Steel wire, tire

Abstract

A steel wire having a flattened-shape cross-section perpendicular to a longitudinal direction thereof. The outer shape of the cross-section has: a pair of straight line sections (11) that oppose each other; and a pair of curved sections (12) that connect the straight line sections (11) together and that oppose each other. Each of the curved sections (12) has: a pair of first regions (131) that are located closer to the straight line sections (11); and a second region (132) that is located between the pair of first regions (131). The radius of curvature R1 of the first region (131) is not less than 0.05 mm but less than 0.15 mm. The radius of curvature R2 of the second region (132) is 0.13-0.2 mm. The respective angles between the straight line sections (11) and the curved sections (12) are at least 165 degrees.

Description

Technical Field

[0001] The present disclosure relates to steel wires and tires.

[0002] This application claims priority based on International Application PCT / JP2020 / 039289 filed under the Patent Cooperation Treaty on October 19, 2020, and incorporates by reference all the descriptions set forth in the above-mentioned international application.

Background Art

[0003] For example, in Patent Document 1, in a pneumatic radial tire provided with a side reinforcing layer formed by arranging a plurality of single-wire steel wires in a region from a bead portion to a sidewall portion and embedding them in rubber, the single-wire steel wire has a flat shape, the flatness ratio of the single-wire steel wire is 40% to 70%, the major axis of the single-wire steel wire 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 wire mass per unit area of the side reinforcing layer is 400 N·kg / m 2 There is disclosed a pneumatic radial tire characterized by the above.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The steel wire of the present disclosure has a flat cross-section perpendicular to the longitudinal direction, the outer shape of the cross-section has a pair of opposing straight portions and a pair of opposing curved portions connecting between the straight portions, the curved portion has a pair of first regions located on the straight portion side and a second region located between the pair of first regions, The radius of curvature R1 of the first region is 0.05 mm or more and less than 0.15 mm, and the radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less. The angle between the straight portion and the curved portion is 165 degrees or more.

Brief Description of the Drawings

[0006]

Figure 1A

Figure 1B

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0007] [Problems to be Solved by the Present Disclosure] Regarding tires, in addition to weight reduction for reducing rolling resistance, for example, it is required to improve durability so as to suppress the frequency of tire replacement and enable use over a longer period. And for the steel wire used in tires, it is also required to be a steel wire that can form a tire excellent in lightweight and durability.

[0008] Therefore, an object is to provide a steel wire that can form a tire excellent in lightweight and durability.

[0009] [Effects of the Present Disclosure]

[0010] According to the present disclosure, it is possible to provide a steel wire capable of forming a tire excellent in lightness and durability.

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0012] (1) The steel wire according to one aspect of the present disclosure has a flat cross-section perpendicular to the longitudinal direction, the outer shape of the cross-section has a pair of opposing straight portions and a pair of opposing curved portions connecting between the straight portions, the curved portion has a pair of first regions located on the straight portion side and a second region located between the pair of first regions, the radius of curvature R1 of the first region is 0.05 mm or more and less than 0.15 mm, and the radius of curvature R2 of the second region is 0.13 mm or more and 0.2 mm or less, the angle between the straight portion and the curved portion is 165 degrees or more.

[0013] The steel wire can be arranged, for example, in the belt layer of a tire. The belt layer has a steel wire and rubber, and the steel wire is embedded in the rubber. Since the thickness of the belt layer can be selected so that the steel wire can be embedded in the rubber, the shape of the cross section perpendicular to the longitudinal direction of the steel wire (hereinafter simply referred to as the "cross section" for the cross section perpendicular to the longitudinal direction of the steel wire) is made into a flat shape, and by suppressing the thickness of the steel wire, the thickness of the belt layer can also be suppressed. Therefore, by using a steel wire having a flat cross-sectional shape, the amount of rubber contained in the belt layer can be suppressed as compared with, for example, the case of using a circular steel wire having the same cross-sectional area. For this reason, by using a steel wire having a flat cross-sectional shape, the belt layer can be lightened, and the tire including the belt layer can also be lightened.

[0014] However, according to the studies of the inventors of the present invention, in a conventional steel wire having a flat cross section, the outer shape of the cross section includes a straight portion and a curved portion, and at the boundary portion between the straight portion and the curved portion, the inclination changes greatly. The inclination means the inclination of the tangent line of the outer shape in the cross section perpendicular to the longitudinal direction of the steel wire (hereinafter also simply referred to as the "inclination"). When a conventional steel wire having a flat shape is applied to a tire, cracks occur in the rubber starting from the boundary portion between such a straight portion and the curved portion, which has been a cause of deterioration of the durability of the tire.

[0015] Therefore, the inventors of the present invention conducted further studies. According to such studies, by forming a first region and a second region in the curved portion and setting the respective radii of curvature within the above range, it is possible to suppress the change in inclination at the boundary portion between the straight portion and the curved portion. For this reason, it has been found that when a steel wire according to an aspect of the present disclosure satisfying such a requirement is applied to a tire, the occurrence of cracks in the rubber can be suppressed, and the durability of the tire can be improved.

[0016] By setting the radius of curvature R1 of the first region to be 0.05 mm or more as described above, it is possible to suppress the change in inclination at the boundary between the straight portion and the curved portion. Therefore, when the steel wire is applied to a tire, it is possible to suppress the occurrence of cracks in the rubber and improve the durability of the tire. By setting the radius of curvature R1 of the first region to be less than 0.15 mm, the length of the straight portion can be ensured, and the steering stability of the tire using the steel wire can be enhanced.

[0017] By setting the radius of curvature R2 of the second region to be 0.13 mm or more, the amount of processing during the manufacture of the steel wire can be suppressed, and the strength of the steel wire can be enhanced. By setting the radius of curvature R2 of the second region to be 0.2 mm or less, the force applied along the thickness T direction of the steel wire can be dispersed, and the durability of the steel wire and the tire including the steel wire can be enhanced.

[0018] The steel wire can be processed into a predetermined shape by, for example, pressing and rolling a pre-processed steel wire having a circular cross-section perpendicular to the longitudinal direction with a rolling roller. Therefore, the above-mentioned processing amount means the processing amount from the pre-processed steel wire to the predetermined shape, that is, the amount of deformation.

[0019] In addition to setting the radii of curvature of the first region and the second region of the curved portion within the ranges described above, by setting the angle between the straight portion and the curved portion to be 165 degrees or more, it is possible to particularly suppress a large change in inclination at the boundary between the straight portion and the curved portion. Therefore, starting from the boundary portion between such a straight portion and the curved portion, it is possible to prevent cracks from occurring in the rubber and enhance the durability of the tire.

[0020] (2) The radius of curvature R1 and the radius of curvature R2 may be different.

[0021] By the fact that the radius of curvature R1 and the radius of curvature R2 are different, that is, in the relationship of R1≠R2, it is possible to particularly suppress the change in inclination at the boundary between the straight portion and the curved portion. Therefore, when the steel wire is applied to a tire, it is possible to particularly suppress the occurrence of cracks in the rubber and further improve the durability of the tire.

[0022] (3) In the cross-section, when two intersection points of a center line equidistant from the pair of opposing straight portions and the pair of opposing curved portions are defined as a first end portion and a second end portion, of the center line, two points each 0.1 mm away from the first end portion and the second end portion are defined as surface side measurement points, when a point equidistant from the first end portion and the second end portion on the center line is defined as a center measurement point, HV1 - HV2, which is the difference between HV1, which is the average value of the Vickers hardness at the two surface side measurement points, and HV2, which is the Vickers hardness at the center measurement point, may be -60 HV0.1 or more and -10 HV0.1 or less.

