the rubber originating from the boundary between the straight portion 11 and the curved portion 12 can be prevented, improving tire durability.

[0076] The upper limit of the angle θ between the straight portion 11 and the curved portion 12 is not particularly limited, but θ is preferably 270 degrees or less, more preferably 200 degrees or less, and even more preferably 180 degrees or less. The steel wire of this embodiment can be processed into a predetermined shape by pressing and rolling the pre-processed steel wire, which has a circular cross-section perpendicular to the longitudinal direction, using rolling rolls in multiple rolling processes. Thus, when the pre-processed steel wire is pressed and rolled in multiple rolling processes, due to the different positions of the pressing in each rolling process, for example, a small protrusion may sometimes form between the straight portion 11 and the curved portion 12. Therefore, as described above, the angle θ is preferably 270 degrees or less, more preferably 200 degrees or less. However, it is preferable not to form this small protrusion, so the angle θ is further preferably 180 degrees or less.

[0077] The angle θ between the straight section 11 and the curved section 12 is calculated as follows.

[0078] like Figure 1B As shown, firstly, at the point of tangency P between the straight section 11 and the curved section 12... 11－12 A tangent 11A of the straight section 11 and a tangent 12A of the curved section 12 are drawn from the straight section 11. Then, the angle formed between the tangent 11A and the tangent 12A can be measured and set as the angle θ between the straight section 11 and the curved section 12.

[0079] The length L of the first straight portion 111 of the steel wire in this embodiment is... 111 The length L of the second straight section 112 112 It is not specifically limited; for example, it can be selected arbitrarily based on the size of the steel wire before it is processed into a flat shape. L 111 L 112 For example, it is preferably set to 0.10 mm or more and 0.36 mm or less, and more preferably 0.12 mm or more and 0.32 mm or less. It should be noted that the length L of the first straight portion 111... 111 The length L of the second straight section 112 112 They can be the same or different.

[0080] Furthermore, the maximum distance between the first curved portion 121 and the second curved portion 122 of the wire 10 in this embodiment, i.e., the specific size of the width W of the wire 10 in this embodiment, is not particularly limited. The width W of the wire 10 in this embodiment is preferably 0.32 mm or more and 0.52 mm or less, more preferably 0.35 mm or more and 0.52 mm or less, and even more preferably 0.42 mm or more and 0.50 mm or less.

[0081] The flatness ratio of the steel wire 10 of the present embodiment is not particularly limited, but is preferably 60% or more. The flatness ratio is the proportion of the thickness T, which is the maximum distance between the first linear portion 111 and the second linear portion 112, with respect to the width W, which is the maximum distance between the first curved portion 121 and the second curved portion 122, and can be calculated according to (flatness ratio (%)) = T / W x 100. The maximum distance between the first linear portion 111 and the second linear portion 112 refers to the distance at the longest portion between the first linear portion 111 and the second linear portion 112.

[0082] According to the research by the inventor of the present application, by making the flatness ratio 60% or more, the durability and impact resistance of the steel wire can be particularly improved. It is considered that this is because, by making the flatness ratio 60% or more, the generation of cracks at the boundary portion between the portion subjected to compression processing and the portion subjected to stretching processing can be suppressed when the shape of the cross section of the steel wire is processed into a flat shape. The flatness ratio is more preferably 62% or more.

[0083] Furthermore, the upper limit of the flatness ratio is not particularly limited, but is preferably 80% or less, and more preferably 75% or less.

[0084] This is because, by making the flatness ratio 80% or less, the thickness of the steel wire can be particularly suppressed, and the thickness of the belt layer can be particularly suppressed when used in a tire, and thus is preferable. Furthermore, by making the flatness ratio 80% or less, the occurrence of spiral-shaped wire wrinkles due to differences in residual stress and surface hardness caused by differences in processing in the thickness direction and the width direction of the steel wire can be particularly suppressed, and the workability is excellent. Thus, the productivity can be improved in the case of use in a tire or the like.

[0085] The thickness T of the steel wire 10 of the present embodiment is not particularly limited, but is preferably 0.200 mm or more, more preferably 0.301 mm or more, and further preferably 0.305 mm or more.

[0086] This is because, by making the thickness T of the steel wire 0.200 mm or more, the durability and impact resistance of the steel wire can be particularly improved.

[0087] The upper limit of the thickness T of the steel wire is not particularly limited, and is preferably 0.50 mm or less, and more preferably 0.42 mm or less, for example. This is because, by making the thickness T of the steel wire 0.50 mm or less, the thickness of the belt layer in which the steel wire is disposed can be suppressed when the steel wire is used in a tire, and further the amount of rubber included in the belt layer can be suppressed. Thus, the belt layer using the steel wire, and the tire including the belt layer, can be made lightweight.

[0088] (2) Regarding the Hardness Distribution of the Steel Wire

[0089] As Figure 1AAs shown, in a cross section perpendicular to the long dimension direction, two points of the center line 14 located at equal distances from the pair of opposing straight portions 11 and the pair of opposing curved portions 12 are set as a first end portion 1411 and a second end portion 1412. Also, two points on the center line 14 that are separated from the first end portion 1411 and the second end portion 1412 by 0.1 mm are set as surface-side measurement points 142.

[0090] Further, a point on the center line 14 located at an equal distance from the first end portion 1411 and the second end portion 1412 is set as a center measurement point 143.

[0091] Note that the center line 14 is a straight line connecting points located at equal distances from the straight portions 11. Therefore, for example, in the case where the first straight portion 111 and the second straight portion 112 are parallel, the distance between the first straight portion 111 and the center line 14 becomes half the thickness T of the steel wire 10, i.e., T / 2. The distance between the second straight portion 112 and the center line 14 is also the same.

