CN108729273B

CN108729273B - Steel cord and tire

Info

Publication number: CN108729273B
Application number: CN201711284542.6A
Authority: CN
Inventors: 中岛彻也; 松冈映史
Original assignee: Sumitomo Electric Tochigi Co Ltd
Current assignee: Sumitomo Electric Tochigi Co Ltd
Priority date: 2017-04-20
Filing date: 2017-12-07
Publication date: 2022-04-26
Anticipated expiration: 2037-12-07
Also published as: CN108729273A; JP6980965B2; JP2018178332A

Abstract

The invention provides a steel cord and a tire, which have excellent impact resistance. The steel cord has a 1 xn structure obtained by twisting n (n-3 or 4) bare wires, and when the area of the maximum circumscribed circle is S1 and the area of the bare wire is S2 in a cross section perpendicular to the longitudinal direction, the void ratio V represented by the following formula (a) is 37% or more and 60% or less, and V (%) - (S1-nS2)/S1 × 100 · (a).

Description

Steel cord and tire

Technical Field

The invention relates to a steel cord and a tire.

Background

A steel cord used for a tire as a reinforcing material is known from patent document 1 and the like. Patent document 1 proposes the following for a steel cord: in order to absorb an impact by sinking to a certain extent when the tire is bumpy and bumpy during running on a road, such as a stone, and to prevent deformation of the tire during high-speed rotation, a predetermined relationship is established between a load and an elongation of the steel cord.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-275772

Disclosure of Invention

However, in recent years, from the viewpoint of improving the durability of a tire against an impact when the tire travels to a protrusion on a road surface or the like, improvement of the impact resistance is required for a steel cord.

However, the tire reinforcing steel cord disclosed in patent document 1 is intended to suppress tire deformation at high-speed rotation by making a predetermined relationship between load and elongation, and absorbing impact without deteriorating ride comfort of a vehicle. Therefore, studies have not been sufficiently made in view of impact resistance.

Accordingly, an object of the present disclosure is to provide a steel cord excellent in impact resistance.

According to one aspect of the present disclosure, there is provided a steel cord having a 1 × n structure in which n is 3 or 4, wherein when an area of a maximum circumscribed circle is S1 and an area of a bare wire is S2 in a cross section perpendicular to a longitudinal direction, a void ratio V represented by the following formula (a) is 37% or more and 60% or less, and V (%) - (S1-nS2)/S1 × 100 … (a).

Further, according to another aspect of the present disclosure, there is provided a steel cord having a 1 × n structure in which n is 5, wherein when an area of a maximum circumscribed circle is S1 and an area of a bare wire is S2 in a cross section perpendicular to a longitudinal direction, a void ratio V represented by the following formula (a) is 33% or more and 55% or less, and V (%) ═ S1-nS2)/S1 × 100 … (a).

According to the present disclosure, a steel cord excellent in impact resistance can be provided.

Drawings

Fig. 1 is an explanatory view of a steel cord of a 1 × 4 structure according to one embodiment of the present disclosure.

Fig. 2 is a sectional view of the steel cord of fig. 1 at a plane perpendicular to the length direction.

Fig. 3 is a cross-sectional view of a steel cord of 1 × 3 structure according to one embodiment of the present disclosure, taken along a plane perpendicular to the longitudinal direction.

Fig. 4 is a cross-sectional view of a steel cord of a 1 × 5 structure according to another embodiment of the present disclosure, taken along a plane perpendicular to the longitudinal direction.

Fig. 5 is an explanatory view of the charpy impact test.

Fig. 6 is an explanatory view of a bare wire in which a bent portion and a non-bent portion are repeatedly formed.

Fig. 7 is an explanatory view of a method of manufacturing a bare wire in which a bent portion and a non-bent portion are repeatedly formed.

Fig. 8 is a sectional view of a tire according to an aspect of the present disclosure.

Fig. 9 is a diagram schematically showing a tape layer.

Fig. 10 is a graph showing the relationship between the void ratio and the impact absorption index in experimental examples 1 to 11.

Fig. 11 is a graph showing the relationship between the area of the center region and the impact absorption index in experimental examples 1 to 11.

Fig. 12 is a graph showing the relationship between the void ratio and the impact absorption index in experimental examples 12 to 16.

Fig. 13 is a graph showing the relationship between the area of the center region and the impact absorption index in experimental examples 12 to 16.

Fig. 14 is a graph showing the relationship between the void ratio and the impact absorption index in experimental examples 17 to 26.

Fig. 15 is a graph showing the relationship between the area of the center region and the impact absorption index in experimental examples 17 to 26.

Description of the reference symbols

10. 30, 40, 91 steel cord

11. 61, 72 bare wires

12 center portion void

13 gap between bare wires

14 maximum circle of circumscribed circle

15 central region

51 test sample

52 hammer

53 rotating shaft

Initial position A

Highest height position of B

62. 62A, 62B, 62C bent part

63 non-bent part

Repeated pitch between P-bend and non-bend portions

h difference in height between adjacent bent portions

71 preform

81 tyre

82 tread portion

83 side wall part

84 bead portion

85 liner

86 tyre body

87 tape layer

88 bead wire

92 rubber.

Detailed Description

Hereinafter, embodiments for implementation will be described.

[ description of embodiments of the present disclosure ]

First, embodiments of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description is not repeated for these elements.

(1) A steel cord according to one embodiment of the present disclosure has a 1 × n structure in which n (n is 3 or 4) bare wires are twisted, and when an area of a maximum circumscribed circle is S1 and an area of a bare wire is S2 in a cross section perpendicular to a longitudinal direction, a void ratio V represented by the following formula (a) is 37% or more and 60% or less.

V(％)＝(S1-nS2)/S1×100…(A)

According to the study of the inventors of the present invention, it is estimated that the plural bare wires included in the steel cord having the 1 × 3 structure or the 1 × 4 structure have integrity to overcome the applied impact by setting the void ratio V to 37% or more, and the voids in the steel cord can absorb the applied impact.

However, if the void ratio V exceeds 60%, the distance between the plurality of bare wires included in the steel cord of the 1 × 3 structure or the 1 × 4 structure becomes large, so that the integrity between the bare wires is weakened, and it is estimated that the plurality of bare wires included in the steel cord are easily individually cut by an impact.