[0023] When HV1 - HV2 is -10 HV0.1 or less, the hardness of the central portion including the center measurement point is higher than the hardness of the surface side including the surface side measurement points. Thus, by making the hardness of the central portion of the steel cord higher than the surface side, the impact received by the aforementioned straight portion 11 can be uniformly received over the entire surface including the straight portion 11. In the case of a flattened steel wire, the impact resistance may decrease, but by using a steel wire having the above hardness distribution, the impact resistance can be enhanced.

[0024] However, in order to make HV1 - HV2 less than -60 HV0.1, it is necessary to particularly increase the hardness of the central portion. For this reason, excessive pressure needs to be applied when flattening for the production of the steel wire, and there is a risk that the material of the steel wire may become brittle. For this reason, as described above, it is preferable that HV1 - HV2 is -60 HV0.1 or more.

[0025] (4) The surface may have a brass plating film containing copper and zinc.

[0026] In the following, copper may also be represented by the chemical symbol Cu and zinc by Zn.

[0027] In one aspect of the present disclosure, a steel wire has a brass plating film containing Cu and Zn on its surface. When the steel wire is coated with rubber and vulcanized to form a tire, an adhesive layer containing Cu₂S can be formed on the rubber side rather than at the interface between the steel wire and the rubber. Note that Zn has the function of promoting the formation of Cu₂S. By forming the adhesive layer, the adhesive force between the steel wire and the rubber can be increased, and a tire with particularly excellent durability can be obtained.

[0028] (5) The brass plating film may further contain one or more elements selected from cobalt, nickel, iron, tin, and bismuth.

[0029] Note that hereinafter, cobalt may also be represented by the chemical symbol Co, nickel by Ni, iron by Fe, tin by Sn, and bismuth by Bi.

[0030] Co, Ni, Fe, Sn, and Bi have a greater ionization tendency than Zn. Therefore, when the brass plating film further contains one or more elements selected from Co, Ni, Fe, Sn, and Bi, one or more elements selected from the group of elements such as Co function as sacrificial corrosion protection, or the composite potential of Cu and Zn is made noble, enhancing the corrosion resistance of the brass plating film. As a result, the adhesive force between the steel wire and the rubber can be further increased, and the durability of the tire can be further enhanced.

[0031] (6) A tire containing the steel wire according to any one of (1) to (5) can also be provided.

[0032] According to a tire of one aspect of the present disclosure, the thickness of the belt layer containing the aforementioned steel wire can be suppressed, and the belt layer can be lightened. Therefore, the tire of one aspect of the present disclosure including such a belt layer can also be lightened, and the rolling resistance of the tire can be suppressed.

[0033] In addition, since the tire of one aspect of the present disclosure uses the aforementioned steel wire, it has excellent durability.

[0034] [Details of Embodiments of the Present Disclosure] Specific examples of a steel wire and a tire according to an embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. Note that the present invention is not limited to these examples, and is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0035] 〔Steel Wire〕 Hereinafter, the steel wire according to this embodiment will be described with reference to FIGS. 1A and 1B.

[0036] (1) Regarding the cross-sectional shape FIG. 1A is a cross-sectional view of the steel wire 10 of this embodiment in a plane perpendicular to the longitudinal direction. FIG. 1B is a view showing an enlarged area around the contact point between the straight portion 11 and the curved portion 12 in the cross-sectional view of the steel wire 10 of this embodiment in a plane perpendicular to the longitudinal direction.

[0037] The steel wire 10 of this embodiment is a single wire, that is, a single-strand wire, and can also be referred to as a single-strand steel wire. Further, it is preferable that the steel wire 10 of this embodiment is not subjected to twisting processing along the longitudinal direction, and it is preferable that it is a straight steel wire.

[0038] 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 here means, for example, a shape where the thickness is shorter than the width and it is flat.

[0039] The steel wire can be arranged, for example, in the belt layer of a tire. As will be 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. Since the thickness of the belt layer can be selected so that the steel wire can be embedded in the rubber, by making the cross-sectional shape of the steel wire a flat shape and suppressing the thickness of the steel wire, the thickness of the belt layer can also be suppressed. Therefore, by using a steel wire having a flat cross-sectional shape, the amount of rubber contained in the belt layer can be suppressed as compared with the case of using a circular steel wire having the same cross-sectional area, for example. For this reason, by using a steel wire having a flat cross-sectional shape, the belt layer can be lightened, and the tire including the belt layer can also be lightened.

[0040] However, according to the study by the inventors of the present invention, when a steel wire having a flat cross-sectional shape is embedded in rubber, cracks occur in the rubber around the boundary between the straight portion and the curved portion of the steel wire, and the adhesion between the steel wire and the rubber may decrease.

[0041] Therefore, the inventors of the present invention further studied a steel wire that can achieve both weight reduction and durability of a tire when used in a tire. As a result, it has been found that by making the cross-sectional shape of the steel wire a predetermined flat shape, the weight and durability of a tire using the steel wire can be improved.

[0042] As shown in FIG. 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 connecting between the straight portions 11.

[0043] The straight portion 11 can have a first straight portion 111 and a second straight portion 112.

[0044] The curved portion 12 can have a first curved portion 121 and a second curved portion 122.

[0045] The curved portion 12 can be arranged to connect between a pair of straight portions 11.

[0046] The first straight portion 111 and the second straight portion 112 are preferably parallel as shown in FIG. 1A. Here, the term "parallel" does not mean parallel in the strict sense, but means that the two straight portions are arranged in parallel.

[0047] The first curved portion 121 and the second curved portion 122 are arranged to face each other. The first curved portion 121 and the second curved portion 122 can each be arranged to connect between the end of the first straight portion 111 and the end of the second straight portion 112. For example, as shown in FIG. 1A, the first curved portion 121 and the second curved portion 122 can each have a curved shape convex to the outside of the steel wire 10.

[0048] The curved portion 12 can have a pair of first regions 131 located on the straight portion 11 side, that is, on both end portions sides of the curved portion 12, and a second region 132 located between the pair of first regions 131.

[0049] And, 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.

[0050] Also, 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.

[0051] According to the study by the inventors of the present invention, in a conventional steel wire having a flat cross-section, the outer shape of the cross-section includes a straight portion and a curved portion, and at the boundary portion between the straight portion and the curved portion, the inclination changes greatly. And when a conventional steel wire having a flat shape is applied to a tire, cracks occur in the rubber starting from the boundary portion between such a straight portion and the curved portion, which has been the cause of the deterioration of the durability of the tire.

[0052] Therefore, the inventors of the present invention conducted further studies. According to such studies, by forming a first region 131 and a second region 132 in the curved portion 12 and setting the respective radii of curvature within the above range, it is possible to suppress a change in inclination at the boundary portion between the straight portion 11 and the curved portion 12. For this reason, when the steel wire of the present embodiment satisfying such regulations is applied to a tire, it has been found that cracking in the rubber can be suppressed and the durability of the tire can be improved.

[0053] The first region 131 can be arranged to be located on the straight portion 11 side within the curved portion 12 as described above. For this reason, as shown in FIG. 1A, for example, the first curved portion 121 can have the first region 131 on the first straight portion 111 side and the second straight portion 112 side, respectively. As shown in FIG. 1A, the first region 131 can be provided so as to be directly connected to the first straight portion 111 and the second straight portion 112 which are the straight portion 11, but is not limited to such a form. For example, a transition region that changes from the straight line of the straight portion 11 to the radius of curvature of the first region 131 can be provided between the straight portion 11 and the first region 131.

