JPH0663184B2 - Steel cord for rubber reinforcement - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber-reinforced steel cord.

(Prior Art) Steel cords with a small cross-sectional area play an important role as a reinforcing material for rubber products and a reinforcing material for radial tires.

Generally, this steel cord is constructed by twisting multiple fine steel wires plated with brass, which has good adhesion to rubber, and placing a core wire in the center when there are 6 or more wires. As illustrated in, the cross section was made to have a perfect circular shape.

Such a steel cord is used as a reinforcing material for a breaker belt or a carcass of a tire, but it is generally said that the internal pressure and the external pressure applied to the tire are directional. Therefore, since the conventional steel cord has a perfect circular cross-section, the bending characteristic (flexibility), which is a characteristic of the conventional steel cord, does not depend on the direction, which is a problem. There is.

For example, in the breaker belt, it is required to react flexibly to small stones scattered on the road surface (riding comfort) and to have good transverse rupture force in the axle direction. This transverse strength means the ability to firmly grip the road surface (steering stability) when turning a curve. A conventional steel cord having a true circular cross section cannot sufficiently satisfy these characteristics.

Also, when used in a carcass, due to bending with a small curvature when folded back at the bead portion, it becomes susceptible to unfavorable effects such as tire fatigue as a tire cord,
Furthermore, since there is a twist, there is a problem such as poor workability during tire manufacturing.

(Purpose of the present invention) The present invention was developed by research to eliminate the problems of the conventional steel cord for rubber reinforcement as described above,
Its purpose is to show good flexibility in the ground contact direction and appropriate bending strength in the axle direction in the belt, and when used in a carcass, it exhibits favorable bendability in the bead portion. The purpose is to provide this kind of steel cord.

Another object of the present invention is to provide a steel cord of this kind which has no twist in the longitudinal direction of the cord, has good linearity, and has good workability during tire manufacturing.

Another object of the present invention is to provide a steel cord of this type which has the above-mentioned features and is easy to manufacture.

(Structure of the Invention) In order to achieve the above object, the present invention is a modification of the idea that it is desirable that there is no difference in the mechanical characteristics of the cross section perpendicular to the longitudinal direction in the steel cord. Therefore, in a steel cord made of a twisted wire of five or more circular cross-sections, the cross-section perpendicular to the longitudinal direction is flattened (cord thickness / cord width) 0.4 to 0.7 and bent in the X-axis direction and the Y-axis direction. It is configured to have different rigidity.

Each wire constituting the cord may have a true circular cross section, or may have a different shape such as an ellipse or a rectangle. In each case, after twisting 5 or more wires, It is made by compressing from the radial direction with a molding roll or the like.

In principle, the steel cord according to the present invention does not have a core, but in the case of a complex cross-sectional structure composed of a large number of cores, a core material made of an easily deformable material such as synthetic fiber or copper alloy may be provided.

(Examples) Examples of the present invention will be described below with reference to the accompanying drawings.

1 to 3 show an embodiment of a steel cord for rubber reinforcement according to the present invention.

The steel cords of FIGS. 1 and 2 are formed by twisting six copper-plated wires 1, 1 ′ without a core, and the cross section perpendicular to the longitudinal direction is the conventional cord of FIG. As described above, it is not a perfect circular shape, but a flat cross-sectional shape having different bending characteristics in the X-axis direction and the Y-axis direction, generally, an elliptical shape or an oval shape.

In the embodiment shown in FIG. 1, each wire 1 has a substantially circular cross section, but it may be twisted by using a wire 1'which has been previously drawn in an irregular shape as shown in FIG.

FIG. 3 shows a twisted body of six ultrafine wires 1 and a strand 2
6 strands 2 are twisted with a core 3 made of brass or the like having adhesiveness with synthetic fibers or rubber in the center, and a cross section perpendicular to the longitudinal direction is bent in the X-axis direction and the Y-axis direction. It is configured to have different characteristics.

In each of the examples, the flat cross-sectional shape needs to be in a specific range, which means that when the cord thickness is t and the cord width is w in FIG. 1, the flatness ratio represented by t / w is 0.4. Set to ~ 0.7. This is to achieve a good balance of fatigue, riding comfort and steering stability, and the flatness ratio is 0.
When it is 4 or less, the difference in the second moment of area can be made large, but the indentation occurs at the contact portion between the wires to deteriorate the fatigue property, and when the flatness is 0.7 or more, the difference in the second moment of area becomes small and the tire This is because the riding comfort and steering stability when used in a vehicle are not improved.