Therefore, according to the steel cord of one embodiment of the present disclosure, by setting the void ratio V to 37% or more and 60% or less, a steel cord having excellent impact resistance can be formed.

(2) In addition, another aspect of the present disclosure provides a steel cord having a 1 × n structure in which n (n ═ 5) bare wires are twisted, and when the area of the maximum circumscribed circle is S1 and the area of the bare wire is S2 in a cross section perpendicular to the longitudinal direction, the void ratio V represented by the following formula (a) is 33% or more and 55% or less.

V(％)＝(S1-nS2)/S1×100…(A)

According to the study of the inventors of the present invention, it is estimated that the plural bare wires included in the steel cord having the 1 × 5 structure have unity to overcome the applied impact by setting the void ratio V to 33% or more, and the voids in the steel cord can absorb the applied impact.

However, when the void ratio V exceeds 55%, the distance between the plurality of bare wires included in the steel cord having the 1 × 5 structure becomes large, and therefore, the integrity between the bare wires is weakened, and it is estimated that the plurality of bare wires included in the steel cord are easily individually cut by an impact.

Therefore, according to the steel cord of another embodiment of the present disclosure, by setting the void ratio V to 33% or more and 55% or less, a steel cord having excellent impact resistance can be formed.

(3) The wire harness may have a 1 × 3 structure in which 3 bare wires are twisted, and an area of a region surrounded by a straight line connecting centers of the bare wires adjacent to each other in a circumferential direction of the maximum circumscribed circle may be 0.07mm in a cross section perpendicular to a longitudinal direction²Above and 0.13mm²The following.

(4) The impact absorption index, which is a ratio of a charpy value to a reference value of a 1 × 3 steel cord having a 1 × 3 structure obtained by twisting 3 bare wires, may be greater than 100% and 110% or less, where the charpy value of the steel cord having the 1 × 3 structure and the porosity V of 35.8% is the reference value.

(5) The wire harness may have a 1 × 4 structure in which 4 bare wires are twisted, and an area of a region surrounded by a straight line connecting centers of the bare wires adjacent in a circumferential direction of the maximum circumscribed circle may be 0.16mm in a cross section of a surface perpendicular to a longitudinal direction²Above and 0.32mm²The following.

(6) The impact absorption index, which is a ratio of a charpy value to a reference value of a steel cord having a 1 × 4 structure obtained by twisting 4 bare wires, may be greater than 100% and 140% or less, the charpy value of the steel cord having the 1 × 4 structure and the porosity V of 36.4% being the reference value.

(7) The wire harness may have a 1 × 5 structure in which 5 bare wires are twisted, and an area of a region surrounded by a straight line connecting centers of the bare wires adjacent to each other in a circumferential direction of the maximum circumscribed circle may be 0.24mm in a cross section perpendicular to a longitudinal direction²Above and 0.45mm²The following。

(8) The impact absorption index, which is a ratio of a charpy value to a reference value of a 1 × 5 steel cord having a 1 × 5 structure in which 5 bare wires are twisted, may be greater than 100% and 115% or less when the charpy value of the steel cord having the 1 × 5 structure in which the void ratio V is 32.0% is the reference value.

(9) At least 1 of the n bare wires may repeatedly have a bent portion and a non-bent portion in a length direction.

(10) All of the n bare wires may have a bending portion and a non-bending portion repeatedly in the longitudinal direction.

(11) When the height from the flat surface to the bent portion on the side farther from the flat surface when the bare wire is placed on the flat surface is defined as a bending height, the bending height may be 0.10mm or more and 0.30mm or less.

(12) The repeated pitch between the bent portion and the non-bent portion may be 5.0mm or more and 30.0mm or less.

(13) The initial elongation at 49N application may be 0.06% or more and 0.35% or less.

(14) The diameter of the bare wire may be 0.22mm or more and 0.42mm or less.

(15) A tire comprising the steel cord according to any one of (1) to (14).

[ details of embodiments of the present disclosure ]

Specific examples of a steel cord and a tire according to an embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described below with reference to the drawings. The present invention is not limited to the above-described examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[ Steel cord ]

Hereinafter, the steel cord of the present embodiment will be described with reference to fig. 1 to 7.

The steel cord of the present embodiment has a 1 × n structure in which n bare wires called filaments are helically twisted.

Here, fig. 1 shows one structural example of the steel cord 10 of the present embodiment. The steel cord 10 shown in fig. 1 has a structure in which 4 bare wires 11 are twisted.

The 1 × n structure is a structure in which n bare wires are twisted into a single layer (1 layer). The single layer is a structure in which bare wires are arranged in a single layer (1 layer) along the circumferential direction of 1 circle in a cross section perpendicular to the longitudinal direction of the steel cord as shown in fig. 2, 3, and 4 described later.

The steel cord 10 shown in fig. 1 has a 1 × 4 structure in which 4 bare wires 11 are twisted into a single layer. A cross-sectional view of the steel cord 10 shown in fig. 1 at a plane perpendicular to the longitudinal direction is shown in fig. 2. The longitudinal direction of the steel cord 10 is the Y-axis direction in the figure. The plane perpendicular to the longitudinal direction is a plane parallel to the XZ plane in the drawing.

As shown in fig. 2, 4 bare wires 11 are twisted, and a central portion gap 12 surrounded by the 4 bare wires 11 is formed in the central portion.

In fig. 2, an example in which the adjacent bare wires 11 are in contact is shown in a cross section perpendicular to the longitudinal direction, but as in the case of the

steel cords

30 and 40 shown in fig. 3 and 4 described later, some or all of the adjacent bare wires 11 may be formed with a gap between the bare wires 11 without being in contact.

Fig. 3 shows a structural example of a cross-sectional view of a plane perpendicular to the longitudinal direction of the steel cord 30 of a 1 × 3 structure. Fig. 4 shows a structural example of a cross-sectional view of a 1 × 5 steel cord 40 in a plane perpendicular to the longitudinal direction.

In the steel cord 30 having a 1 × 3 structure shown in fig. 3, 3 bare wires 11 are twisted into a single layer, and a central space 12 surrounded by the 3 bare wires 11 is formed in the central portion. In the steel cord 40 having a 1 × 5 structure shown in fig. 4, 5 bare wires 11 are twisted into a single layer, and a central space 12 surrounded by the 5 bare wires 11 is formed in the central portion.