[0054] The second region 132 can be arranged between the pair of first regions 131. The second region 132 can be arranged, for example, at the central portion in the longitudinal direction of the curved portion 12. Since the curved portion 12 is arranged along the thickness T direction of the steel wire 10, the central portion in the longitudinal direction of the curved portion 12 can also be referred to as the central portion in the thickness T direction. The first region 131 and the second region 132 can be continuously provided on the curved portion 12 as shown in FIG. 1A, but are not limited to such a form. For example, a transition region that changes from the radius of curvature of the first region 131 to the radius of curvature of the second region 132 can be provided between the first region 131 and the second region 132.

[0055] In FIG. 1A, only the first region 131 and the second region 132 are shown on the first curved portion 121 side, but the second curved portion 122 can similarly have the first region and the second region.

[0056] By setting the radius of curvature R1 of the first region 131 to 0.05 mm or more as described above, it is possible to suppress the change in inclination at the boundary between the straight portion 11 and the curved portion 12. Therefore, when the steel wire is applied to a tire, it is possible to suppress the occurrence of cracks in the rubber and improve the durability of the tire. By setting the radius of curvature R1 of the first region 131 to less than 0.15 mm, the length of the straight portion 11 can be ensured, and the steering stability of the tire using the steel wire can be enhanced. Note that the steering stability means the follow-up performance of the tire with respect to the operation of the steering wheel when the steering wheel of the vehicle is operated. The higher the steering stability, the higher the follow-up performance of the tire with respect to the operation of the steering wheel.

[0057] By setting the radius of curvature R2 of the second region 132 to 0.13 mm or more, the processing amount during the manufacture of the steel wire can be suppressed, and the strength of the steel wire can be enhanced. By setting the radius of curvature R2 of the second region 132 to 0.2 mm or less, the force applied along the thickness T direction of the steel wire can be dispersed, and the durability of the steel wire and the tire including the steel wire can be enhanced.

[0058] Among the curved portion 12, as long as the radius of curvature R1 of the first region 131 and the radius of curvature R2 of the second region 132 satisfy the above ranges respectively. Therefore, the radius of curvature R1 of the first region and the radius of curvature R2 of the second region may be the same or different. However, it is preferable that the radius of curvature R1 and the radius of curvature R2 are different. By the fact that the radius of curvature R1 and the radius of curvature R2 are different, that is, in the relation of R1≠R2, the change in inclination at the boundary between the straight portion and the curved portion can be particularly suppressed. Therefore, when the steel wire is applied to a tire, the occurrence of cracks in the rubber can be particularly suppressed, and the durability of the tire can be further improved.

[0059] Furthermore, according to the study by the inventors of the present invention, among the curved portions 12, it is preferable that the relationship between the radius of curvature R1 of the first region 131 located on the straight line portion 11 side and the radius of curvature R2 of the second region 132 satisfies the relationship of R2 > R1. This is because by setting R2 > R1, the steering stability of the tire using the steel wire can be enhanced.

[0060] And, as shown in FIG. 1B, the angle θ between the straight line portion 11 and the curved portion 12 is preferably 165 degrees or more, and more preferably 170 degrees or more.

[0061] In addition to setting the radii of curvature of the first region 131 and the second region 132 of the curved portion 12 within the above-described ranges, by setting the angle θ between the straight line portion 11 and the curved portion 12 to 165 degrees or more, it is possible to particularly suppress a large change in inclination at the boundary portion between the straight line portion 11 and the curved portion 12. For this reason, starting from the boundary portion between the straight line portion 11 and the curved portion 12, it is possible to prevent cracks from occurring in the rubber and enhance the durability of the tire.

[0062] The upper limit of the angle θ between the straight line portion 11 and the curved portion 12 is not particularly limited, and the 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 the present embodiment can be processed into a predetermined shape by pressurizing and rolling a pre-processed steel wire having a circular cross-section perpendicular to the longitudinal direction with a rolling roller in a plurality of rolling processes. In this way, when the pre-processed steel wire is pressurized and rolled in a plurality of rolling processes, due to the difference in the pressurized locations in each rolling process, for example, minute convex portions may be formed between the straight line portion 11 and the curved portion 12. For this reason, as described above, the angle θ is preferably 270 degrees or less, more preferably 200 degrees or less. However, since it is preferable that such minute convex portions are not formed, the angle θ is even more preferably 180 degrees or less.

[0063] The angle θ between the straight line portion 11 and the curved portion 12 is obtained as follows.

[0064] As shown in FIG. 1B, first, at the contact point P between the straight portion 11 and the curved portion 12 11-12 draw a tangent line 11A of the straight portion 11 and a tangent line 12A of the curved portion 12. Then, measure the angle formed between the tangent line 11A and the tangent line 12A, and this can be defined as the angle θ between the straight portion 11 and the curved portion 12.

[0065] The length L of the first straight portion 111 of the steel wire in this embodiment 111 and the length L of the second straight portion 112 112 are not particularly limited and can be arbitrarily selected according to, for example, the size of the steel wire before being processed into a flat shape. L 111 and L 112 are preferably, for example, 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. Note that the length L of the first straight portion 111 111 and the length L of the second straight portion 112 112 may be the same or different.

[0066] Also, the maximum distance between the first curved portion 121 and the second curved portion 122 of the steel wire 10 in this embodiment, that is, the specific size of the width W of the steel wire 10 in this embodiment, is not particularly limited. The width W of the steel wire 10 in this embodiment is preferably, for example, 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.

[0067] The flatness ratio of the steel wire 10 in this embodiment is not particularly limited, but the flatness ratio is preferably 60% or more. The flatness ratio is the ratio of the thickness T, which is the maximum distance between the first straight portion 111 and the second straight portion 112, 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 by (flatness ratio (%)) = T / W × 100. The maximum distance between the first straight portion 111 and the second straight portion 112 means the distance between the first straight portion 111 and the second straight portion 112 at the longest part.

[0068] According to the study by the inventors of the present invention, by setting the flatness ratio to 60% or more, the durability and impact resistance of the steel wire can be particularly enhanced. It is considered that by setting the flatness ratio to 60% or more, when processing the cross-sectional shape of the steel wire into a flat shape, the occurrence of cracks at the boundary between the portion subjected to compression processing and the portion subjected to tensile processing can be suppressed. More preferably, the flatness ratio is 62% or more.

[0069] Moreover, although the upper limit of the flatness ratio is not particularly limited, it is preferably 80% or less, and more preferably 75% or less.

[0070] This is because by setting the flatness ratio to 80% or less, the thickness of the steel wire can be particularly suppressed, and when used in a tire, the thickness of the belt layer can be particularly suppressed, which is preferable. Further, by setting the flatness ratio to 80% or less, it is possible to particularly suppress the occurrence of a line twist in a spiral shape due to the residual stress caused by the processing difference between the thickness direction and the width direction of the steel wire and the difference in surface hardness, and the handleability is excellent. Therefore, the productivity can be increased when used in a tire or the like.

[0071] 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 even more preferably 0.305 mm or more.

[0072] This is because by setting the thickness T of the steel wire to 0.200 mm or more, the durability and impact resistance of the steel wire can be particularly enhanced.

[0073] The upper limit of the thickness T of the steel wire is not particularly limited, but for example, it is preferably 0.50 mm or less, and more preferably 0.42 mm or less. By setting the thickness T of the steel wire to 0.50 mm or less, when the steel wire is used in a tire, the thickness of the belt layer in which the steel wire is arranged and further the amount of rubber contained in the belt layer can be suppressed. For this reason, the belt layer using the steel wire and the tire including the belt layer can be lightened.

[0074] (2) Regarding the hardness distribution of the steel wire As shown in FIG. 1A, in a cross section perpendicular to the longitudinal direction, two intersection points of the center line 14 equidistant from a pair of opposing straight portions 11 and a pair of opposing curved portions 12 are defined as the first end portion 1411 and the second end portion 1412. Then, among the points on the center line 14, two points each 0.1 mm away from the first end portion 1411 and the second end portion 1412 are defined as the surface side measurement points 142.