[0092] As described above, the curved portion 12 has a first curved portion 121 and a second curved portion 122. Therefore, the surface-side measurement points 142 become two measurement points, a first surface-side measurement point 1421 located on the first curved portion 121 side and a second surface-side measurement point 1422 located on the second curved portion 122 side. Here, as described above, the intersection of the center line 14 and the first curved portion 121 is set as the first end portion 1411, and the intersection of the center line 14 and the second curved portion 122 is set as the second end portion 1412. In this case, the distance L 1421 between the first end portion 1411 and the first surface-side measurement point 1421 becomes 0.1 mm. Also, the distance L 1422 between the second end portion 1412 and the second surface-side measurement point 1422 becomes 0.1 mm.

[0093] As described above, the center measurement point 143 is located at an equal distance from the first end portion 1411 and the second end portion 1412 on the center line 14. In the case where the distance between the first end portion 1411 and the second end portion 1412 is identical to the width W of the steel wire 10, the distance L 143 between the first end portion 1411 and the center measurement point 143 becomes W / 2. The distance between the second end portion 1412 and the center measurement point 143 is also the same.

[0094] Also, the difference between the Vickers hardness HV1 at the two surface-side measurement points 142 and the Vickers hardness HV2 at the center measurement point 143, i.e., HV1 - HV2, is preferably -60 HV0.1 or more and -10 HV0.1 or less, and more preferably -60 HV0.1 or more and -20 HV0.1 or less.

[0095] In the case where HV1 - HV2 is -10HV0.1 or less, the hardness of the center portion of the steel wire including the center measurement point 143 is higher than the hardness of the surface side including the surface side measurement point. Thus, by making the hardness of the center portion of the steel wire higher than the hardness of the surface side, the impact received by the straight portion 11 can be uniformly received by the entire surface including the straight portion 11. In the case of a flattened steel wire, the impact resistance can sometimes decrease, but by using a steel wire having the above-described hardness distribution, the impact resistance can be improved.

[0096] However, in order to make HV1 - HV2 less than -60HV0.1, the hardness of the center portion needs to be particularly increased. Thus, when flattening is performed in order to manufacture the steel wire, excessive pressure needs to be applied, and the material of the steel wire can be embrittled or the like. Thus, as described above, HV1 - HV2 is preferably -60HV0.1 or more.

[0097] Note that the Vickers hardness at each of the above-described measurement points can be measured in accordance with JIS Z 2244 (2009) by setting the test force to 0.1 kgf, that is, 0.9807 N, and setting the holding time of the test force to 5 seconds. The unit of the Vickers hardness, HV0.1, is a unit defined in JIS Z 2244 (2009), and the 0.1 of HV0.1 means a test force of 0.1 kgf.

[0098] (3) Material of Steel Wire

[0099] The material of the steel wire of the present embodiment is not particularly limited. The steel wire of the present embodiment can have, for example, a steel wire 101 and a plated film 102 disposed on the surface of the steel wire.

[0100] As the steel wire 101, a high-carbon steel wire can be preferably used.

[0101] Further, as the plated film 102, for example, a plated film in which the metal component is composed only of Cu (copper) and Zn (zinc), that is, a brass plated film can be used, but the plated film can also contain a metal component other than Cu and Zn. The plated film can also contain, for example, one or more elements selected from Co (cobalt), Ni (nickel), Fe (iron), Sn (tin), and Bi (bismuth) as the metal component.

[0102] That is, the steel wire of the present embodiment can have, on the surface, for example, a brass plated film containing Cu and Zn. Further, the brass plated film can also contain one or more elements selected from Co, Ni, Fe, Sn, and Bi. Note that, as described above, the brass plated film can be disposed on the surface of the steel wire, for example.

[0103] The steel wire of the present embodiment has a brass plating film containing Cu and Zn, whereby, in the case where the steel wire is coated with rubber and vulcanized to produce a tire, a Cu2S-containing adhesive layer can be formed on the rubber side of the interface between the steel wire and the rubber. Note that Zn has the effect of promoting the generation of Cu2S. By forming this adhesive layer, the adhesion between the steel wire and the rubber can be improved, and a tire with particularly excellent durability can be produced.

[0104] Further, the ionization tendency of Co, Ni, Fe, Sn, and Bi is greater than that of Zn. Therefore, by the brass plating film also containing one or more elements selected from Co, Ni, Fe, Sn, and Bi, one or more elements selected from the above group of Co and the like can function in the form of sacrificing corrosion resistance, or the combined potential of Cu and Zn can be made higher, thereby improving the corrosion resistance of the brass plating film. As a result, the adhesion between the steel wire and the rubber can be further improved, and the durability of the tire can be further improved.

[0105] (4) Steel wire manufacturing method

[0106] The steel wire manufacturing method of the present embodiment is not particularly limited, and can be manufactured in such a manner that the shape of the cross section thereof becomes the aforementioned shape.

[0107] The steel wire manufacturing method of the present embodiment may, for example, have the following steps.

[0108] Pre-manufactured steel wire preparation step: preparing a pre-manufactured steel wire whose shape in a cross section perpendicular to the longitudinal direction is circular.

[0109] First axial direction rolling step: supplying the pre-manufactured steel wire to a pair of first rolling rollers and a pair of second rolling rollers facing each other, and pressing in a first axial direction parallel to the diameter in the cross section of the pre-manufactured steel wire perpendicular to the longitudinal direction.

[0110] Second axial direction rolling step: supplying the pre-manufactured steel wire after the first axial direction rolling step to a pair of third rolling rollers facing each other, and pressing in a second axial direction orthogonal to the aforementioned first axial direction in the cross section of the pre-manufactured steel wire perpendicular to the longitudinal direction.

[0111] As the aforementioned first rolling rollers, flat rollers having flat pressing surfaces can be used. Further, as the aforementioned second rolling rollers, concave rollers having grooves in the portions that press the pre-manufactured steel wire 21 in the cross section at the face passing through the center axis of the second rolling rollers can be used.