In fig. 3 and 4, the bare wire gap 13 is formed between the adjacent bare wires 11, but a part or all of the adjacent bare wires 11 may be in contact with each other, for example, as in the steel cord 10 shown in fig. 2.

When the steel cord of the present embodiment has a 1 × 3 structure or a 1 × 4 structure, the void ratio V represented by the following formula (a) is 37% or more and 60% or less when the area of the maximum circumscribed circle is S1 and the area of each bare wire is S2 in a cross section perpendicular to the longitudinal direction.

When the steel cord of the present embodiment has a 1 × 5 structure, the void ratio V represented by the following formula (a) is 33% to 55% when the area of the maximum circumscribed circle is S1 and the area of each bare wire is S2 in a cross section perpendicular to the longitudinal direction.

A(％)＝(S1-nS2)/S1×100…(A)

Here, in the case of the cross section of the steel cord 10 of the 1 × 4 structure shown in fig. 2, the maximum circumscribed circle at the cross section perpendicular to the longitudinal direction of the steel cord is the maximum circumscribed circle 14 inscribed in the outer peripheries of the 4 bare wires 11. In the case of the cross section of the steel cord 30 shown in fig. 3, the maximum circumscribed circle 14 inscribed in the outer peripheral edge of the 3 bare wires 11 is referred to. In the case of the cross section of the steel cord 40 shown in fig. 4, it means the maximum circumscribed circle 14 inscribed in the outer peripheral edge of the 5 bare wires 11. In either case, the maximum circumscribed circle 14 becomes a perfect circle.

The maximum circumscribed circle 14 also corresponds to the outer shape of the steel cord, and therefore, in this specification, the diameter of the maximum circumscribed circle 14 is sometimes referred to as a cord diameter.

The void ratio V represents a ratio of an area of a region not occupied by the bare wire 11 in a region surrounded by the maximum circumscribed circle 14 in a cross section perpendicular to the longitudinal direction of the steel cord, and can be calculated by the above formula (a). In addition, in the same steel cord, the void ratio in the cross section perpendicular to the longitudinal direction of the steel cord is constant without depending on the position of the measured cross section, and therefore, the void ratio can be measured and calculated using the cross section at an arbitrary position in the longitudinal direction of the steel cord.

The void ratio V in the cross section perpendicular to the longitudinal direction of the steel cord can be adjusted by, for example, the presence or absence of the bare wire gap 13 between the adjacent bare wires 11, the size thereof, the size of the central portion void 12, and the like as described above.

As a method for evaluating the impact resistance of a steel cord, a charpy impact test is exemplified. The charpy impact test can be performed, for example, by rotating a weight 52 having a mass m from an initial position a around a rotation axis 53 and striking a sample 51 set in advance on a movement path of the weight 52 downward, as shown in fig. 5. The hammer 52 further moves in the rotation direction after breaking the sample 51, and reaches the maximum height position B.

Here, the height of the initial position a with reference to the position of the sample 51 is h1, and the height of the maximum height position B with reference to the position of the sample 51 is h 2. In this case, mg (h1-h2), which is the difference between the position energy at the initial position A and the position energy at the maximum height position B, is the absorption energy at the time of breaking the sample. The above absorption energy is a charpy impact value, and a larger numerical value indicates a steel cord having more excellent impact resistance.

The charpy impact test is widely used to evaluate the impact resistance of various wire materials such as piano wire because the energy required for breaking a sample can be evaluated. Conventionally, the charpy impact value is mainly affected by the elongation and breaking load of the material of the wire rod, and the effect on the structure of the wire rod and the like is unknown.

However, according to the study of the present inventors, in the steel cord having the 1 × 3 structure or the 1 × 4 structure, it was confirmed that the charpy impact value was increased by setting the void ratio V to 37% or more and 60% or less, as compared with the case where the void ratio V was less than 37%. In addition, in the steel cord having the 1 × 5 structure, it was confirmed that the charpy impact value was increased by setting the void ratio V to 33% or more and 55% or less, as compared with the case where the void ratio V was less than 33%. That is, the impact resistance evaluated by the charpy impact test was affected by the structure of the wire rod as a sample.

This is presumed to be because, by setting the void ratio V of the steel cord to the above-described predetermined value or more corresponding to the structure, the plural bare wires included in the steel cord have unity and can overcome the applied impact, and the voids in the steel cord absorb the applied impact.

However, in the steel cord having the 1 × 3 structure or the 1 × 4 structure, if the void ratio V of the steel cord exceeds 60%, the distance between a plurality of bare wires included in the steel cord becomes large, and therefore, it is considered that the unity between the bare wires is weakened. Therefore, it is estimated that the impact resistance is lowered because the plurality of bare wires included in the steel cord are easily cut individually by the impact.

In addition, in the steel cord having a 1 × 5 structure, when the void ratio V of the steel cord exceeds 55%, it is presumed that the impact resistance is lowered for the same reason.

As described above, the steel cord of the present embodiment can improve impact resistance by setting the void ratio V in a predetermined range. Therefore, in a cross section perpendicular to the longitudinal direction of the steel cord, it is preferable to adjust the arrangement of the plurality of bare wires or the like so that the void ratio V is in the above range.

As shown in fig. 2 to 4, the steel cord of the present embodiment preferably has a central void 12, which is a void surrounded by bare wires, in the central portion in a cross section perpendicular to the longitudinal direction of the steel cord. This is because the impact can be absorbed by the central portion void 12, and particularly, the impact resistance can be improved. Therefore, the steel cord of the present embodiment preferably has 3 or more bare wires. However, if the number of bare wires exceeds 5, the diameter of the bare wires, i.e., the diameter of the bare wires, needs to be reduced, which is not preferable because the manufacturing cost increases. Therefore, the steel cord of the present embodiment preferably includes 3 or more and 5 or less bare wires.

In order to improve impact resistance, it is conceivable to form the steel cord not as a single layer but as a multi-layer twisted structure having two or more layers, but there is a possibility that the manufacturing process becomes complicated, such as making the diameter of the bare wire of each layer smaller and making the twisting process 2 or more steps. Therefore, the steel cord of the present embodiment is preferably a single-layer structure of 1 × n structure. In addition, the multilayer refers to the following structure: in a cross section perpendicular to the longitudinal direction of the steel cord, 1 layer is formed by aligning bare wires in the circumferential direction of 1 circle, and the layer has multiple layers in a concentric circle shape.