[0075] Also, among the points on the center line 14, a point equidistant from the first end portion 1411 and the second end portion 1412 is defined as the center measurement point 143.

[0076] Note that the center line 14 is a straight line connecting points equidistant from the straight portion 11. For this reason, for example, when 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 is half of the thickness T of the steel wire 10, that is, T / 2. The same applies to the distance between the second straight portion 112 and the center line 14.

[0077] The curved portion 12 has the first curved portion 121 and the second curved portion 122 as described above. For this reason, the surface side measurement points 142 are two measurement points, namely, the first surface side measurement point 1421 located on the first curved portion 121 side and the second surface side measurement point 1422 located on the second curved portion 122 side. Here, the intersection point of the center line 14 and the first curved portion 121 is defined as the first end portion 1411 as described above, and the intersection point of the center line 14 and the second curved portion 122 is defined as the second end portion 1412. In this case, the distance L between the first end portion 1411 and the first surface side measurement point 1421 1421and the distance L between the second end portion 1412 and the second surface-side measurement point 1422 1422 are all 0.1 mm.

[0078] The center measurement point 143 is equidistant from the first end portion 1411 and the second end portion 1412 on the center line 14 as described above. When the distance between the first end portion 1411 and the second end portion 1412 matches the width W of the steel wire 10, the distance L 143 between the first end portion 1411 and the center measurement point 143 is W / 2. The same applies to the distance between the second end portion 1412 and the center measurement point 143.

[0079] And the difference HV1 - HV2 between HV1, which is the average value of the Vickers hardness at the two surface-side measurement points 142, and HV2, which is the Vickers hardness at the center measurement point 143, 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.

[0080] When the above HV1 - HV2 is -10 HV0.1 or less, the hardness of the central portion including the center measurement point 143 of the steel wire is higher than the hardness of the surface side including the surface-side measurement points. In this way, by making the hardness of the central portion of the steel cord higher than the surface side, the impact received by the above-described straight portion 11 can be evenly received by the entire surface including the straight portion 11. In the case of a flattened steel wire, the impact resistance may decrease, but by using a steel wire having the above hardness distribution, the impact resistance can be enhanced.

[0081] However, in order to make HV1 - HV2 less than -60 HV0.1, it is necessary to particularly increase the hardness of the central portion. For this reason, excessive pressure needs to be applied when flattening for the production of the steel wire, and there is a risk that the material of the steel wire may become brittle. For this reason, as described above, HV1 - HV2 is preferably -60 HV0.1 or more.

[0082] Note that the Vickers hardness at each of the above measurement points can be measured in accordance with JIS Z 2244 (2009) with a test force of 0.1 kgf, that is, 0.9807 N, and a test force holding time of 5 seconds. The unit HV0.1 of Vickers hardness is the unit defined in JIS Z 2244 (2009), and 0.1 in HV0.1 means a test force of 0.1 kgf. (3) Regarding the material of the steel wire The material of the steel wire of this embodiment is not particularly limited. The steel wire of this embodiment can have, for example, a steel wire 101 and a plating film 102 disposed on the surface of the steel wire.

[0083] High-carbon steel wire can be preferably used as the steel wire 101.

[0084] Also, as the plating film 102, for example, a plating film composed only of metal components Cu (copper) and Zn (zinc), that is, a brass plating film can be used, but it can also further contain metal components other than Cu and Zn. The plating film can further contain, for example, one or more elements selected from Co (cobalt), Ni (nickel), Fe (iron), Sn (tin), and Bi (bismuth) as metal components.

[0085] That is, the steel wire of this embodiment can have a brass plating film containing, for example, Cu and Zn on the surface. Also, such a brass plating film can further contain one or more elements selected from Co, Ni, Fe, Sn, and Bi. Note that the brass plating film can be disposed on the surface of the steel wire as described above.

[0086] Since the steel wire of this embodiment has a brass plating film containing Cu and Zn, when the steel wire is coated with rubber and vulcanized to form a tire, an adhesive layer containing Cu2S can be formed on the rubber side rather than at the interface between the steel wire and the rubber. Note that Zn has the function of promoting the formation of Cu2S. By forming such an adhesive layer, the adhesive force between the steel wire and the rubber can be increased, and a tire with particularly excellent durability can be obtained.

[0087] In addition, Co, Ni, Fe, Sn, and Bi have a greater ionization tendency than 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 elements such as Co function as sacrificial corrosion protection, or the composite potential of Cu and Zn is made noble, enhancing the corrosion resistance of the brass plating film. As a result, the adhesive force between the steel wire and the rubber can be further increased, and the durability of the tire can be further enhanced. (4) Regarding the manufacturing method of the steel wire The manufacturing method of the steel wire of the present embodiment is not particularly limited, and it can be manufactured so that the cross-sectional shape thereof becomes the shape described above.

[0088] The manufacturing method of the steel wire of the present embodiment can include, for example, the following steps.

[0089] A pre-processing steel wire preparation step of preparing a pre-processing steel wire having a circular cross-sectional shape perpendicular to the longitudinal direction. A first axial direction rolling step of supplying the pre-processing steel wire to a pair of first rolling rollers and a second rolling roller whose pressing surfaces face each other, and pressing along a first axial direction parallel to the diameter in the cross-section perpendicular to the longitudinal direction of the pre-processing steel wire. A second axial direction rolling step of supplying the pre-processing steel wire after the first axial direction rolling step between a pair of third rolling rollers whose pressing surfaces face each other, and pressing along a second axial direction orthogonal to the first axial direction in the cross-section perpendicular to the longitudinal direction of the pre-processing steel wire. As the first rolling roller, a flat roll with a flat pressing surface can be used. Also, as the second rolling roller, a concave roll provided with a groove in the portion that presses the pre-processing steel wire 21 in the cross-section on the plane passing through the central axis of the second rolling roller can be used.

[0090] The first axial direction rolling step and the second axial direction rolling step can be implemented by, for example, the rolling device 20 shown in FIG. 2.

[0091] The rolling device 20 has a pair of first rolling rollers 221 and 222 with opposing pressure surfaces, and a pair of second rolling rollers 231 and 232 with opposing pressure surfaces.

[0092] The first rolling rollers 221 and 222, and the second rolling rollers 231 and 232 can press the pre-process steel wire 21 along a first axial direction parallel to the diameter in the cross-section of the pre-process steel wire 21, for example, the thickness direction. In the case of the rolling device 20 shown in FIG. 2, the first axial direction corresponds to the Z-axis direction. Therefore, the pair of first rolling rollers 221 and 222, and the second rolling rollers 231 and 232 can press the pre-process steel wire 21 from above and below in the Z-axis direction in FIG. 2, and perform the above-described first axial direction rolling process.

[0093] The above-described first rolling rollers 221 and 222 are flat rolls, and the pressure surfaces, which are the surfaces facing the pre-process steel wire 21, are flat surfaces. That is, the first rolling rollers 221 and 222 have a linear shape in the portion that presses the pre-process steel wire 21 in a cross-section passing through the central axes of the first rolling rollers 221 and 222, for example.

[0094] The second rolling rollers 231 and 232 are concave rolls, and in the cross-section in the plane passing through the central axes of the second rolling rollers 231 and 232, the portions that press the pre-process steel wire 21 can each include grooves 231A and 232A that are recesses. The grooves 231A and 232A can have a shape corresponding to the first curved portion 121 and the second curved portion 122, particularly the first region 131.