[0112] The first axial direction rolling step and the second axial direction rolling step may, for example, be implemented by the rolling device 20 shown in FIG. 1. Figure 2

[0113] ​The rolling device 20 has a pair of first rolling rollers 221, 222 with pressure surfaces facing each other and a pair of second rolling rollers 231, 232 with pressure surfaces facing each other.

[0114] The first rolling rollers 221, 222 and the second rolling rollers 231, 232 can press the pre-process wire 21 in a first axial direction parallel to a diameter, for example, a thickness direction in a cross section of the pre-process wire 21. Note that, in the present embodiment, the first axial direction corresponds to the Z-axis direction. Figure 2 In the case of the rolling device 20 shown in the drawing, the first axial direction corresponds to the Z-axis direction. Thus, the pair of first rolling rollers 221, 222 and the pair of second rolling rollers 231, 232 can press the pre-process wire 21 in the Z-axis direction in the cross section of the pre-process wire 21 from the top-to-bottom direction of the pre-process wire 21. Figure 2

[0115] The first rolling rollers 221, 222 are flat rollers, and the pressure surfaces thereof are flat surfaces as surfaces facing the pre-process wire 21. That is, the portions of the first rolling rollers 221, 222 that press the pre-process wire 21 in the cross section passing through the center axes of the first rolling rollers 221, 222 are linear shapes.

[0116] The second rolling rollers 231, 232 are concave rollers, and the portions thereof that press the pre-process wire 21 in the cross section at the surfaces passing through the center axes of the second rolling rollers 231, 232 include grooves 231A, 232A as concave portions, respectively. The grooves 231A, 232A can have shapes corresponding to the first curved portion 121 and the second curved portion 122, particularly, the first region 131.

[0117] In the first axial direction rolling process, first, the pre-process wire 21 is pressed and rolled by the first rolling rollers 221, 222, whereby the first linear portion 111 and the second linear portion 112 of the cross section of the wire 10 shown in the drawing can be formed. Figure 1A In addition, the first rolling rollers 221, 222 are flat rollers, and the pressure surfaces thereof are flat surfaces, and thus the hardness of the central portion of the wire can be increased, and the hardness of the peripheral portion of the central portion can be made uniform.

[0118] However, in the case where the rolling is performed only by the first rolling rollers 221, 222, it is sometimes difficult to form the first region 131 described above. Thus, it is preferable that, after the pre-process wire 21 is pressed and rolled by the first rolling rollers 221, 222, the pre-process wire 21 is pressed and rolled by the second rolling rollers 231, 232 that are concave rollers having prescribed grooves 231A, 232A in the pressure surfaces. By pressing and rolling the pre-process wire 21 by the pair of second rolling rollers 231, 232, the first region 131 described above can be formed.

[0119] ​It should be noted that if the first rolling rolls 221 and 222 are not used for pressure and rolling, but only the second rolling rolls 231 and 232, which are concave rolls, it is difficult to form the first straight portion 111 and the second straight portion 112. In addition, it is sometimes impossible to sufficiently increase the hardness of the center portion of the steel wire 10.

[0120] The rolling apparatus 20 may have a pair of third rolling rolls 241, 242 downstream of the conveying direction of the steel wire 21 before processing from the first rolling rolls 221, 222 and the second rolling rolls 231, 232. The third rolling rolls 241, 242 may apply pressure to the steel wire 21 after the first axial rolling process along a second axial direction orthogonal to the first axial direction in the cross-section of the steel wire 21, for example, the width direction. It should be noted that... Figure 2 In the case of the rolling apparatus 20 shown, the second axial direction corresponds to the X-axis direction, and the third rolling rolls 241 and 242 can move along... Figure 2 The X-axis direction applies pressure to the steel wire 21 before processing after the first axial rolling process from the left and right directions, thus implementing the second axial rolling process described above. The orthogonality mentioned here does not refer to strict orthogonality; it is sufficient to include a certain amount of error while maintaining substantive orthogonality.

[0121] In the second axial rolling process, a pair of third rolling rolls 241 and 242 are used to pressurize and roll the steel wire 21 before processing after the first axial rolling process, thereby forming... Figure 1A The steel wire 10 shown has a first curved portion 121 and a second curved portion 122 in its cross-section. Therefore, it is preferable that the pressure surfaces of each of the pair of third rolling rolls 241 and 242, i.e., the surfaces that contact the steel wire 21 before processing, have shapes corresponding to the first curved portion 121 and the second curved portion 122. The third rolling rolls 241 and 242 may, for example, include grooves 241A and 242A on the surfaces passing through the central axes of the third rolling rolls 241 and 242, respectively, with cross-sectional shapes corresponding to the first curved portion 121 and the second curved portion 122. Furthermore, by performing the above-described first axial rolling process and second axial rolling process, the angle θ between the straight portion 11 and the curved portion 12 can be adjusted to a desired range.

[0122] It should be noted that if the specified cross-sectional shape is formed through the first axial rolling process, the second axial rolling process may not be performed.

[0123] In the first axial rolling process and the second axial rolling process, the pressure and rolling degree can be adjusted in a manner that satisfies the cross-sectional shape of the steel wire in this embodiment, which has already been described.

[0124] Furthermore, for the steel wire 21 before processing, along... Figure 2The steel wire of the present embodiment can be manufactured by the following method. First, a steel wire is manufactured by the method described above. Next, the steel wire is cut to a predetermined length. Then, the arrow A in the drawing, that is, the direction along the Y axis is conveyed, and the first axial rolling process and the second axial rolling process described above are performed on the entire long dimension direction, whereby the steel wire of the present embodiment can be manufactured.

[0125] Note that, in this embodiment, a case in which the first axial rolling process and the second axial rolling process are performed is exemplified, but the manufacturing method of the steel wire of the present embodiment is not limited to this. For example, the steel wire before processing can be made into a steel wire of a desired shape by passing through a die of a shape corresponding to the shape required of the steel wire.

