JP4097812B2 - Steel cords for reinforcing rubber articles and pneumatic tires - Google Patents

Description

【００２２】
【発明の効果】
この発明によれば、繰り返しの圧縮変形を受ける苛酷な条件下での使用においても、十分な耐久性能を発揮し得るスチールコードを提供できる。従って、このスチールコードをタイヤのベルトの少なくとも最外側に適用することによって、従来、特に溝底に集中していた圧縮歪みに対する耐久性が大幅に改善され、耐久性に優れるタイヤの提供が可能になる。
【図面の簡単な説明】
【図１】この発明に従う、撚り構造５×（１＋４）構造コードの断面図である。
【図２】この発明に好適のタイヤを示す断面図である。
【符号の説明】
１ ストランド
２ コア
３ シース
４ カーカス
５ ベルト
６ トレッド
７ ラグ溝[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel cord used as a reinforcing material for rubber articles such as pneumatic tires and industrial belts, and particularly intends to improve durability.
[0002]
[Prior art]
Pneumatic tires that are typical examples of rubber articles, especially tires for construction vehicles, are mounted on large dump trucks used at large civil engineering work sites and ore mining sites, for example, and are severely subjected to heavy loads on rough surfaces. Operating conditions are imposed. This type of tire generally has a structure in which a carcass straddling a toroidal shape between a pair of bead cores is used as a skeleton, and a multilayer belt is disposed on the outer side in the radial direction of the carcass for reinforcement.
[0003]
[Problems to be solved by the invention]
The above-mentioned construction vehicle tires run under heavy loads, particularly on rough uneven surfaces, and as a result, the tread is subjected to large deformations. As a result, the bottom surface of grooves such as lug grooves formed on the tread A large compressive force is repeatedly applied. Then, when a large compressive force is applied to the bottom surface of the groove formed in the tread, a compressive strain is generated in the belt layer on the tread side (outside) of the belt, and this compressive strain is repeatedly generated by a long running of the tire. In particular, fatigue is accumulated in the cord of the belt layer on the tread side, and the cord breaks. Due to this cord breakage, the tire strength is reduced, and if a protrusion such as a rock is stepped on, the tire may be destroyed.
[0004]
Accordingly, the object of the present invention is to propose a steel cord capable of exhibiting sufficient durability performance together with a pneumatic tire excellent in durability even when used under severe conditions that are subjected to repeated compression deformation as described above. And
[0005]
[Means for Solving the Problems]
The steel cord that constitutes the belt of a tire for a construction vehicle generally employs a so-called double twist structure in which a plurality of strands made of a plurality of steel filaments are twisted together. Above all, the outermost layer is a strand with a layer twist structure in which a plurality of filaments are twisted around a core of one or a plurality of filaments so as to follow the tread deformation when a projection is stepped on during travel. A 1 × n-structured, double-twisted structure cord obtained by twisting a plurality of cords is preferably used particularly in the outermost layer of a belt for construction vehicle tires.
[0006]
According to the inventors' research, it was found that when the above-mentioned double twisted structure cord is subjected to compressive strain, the sheath filament of each strand breaks first, that is, a large compressive strain occurs in the sheath filament of the strand. . When the sheath filament breaks, the remaining filament is also subjected to a large compressive strain and breaks one after another, resulting in a cord break. Furthermore, the cord breaking process occurs one after another in another cord, and the cord is successively broken in the outermost belt layer of the belt, resulting in a decrease in tire strength. If the tire in this state is subjected to a large impact, for example, over a protrusion, the risk of the tire being damaged increases.
[0007]
Here, it has been clarified that the breakage in the cord of the double twist structure is caused by the fact that a large compressive strain is generated in the sheath filament of the strand and the filament is preliminarily broken. Therefore, as a result of intensive investigations on means for suppressing large compressive strain generated in the sheath filament, it has been found that it is extremely effective to improve the fatigue resistance of the cord to properly define the twist angle of the sheath filament. It was.
[0008]
In the belt layer arranged on the outermost side of the belt, the gap between the filaments of the cord is securely made of rubber so that moisture entering from the cut scratches received on the tire does not enter the inside of the cord and cause corrosion. It is also important to have a filament arrangement that can be buried in.
[0009]
The present invention is based on the above findings.
That is, the present invention is obtained by twisting 4 to 5 strands obtained by twisting a core made of one steel filament and a sheath formed by arranging 4 to 5 steel filaments around the core. comprising a steel cord, the ratio d _s / d _c the diameter d _s of the filaments constituting the filament diameter d _c and the sheath of the core is in the range of 1.00 to 1.75, the twist direction and code of the sheath in each strand A steel cord for reinforcing rubber articles characterized in that the twisting direction α of the sheath in each strand with respect to the cord axis is 30 to 52 °, the twisting directions being the same, and the following formula (1).
Α = α ₁ + α ₂ −90 ---- (1)
Here, α ₁ = tan ⁻¹ {P ₁ / π · (d _c + d _s )}
α ₂ = tan ⁻¹ {P ₂ / π · (A−d _c −2d _s )}
Where P ₁ : Strand twist pitch (mm)
P ₂ : Cord twist pitch (mm)
A: Cord diameter (mm)
The twist angle α is an average value in the longitudinal direction of the cord.
[0010]