In the case where the number n of bare wires included in the steel cord of the present embodiment is 3, the area of the region surrounded by the straight lines connecting the centers of the bare wires adjacent in the circumferential direction of the maximum circumscribed circle in the cross section perpendicular to the longitudinal direction is preferably 0.07mm²Above and 0.13mm²The following.

A region (hereinafter, also referred to as a "central region") surrounded by straight lines connecting the centers of bare wires adjacent in the circumferential direction of the maximum circumscribed circle in a cross section perpendicular to the longitudinal direction when the number n of bare wires is 3 will be described with reference to fig. 3. Fig. 3 shows a cross-sectional view of a plane perpendicular to the longitudinal direction of a steel cord 30 in which the number of bare wires 11 is 3 as described above. When the number n of bare wires of the steel cord is 3, if the centers of the bare wires 11 adjacent to each other in the circumferential direction of the maximum circumscribed circle 14 are connected by a straight line, a composed line segment O is formed₃₁-O₃₂Line segment O₃₂-O₃₃Line segment O₃₃-O₃₁A central region 15 of the enclosed triangle.

The number n of bare wires was 3, and the area of the central region 15 was 0.07mm as described above²In the above case, a steel cord having excellent impact resistance can be formed, which is preferable.

The number n of bare wires is 3, and the area of the central region 15 is 0.07mm²In the above, it is considered that the central region 15 includes the central portion void 12 of a size sufficient to absorb an impact. Therefore, when an impact is applied to the steel cord 30, the central region 15 can sufficiently absorb the impact, and it is estimated that the impact resistance can be improved.

However, when the number n of bare wires is 3, it is considered that the area of the central region 15 exceeds 0.13mm²The distance between bare wires also becomes large, and therefore the integrity between bare wires is weakened. Therefore, the plurality of bare wires 11 included in the steel cord 30 are easily cut individually by impact, and there is a possibility that the impact resistance is lowered. Therefore, when the number n of bare wires is 3, the area of the central region 15 is preferably 0.13mm²The following.

In addition, when the number n of bare wires included in the steel cord of the present embodiment is 4, the area of a region surrounded by a straight line connecting the centers of the bare wires adjacent in the circumferential direction of the maximum circumscribed circle in a cross section perpendicular to the longitudinal direction is preferably 0.16mm²Above and 0.32mm²The following.

The central region in the case where the number n of bare wires is 4 will be described with reference to fig. 2. Fig. 2 shows a cross-sectional view of a plane perpendicular to the longitudinal direction of the steel cord 10 having 4 bare wires 11 as described above. When the number n of bare wires of the steel cord is 4, if the centers of the bare wires 11 adjacent to each other in the circumferential direction of the maximum circumscribed circle 14 are connected by a straight line, a composed line segment O is formed₁₁-O₁₂Line segment O₁₂-O₁₃Line segment O₁₃-O₁₄Line segment O₁₄-O₁₁A central area 15 of the enclosed quadrilateral.

The number n of bare wires was 4, and the area of the central region 15 was 0.16mm as described above²In the above case, a steel cord having excellent impact resistance can be formed, which is preferable.

The number n of bare wires was 4 and the area of the central region was 0.16mm²In the above, it is considered that the central region 15 includes the central portion void 12 of a size sufficient to absorb an impact. Therefore, when an impact is applied to the steel cord 10, the impact can be sufficiently absorbed by the central region 15, and it is estimated that the impact resistance can be improved.

However, when the number n of bare wires is 4, it is considered that the area of the central region 15 exceeds 0.32mm²The distance between bare wires also becomes large, and therefore the integrity between bare wires is weakened. Therefore, the plurality of bare wires included in the steel cord are easily cut individually by impact, and the impact resistance may be lowered. Therefore, when the number n of bare wires is 4, the area of the central region 15 is preferably 0.32mm²The following.

In addition, when the number n of bare wires included in the steel cord of the present embodiment is 5, the area of a region surrounded by a straight line connecting the centers of the bare wires adjacent in the circumferential direction of the maximum circumscribed circle in a cross section perpendicular to the longitudinal direction is preferably 0.24mm²Above and 0.45mm²The following.

The central region in the case where the number n of bare wires is 5 will be described with reference to fig. 4. Fig. 4 shows the steel cords 40 having 5 bare wires as described above in the longitudinal directionCross-sectional view at the vertical plane. When the number n of bare wires of the steel cord is 5, if the centers of the bare wires 11 adjacent to each other in the circumferential direction of the maximum circumscribed circle 14 are connected by a straight line, a composed line segment O is formed₄₁-O₄₂Line segment O₄₂-O₄₃Line segment O₄₃-O₄₄Line segment O₄₄-O₄₅Line segment O₄₅-O₄₁A central region 15 of the enclosed pentagon.

The number n of bare wires was 5, and the area of the central region 15 was 0.24mm as described above²In the above case, a steel cord having excellent impact resistance can be formed, which is preferable.

The number n of bare wires was 5, and the area of the central region was 0.24mm²In the above, it is considered that the central region 15 includes the central portion void 12 of a size sufficient to absorb an impact. Therefore, when an impact is applied to the steel cord 40, the impact can be sufficiently absorbed by the central region, and it is estimated that the impact resistance can be improved.

However, when the number n of bare wires is 5, it is considered that the area of the central region 15 exceeds 0.45mm²The distance between bare wires also becomes large, and therefore the integrity between bare wires is weakened. Therefore, the plurality of bare wires included in the steel cord are easily cut individually by impact, and the impact resistance may be lowered. Therefore, when the number n of bare wires is 5, the area of the central region is preferably 0.45mm²The following.

At least 1 bare wire of the n bare wires included in the steel cord of the present embodiment may have a bent portion and a non-bent portion repeatedly in the longitudinal direction. In addition, all of the n bare wires included in the steel cord of the present embodiment may have a bent portion and a non-bent portion repeatedly in the longitudinal direction.

Fig. 6 schematically shows a bare wire 61 repeatedly having a bent portion and a non-bent portion in the length direction. The bare wire 61 shown in fig. 6 alternately repeats a bending portion 62 and a non-bending portion 63 in the longitudinal direction.