The steel cord of the present invention is basically a belt-shaped cord in which a cross-sectional shape having different bending characteristics in the X-axis direction and the Y-axis direction is formed over the entire length. The cross-sectional shape portion having different bending characteristics in the X-axis direction and the Y-axis direction and the cross-sectional shape portion having similar bending characteristics in the X-axis direction and the Y-axis direction may be repeated.

The steel cord for rubber reinforcement according to the present invention is a wire 1,
It is obtained by twisting 5 or more 1'and then compression molding. This compression molding is achieved by passing a pair of molding rolls in the final step. The forming roll may be a flat roll or a caliber roll. If the bending characteristics of the steel cord in the X-axis direction and the Y-axis direction are different, the cord thickness / cord width is the roll gap or caliber depth of the forming roll. Can be adjusted by.

Specific examples of the present invention are as follows.

Six brass-plated wires with a diameter of 0.25 mm were twisted in a conventional manner with twist lengths (P) of 7.7 and 11.6, respectively. The diameter of these two steel cords is 0.75 mm. The cord was compression-molded with one pass between a pair of molding rolls.

The obtained cord is elliptical, and when the twist length is 7.7, the cord thickness is 0.576 mm, the cord width is 0.918 mm, and the flatness (cord thickness / cord width) is about 63%. Cord thickness for twist length 11.6
0.533mm, cord width 0.909mm, flatness (cord thickness / cord width) about 60%. And the cutting strength of the former is 75.9 Kg
f, the latter was 75.4Kgf.

As described above, the steel cord of the present invention has a cross-sectional shape with different bending characteristics in the X-axis direction and the Y-axis direction, and in the illustrated one, the bending stress (repulsive force) in the Y-axis direction is smaller than that in the X-axis direction. . According to an experiment by the present inventor, the cord was fixed at a position of a length of 40 mm, the free ends were bent to 22.5 ° and 45 ° in the directions of the X axis and the Y axis, respectively, and the repulsive force was measured by an autograph. Repulsion index (X-axis direction / Y-axis direction x 10
0) was about 121 at a bending angle of 22.5 ° and about 135 at a bending angle of 45 °, indicating that bending in the Y-axis direction was significantly easier than in the X-axis direction.

Therefore, if the steel cord of the present invention is used for a belt of a tire, the steel cord is easily displaced in response to an external force due to projections such as pebbles scattered on the road surface, but the steel cord is inclined at a constant angle with respect to the tread. Since they are arranged in rows, they exhibit sufficient transverse rupture force against an external force in the axle direction, and can maintain a stable shape as a tire.

When used in a carcass, it can reduce the radius of curvature when each cord ply descends from both sides and wraps around the bead wire and folds back upwards, thus reducing the undesired effects on the steel cord. In addition, the bending process becomes easy.

Moreover, since the cross-sectional shape having different bending characteristics in the X-axis direction and the Y-axis direction is formed by compression molding after twisting, there is no twist,
Shows good linearity. Therefore, the work of rubberizing the steel cord called calendering is facilitated, and twisting of the rubber-coated steel cord layer caused by rotational displacement of the steel cord embedded in the rubber can be prevented. . Therefore, the tire manufacturing work can be facilitated.

The steel cord according to the present invention has various embedding methods such that the X-axis direction is oriented in the rubber thickness direction, the Y-axis direction is oriented in the rubber thickness direction, or even obliquely depending on the purpose of use and conditions. Is adopted. Further, of course, it may be used in combination with a conventional steel cord having a perfect circular cross section.

(Effect) When using the steel cord for rubber reinforcement of the present invention described above, in a steel cord composed of a twisted body of five or more circular cross-sections, the flatness (cord thickness / cord width) of the cross section perpendicular to the longitudinal direction is obtained. ) 0.4 to 0.7, so that the bending rigidity differs in the X-axis direction and the Y-axis direction,
Since it can exhibit appropriate flexibility (comfortability) and bending resistance in the axle direction (steering stability), it can be manufactured by compressing with a forming roll etc. after twisting using a circular wire, so a simple process The excellent effect that it can be manufactured at low cost is obtained.

[Brief description of drawings]

1 to 3 are sectional views showing an embodiment of a rubber reinforcing steel cord according to the present invention, and FIG. 4 is a sectional view of a conventional steel cord. 1,1 ′ …… Wire

Claims (1)

[Claims] 1. A steel cord made of a twisted wire of five or more circular cross-sections, wherein the flatness (cord thickness / cord width) of the cross section perpendicular to the longitudinal direction is 0.4 to 0.7 and the X-axis direction and the Y-axis direction. Steel cord for rubber reinforcement, which is characterized by different bending rigidity.