Further, the present invention provides a pneumatic tire having a carcass extending in a toroidal shape between a pair of bead portions and having a plurality of layers of belts on a radially outer side of the carcass. This is a pneumatic tire characterized by applying a steel cord.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Now, the steel cord for reinforcing rubber articles according to the present invention is limited to 4-5 strands m and 4-5 sheath filaments n when the basic structure is mx (1 + n). Because when m is 3 or less, when used as a cord of the outermost belt of a huge tire such as a tire for construction vehicles, it is necessary to make the filament thicker in order to obtain a predetermined tire strength. When it gets thicker, local bending between the filaments when the cord is bent and deformed by stepping on the protrusion increases the strain on the filament surface, and the cord breaks easily. On the other hand, when m is 6 or more, it becomes difficult to manufacture the strands in a concentric circle, and the twisting property is deteriorated, so that the breaking load of the cord is reduced.
[0012]
In addition, the core in the strand is made into one filament, but in order for the rubber to penetrate into the cord, it is inevitably one or two, but if it is two, the strand is bundled to make the cord In the process, twist failure is likely to occur due to the difference in the amount of twist and shrinkage between the core and the sheath.
Next, when the core and sheath diameters are within the scope of the invention to be described later, if the number of filaments n in the sheath is 3 or less, the gap between the filaments in the sheath becomes too large and the twisted shape becomes unstable. If the number is 6 or more, a sufficient gap for the rubber to enter cannot be secured.
[0013]
A typical example of a cord having a basic structure of m × (1 + n) according to the present invention is shown in cross section in FIG. This cord is a twisted structure 5 × (1 + 4) formed by twisting five strands 1 having a 1 + 4 structure, and each strand 1 forms a core 2 with one steel filament, and around these cores 2. The sheath 3 is formed by four steel filaments arranged adjacent to each other.
[0014]
Furthermore, in the cord of the present invention, the direction in which m strands are twisted, that is, the cord twist direction, needs to be the same as the direction in which the filaments of the sheath in each strand are twisted, that is, the strand twist direction. Because, if the twisting direction of the cord and the twisting direction of the strand are different, the filaments of the strands are in point contact with each other. Therefore, the loss of the cord breakage when the total loss of twisting loss, that is, the filament breakage is 100% This is because the rate increases, and even if the breaking load of the cord is increased, it cannot be exhibited.
[0015]
Furthermore, the ratio d _s / d _c the diameter d _s of the filaments constituting the filament diameter d _c and the sheath of the core in the range of 1.00 to 1.75. This is because, it is less than d _s / d _c is 1.00, the difference in twist contraction amount between the core and the sheath in the manufacturing process of a code bundled strands, core will jump out, whereas d _s / d _c exceeds 1.75 This is because the arrangement of the sheath filaments is uneven and the twisting property of the cord becomes non-uniform.
[0016]
Finally, it is important to set the twist angle α of the sheath in each strand with respect to the cord axis, which is obtained by the above formula (1), to 30 to 52 °. That is, in order to make α less than 30 °, the twist pitch must be very short, so it is indispensable to strongly process the filament in the cord manufacturing process, and troubles such as disconnection are likely to occur, On the other hand, when α exceeds 52 °, the fatigue life is shorter than the 4 × (1 + 5 × 0.25) steel cord, which is often used in the outermost belt layer of construction vehicle tires. There is a risk of destruction.
[0017]
Next, the above-described cord is used for reinforcing a carcass by applying a ply formed by arranging a plurality of cords in parallel to each other and embedded in a rubber sheet to a tire belt. For example, a belt structure shown in FIG. 2 can be advantageously adapted to the conventional pneumatic tire for construction vehicles. Here, in the figure, reference numeral 4 denotes a carcass 5 straddling a toroid between a pair of bead cores (not shown) and wound around the bead cores from the inside to the outside of the tire. A layer structure, a belt of 6 layers in the illustrated example, 6 is a tread disposed on the belt, and 7 is a lug groove.
[0018]
The belt 5 is inclined with respect to the ply cord of the carcass 2, and a plurality of layers of rubber covering layers made of a plurality of steel cords arranged preferably at an inclination angle of 50 to 80 °, and the steel cords cross each other between the layers. It has a structure that is superposed in an arrangement. And the cord according to this invention is applied as the steel cord of at least the outermost belt layer.
[0019]
【Example】
The durability of the steel cord having the structure shown in Table 1 was measured. That is, for each cord, a fatigue test is performed to repeatedly generate a predetermined compressive strain in the cord axis direction, and the number of repeated occurrences of compressive strain until any one filament constituting the cord breaks is measured. did. The measurement results are also shown in Table 1.
[0020]
In addition, each steel cord shown in Table 1 is applied to the outermost belt ply of a radial tire for off-road tires with tire size: 40.00 R57: 13.1 / 5cm, and the tire is filled with an internal pressure of 7.0kgf / cm ² Then, after running on the ground and the tread was completely worn out, the tire was dissected, 50 cords were taken out, the number of filament breaks was examined, and the result was an index when the tire using the cord of Comparative Example 1 was taken as 100 It shows with. Among the remaining belt layers, 7 × (3 + 9 × 0.32 mm) steel cord was applied to the middle two layers, and 7 × (3 + 9 × 0.23 mm) steel cord was applied to the innermost three layers.
[0021]
[Table 1]