[0126] 〔Tire〕

[0127] Next, based on Figure 3 , Figure 4 the tire of the present embodiment will be described.

[0128] The tire of the present embodiment can include the steel wire described above.

[0129] Figure 3 A cross-sectional view at a surface perpendicular to the circumferential direction of the tire 30 of the present embodiment is shown. In Figure 3 only the portion on the left side of the CL (center line) is shown, but the same structure is continuously present on the right side of the CL with the CL as a symmetric axis.

[0130] As shown in Figure 3 , the tire 30 includes a tread portion 31, a side portion 32, and a bead portion 33.

[0131] The tread portion 31 is a portion that comes into contact with the road surface. The bead portion 33 is provided on the inner diameter side of the tire 30 than the tread portion 31. The bead portion 33 is a portion that comes into contact with the rim of the wheel of the vehicle. The side portion 32 connects the tread portion 31 and the bead portion 33. When the tread portion 31 is impacted from the road surface, the side portion 32 elastically deforms and absorbs the impact.

[0132] The tire 30 includes an inner liner 34, a carcass 35, a belt 36, and a bead wire 37.

[0133] The inner liner 34 is composed of rubber and seals the space between the tire 30 and the wheel.

[0134] The carcass 35 forms the skeleton of the tire 30. The carcass 35 is composed of an organic fiber such as polyester, nylon, rayon, or a steel wire and rubber. Note that the steel wire described above can be used for the carcass 35.

[0135] The bead wire 37 is provided in the bead portion 33. The bead wire 37 receives the tensile force acting on the carcass.

[0136] The belt layer 36 secures the tire carcass 35 to improve the rigidity of the tread 31. Figure 3 In the example shown, tire 30 has two belt layers 36.

[0137] Figure 4 The diagram schematically illustrates the two belt layers 36. Figure 4 A cross-sectional view of the belt layer 36 is shown at a plane perpendicular to the longitudinal direction, i.e., the circumferential direction of the tire 30.

[0138] like Figure 4 As shown, two belt layers 36 are overlapped together radially in the tire 30. Each belt layer 36 has multiple steel wires 10 and rubber 41. The multiple steel wires 10 are arranged in a row. The aforementioned steel wires can be used as the steel wires 10.

[0139] It should be noted that the aforementioned steel wire has a flat cross-section perpendicular to its length direction, and is preferably arranged such that the thickness direction of the steel wire is consistent with the thickness direction of the belt layer. Therefore, for example, it is preferable to arrange the steel wire 10 such that the first straight portion 111 and the second straight portion 112 are along the width direction of the belt layer.

[0140] Furthermore, the rubber 41 is covered with steel wires 10, and the entire circumference of each steel wire 10 is covered by the rubber 41. The steel wires 10 are embedded in the rubber 41.

[0141] The aforementioned steel wire has a flat cross-section perpendicular to its longitudinal direction. Therefore, even if the first rubber thickness t1 (the thickness of the rubber 41 disposed at the lower part of the steel wire 10) and the second rubber thickness t2 (the thickness of the rubber 41 disposed at the upper part of the steel wire 10) in the belt layer 36 are reduced, steel wire 10 exposure can be suppressed. Therefore, the overall thickness of the belt layer 36 can be reduced.

[0142] Thus, the tire according to this embodiment can suppress the overall thickness of the belt layer 36 including the aforementioned steel wire 10, making the belt layer 36 lighter. Therefore, the tire of this embodiment including this belt layer can also be made lighter, and the rolling resistance of the tire can be suppressed.

[0143] Furthermore, the tire of this embodiment uses the aforementioned steel wire, thus exhibiting excellent durability.

[0144] The embodiments have been described in detail above, but are not limited to specific embodiments. Various modifications and alterations can be made within the scope of the claims.

[0145] Example

[0146] The following are specific embodiments for illustration, but the present invention is not limited to these embodiments.

[0147] (Evaluation Method)

[0148] First, the evaluation method for the steel wire produced in the following experimental examples will be explained.

[0149] (1) Evaluation of the cross-sectional shape of the steel wire

[0150] The obtained steel wire is embedded in transparent resin, and the sample is cut out so that the surface (section) of the steel wire perpendicular to the longitudinal direction is exposed.

[0151] Then, the length and distance of each part in the cross section were measured using a projector.

[0152] Specifically, the length L of the first straight section 111 was measured. 111 The length L of the second straight section 112 112 And the thickness T, which is the maximum distance between the first straight section 111 and the second straight section 112.

[0153] In addition, the maximum distance between the first curved section 121 and the second curved section 122, i.e. the width W of the wire 10, was measured.

[0154] Furthermore, the radius of curvature R1 of the first region 131 and the radius of curvature R2 of the second region 132 of the first curve portion 121 and the second curve portion 122 were measured respectively.

[0155] In addition, such as Figure 1B As shown, the angle θ between the straight section 11 and the curved section 12 was measured. During measurement, the point of tangency P between the straight section 11 and the curved section 12 was first measured. 11－12 Tangent 11A of the straight section 11 and tangent 12A of the curved section 12 are drawn out. Then, the angle θ is determined by measuring the angle formed between tangent 11A and tangent 12A.

[0156] Multiple measurements were performed on the same location, and the results confirmed that the angle θ was distributed within ±2.5 degrees of the central value, with a measurement accuracy within 5 degrees. Tables 1 and 2 show the central values ​​of angle θ when the same location was measured 5 times.

[0157] It should be noted that in the following experimental examples, the first curved portion 121 and the second curved portion 122 have the same shape. Furthermore, in the steel wires produced in the following experimental examples, the central value of the angle θ at a total of four points between the straight portion 11 and the curved portion 12 is the same. Additionally, in the steel wires produced in Experimental Examples 1-1 to 1-4, Experimental Examples 2-1, 2-2, and Experimental Examples 3-2 to 3-4, the radius of curvature R1 of the first region 131 at a total of four points in the first curved portion 121 and the second curved portion 122 is the same.