[0095] In the first rolling process, first, the first rolling rollers 221 and 222 press and roll the pre-process steel wire 21, thereby forming the first straight portion 111 and the second straight portion 112 of the cross-section of the steel wire 10 shown in FIG. 1A. Further, since the first rolling rollers 221 and 222 are flat rolls and the pressure surfaces are flat surfaces, the hardness of the central portion of the steel wire can be increased, and the hardness around the central portion can be made uniform.

[0096] However, when rolling is performed only by the first rolling rollers 221 and 222, it may be difficult to form the first region 131 described above. Therefore, after pressurization and rolling by the first rolling rollers 221 and 222, it is preferable to pressurize and roll the pre-process steel wire 21 with the second rolling rollers 231 and 232, which are concave rollers provided with predetermined grooves 231A and 232A on the pressurized surfaces. By performing pressurization and rolling with the pair of second rolling rollers 231 and 232, the first region 131 described above can be formed.

[0097] Note that if pressurization and rolling are performed only by the second rolling rollers 231 and 232, which are concave rollers, without performing pressurization and rolling by the first rolling rollers 221 and 222, it becomes difficult to form the first straight portion 111 and the second straight portion 112. Also, there may be a case where the hardness of the central portion of the steel wire 10 cannot be sufficiently increased.

[0098] The rolling device 20 can have a pair of third rolling rollers 241 and 242 on the downstream side in the conveyance direction of the pre-process steel wire 21 of the first rolling rollers 221 and 222 and the second rolling rollers 231 and 232. The third rolling rollers 241 and 242 can pressurize the pre-process steel wire 21 after the first axial direction rolling process along the second axial direction, which is orthogonal to the first axial direction in the cross-section of the pre-process steel wire 21, for example, the width direction. In the case of the rolling device 20 shown in FIG. 2, the second axial direction corresponds to the X-axis direction, and the third rolling rollers 241 and 242 pressurize the pre-process steel wire 21 after the first rolling process from the left and right directions along the X-axis direction in FIG. 2, and the second axial direction rolling process described above can be implemented. The orthogonal here does not mean orthogonal in a strict sense, and it suffices if it is substantially orthogonal including a certain amount of error.

[0099] In the second-axis direction rolling process, by pressing and rolling the pre-process steel wire 21 after the first-axis direction rolling process with a pair of third rolling rollers 241 and 242, the first curve portion 121 and the second curve portion 122 of the cross-section of the steel wire 10 shown in FIG. 1A can be formed. For this reason, it is preferable that each of the pair of third rolling rollers 241 and 242 has a shape corresponding to the first curve portion 121 and the second curve portion 122 on the respective pressing surfaces, that is, the surfaces in contact with the pre-process steel wire 21. The third rolling rollers 241 and 242 can each include grooves 241A and 242A having a shape corresponding to the first curve portion 121 and the second curve portion 122, for example, in a cross-sectional shape in a plane passing through the central axes of the third rolling rollers 241 and 242. Further, by performing the above-described first-axis direction rolling process and second-axis direction rolling process, the angle θ between the straight portion 11 and the curve portion 12 can be adjusted to a desired range.

[0100] Note that when a predetermined cross-sectional shape is obtained by the first-axis direction rolling process, the second-axis direction rolling process may not be performed.

[0101] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling, etc. can be adjusted so as to satisfy the cross-sectional shape of the steel wire of the present embodiment already described.

[0102] Then, the pre-process steel wire 21 is conveyed along the arrow A in FIG. 2, that is, along the Y-axis direction, and the steel wire of the present embodiment can be manufactured by performing the above-described first-axis direction rolling process and second-axis direction rolling process on the entire longitudinal direction thereof.

[0103] Here, the configuration example of the manufacturing method of the steel wire of the present embodiment has been described by taking the case where the first-axis direction rolling process and the second-axis direction rolling process are performed as an example, but the present invention is not limited to such a form. For example, the pre-process wire can be passed through a die having a shape corresponding to the shape required for the steel wire to obtain a steel wire having a desired shape.

[0104] 〔Tire〕 Next, the tire in the present embodiment will be described with reference to FIGS. 3 and 4.

[0105] The tire of the present embodiment can include the above-described steel wire.

[0106] FIG. 3 shows a cross-sectional view of the tire 30 according to the present embodiment in a plane perpendicular to the circumferential direction. In FIG. 3, only the left side portion of the tire 30 is shown with respect to the CL (center line). However, the tire 30 has a similar structure continuously on the right side of the CL with the CL as the axis of symmetry.

[0107] As shown in FIG. 3, the tire 30 includes a tread portion 31, a sidewall portion 32, and a bead portion 33.

[0108] The tread portion 31 is a portion that contacts the road surface. The bead portion 33 is provided on the inner diameter side of the tire 30 with respect to the tread portion 31. The bead portion 33 is a portion that contacts the rim of the wheel of the vehicle. The sidewall portion 32 connects the tread portion 31 and the bead portion 33. When the tread portion 31 receives an impact from the road surface, the sidewall portion 32 elastically deforms to absorb the impact.

[0109] The tire 30 includes an inner liner 34, a carcass 35, a belt layer 36, and a bead wire 37.

[0110] The inner liner 34 is made of rubber and seals the space between the tire 30 and the wheel.

[0111] The carcass 35 forms the skeleton of the tire 30. The carcass 35 is composed of organic fibers such as polyester, nylon, rayon, or steel wire, and rubber. The above-described steel wire can also be used for the carcass 35.

[0112] The bead wire 37 is provided in the bead portion 33. The bead wire 37 receives the tensile force acting on the carcass.

[0113] The belt layer 36 tightens the carcass 35 to increase the rigidity of the tread portion 31. In the example shown in FIG. 3, the tire 30 has two belt layers 36.

[0114] FIG. 4 is a diagram schematically showing two belt layers 36. FIG. 4 shows a cross-sectional view in a plane perpendicular to the longitudinal direction of the belt layer 36, that is, the circumferential direction of the tire 30.

[0115] As shown in FIG. 4, the two belt layers 36 are superposed in the radial direction of the tire 30. Each belt layer 36 has a plurality of steel wires 10 and rubber 41. The plurality of steel wires 10 are arranged in parallel in a row. As the steel wire 10, the above-described steel wire can be used.

[0116] Incidentally, the above-described steel wire has a flat cross-section perpendicular to the longitudinal direction, and it is preferable to arrange the steel wire 10 so that the thickness direction of the steel wire coincides with the thickness direction of the belt layer. For this reason, for example, it is preferable to arrange the steel wire 10 so that the first straight portion 111 and the second straight portion 112 of the above-described steel wire 10 are along the width direction of the belt layer.

[0117] And the rubber 41 covers the steel wire 10, and the entire circumference of each individual steel wire 10 is covered with rubber 41. The steel wire 10 is embedded in the rubber 41.

[0118] The above-described steel wire has a flat cross-section perpendicular to the longitudinal direction. For this reason, even if the first rubber thickness t1, which is the thickness of the rubber 41 disposed below the steel wire 10 in the belt layer 36, and the second rubber thickness t2, which is the thickness of the rubber 41 disposed above the steel wire 10, are made thinner, it is possible to suppress the steel wire 10 from being exposed. Therefore, the thickness of the entire belt layer 36 can be made thinner. Thus, according to the tire of the present embodiment, the thickness of the entire belt layer 36 including the aforementioned steel wire 10 can be suppressed, and the belt layer 36 can be lightened. Therefore, the tire of the present embodiment including such a belt layer can also be lightened, and the rolling resistance of the tire can be suppressed.

[0119] Moreover, since the tire of the present embodiment uses the aforementioned steel wire, it has excellent durability.

[0120] Although the embodiments have been described in detail above, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope described in the claims.