In addition, although fig. 6 shows an example in which the bent portion 62 is bent at an angle close to 90 degrees, the bending is not limited to the above-described embodiment, and the bent portion may be bent at an angle smaller than 90 degrees or larger than 90 degrees, for example. The bare wire does not need to have a clear bending point at the bent portion 62, and may have a shape curved in an arc shape, for example.

The void ratio V can be adjusted by providing 1 or more of the n bare wires included in the steel cord of the present embodiment with a shape having a repeated bent portion and non-bent portion in the longitudinal direction. Therefore, the degree of impact resistance of the obtained steel cord can be selected.

However, the steel cord includes a bare wire having a shape in which a bent portion and a non-bent portion are repeated in the longitudinal direction, and thereby not only the void ratio V but also the characteristics such as the initial elongation are affected. Therefore, the number of bare wires having a bent portion and a non-bent portion repeatedly in the longitudinal direction and the shape thereof included in the steel cord are preferably selected according to the characteristics such as the void ratio V and the initial elongation required for the steel cord.

In the bare wire having the bent portion and the non-bent portion repeatedly in the longitudinal direction, the repeated pitch between the bent portion and the non-bent portion is preferably 5.0mm or more and 30.0mm or less, and more preferably 5.0mm or more and 20.0mm or less.

The overlapping pitch between the bent portion and the non-bent portion is a distance between the bent portions having the same shape, and is a length of the steel cord in a longitudinal direction from the reference bent portion to two adjacent bent portions. Therefore, in the example shown in fig. 6, the overlapping pitch P between the bent portion and the non-bent portion is, for example, a distance from the bent portion 62A to the two adjacent bent portions 62C thereof.

By setting the repeated pitch between the bent portion and the non-bent portion to 5.0mm or more, the bent portion and the non-bent portion can be easily formed on the bare wire, and the void ratio V of the steel cord can be easily and accurately controlled as required, which is preferable. However, if the repeated pitch between the bent portion and the non-bent portion is intended to be longer than 30.0mm, the apparatus for forming the bent portion and the non-bent portion may become large, and the manufacturing cost may increase.

When the bare wire is placed on the plane S, the height from the plane S to the bent portion 62B on the side farther from the plane S is defined as a bent height h.

The bending height h is preferably 0.10mm or more and 0.30mm or less, and more preferably 0.12mm or more and 0.28mm or less.

This is because the void ratio V can be particularly increased when forming a steel cord by setting the bending height h to 0.10mm or more. However, if the bending height h is made longer than 0.30mm, other bare wires may be damaged when twisting the bare wires with each other. Therefore, the bending height h is preferably 0.30mm or less.

As shown in fig. 7, a bare wire repeatedly having a bent portion and a non-bent portion in the longitudinal direction can be formed, for example, by arranging a plurality of preforms 71 and passing a bare wire 72 between the plurality of preforms 71. The configuration, size, and shape of the preform 71 can be changed to select the shape of the bent portion, the length of the non-bent portion, and the like. The preform 71 may have a shape of, for example, a pin type (cylindrical type) or a gear type.

The bare wire diameter, which is the diameter of the bare wire included in the steel cord of the present embodiment, is preferably 0.22mm or more and 0.42mm or less, and more preferably 0.25mm or more and 0.38mm or less.

By setting the bare wire diameter to 0.22mm or more, the breaking load can be sufficiently increased for a steel cord including the bare wire.

However, if the bare wire diameter is too large, the weight of the steel cord including the wire or the tire using the steel cord increases, which is not preferable. Therefore, the bare wire diameter is preferably 0.42mm or less.

The initial elongation of the steel cord of the present embodiment when 49N is applied is preferably 0.06% or more and 0.35% or less, and more preferably 0.07% or more and 0.30% or less.

The initial elongation is an elongation when a load is applied to a steel cord in a longitudinal direction after the steel cord is made by twisting a bare wire. The initial elongation is an elongation generated in the process of bringing a plurality of bare wires twisted in a spiral shape into a tight contact state by applying a load. The initial elongation described above is a ratio of the elongation per 500mm of the steel cord to the steel cord of the present embodiment to which 49N is applied.

The steel cord of the present embodiment can be embedded in a tire, for example, as described later. By setting the initial elongation of the steel cord of the present embodiment to 0.06% or more, the impact absorption performance, which is the absorption performance of the unevenness of the road surface, can be improved for the tire in which the steel cord is embedded, and the ride comfort can be improved. However, if the initial elongation of the steel cord exceeds 0.35%, the workability in the treatment in the twisting step or the like may be reduced, and therefore, it is preferably 0.35% or less.

The charpy impact value measured by the charpy impact test described above is affected by the ambient temperature and humidity. Therefore, the results of the charpy impact test indicate the relative proportion of charpy impact values with respect to a reference substance serving as a reference.

Specifically, a reference material serving as a reference in the charpy impact test is determined, and the charpy impact test is performed under the same environment for the reference material and the evaluation material. The charpy impact value of the evaluation object is expressed by an impact absorption index which is a ratio of the charpy impact value of the reference object to the reference value (100%). When the impact absorption index is 100%, the charpy impact value is the same between the reference and the evaluated value.

In the steel cord of the present embodiment, a steel cord having excellent impact resistance can be formed by selecting the void ratio V. Therefore, when the effect of the void ratio V is confirmed, it is preferable that the bare wire diameters of the bare wires included in the steel cord be the same for the reference material and the evaluation material used for calculating the impact absorption index.

In the steel cord of the present embodiment, when the number n of bare wires included is 3, the charpy impact value of the steel cord having a 1 × 3 structure with a void ratio V of 35.8% can be used as a reference value for the impact absorption index. When the number n of bare wires included in the steel cord of the present embodiment is 3, the impact absorption index, which is a percentage of the reference value with respect to the charpy impact value, is preferably greater than 100% and not greater than 110%. By setting the impact absorption index to be more than 100% and 110% or less, a steel cord having excellent impact resistance can be formed.

A steel cord having a 1 × 3 structure with a void ratio V of 35.8% used as a reference for the impact absorption index can be produced by twisting, for example, 3 bare wires in which a bent portion and a non-bent portion are not formed in advance. The void ratio V of the steel cord is relatively small in the case of a steel cord of a 1 × 3 structure.

Further, according to the study of the present inventors, it is possible to improve the impact resistance of the steel cord by increasing the void ratio V. Therefore, the impact absorption index based on the steel cord of the 1 × 3 structure having the void ratio V of 35.8% is preferably more than 100%.