[0158] Then, the flatness is calculated from the thickness T and the width W by the following formula.

[0159] (Flatness (%)) = T / W x 100

[0160] (2) Evaluation of hardness distribution

[0161] In each of the following experimental examples, the Vickers hardness was measured at the aforementioned surface-side measurement point 142 and the center measurement point 143 on the center line 14 located at an equal distance from the pair of opposing straight portions 11 in one cross section of the steel wire perpendicular to the longitudinal direction. The Vickers hardness was measured in accordance with JIS Z 2244 (2009). Note that, at the time of measurement, the test force was set to 0.1 kgf, i.e., 0.9807 N, and the test force retention time was set to 5 seconds. The surface-side measurement point 142 and the center measurement point 143 have already been described, and thus the description thereof is omitted here.

[0162] Then, the difference between HV1, which is the average of the Vickers hardness at the two surface-side measurement points, and HV2, which is the Vickers hardness at the center measurement point, i.e., HV1-HV2, was calculated. In Table 1, the evaluation results are shown in terms of HV1-HV2.

[0163] (3) Durability test

[0164] The steel wire produced in each of the following experimental examples was arranged on a rubber sheet, and a rubber sheet was further overlaid thereon. Thus, a laminate of a rubber sheet and a steel wire having a rectangular parallelepiped shape with a total thickness of five times the thickness of the steel wire was prepared. Then, the laminate of the rubber sheet and the steel wire was vulcanized under conditions of 160°C for 20 minutes.

[0165] Note that, as the rubber sheet, a sheet of rubber in which carbon, other various accelerators, anti-deterioration agents, and the like were compounded in a rubber main component was used.

[0166] After being left to cool naturally, a test piece in the form of a rope having a cross-sectional shape of a thickness of 5 mm and a width of 10 mm, which contained the steel wire, was taken out from the obtained steel wire / rubber composite using a cutting knife.

[0167] As shown in Figure 5 The obtained test piece 50 was hung on a first roller 511, a second roller 512, and a third roller 513 each having a roller diameter of 25 mm. At this time, as shown in Figure 5The positions of the rollers were adjusted in parallel with the test piece 50 between the first roller 511 and the second roller 512 and the test piece 50 between the second roller 512 and the third roller 513 as shown in FIG. 6. In addition, a load of 29.4 N was applied to the test piece 50 hung on the first roller 511 to the third roller 513 in the longitudinal direction thereof. Then, the first roller 511 to the third roller 513 were rotated to move the test piece 50 in the direction of the arrow B in FIG. 6. Subsequently, the first roller 511 to the third roller 513 were counter-rotated to move the test piece 50 in the direction opposite to the arrow B. The above reciprocating movement of the test piece 50 was set as one set, and the movement was repeated. The rotation speed of each roller was set so that 100 sets of the above reciprocating movement could be performed in 1 minute. Then, the number of sets of the above reciprocating movement of the test piece until the test piece was broken was counted. Figure 5

[0168] The more the number of sets of the above reciprocating movement, the higher the durability.

[0169] The evaluation results of the steel wires of Experimental Examples 1-5, Experimental Examples 2-3 or Experimental Examples 3-1 were set to 100, and the evaluation results of the steel wires of each of the experimental examples were expressed by a durability index. Note that in Experimental Examples 1-1 to Experimental Example 1-7, the evaluation results of Experimental Example 1-5 were set to 100 to show the results. In addition, in Experimental Examples 2-1 to Experimental Example 2-3, the evaluation results of Experimental Example 2-3 were set to 100 to show the results. In Experimental Examples 3-1 to Experimental Example 3-5, Experimental Example 4-1, the evaluation results of Experimental Example 3-1 were set to 100 to show the results.

[0170] The greater the durability index, the more excellent the durability of the belt layer can be formed, i.e., the more excellent the durability of the tire can be formed.

[0171] (4) Weight Index

[0172] In the evaluation of the weight index, a rubber sheet was produced using the steel wire produced in each of the experimental examples.

[0173] As the rubber composition, as a rubber component, a natural rubber was used as a base, and as an additive, carbon black, sulfur, zinc oxide, cobalt naphthenate, and cobalt stearate were contained.

[0174] The steel wire and the rubber composition produced in each of the experimental examples were used to produce a rubber sheet having the same structure as the belt layer 36 shown in FIG. 6. Figure 4

[0175] ​​And, the weight of the rubber sheet made using the steel wire of Experimental Example 1-5, Experimental Example 2-3 or Experimental Example 3-1 was set to 100, and the weight of the rubber sheet made using the steel wire of each experimental example was expressed by an index. Note that in Experimental Examples 1-1 to 1-7, the weight of the rubber sheet made in Experimental Example 1-5 was set to 100 to show the results. Further, in Experimental Examples 2-1 to 2-3, the weight of the rubber sheet made in Experimental Example 2-3 was set to 100 to show the results. In Experimental Examples 3-1 to 3-5, Experimental Example 4-1, the weight of the rubber sheet made in Experimental Example 3-1 was set to 100 to show the results.

[0176] The smaller the weight index, the lighter the belt layer that can be formed, i.e., the lighter the tire that can be formed.

[0177] (5) Impact resistance index

[0178] Using Figure 6 a Charpy impact test device as shown in FIG. 6, the Charpy impact value was measured by a Charpy impact test, and the impact absorption index was calculated from the measured Charpy impact value.

[0179] For example, as shown in Figure 6 , the Charpy impact test can be performed by rotating a pendulum 61 of mass m from an initial position PI with the rotational shaft 62 as the center, and striking a test piece 63 that is previously disposed on the moving path of the pendulum 61. The pendulum 61 further travels in the rotational direction after breaking the test piece 63, and reaches the highest height position P2.