Example

[0121] Specific examples will be given below for explanation, but the present invention is not limited to these examples. (Evaluation Method) First, the evaluation method of the steel wire produced in the following experimental examples will be described. (1) Evaluation of the cross-sectional shape of the steel wire The obtained steel wire was embedded in a transparent resin, and a sample was cut out so that a plane (cross-section) perpendicular to the longitudinal direction of the steel wire was exposed.

[0122] Then, the lengths and distances of each part in such a cross-section were measured using a projector.

[0123] Specifically, the length L of the first straight portion 111 111 , the length L of the second straight portion 112 112 , and the thickness T, which is the maximum distance between the first straight portion 111 and the second straight portion 112, were measured.

[0124] Also, the maximum distance between the first curved portion 121 and the second curved portion 122, that is, the width W of the steel wire 10, was measured.

[0125] Furthermore, the radius of curvature R1 of the first region 131 of the first curved portion 121 and the second curved portion 122, and the radius of curvature R2 of the second region 132 were measured respectively.

[0126] Also, as shown in FIG. 1B, the angle θ between the straight portion 11 and the curved portion 12 was measured. In the measurement, first, at the contact point P between the straight portion 11 and the curved portion 12 11-12 tangents 11A of the straight portion 11 and 12A of the curved portion 12 were drawn. Then, the angle θ was obtained by measuring the angle formed between the tangent 11A and the tangent 12A.

[0127] When measuring the same location multiple times, it was confirmed that the angle θ was distributed within the median ±2.5 degrees, and the measurement accuracy was within 5 degrees. Tables 1 and 2 show the median values when the angle θ was measured 5 times at the same location.

[0128] In all of the following experimental examples, the first curved portion 121 and the second curved portion 122 had the same shape. And in the steel wires produced in the following experimental examples, the median values of the total 4 angles θ between the straight portion 11 and the curved portion 12 were the same. Also, in each of the steel wires produced in the following Experimental Examples 1-1 to 1-4, Experimental Example 2-1, Experimental Example 2-2, and Experimental Examples 3-2 to 3-4, the radius of curvature R1 of the total 4 first regions 131 of the first curved portion 121 and the second curved portion 122 was the same value.

[0129] Then, from the thickness T and the width W, the flatness ratio was calculated by the following formula.

[0130] (Flatness ratio (%)) = T / W × 100 (2) Evaluation of hardness distribution In a cross-section perpendicular to the longitudinal direction of the steel wire produced in each of the following experimental examples, the Vickers hardness was measured at the surface-side measurement point 142 and the center measurement point 143 on the center line 14 that is equidistant from a pair of opposing straight portions 11. The Vickers hardness was measured in accordance with JIS Z 2244 (2009). In the measurement, the test force was 0.1 kgf, that is, 0.9807 N, and the holding time of the test force was 5 seconds. Since the surface-side measurement point 142 and the center measurement point 143 have already been described, the description is omitted here.

[0131] Then, HV1 - HV2, which is the difference between HV1, the average value of the Vickers hardness at the two surface-side measurement points, and HV2, the Vickers hardness at the center measurement point, was calculated. In Table 1, the evaluation results are shown as HV1 - HV2. (3) Durability test The steel wires produced in each of the following experimental examples were placed on a rubber sheet, and then the rubber sheet was covered on top of them. Thereby, a laminate of a rubber sheet having a rectangular parallelepiped shape with a total thickness five times the thickness of the steel wire and the steel wire was prepared. Then, the laminate of the rubber sheet and the steel wire was vulcanized under the conditions of 160°C for 20 minutes.

[0132] As the rubber sheet, a rubber sheet in which carbon, various accelerators, anti-degradants, etc. were blended in the rubber main component was used.

[0133] After natural air cooling, a strip-shaped test piece with a cross-sectional shape including the steel wire having a thickness of 5 mm and a width of 10 mm was taken out from the obtained steel wire / rubber composite by a cutter knife.

[0134] As shown in Fig. 5, the obtained test piece 50 was applied to 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 Fig. 5, the positions of the rollers were adjusted so that the test piece 50 located between the first roller 511 and the second roller 512 and the test piece 50 located between the second roller 512 and the third roller 513 were parallel. Further, a load of 29.4 N was applied to the test piece 50 applied to the first roller 511 to the third roller 513 along its longitudinal direction. Then, the first roller 511 to the third roller 513 were rotated, and the test piece 50 was moved in the direction of arrow B in Fig. 5. Next, the first roller 511 to the third roller 513 were rotated in the reverse direction, and the test piece 50 was moved in the direction opposite to arrow B. The above reciprocating motion of the test piece 50 was taken as one set, and such an operation was repeatedly performed. Each roller was set at a rotational speed so that the above reciprocating movement could be performed 100 sets per minute. Then, the number of sets of the above reciprocating movement of the test piece until the test piece broke was counted.

[0135] It shows that the higher the number of sets of the above reciprocating movement, the higher the durability.

[0136] Regarding the evaluation results of the steel wires in the following Experimental Example 1-5, Experimental Example 2-3, or Experimental Example 3-1 as 100, the evaluation results of the steel wires in each experimental example were expressed as durability indices. Note that Experimental Example 1-1 to Experimental Example 1-7 showed the results with the evaluation result of Experimental Example 1-5 as 100. Also, Experimental Example 2-1 to Experimental Example 2-3 showed the results with the evaluation result of Experimental Example 2-3 as 100. In Experimental Example 3-1 to Experimental Example 3-5 and Experimental Example 4-1, the results were shown with the evaluation result of Experimental Example 3-1 as 100.

[0137] The durability index means that the larger it is, the better the belt layer with excellent durability can be formed, that is, the better the tire with excellent durability can be formed. (4) Weight index In evaluating the weight index, a rubber sheet was produced using the steel wires produced in the following respective experimental examples.

[0138] As the rubber composition, it is based on natural rubber as the rubber component and contains carbon black, sulfur, zinc oxide, cobalt organic acid, and cobalt stearate as additives.

[0139] Using the steel wires and the rubber composition prepared in each experimental example, a rubber sheet having the same structure as the belt layer 36 shown in FIG. 4 was prepared.

[0140] Then, taking the weight of the rubber sheet prepared using the steel wire of Experimental Example 1-5, Experimental Example 2-3, or Experimental Example 3-1 as 100, the weights of the rubber sheets prepared using the steel wires of each experimental example were expressed as indices. Note that Experimental Examples 1-1 to 1-7 show the results with the weight of the rubber sheet prepared in Experimental Example 1-5 as 100. Also, Experimental Examples 2-1 to 2-3 show the results with the weight of the rubber sheet prepared in Experimental Example 2-3 as 100. Experimental Examples 3-1 to 3-5 and Experimental Example 4-1 show the results with the weight of the rubber sheet prepared in Experimental Example 3-1 as 100.

[0141] The smaller the weight index, the lighter the belt layer can be formed, that is, it means that a tire with excellent light weight can be formed. (5) Impact resistance index Using the Charpy impact test apparatus shown in FIG. 6, the Charpy impact value was measured by the Charpy impact test, and the impact absorption index was calculated from the measured Charpy impact value.

[0142] The Charpy impact test can be carried out, for example, as shown in FIG. 6, by rotating a hammer 61 of mass m from an initial position P1 around a rotation axis 62 and dropping it onto a sample 63 set in advance on the moving path of the hammer 61. After breaking the sample 63, the hammer 61 further progresses in the rotational direction and reaches the highest height position P2.