However, if the impact absorption index is to be made larger than 110%, not only the void ratio V, for example, but also the bare wire diameter may need to be thickened. If the bare wire diameter becomes large, the weight of the steel cord and the tire using the steel cord increases, which is not preferable. Therefore, the impact absorption index is preferably 110% or less.

In the steel cord of the present embodiment, when the number n of bare wires included is 4, the charpy impact value of the steel cord having a 1 × 4 structure with a porosity V of 36.4% can be used as a reference value for the impact absorption index. In the steel cord of the present embodiment, when the number n of bare wires included is 4, the impact absorption index, which is the percentage of the reference value to the charpy impact value, is preferably greater than 100% and 140% or less. By setting the impact absorption index to be more than 100% and 140% or less, a steel cord having excellent impact resistance can be formed.

A steel cord having a 1 × 4 structure with a void ratio V of 36.4% serving as a reference of the impact absorption index can be produced by twisting, for example, 4 bare wires in which a bent portion and a non-bent portion are not formed in advance. The void ratio V of the steel cord is relatively small in the case of a steel cord of a 1 × 4 structure.

Further, according to the study of the present inventors, it is possible to improve the impact resistance of the steel cord by increasing the void ratio V. Therefore, the impact absorption index based on the steel cord of the 1 × 4 structure having the void ratio V of 36.4% is preferably more than 100%.

However, if the impact absorption index is larger than 140%, not only the void ratio V, for example, but also the bare wire diameter may need to be thickened. If the bare wire diameter becomes large, the weight of the steel cord and the tire using the steel cord increases, which is not preferable. Therefore, the impact absorption index is preferably 140% or less.

In the steel cord of the present embodiment, when the number n of bare wires included is 5, the charpy impact value of a steel cord having a 1 × 5 structure with a porosity V of 32.0% can be used as a reference value for the impact absorption index. In the steel cord of the present embodiment, when the number n of bare wires included is 5, the impact absorption index, which is the percentage of the reference value with respect to the charpy impact value, is preferably greater than 100% and not greater than 115%. By setting the impact absorption index to be more than 100% and 115% or less, a steel cord having excellent impact resistance can be formed.

A steel cord having a 1 × 5 structure with a void ratio V of 32.0% serving as a reference of the impact absorption index can be produced by twisting, for example, 5 bare wires in which a bent portion and a non-bent portion are not formed in advance. The void ratio V of the steel cord is relatively small in the case of a steel cord of a 1 × 5 structure.

Further, according to the study of the present inventors, it is possible to improve the impact resistance of the steel cord by increasing the void ratio V. Therefore, the impact absorption index based on the steel cord of the 1 × 5 structure having the void ratio V of 32.0% is preferably more than 100%.

However, if the impact absorption index is larger than 115%, not only the void ratio V, but also the bare wire diameter may need to be increased. If the bare wire diameter becomes large, the weight of the steel cord and the tire using the steel cord increases, which is not preferable. Therefore, the impact absorption index is preferably 115% or less.

[ tire ]

Next, a tire according to the present embodiment will be described with reference to fig. 8 and 9.

The tire of the present embodiment may contain the already described steel cord.

Fig. 8 shows a cross-sectional view of a tire 81 according to the present embodiment on a plane perpendicular to the circumferential direction. Fig. 8 shows only the left side of CL (center line), but the same structure is also provided continuously on the right side of CL with CL as the axis of symmetry.

As shown in fig. 8, the tire 81 includes a tread portion 82, a sidewall portion 83, and a bead portion 84.

The tread portion 82 is a portion that contacts the road surface. The bead portion 84 is provided on the inner diameter side of the tire 81 with respect to the tread portion 82. The bead portion 84 is a portion that contacts the rim of the wheel of the vehicle. The sidewall portion 83 connects the tread portion 82 and the bead portion 84. When the tread portion 82 receives an impact from a road surface, the sidewall portion 83 is elastically deformed to absorb the impact.

The tire 81 includes a liner 85, a carcass 86, a belt layer 87, and a bead wire 88.

The liner 85 is made of rubber, and seals a space between the tire 81 and the wheel.

Carcass 86 forms the carcass of tire 81. The carcass 86 is made of organic fibers such as polyester, nylon, or rayon, or a steel cord, and rubber.

Bead wires 88 are provided to the bead portions 84. The bead wire 88 receives a tensile force acting on the carcass.

The belt layer 87 fastens the carcass 86 and increases the rigidity of the tread portion 82. In the example shown in fig. 8, the tire 81 has two belt layers 87.

Fig. 9 is a schematic view of the two tape layers 87. Fig. 9 shows a cross-sectional view of the belt layer 87 at a plane perpendicular to the longitudinal direction, i.e., the circumferential direction of the tire 81.

As shown in fig. 9, the two belt layers 87 are superposed in the radial direction of the tire 81. Each belt layer 87 has a plurality of steel cords 91 and rubber 92. A plurality of steel cords 91 are arranged in a row. The rubber 92 covers the steel cord 91, and the entire circumference of each steel cord is covered with the rubber 92. The steel cord 91 is embedded in the rubber 92.

The tire according to the present embodiment includes the steel cord having excellent impact resistance as described above as the steel cord 91. Therefore, the tire of the present embodiment can also be formed with excellent impact resistance.

Although the embodiments have been described in detail above, the embodiments are not limited to the specific embodiments, and various modifications and changes can be made within the scope of the claims.

Examples

The following description will be given by way of specific examples, but the present invention is not limited to these examples.

(evaluation method)

First, a method for evaluating a steel cord produced in the following experimental example will be described.

(1) Bare wire diameter

Bare wire diameter was measured using a micrometer.

(2) Cord diameter

The steel cord to be evaluated was embedded in a transparent resin, and a sample was cut out so that a surface (cross section) perpendicular to the longitudinal direction of the steel cord was exposed.

Then, the diameters of the maximum circumscribed circles of the plurality of bare wires included in the cross section are measured as the cord diameters using a projector.

(3) Void fraction

From the bare wire diameter and the cord diameter measured in (1) and (2), the area S1 of the maximum circumscribed circle and the area S2 of each bare wire were calculated, and the void ratio V was calculated using the following formula (a).