[0180] Here, the height of the initial position PI with the position of the test piece 63 as the reference is set to hi, and the height of the highest height position P2 with the position of the test piece 63 as the reference is set to h2. In this case, the difference between the potential energy of the initial position PI and the potential energy of the highest height position P2, i.e., mg(h1-h2), becomes the absorbed energy at the time of breaking the test piece. This absorbed energy is the Charpy impact value, and the larger the value, the more excellent the impact resistance of the steel wire.

[0181] The evaluation results of the steel wire of Experimental Example 1-5, Experimental Example 2-3 or Experimental Example 3-1 were set to 100, and the evaluation results of the steel wire of each experimental example were expressed by an impact resistance index. Note that in Experimental Examples 1-1 to 1-7, the evaluation results of Experimental Example 1-5 were set to 100 to show the results. Further, in Experimental Examples 2-1 to 2-3, the evaluation results of Experimental Example 2-3 were set to 100 to show the results. In Experimental Examples 3-1 to 3-5, Experimental Example 4-1, the evaluation results of Experimental Example 3-1 were set to 100 to show the results.

[0182] A higher impact resistance index means that the steel wire has better impact resistance.

[0183] (Experimental Example)

[0184] The experimental conditions are described below. Examples 1-1 to 1-3, 2-1, 3-1 to 3-3 are considered examples, while examples 1-4 to 1-7, 2-2, 2-3, 3-4, 3-5, and 4-1 are considered comparative examples.

[0185] [Experimental Example 1-1]

[0186] A pre-processing steel wire 21 with a diameter of 0.4 mm and a circular cross-section was prepared (pre-processing steel wire preparation process). It should be noted that the pre-processing steel wire 21 has a brass coating with a metal composition of Cu and Zn on the surface of the high carbon steel wire.

[0187] Then, the steel wire before processing is supplied to Figure 2 The rolling apparatus 20 shown is used to become Figure 1A The process was carried out in accordance with the specified cross-sectional shape shown.

[0188] As described above, the rolling apparatus 20 has a pair of first rolling rolls 221, 222 with their pressure surfaces facing each other, and a pair of second rolling rolls 231, 232 with their pressure surfaces facing each other. The first rolling rolls 221, 222 are flat rolls, and their pressure surfaces, which face the steel wire 21 before processing, are flat. The second rolling rolls 231, 232 are concave rolls, and the portion of the steel wire 21 before processing that applies pressure in the cross-section at the surface through which the central axis of the second rolling rolls 231, 232 passes includes grooves 231A, 232A, which are concave portions. The grooves 231A, 232A have shapes corresponding to the first curved portion 121 and the second curved portion 122 to be formed, particularly the first region 131.

[0189] The pre-processed steel wire 21 is supplied to the rolling mill 20. Then, using a pair of first rolling rolls 221, 222 and a pair of second rolling rolls 231, 232, the wire is rolled along... Figure 2 The steel wire 21 before processing was pressurized in the Z-axis direction (first axial rolling process). That is, pressure was applied from the top and bottom along the thickness direction of the steel wire 21 before processing.

[0190] like Figure 2 As shown, a pair of third rolling rolls 241 and 242 are arranged downstream of the conveying direction of the steel wire 21 before processing by the first rolling rolls 221 and 222 and the second rolling rolls 231 and 232. The steel wire 21 before processing after the first axial rolling process is supplied between the pair of third rolling rolls 241 and 242.

[0191] Then, the first axially rolled wire before the process 21 is pressed in the X-axis direction in the figure, that is, in the left-right direction of the first axially rolled wire before the process 21 along the width direction of the wire before the process 21 after the first axially rolling process by the third rolling rollers 241, 242 (second axially rolling process). Note that the third rolling rollers 241, 242 are used which have grooves 241A, 242A in the respective pressing surfaces having a shape corresponding to the first curved portion 121 and the second curved portion 122 in the cross-sectional shape in the surface passing through the center axis of the third rolling rollers 241, 242. Figure 2

[0192] Then, the first axially rolled wire before the process 21 is pressed in the X-axis direction in the figure, that is, in the left-right direction of the first axially rolled wire before the process 21 along the width direction of the wire before the process 21 after the first axially rolling process by the third rolling rollers 241, 242 (second axially rolling process). Note that the third rolling rollers 241, 242 are used which have grooves 241A, 242A in the respective pressing surfaces having a shape corresponding to the first curved portion 121 and the second curved portion 122 in the cross-sectional shape in the surface passing through the center axis of the third rolling rollers 241, 242. Figure 2

[0193] In the first axially rolling process and the second axially rolling process, the degree of pressing and rolling was adjusted so that the shape of the obtained wire became the desired shape.

[0194] Specifically, the degree of pressing and rolling was adjusted so that the thickness T became 0.308 mm, the width W became 0.49 mm, and the curvature radius R1 of the first region 131, the curvature radius R2 of the second region 132, and the angle θ in the curved portion 12 became 0.05 mm, 0.2 mm, and 177.5 degrees, respectively.

[0195] Further, based on the results of the preliminary test, in the first axially rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the obtained wire was adjusted.

[0196] The obtained wire was subjected to the aforementioned evaluation. The evaluation results are shown in Table 1.

[0197] [Experiment Example 1-2 to Experiment Example 1-4]

[0198] In the first axially rolling process and the second axially rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R1 of the first region 131, the curvature radius R2 of the second region 132, and the angle θ in the curved portion 12 became the values shown in Table 1. Further, in the first axially rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the obtained wire was adjusted.

[0199] Except for the above points, the wire was manufactured in the same manner as in Experiment Example 1-1, and the evaluation thereof was performed. ​​

[0200] The evaluation results are shown in Table 1.