[0143] Here, let the height of the initial position P1 with respect to the position of the sample 63 be h1, and the height of the highest height position P2 with respect to the position of the sample 63 be h2. In this case, mg(h1 - h2), which is the difference between the potential energy of the initial position P1 and the potential energy of the highest height position P2, becomes the absorption energy when the sample is destroyed. Such absorption energy is the Charpy impact value, and the larger the numerical value, the better the impact resistance of the steel wire.

[0144] Regarding the evaluation results of the steel wires in the following Experimental Examples 1-5, Experimental Examples 2-3, or Experimental Example 3-1, taking the evaluation result of 100, the evaluation results of the steel wires in each experimental example were expressed as impact resistance indices. Note that Experimental Examples 1-1 to 1-7 showed the results with the evaluation result of Experimental Example 1-5 as 100. Also, Experimental Examples 2-1 to 2-3 showed the results with the evaluation result of Experimental Example 2-3 as 100. In Experimental Examples 3-1 to 3-5 and Experimental Example 4-1, the results were shown with the evaluation result of Experimental Example 3-1 as 100.

[0145] The larger the impact resistance index, the better the impact resistance of the steel wire. (Experimental Example) Hereinafter, the experimental conditions will be described. Experimental Examples 1-1 to 1-3, Experimental Example 2-1, and Experimental Examples 3-1 to 3-3 are examples, and Experimental Examples 1-4 to 1-7, Experimental Example 2-2, Experimental Example 2-3, Experimental Example 3-4, Experimental Example 3-5, and Experimental Example 4-1 are comparative examples. [Experimental Example 1-1] A pre-processed steel wire 21 with a wire diameter of 0.4 mm and a circular cross-sectional shape was prepared (pre-processed steel wire preparation step). Note that the pre-processed steel wire 21 has a structure in which a brass plating film composed of metal components Cu and Zn is disposed on the surface of the high-carbon steel wire.

[0146] Then, such a pre-processed steel wire was supplied to the rolling device 20 shown in FIG. 2 and processed to have the predetermined cross-sectional shape shown in FIG. 1A.

[0147] As described above, the rolling device 20 has a pair of first rolling rollers 221 and 222 with opposing pressure surfaces, and a pair of second rolling rollers 231 and 232 with opposing pressure surfaces. The first rolling rollers 221 and 222 are flat rolls, and the pressure surface, which is the surface facing the pre-process steel wire 21, is a flat surface. The second rolling rollers 231 and 232 are concave rolls, and in the cross-section along the plane passing through the central axes of the second rolling rollers 231 and 232, they each include grooves 231A and 232A, which are recessed portions, in the part that presses the pre-process steel wire 21. The grooves 231A and 232A have a shape corresponding to the first curved portion 121 and the second curved portion 122 to be formed, particularly the first region 131.

[0148] The pre-process steel wire 21 was supplied to the rolling device 20. Then, the pre-process steel wire 21 was pressed along the Z-axis direction in FIG. 2 (first axial direction rolling process) by the pair of first rolling rollers 221 and 222 and the pair of second rolling rollers 231 and 232. That is, it was pressed from above and below along the thickness direction of the pre-process steel wire 21.

[0149] As shown in FIG. 2, a pair of third rolling rollers 241 and 242 are arranged on the downstream side in the conveying direction of the pre-process steel wire 21 of the first rolling rollers 221 and 222 and the second rolling rollers 231 and 232. The pre-process steel wire 21 after the first rolling process was supplied between the pair of third rolling rollers 241 and 242.

[0150] Then, the pre-process steel wire 21 after the first axial direction rolling process was pressed along the X-axis direction in FIG. 2, that is, from the left and right directions along the width direction of the pre-process steel wire 21, by the third rolling rollers 241 and 242 (second axial direction rolling process). Note that for the third rolling rollers 241 and 242, those having grooves 241A and 242A with a cross-sectional shape corresponding to the first curved portion 121 and the second curved portion 122 on the respective pressure surfaces were used.

[0151] Then, the pre-processed steel wire 21 was conveyed along the arrow A in Fig. 2, and the steel wire of this experimental example was manufactured by performing the above-described first axial rolling process and second axial rolling process on the entire longitudinal direction thereof.

[0152] In the first axial rolling process and the second axial rolling process, the degree of pressurization and rolling was adjusted so that the shape of the obtained steel wire became a desired shape.

[0153] Specifically, the degree of pressurization and rolling was adjusted so that, among the curved portions 12, the radius of curvature R1 of the first region 131 was 0.05 mm, the radius of curvature R2 of the second region 132 was 0.2 mm, and the angle θ was 177.5 degrees, so that the thickness T was 0.308 mm and the width W was 0.49 mm.

[0154] Also, based on the results of preliminary tests, in the first axial rolling process, the degree of pressurization by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire.

[0155] The obtained steel wire was evaluated as described above. The evaluation results are shown in Table 1. [Experimental Examples 1-2 to 1-4] In the first axial rolling process and the second axial rolling process, the degree of pressurization and rolling was adjusted so that the thickness T, the width W, the radius of curvature R1 of the first region 131 in the curved portion 12, the radius of curvature R2 of the second region 132, and the angle θ became the values shown in Table 1. Also, in the first axial rolling process, the degree of pressurization by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire.

[0156] Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 1-1, and it was evaluated.

[0157] The evaluation results are shown in Table 1. [Experimental Examples 1-5 to 1-7] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R2 of the second region 132 in the curved portion 12, and angle θ would be the values shown in Table 1. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire. The curved portion 12 was made into a curve with a constant radius of curvature where the radius of curvature R2 is the value shown in Table 1. That is, the radius of curvature R1 and the radius of curvature R2 are in the relationship of R1 = R2. Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 1-1 and evaluated.

[0158] The evaluation results are shown in Table 1. [Experimental Example 2-1] The pre-processed steel wire 21 with a wire diameter of 0.3 mm and a circular cross-sectional shape was used. Also, in the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R1 of the first region 131 in the curved portion 12, radius of curvature R2 of the second region 132, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire. Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 1-1 and evaluated.

[0159] The evaluation results are shown in Table 2. [Experimental Example 2-2] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R1 of the first region 131 in the curved portion 12, radius of curvature R2 of the second region 132, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire.

[0160] Except for the above points, a steel wire was produced and evaluated in the same manner as in Experimental Example 2-1.

[0161] The evaluation results are shown in Table 2. [Experimental Example 2-3] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R2 of the second region 132 in the curved portion 12, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the resulting steel wire. The curved portion 12 was a curve with a constant radius of curvature R2 that was the value shown in Table 2. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship of R1 = R2. Except for the above points, a steel wire was produced and evaluated in the same manner as in Experimental Example 2-1.

[0162] The evaluation results are shown in Table 2. [Experimental Example 3-1] A pre-processed steel wire 21 with a wire diameter of 0.26 mm and a circular cross-sectional shape was used. Also, in the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R2 of the second region 132 in the curved portion 12, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the resulting steel wire. The curved portion 12 was a curve with a constant radius of curvature R2 that was the value shown in Table 2. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship of R1 = R2. Except for the above points, a steel wire was produced and evaluated in the same manner as in Experimental Example 1-1.

[0163] The evaluation results are shown in Table 2. [Experimental Examples 3-2 to 3-4] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R1 of the first region 131 in the curved portion 12, radius of curvature R2 of the second region 132, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221 and 222 and the second rolling rollers 231 and 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire.

[0164] Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 3-1 and evaluated.

[0165] The evaluation results are shown in Table 2. [Experimental Example 3-5] In the first-axis direction rolling process and the second-axis direction rolling process, the degree of pressing and rolling was adjusted so that the thickness T, width W, radius of curvature R2 of the second region 132 in the curved portion 12, and angle θ would be the values shown in Table 2. Also, in the first-axis direction rolling process, the degree of pressing by the first rolling rollers 221 and 222 and the second rolling rollers 231 and 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire. The curved portion 12 was a curve with a constant radius of curvature where the radius of curvature R2 was the value shown in Table 2, similar to Experimental Example 3-1. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship of R1 = R2. Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 3-1 and evaluated.