V(％)＝(S1-nS2)/S1×100…(A)

(4) Area of central region

From the observation result of the cross section perpendicular to the longitudinal direction of the steel cord measured when calculating the cord diameter of (2), the area of the central region, which is a region where the centers of the bare wires adjacent in the circumferential direction along the maximum circumscribed circle are connected by a straight line, is calculated.

(5) Initial elongation

The percentage of elongation per 500mm of the steel cord at 49N application was measured and calculated as the initial elongation using an Autograph (model AGS-J1 kN manufactured by Shimadzu corporation).

(6) Breaking load

A load was applied in the longitudinal direction of the steel cord using an Autograph (model AGS-H10 kN manufactured by Shimadzu corporation), and the load applied to the steel cord at the time of breakage was defined as a breaking load.

(7) Impact absorption index

Using the charpy impact test apparatus shown in fig. 5, a charpy impact value was measured by a charpy impact test, and an impact absorption index was calculated from the measured charpy impact value.

Specifically, charpy impact tests were performed under the same environment for the reference material and the sample to be evaluated. Then, the charpy impact value of the sample to be evaluated was converted into an impact absorption index, which is a ratio to the reference value, with the charpy impact value of the reference material as the reference value (100%).

In experimental examples 2 to 11, the steel cord produced in experimental example 1 was used as a reference (reference cord).

In experimental examples 13 to 16, the steel cord produced in experimental example 12 was used as a reference (reference cord).

In experimental examples 18 to 26, the steel cord produced in experimental example 17 was used as a reference (reference cord).

(Experimental example)

Steel cords of the following experimental examples were produced and evaluated as described above. In addition, all of the steel cords were produced by twisting bare wires using a bunching twisting machine so that the twisting pitch was 17.0 mm.

Examples 3 to 10, 13 to 15 and 18 to 25 are examples, and comparative examples 1, 2, 11, 12, 16, 17 and 26 are comparative examples.

(Experimental examples 1 to 11)

As experimental examples 1 to 11, steel cords having different void ratios and containing bare wires of 4 were produced and evaluated.

[ Experimental example 1]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In addition, all of the 4 bare wires used were bare wires in which no bent portion and no bent portion were formed.

The evaluation results are shown in table 1.

[ Experimental example 2]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, as 1 bare wire out of 4 bare wires, a bare wire in which a bent portion and a non-bent portion are formed so that the bending height h is 0.25mm and the repetition pitch P between the bent portion and the non-bent portion is 10mm was used. In addition, the remaining 3 bare wires used were bare wires in which the bent portion and the non-bent portion were not formed. The evaluation results are shown in table 1.

[ Experimental example 3]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, as 1 bare wire out of 4 bare wires, a bare wire in which a bent portion and a non-bent portion are formed so that the bending height h is 0.30mm and the repetition pitch P between the bent portion and the non-bent portion is 10mm was used. In addition, the remaining 3 bare wires used were bare wires in which the bent portion and the non-bent portion were not formed. The evaluation results are shown in table 1.

[ Experimental example 4]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 10 mm. The evaluation results are shown in table 1.

[ Experimental example 5]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.27mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 6]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 7]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.28mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 8]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 12 mm. The evaluation results are shown in table 1.

[ Experimental example 9]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 8 mm. The evaluation results are shown in table 1.

[ Experimental example 10]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 11]

A steel cord having a twisted structure of 1X 4 was produced using 4 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 4 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 8 mm. The evaluation results are shown in table 1.

[ Table 1]

The relationship between the void ratio and the impact absorption index of experimental examples 1 to 11 shown in table 1 is shown in fig. 10, and the relationship between the area of the central region and the impact absorption index is shown in fig. 11.

From the results shown in fig. 10, it was confirmed that the values of the impact absorption index with respect to the void ratio in each experimental example were distributed on an approximate curve, and the impact absorption index peaked at a void ratio of 49.6%.

Thus, it was found that there was a correlation between the void ratio and the impact absorption index, and it was confirmed that the impact resistance was improved by selecting the void ratio. Further, it was confirmed that the impact absorption index was higher than 100% and the impact resistance was excellent by setting the porosity to 37% or more and 60% or less.

From the results shown in fig. 11, it was confirmed that the impact absorption index with respect to the area of the central region in each experimental example was also distributed on an approximate curve, and the area of the central region was 0.220mm²The left and right sides obtain peaks.

Thus, it can be seen that there is also a correlation between the area of the central region and the impact absorption index, and it can be confirmed that the impact resistance is improved by selecting the area of the central region. Further, from the evaluation results of the steel cords of experimental examples 1 to 11 in which the number of bare wires included was 4, it was confirmed that the area of the central region was 0.16mm²Above and 0.32mm²Hereinafter, the impact absorption index is higher than 100% and the impact resistance is excellent.

(Experimental examples 12 to 16)

Next, as experimental examples 12 to 16, steel cords containing bare wires having 3 bare wires and different void ratios were produced and evaluated in the same manner as in experimental examples 1 to 11.

[ Experimental example 12]

A steel cord having a twisted structure of 1X 3 was produced using 3 bare wires having a bare wire diameter of 0.370 mm. In addition, all of the 3 bare wires used were bare wires in which no bent portion and no bent portion were formed.

The evaluation results are shown in table 1.

[ Experimental example 13]

A steel cord having a twisted structure of 1X 3 was produced using 3 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 3 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 14]

A steel cord having a twisted structure of 1X 3 was produced using 3 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 3 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 15]

A steel cord having a twisted structure of 1X 3 was produced using 3 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 3 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 10 mm. The evaluation results are shown in table 1.

[ Experimental example 16]

A steel cord having a twisted structure of 1X 3 was produced using 3 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 3 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 10 mm. The evaluation results are shown in table 1.

The relationship between the void ratio and the impact absorption index of experimental examples 12 to 16 shown in table 1 is shown in fig. 12, and the relationship between the area of the central region and the impact absorption index of experimental examples 12 to 16 is shown in fig. 13.

From the results shown in fig. 12, it was confirmed that the values of the impact absorption index with respect to the void ratio in each experimental example were distributed on an approximate curve, and the impact absorption index peaked when the void ratio was about 52.5%.

From the results shown in fig. 13, it was confirmed that the impact absorption index with respect to the area of the central region of each experimental example was also distributed on an approximate curve, and the area of the central region was 0.10mm²The left and right sides obtain peaks.