[0201] [Experiment Example 1-5 - Experiment Example 1-7]

[0202] In the first axial rolling process, the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 1. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted.

[0203] The evaluation results are shown in Table 1.

[0204] [Experiment Example 2-1]

[0205] A pre-processed steel wire 21 having a wire diameter of 0.3 mm and a circular cross-sectional shape was used. Further, in the first axial rolling process, the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R1 of the first region 131, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted.

[0206] The steel wire was manufactured in the same manner as in Experiment Example 1-1 except for the above points, and was evaluated.

[0207] The evaluation results are shown in Table 2.

[0208] [Experiment Example 2-2]

[0209] In the first axial rolling process, the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R1 of the first region 131, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted.

[0210] The steel wire was manufactured in the same manner as in Experiment Example 2-1 except for the above points, and was evaluated.

[0211] The evaluation results are shown in Table 2.

[0212] [Experiment Example 2-3]

[0213] In the first axial rolling process and the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted.

[0214] The evaluation results are shown in Table 2.

[0215] [Experiment Example 3-1]

[0216] A pre-processed steel wire 21 having a wire diameter of 0.26 mm and a circular cross-sectional shape was used. Further, in the first axial rolling process and the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted. The curved portion 12 was provided as a curve having a constant curvature radius of the value shown in Table 2 for the curvature radius R2. That is, the curvature radius R1 and the curvature radius R2 were in the relationship of R1 = R2. Except for the above points, the steel wire was manufactured in the same manner as in Experiment Example 1-1, and the evaluation was performed.

[0217] The evaluation results are shown in Table 2.

[0218] [Experiment Examples 3-2 to 3-4]

[0219] In the first axial rolling process and the second axial rolling process, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the curvature radius R1 of the first region 131, the curvature radius R2 of the second region 132 in the curved portion 12, and the angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted.

[0220] The steel wire was manufactured in the same manner as in Experimental Example 3-1 except for the above points, and evaluation thereof was performed.

[0221] The evaluation results are shown in Table 2.

[0222] [Experimental Example 3-5]

[0223] In the first axial rolling step and the second axial rolling step, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the radius of curvature R2 of the second region 132 in the curved portion 12, and the angle θ would become the values shown in Table 2. In the first axial rolling step, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted. As in Experimental Example 3-1, the curved portion 12 was provided as a curve having a constant radius of curvature R2 of the value shown in Table 2. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship R1 = R2. The steel wire was manufactured in the same manner as in Experimental Example 3-1 except for the above points, and evaluation thereof was performed.

[0224] The evaluation results are shown in Table 2.

[0225] [Experimental Example 4-1]

[0226] A pre-processed steel wire 21 having a wire diameter of 0.2 mm and a circular cross-sectional shape was used. In the first axial rolling step and the second axial rolling step, the degree of pressing and rolling was adjusted so that the thickness T, the width W, the radius of curvature R2 of the second region 132 in the curved portion 12, and the angle θ would become the values shown in Table 2. In the first axial rolling step, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted, and the hardness of the center portion of the resulting steel wire was adjusted. The curved portion 12 was provided as a curve having a constant radius of curvature R2 of the value shown in Table 2. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship R1 = R2. The steel wire was manufactured in the same manner as in Experimental Example 1-1 except for the above points, and evaluation thereof was performed.

[0227] The evaluation results are shown in Table 2.

[0228] [Table 1]

[0229]

[0230] [Table 2]

[0231]

[0232] According to Table 1, in the case of the steel wire of Experimental Example 1-1, the cross section perpendicular to the long dimension direction has a flat shape, and the relationship that the radius of curvature Rl of the first region is 0.05 mm or more and less than 0.15 mm, the radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less, and the angle θ is 165 degrees or more is satisfied. In the case of the steel wire of Experimental Example 1-1, it was confirmed that the durability index was 118, the weight index was 100, and the impact resistance index was 100, and it was a steel wire that could form a tire that was lightweight and excellent in durability. The same tendency was confirmed in the case of the steel wire of Experimental Example 1-2. In the case of Experimental Example 1-3, it was confirmed that the durability index was 119, and the weight index was 100, and it was a steel wire that could form a tire that was lightweight and excellent in durability. However, the impact resistance index became a result that was worse than Experimental Example 1-1 and Experimental Example 1-2. It was understood that this was because HV1-HV2 was 8.8 HV0.1, and the hardness of the center portion of the steel wire was lower than the hardness of the surface side.

[0233] In the case of the steel wire of Experimental Example 1-4, the radius of curvature Rl of the first region was 0.025 mm, which was less than 0.05 mm, and thus it was confirmed that the durability index was 96, and the durability was worse than the steel wires of Experimental Example 1-1 and Experimental Example 1-2.

[0234] In addition, in the case of the steel wires of Experimental Examples 1-5 to 1-7 in which the angle θ was less than 165 degrees, it was confirmed that the durability index was 100 to 116, and the durability was worse than the steel wire of Experimental Example 1-1.

[0235] The steel wire of Experimental Example 1-6 was a steel wire in which the value of the flatness ratio was small, that is, a flat steel wire, and thus the weight index was 95, which was relatively low. However, in the case of the steel wire of Experimental Example 1-6, the amount of processing for increasing the flatness ratio at the time of manufacture was large, and thus it was confirmed that the impact resistance index became 90 or less, and greatly deteriorated.

[0236] The steel wire of Experimental Example 1-7 was a steel wire in which the value of the flatness ratio was large, and the cross-sectional shape was close to a circular shape, and thus the durability index was 116, which was relatively high. However, it was confirmed that the weight index greatly deteriorated.

