JPS6241338A - Steel cord for reinforcing rubber article - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a steel cord used as a reinforcing material for molded rubber articles such as pneumatic tires and industrial belts.

(Conventional technology and problems) Conventionally, it has been thought that penetration of rubber into the interior of the cord is effective mainly to improve the corrosion fatigue resistance of steel cords, and a twisted structure has been developed to obtain sufficient penetration of rubber. Many structures (referred to as rubber penetration structures) have been devised. However, such as the carcass ply and belt layer of truck bus or light truck tires, there are two or eight layers.
For twisted cords, it is extremely difficult to cause the rubber to completely penetrate into the inner layer of the cord, and in such cords, even the rubber penetration structure does not significantly improve the corrosion fatigue resistance of the cord.

On the other hand, as a method to improve the corrosion fatigue resistance of multilayer twisted cords, the contact area between the filaments of the inner layer (core) and outer layer (sheath) is increased by creating a compact structure in which each layer has the same twist direction and twist pitch. It is said that this is effective.

However, when a cord is constructed using filaments with a wire diameter equal to that gap (a so-called normal compact cord), when the cord is pulled under tension, a large contact pressure is generated between adjacent filaments in the outer layer, causing The filament breaks early due to fretting.

As a result, the breaking life of the cord is lower than that of a normal layer-twisted cord having a different twist pitch.

In addition, in order to reduce the contact pressure between adjacent filaments in R in the normal compact cord, it is necessary to
It was found that it is only necessary to make the thickness slightly thinner than that of the inner layer, and that the effect of increasing the contact area between the inner layer and the outer layer is exhibited, and the corrosion fatigue resistance is improved.
No. 60-85216.

Generally, when a steel cord is running on a tire, the filament cross-sectional area of the steel cord decreases due to fretting wear, and the strength of the cord decreases. At that time, if the cross-sectional area of only some filaments in the cord is significantly reduced, that filament is likely to break due to impact tension or repeated bending. Once a filament breaks, the tensile stress in other filaments increases, promoting fatigue failure of the cord. Therefore, in order to increase the durability of the cord, it is necessary to prevent some of the filaments within the cord from breaking prematurely, and it is desirable that the strength reduction of the filaments within the cord be uniform.

Based on this premise, the present inventors investigated the decrease in filament strength due to tire running on cords with a twisted structure of 1 x 12 and stabilized by wrapping the cords with spiral wrapped filaments. Compared to each filament of the coaxial layer contacting both the mutually adjacent filaments of the inner sheath i.e. the inner layer steel filaments within the (core) and outer layer (sheath).
It was discovered that the strength of the outer sheath filament, that is, the filament of the remaining coaxial layer, was extremely reduced, and that the main cause of the strength loss was fretting wear with the spiral. And the strength reduction of the outer sheath is usually greater than that of the 3+9 cord sheath. This phenomenon occurs in the case of the normal compact cord shown in Figure 1, in which all the constituent filaments have the same diameter, that is, in the case of the filament of the same wire diameter, and in the case of a part of the sheath or all of the sheath as shown in Figure 2. A similar problem occurs in improved compact cords in which the filament is made slightly thinner than the core. Figure 1 shows a cross section of a normal compact cord, and Figure 2 shows a cross section of an improved compact cord. In each figure, a core 1 is formed by steel cords indicated by cross hatching, and adjacent cores 1 are formed around these cores 1. A sheath is formed by nine arranged steel cords, and in the normal compact cord, they all have the same diameter as each steel filament in core 1, and in the improved compact cord, they have a slightly smaller diameter than the filaments in core 1, and in addition, The filaments marked with diagonal lines in the figure that are in common contact with two of the steel filaments are inner sheath filaments 2, the remaining filaments are outer sheath filaments 3, and 4 is a wrapped filament made by wrapping the cord in a spiral manner. be.

As mentioned above, in a compact cord with a twist configuration of 1 x 12, it remains a problem to reduce the 7 retting wear between the wrap filament and the outer sheath filament, and to prevent a decrease in the strength of the outer sheath filament. There is.

(Means to Solve the Problems) The present invention provides a 1×12 compact structure cord in which the inner layer and outer layer are twisted in the same direction and the twist pitch is equal, and the Vickers hardness is 60% higher than that of the filament material of the cord body. This is based on the knowledge that by using a wrap filament made of a soft metal material of ~90%, it is possible to suppress a decrease in strength due to retting of the outer sheath filament with the wrap filament.

That is, in a steel cord made of steel filaments for reinforcing rubber articles according to the present invention, the cross section has densely overlapped polygonal contours that are uniform in the longitudinal direction.
As a spiral wrapped filament in the outer layer of the cord,
V with a Vickers hardness of 60 to 90%, preferably 70 to 85%, of the cord body! O (Function) Non-uniformity in the strength reduction of the filament of the compact cord, especially the extreme strength reduction of the outer sheath filament while the tire is running. is due to its unique geometric structure. In other words, in a cord with a normal twisted structure 3+9, the cross-sectional shape is close to a circle, so the contact pressure between the sheath filament and the spiral wrap filament that wraps it is equal on each filament, but with a twisted structure 1X1
In cord No. 2, the cross-sectional shape of the cord is close to a triangle, and the contact pressure between the sheath filament and the wrap filament is not equal on each filament. It will be lower.