[0022]
【The invention's effect】
According to the present invention, it is possible to provide a steel cord capable of exhibiting sufficient durability performance even when used under severe conditions that undergo repeated compressive deformation. Therefore, by applying this steel cord to at least the outermost part of the tire belt, the durability against compression strain that has been concentrated mainly on the groove bottom in the past has been greatly improved, and it is possible to provide a tire with excellent durability. Become.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a twisted structure 5 × (1 + 4) structure cord according to the present invention.
FIG. 2 is a cross-sectional view showing a tire suitable for the present invention.
[Explanation of symbols]
1 Strand 2 Core 3 Sheath 4 Carcass 5 Belt 6 Tread 7 Lug Groove

Claims (2)

A steel cord formed by twisting 4 to 5 strands obtained by twisting together a core made of one steel filament and a sheath in which 4 to 5 steel filaments are arranged around the core. ,
In the range of the ratio d _s / d _c the diameter d _s of the filaments constituting the filament diameter d _c and the sheath of the core is from 1.00 to 1.75, it is the same lay direction of twist direction and code of the sheath in each strand, A steel cord for reinforcing rubber articles, characterized in that the twist angle α of the sheath in each strand with respect to the cord axis, determined by the following formula (1), is 30 to 52 °.
Α = α ₁ + α ₂ −90 ---- (1)
Here, α ₁ = tan ⁻¹ {P ₁ / π · (d _c + d _s )}
α ₂ = tan ⁻¹ {P ₂ / π · (A−d _c −2d _s )}
Where P ₁ : Strand twist pitch (mm)
P ₂ : Cord twist pitch (mm)
A: Cord diameter (mm) The pneumatic tire according to claim 1, wherein a carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and a plurality of belts are provided on a radially outer side of the carcass, and at least an outermost layer of the belt. Pneumatic tire characterized by applying cord.

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