[0166] The evaluation results are shown in Table 2.

[0167] [Experimental Example 4-1] A pre-processed steel wire 21 with a wire diameter of 0.2 mm and a circular cross-sectional shape was used. Also, in the first axial rolling process and the second axial rolling process, the degree of pressurization and rolling was adjusted so that the thickness T, width W, radius of curvature R2 of the second region 132 in the curved portion 12, and angle θ would be the values shown in Table 2. Further, in the first axial rolling process, the degree of pressurization by the first rolling rollers 221, 222 and the second rolling rollers 231, 232 was adjusted to adjust the hardness of the central portion of the obtained steel wire. The curved portion 12 was a curve with a constant radius of curvature where the radius of curvature R2 was the value shown in Table 2. That is, the radius of curvature R1 and the radius of curvature R2 were in the relationship of R1 = R2. Except for the above points, a steel wire was manufactured in the same manner as in Experimental Example 1-1 and evaluated.

[0168] The evaluation results are shown in Table 2.

[0169]

Table 1

[0170]

Table 2

[0171] Since the curvature radius R1 of the first region of the steel wire of Experimental Example 1-4 is 0.025 mm, which is less than 0.05 mm, the durability index is 96, and it was confirmed that the durability is inferior compared to the steel wires of Experimental Example 1-1 and Experimental Example 1-2.

[0172] In addition, for the steel wires of Experimental Example 1-5 to Experimental Example 1-7 where the angle θ is less than 165 degrees, the durability index is 100 to 116, and it was confirmed that the durability is inferior compared to the steel wire of Experimental Example 1-1.

[0173] Since the steel wire of Experimental Example 1-6 has a small flatness value, that is, it is a flat steel wire, the weight index became relatively low at 95. However, since the steel wire of Experimental Example 1-6 has a large processing amount for increasing the flatness during manufacturing, the impact resistance index is 90 or less, and it was confirmed that it is significantly inferior.

[0174] The steel wires in Experimental Examples 1-7 had a large flatness ratio value and a cross-sectional shape close to circular, so the durability index was relatively high at 116. However, it was confirmed that the weight index was significantly inferior.

[0175] The same tendency was also observed for Experimental Examples 2-1 to 2-3. The steel wire of Experimental Example 2-1 had a flat cross-section perpendicular to the longitudinal direction, satisfying the relationship that the curvature radius R1 in the first region was 0.05 mm or more and less than 0.15 mm, the curvature radius R2 in the second region was 0.13 mm or more and 0.2 mm or less, and the angle θ was 165 degrees or more. It was confirmed that the steel wire of Experimental Example 2-1 had a durability index of 102, a weight index of 100, and an impact resistance index of 100, and was a steel wire capable of forming a tire excellent in light weight and durability.

[0176] Since the curvature radius R1 in the first region of the steel wire of Experimental Example 2-2 was 0.025 mm, less than 0.05 mm, the durability index was 94, and it was confirmed that the durability was inferior compared to the steel wire of Experimental Example 2-1.

[0177] Also, for the steel wire of Experimental Example 2-3 where the angle θ was less than 165 degrees, the durability index was 100, and it was confirmed that the durability was inferior compared to the steel wire of Experimental Example 2-1.

[0178] The same tendency was also observed for Experimental Examples 3-1 to 3-5. The steel wires of Experimental Examples 3-1 to 3-3 had a flat cross-section perpendicular to the longitudinal direction, satisfying the relationship that the curvature radius R1 in the first region was 0.05 mm or more and less than 0.15 mm, the curvature radius R2 in the second region was 0.13 mm or more and 0.2 mm or less, and the angle θ was 165 degrees or more. It was confirmed that the durability indices of the steel wires of Experimental Examples 3-1 to 3-3 were 100 to 103, the weight index was 100, and the impact resistance index was 100.

[0179] On the other hand, for the steel wire of Experimental Example 3-4, the radius of curvature R1 in the first region was not in the range of 0.05 mm or more and less than 0.15 mm. Also, for Experimental Example 3-5, the angle θ was less than 165 degrees.

[0180] Therefore, it was confirmed that the steel wires of Experimental Examples 3-1 to 3-3 are steel wires capable of forming a tire having excellent durability compared with the steel wires of Experimental Examples 3-4 and 3-5.

[0181] Regarding Experimental Example 4-1, the radius of curvature R2 in 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. For this reason, it was confirmed that both the durability index and the impact resistance index of the steel wire of Experimental Example 4-1 were lower than those of the steel wires of Experimental Example 3-1 etc.

Explanation of Signs

[0182] 10 Steel wire 101 Steel wire 102 Plating film 11 Straight part 111 First straight part 112 Second straight part L 111 、L 112 Length 12 Curved part 121 First curved part 122 Second curved part 131 First region 132 Second region 14 Center line 1411 First end 1412 Second end 142 Surface side measurement point 1421 First surface side measurement point 1422 Second surface side measurement point 143 Center measurement point L 1421 、L 1422 、L 143 Distance R1, R2 Radius of curvature W Width T Thickness 11A Wiring 12A Wiring P 11-12 Contact Point θ Angle 20 Rolling Device 21 Steel Wire before Processing 221, 222 First Rolling Roller 231, 232 Second Rolling Roller 231A, 232A Groove 241, 242 Third Rolling Roller 241A, 242A Groove Arrow A 30 Tire 31 Tread Portion 32 Sidewall Portion 33 Bead Portion 34 Inner Liner 35 Carcass 36 Belt Layer 37 Bead Wire CL Center Line 41 Rubber t1 First Rubber Thickness t2 Second Rubber Thickness 50 Test Specimen 511 First Roller 512 Second Roller 513 Third Roller Arrow B 61 Hammer 62 Rotation Axis 63 Specimen P1 Initial Position P2 Highest Height Position h1, h2 Height

Claims

1. A steel wire having a flat cross-section perpendicular to the longitudinal direction, wherein the outer shape of the cross-section has a pair of opposing straight portions and a pair of opposing curved portions connecting between the straight portions, the curved portion has a pair of first regions located on the straight portion side and a second region located between the pair of first regions, The radius of curvature R of the first region １ is 0.05 mm or more and less than 0.15 mm, and the radius of curvature R of the second region ２ is 0.13 mm or more and 0.2 mm or less, and an angle between the straight portion and the curved portion is 165 degrees or more.

2. the radius of curvature R １ and the radius of curvature R ２ The steel wire according to claim 1, wherein they are different.

3. In the cross-section, when two intersection points of a center line equidistant from the pair of opposing straight portions and the pair of opposing curved portions are defined as a first end portion and a second end portion, two points on the center line, each 0.1 mm away from the first end portion and the second end portion, are defined as surface side measurement points, when a point on the center line equidistant from the first end portion and the second end portion is defined as a center measurement point, the steel wire according to Claim 1 or Claim 2, wherein HV1 - HV2, which is the difference between HV1, which is the average value of Vickers hardness at the two surface side measurement points, and HV2, which is the Vickers hardness HV2 at the center measurement point, is -60 HV0.1 or more and -10 HV0.1 or less.

4. The steel wire according to any one of Claims 1 to 3, having a brass plating film containing copper and zinc on the surface.

5. The steel wire according to Claim 4, wherein the brass plating film further contains one or more elements selected from cobalt, nickel, iron, tin, and bismuth.

6. A tire including the steel wire according to any one of Claims 1 to 5.

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