Furthermore, by using a material softer than the filament of the cord body for the metal material of the wrap filament that wraps the compact cord, fretting wear due to contact between the outer sheath filament and the spiral occurs on the spiral side. This suppresses a decrease in the cross-sectional area and strength of the outer sheath filament. A similar effect can be obtained when a flat spiral wire is wrapped instead of a spiral with a circular cross section.

In the present invention, the Vickers hardness of the metal material constituting the spiral wrap filament is set to 60 to 60 to that of the cord body.
90%, preferably in the range of 70-85%. If the Vickers hardness exceeds 90% of the main body ratio, the effect is not achieved, fretting wear cannot be suppressed, and the strength of the outer sheath filament is significantly reduced. On the other hand, if the Vickers hardness is less than 60% of the main body ratio, the 7 retting wear on the wrapped filament side of the compact cord of the present invention cannot be reduced, and the wrapped filament is likely to break. Breakage of the wrapped filament is undesirable because its end becomes a core of nearby rubber breakage and adhesion failure, causing separation.

Regarding wrap filament, please refer to Special Publication No. 55-441.
In order to prevent damage to steel tires, Japanese Patent Publication No. 67 states that ``a metal wire having a Vickers hardness of steel wire of 14 or less is wrapped around the outer periphery of a steel tire cord,'' and Japanese Patent Application Laid-Open No. 60-84689 The official bulletin states, ``The hardness of the envelope is significantly lower than the ms of the reinforced cord.''
Contains the reinforcement code. In the former case, the Vickers hardness of the wrapped filament relative to the main body wire is 50% or less, and in the latter case, it is 80 to 60%, preferably 30 to 5.
However, these are insufficient to improve the fatigue resistance and strong retention properties of the compact cord of the present invention.

(Example) The present invention will be explained below with reference to Examples and Comparative Examples.

Examples 1-4. Comparative Examples 1 to 4 Eight types of tires of the sizes shown below were manufactured using prototype cords with the hardness of the spiral material changed as shown in Table 1 for the carcass ply, and were run on drums according to the evaluation method below. The decrease in filament strength and spiral fracture were investigated, and the results obtained are also listed in Table 1. In addition, the tire of Comparative Example 1 in Table 1 has a carcass ply structure in which the number of steel filaments is the same (3 + 9 + 1 p).
A The tires of Comparative Examples 2 and 8 of A2 to 7, Examples 1 to 8, and Comparative Example 4 had carcass plies having the structure lX shown in FIG.
A compact cord having a 12+1 steel filament arrangement was used, and the Example 4 tire with a flatness of 8 used a similar compact cord using a flattened spiral wire for the spiral.

Tire size: 1000 R2014PR (radial tire for rack pass) Number of carcass impressions: 15.2 pieces/2, 5 cta Drum running conditions: aob, 'h Internal pressure: 7.25'19f/Cf12 J
IS 100% load However, the hardness of the spiral material was reduced by changing the surface loss ratio during final wire drawing and by using a low carbon material.

Evaluation method (a) Decrease in filament strength After running the tire on a drum for 100,000 times, the cord was taken out, the strength of the filament was measured, and the strength decrease rate was calculated using the following formula: For cord structure 8+9 cords, average of 9 cords. value, 1
Regarding the x12 Funbakuto cord, the average values for the six outer sheaths and the three inner sheaths are shown in the table.

(b) Spiral destruction After running, the cord was examined to see if there was any spiral breakage.

(Effects of the Invention) As explained above, in the steel cord of the present invention, the Vickers hardness of the spile material in the compact cord is in the range of 60 to 90% of that of the cord main filament, thereby reducing the 7 retting wear of the outer sheath. This has the effect of significantly reducing the reduction in strength.

[Brief explanation of the drawing]

FIGS. 1 and 2 are respectively cross-sectional views of a continuous cord with a twist structure of 1.times.12+1. 1... Core 2... Inner sheath filament 8... Outer sheath filament 4... Spiral wrap filament Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. Consisting of 12 steel filaments twisted in the same direction and at the same twisting pitch of the steel filaments of the inner layer and outer layer, densely packed polygonal contours with a uniform cross section in the longitudinal direction In a steel cord with a layered layer, the outer layer of the cord is a spiral wrapped filament with a Vickers hardness of 60 to 9 that of the cord body.
A steel cord for reinforcing rubber articles, characterized in that it is wrapped with a filament made of a metal material in the range of 0%. 2. The Vickers hardness of the metal material above is 70 for the cord body.
A steel cord for reinforcing rubber articles according to claim 1, wherein the steel cord is in the range of 85%.