[0237] The same tendency was observed in Experimental Examples 2-1 to 2-3. In the case of the steel wire of Experimental Example 2-1, the cross section perpendicular to the long dimension direction had a flat shape, and the relationship that the radius of curvature Rl of the first region was 0.05 mm or more and less than 0.15 mm, the radius of curvature R2 of the second region was 0.13 mm or more and 0.2 mm or less, and the angle θ was 165 degrees or more was satisfied. In the case of the steel wire of Experimental Example 2-1, it was confirmed that the durability index was 102, the weight index was 100, and the impact resistance index was 100, and it was a steel wire that could form a tire that was lightweight and excellent in durability.

[0238] As for the steel wire of Experimental Example 2-2, the radius of curvature Rl of the first region was 0.025 mm, which was smaller than 0.05 mm, and thus it was confirmed that the durability index was 94, and the durability was inferior to that of the steel wire of Experimental Example 2-1.

[0239] Further, as for the steel wire of Experimental Example 2-3 in which the angle θ was smaller than 165 degrees, it was confirmed that the durability index was 100, and the durability was inferior to that of the steel wire of Experimental Example 2-1.

[0240] The same tendency was observed with respect to Experimental Examples 3-1 to 3-5. As for the steel wires of Experimental Examples 3-1 to 3-3, the cross section perpendicular to the long dimension direction had a flat shape, and the relationship of the radius of curvature Rl of the first region being 0.05 mm or more and smaller than 0.15 mm, the radius of curvature R2 of the second region being 0.13 mm or more and 0.2 mm or less, and the angle θ being 165 degrees or more was satisfied. As for the steel wires of Experimental Examples 3-1 to 3-3, it was confirmed that the durability index was 100 to 103, the weight index was 100, and the impact resistance index was 100.

[0241] On the other hand, as for the steel wire of Experimental Example 3-4, the radius of curvature Rl of the first region was not in the range of 0.05 mm or more and smaller than 0.15 mm. Further, as for Experimental Example 3-5, the angle θ was smaller than 165 degrees.

[0242] Thus, as for the steel wires of Experimental Examples 3-1 to 3-3, it was confirmed that they were steel wires capable of forming a tire having superior durability to that of the tires of Experimental Examples 3-4 and 3-5.

[0243] With respect to Experimental Example 4-1, the radius of curvature R2 of the second region was not in the range of 0.13 mm or more and 0.2 mm or less, and the angle θ was not in the range of 165 degrees or more. Thus, as for the steel wire of Experimental Example 4-1, it was confirmed that both the durability index and the impact resistance index were lower than those of the steel wires of Experimental Examples 3-1 and the like.

[0244] Explanation of Reference Numerals

[0245] 10: Steel wire

[0246] 101: Steel cord

[0247] 102: Coating film

[0248] 11: Straight portion

[0249] 111: First straight portion

[0250] 112: Second straight portion

[0251] L 111 , L 112 : Length

[0252] 12: Curved section

[0253] 121: First Curve Section

[0254] 122: Second Curve Section

[0255] 131: Area 1

[0256] 132: Second Region

[0257] 14: Center line

[0258] 1411: First end

[0259] 1412: Second end

[0260] 142: Surface side measurement point

[0261] 1421: First surface side measurement point

[0262] 1422: Second surface side measurement point

[0263] 143: Central measuring point

[0264] L 1421 L 1422 L 143 :distance

[0265] R1, R2: Radius of curvature

[0266] W: Width

[0267] T: Thickness

[0268] 11A: Tangent

[0269] 12A: Tangent

[0270] P 11－12 : tangent point

[0271] θ: Angle

[0272] 20: Rolling equipment

[0273] 21: Steel wire before processing

[0274] 221, 222: First rolling roll

[0275] 231, 232: Second rolling rolls

[0276] 231A, 232A: Slots

[0277] 241, 242: Third rolling rolls

[0278] 241A, 242A: Slots

[0279] A: Arrow

[0280] 30: Tire

[0281] 31: Tread portion

[0282] 32: Sidewall portion

[0283] 33: Bead portion

[0284] 34: Inner liner

[0285] 35: Carcass

[0286] 36: Belt

[0287] 37: Bead wire

[0288] CL: Center line

[0289] 41: Rubber

[0290] t1: First rubber thickness

[0291] t2: Second rubber thickness

[0292] 50: Test piece

[0293] 511: First roller

[0294] 512: Second roller

[0295] 513: Third roller

[0296] B: Arrow

[0297] 61: Pendulum

[0298] 62: Rotation axis

[0299] 63: Test sample

[0300] P1: Initial position

[0301] P2: Highest position

[0302] h1, h2: Height

Claims

1. A steel wire, wherein a cross section of the steel wire perpendicular to a long dimension direction has a flat shape, an outline of the cross section has a pair of opposing straight line portions and a pair of opposing curved line portions connecting between the straight line portions, the curved line portions have a pair of first regions on the straight line portion side and a second region between the pair of first regions, a radius of curvature Rl of the first regions is 0.05 mm or more and less than 0.15 mm, and a radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less, an angle between the straight line portions and the curved line portions is 165 degrees or more, the radius of curvature R2 of the second region is larger than the radius of curvature Rl of the first regions, in the cross section, in a case where a center line located at a distance equal to that of the pair of opposing straight line portions and two intersection points of the pair of opposing curved line portions are set as a first end portion and a second end portion, and, in a case where two points on the center line which are apart from the first end portion and the second end portion by 0.1 mm are set as surface side measurement points, and a point on the center line which is located at a distance equal to that of the first end portion and the second end portion is set as a center measurement point, a difference between an average value of Vickers hardness at the two surface side measurement points and Vickers hardness at the center measurement point, that is, HVl - HV2 is -60 HV0.1 or more and -10 HV0.1 or less.

2. The steel wire according to claim 1, wherein a brass plating film containing copper and zinc is provided on a surface.

3. The steel wire according to claim 2, wherein the brass plating film further contains one or more elements selected from cobalt, nickel, iron, tin, and bismuth.

4. A tire comprising the steel wire according to any one of claims 1 to 3.

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