Thus, it can be seen that there is also a correlation between the area of the central region and the impact absorption index, and it can be confirmed that the impact resistance is improved by selecting the area of the central region. Further, from the evaluation results of the steel cords of experimental examples 12 to 16 in which the number of bare wires contained was 3, it was confirmed that the area of the central region was 0.07mm²Above and 0.13mm²The impact absorption index is 100% or less, and the impact resistance is excellent.

(Experimental examples 17 to 26)

Next, as experimental examples 17 to 26, steel cords having 5 bare wires and different void ratios were produced, and evaluated in the same manner as in experimental examples 1 to 11.

[ Experimental example 17]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In addition, as the bare wire, a bare wire in which a bent portion and a non-bent portion are not formed is used.

The evaluation results are shown in table 1.

[ Experimental example 18]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, as 3 bare wires out of 5, bare wires in which the bent portion and the non-bent portion were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 14mm were used. In addition, the remaining 2 bare wires used were bare wires in which no bent portion and no bent portion were formed. The evaluation results are shown in table 1.

[ Experimental example 19]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.28mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 20]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 21]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 12 mm. The evaluation results are shown in table 1.

[ Experimental example 22]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 14 mm. The evaluation results are shown in table 1.

[ Experimental example 23]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 12 mm. The evaluation results are shown in table 1.

[ Experimental example 24]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.25mm and the overlapping pitch P between the bent portion and the non-bent portion was 10 mm. The evaluation results are shown in table 1.

[ Experimental example 25]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.24mm and the overlapping pitch P between the bent portion and the non-bent portion was 8 mm. The evaluation results are shown in table 1.

[ Experimental example 26]

A steel cord having a twisted structure of 1X 5 was produced using 5 bare wires having a bare wire diameter of 0.370 mm. In this case, all of the 5 bare wires were used in which the bent portions and the non-bent portions were formed so that the bending height h was 0.30mm and the overlapping pitch P between the bent portion and the non-bent portion was 8 mm. The evaluation results are shown in table 1.

The relationship between the void ratio and the impact absorption index of experimental examples 17 to 26 shown in table 1 is shown in fig. 14, and the relationship between the area of the central region and the impact absorption index is shown in fig. 15.

From the results shown in fig. 14, it was confirmed that the values of the impact absorption index with respect to the void ratio in each experimental example were distributed on an approximate curve, and the impact absorption index peaked when the void ratio was about 42.0%.

Thus, it was found that there was a correlation between the void ratio and the impact absorption index, and it was confirmed that the impact resistance was improved by selecting the void ratio. Further, it was confirmed that the impact absorption index was higher than 100% and the impact resistance was excellent by setting the porosity to 33% or more and 55% or less.

From the results shown in fig. 15, it was confirmed that the impact absorption index with respect to the area of the central region in each experimental example was also distributed on an approximate curve, and the area of the central region was 0.35mm²The left and right sides obtain peaks.

Thus, it can be seen that there is also a correlation between the area of the central region and the impact absorption index, and it can be confirmed that the impact resistance is improved by selecting the area of the central region. Further, from the evaluation results of the steel cords of experimental examples 17 to 26 in which the number of bare wires included was 5, it was confirmed that the area of the central region was 0.24mm²Above and 0.45mm²The following means for absorbing impactThe ratio is 100% or higher, and the impact resistance is excellent.

In addition, it was confirmed from experimental examples 1 to 26 that there was no correlation between the initial elongation, the breaking load which has been conventionally considered to have a large influence on the impact resistance, and the impact absorption index.

Claims

1. A steel cord, characterized in that,

the steel cord has a 1 x 3 structure in which 3 bare wires are twisted,

in a cross section perpendicular to the length direction,

when the area of the maximum circumscribed circle is S1 and the area of the bare wire is S2, the void ratio V represented by the following formula (A) is 37% to 60%,

V(％)＝(S1-nS2)/S1×100…(A)，

the area of a region surrounded by a straight line connecting the centers of the bare wires adjacent in the circumferential direction of the maximum circumscribed circle is 0.07mm²Above and 0.13mm²In the following, the following description is given,

at least 1 of the 3 bare wires has a bending part and a non-bending part repeatedly along a length direction.

2. A steel cord according to claim 1,

an impact absorption index, which indicates a ratio of the charpy value to a reference value of the 1 × 3 steel cord having the porosity V of 35.8%, is greater than 100% and not greater than 110%.

3. A steel cord according to claim 1,

all of the 3 bare wires have a bent portion and a non-bent portion repeatedly in the longitudinal direction.

4. A steel cord according to claim 1,

when the height from the flat surface to the bent portion on the side farther from the flat surface when the bare wire is placed on the flat surface is defined as a bending height,

the bending height is more than 0.10mm and less than 0.30 mm.

5. A steel cord according to claim 1,

the repeated interval between the bent portion and the non-bent portion is 5.0mm or more and 30.0mm or less.

6. A steel cord according to claim 1,

the initial elongation at 49N application is 0.06% or more and 0.35% or less.

7. A steel cord according to claim 1,

the diameter of the bare wire is 0.22mm to 0.42 mm.

8. A steel cord, characterized in that,

the steel cord has a 1 x 4 structure in which 4 bare wires are twisted,

in a cross section perpendicular to the length direction,

V(％)＝(S1-nS2)/S1×100…(A)，

the area of a region surrounded by a straight line connecting the centers of the bare wires adjacent in the circumferential direction of the maximum circumscribed circle is 0.16mm²Above and 0.32mm²In the following, the following description is given,

at least 1 of the 4 bare wires has a bending part and a non-bending part repeatedly along the length direction.

9. A steel cord according to claim 8,

an impact absorption index, which indicates a ratio of the charpy value to a reference value of the 1 × 4 steel cord having the porosity V of 36.4%, is greater than 100% and 140% or less.

10. A steel cord according to claim 8,

all of the 4 bare wires have a bent portion and a non-bent portion repeatedly in the longitudinal direction.

11. A steel cord according to claim 8,

the bending height is more than 0.10mm and less than 0.30 mm.

12. A steel cord according to claim 8,

13. A steel cord according to claim 8,

the initial elongation at 49N application is 0.06% or more and 0.35% or less.

14. A steel cord according to claim 8,

the diameter of the bare wire is 0.22mm to 0.42 mm.

15. A tire comprising the steel cord of any one of claims 1 to 14.