JPH044163B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to improvements in steel cords for reinforcing tires, which can be used in carcass plies, cheerers, belts, etc., particularly in radial tires. [Prior Art] Conventionally, as this type of steel cord, a 2+7 structure shown in FIG. 3, a 3+9 structure shown in FIG. 4, or a 1×12 structure shown in FIG. 5 have been used. [Problems to be Solved by the Invention] However, in the steel cord 3 with the 2+7 structure shown in FIG. The cross-sectional parts arranged in a vertical line (Fig. 3) and the cross-sectional parts arranged in a horizontal line (Fig. 3 A) appear in the longitudinal direction, and due to the twisted structure, this structure occurs every 1/4 pitch, There will be parts on the same cord that have different bending stiffness, and when applied to tires, especially those shown in Figure 3 A, which have soft bending stiffness.
Concentrated fatigue failure occurs in the cross-sectional area in that line shown in . In addition, as shown in the figure, the side element wire 5 constituting the side 7 tends to fall inward from the circumscribed circle of the core 6 due to its structure, so the side element wire 5 that constitutes the side 7 tends to fall inward from the circumscribed circle of the core 6. As a result of the line 5a sinking into the position indicated by the solid line, the difference in bending stiffness between the vertical and horizontal cross sections became even more remarkable, resulting in a major problem in fatigue resistance. In addition, when embedded in rubber, all the wires in this structure are covered with rubber, making it difficult for air pockets mixed in during tire molding to travel inside the steel cord and disperse to the outside, resulting in air pockets remaining. However, when the tires were manufactured as they were, there was a problem that they were prone to early failure due to this when the tires were running. On the other hand, steel cord 3 with 3+9 structure,
On the other hand, as shown in FIG. 4, since the gap between the side strands 5 is extremely small, the penetration of rubber into the inside of the cord is insufficient, resulting in the phenomenon that the lateral strands 5 come into contact with each other and wear out. This caused a problem in that fatigue resistance deteriorated. In addition, as shown in Fig. 5, a steel cord with a 1 x 12 structure consists of 12 strands of the same diameter twisted in the same direction.
Since the strands are twisted at the same pitch, the side strands 5 fit into the valleys of the core strands, which prevents rubber from penetrating and causes the core strands 4 to easily come out while the tire is running. As described above, none of the conventionally constructed steel cords satisfies both the requirements of uniformity of bending stiffness and penetrability of rubber throughout the cord in a well-balanced manner. Therefore, the purpose of this invention is to eliminate bending rigidity changes due to changes in cross-sectional structure that occur at certain pitches in the longitudinal direction of steel cords, as in the past, and to ensure that rubber penetration is also appropriate. Furthermore, it is an object of the present invention to provide a radial tire reinforced with steel cords, which has a strong structure in which the contact between each strand is relaxed, has excellent shape stability, and has a strong structure. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention aims to solve the problems by specifically specifying each component of the steel cord, such as the cross-sectional structure, the twisting direction, and the twisting pitch. In other words, if the rubber penetrates more than necessary, air pockets generated during tire manufacturing will remain as described above, and if this cord is used in a tire, the tire will be defective and will separate in a short period of time even when the tire is being driven. On the other hand, if the rubber penetration is insufficient, wear occurs due to contact between the strands, fatigue is likely to occur, and rust is likely to occur.
Therefore, it is important to provide a structure that resolves both of these contradictions, and has an internal structure that provides air permeability to the extent that air pockets generated during tire vulcanization do not remain during tire manufacturing, and to the extent that premature failure does not occur. structure and control the intrusion of rubber. Therefore, as a means of achieving this, the diameters of the strands that make up the steel cord are all the same, and 5 more strands than the number of strands are placed around a core made of 3 or 4 strands twisted together. The tire is equipped with at least one of a carcass, a belt, and a cheerer reinforced with a two-layer steel cord twisted in the same direction with a pitch twice that of the core. The reason why the core and side layers are twisted in the same direction is that if the twisting direction is the same, the crossing angle between the core and side strands can be reduced, and the contact pressure between the core and side strands can be reduced. This is because it leads to improvement in fatigue resistance. In addition, the structure of twisting at different pitches is because if the core sides are twisted at the same pitch and in the same direction, the side strands will fit into the valleys of the twists of the core, similar to the 3+9 cord cross section shown in Figure 5. This is undesirable because it causes a shortage of rubber to fill the space formed by the core and the sides. When the twist angle of the side strands is equal to the twist angle of the core strands and a load is applied to the cord, each strand shares the stress evenly to increase the strength utilization rate, and the twist angle of the steel cord For reasons of equipment simplification, it is optimal for the twisting pitch of the side strands to be twice the pitch of the core strands. The reason why the core is made up of 3 to 4 strands is that if there are 2 cores, as mentioned above, there will be a difference in bending stiffness in the longitudinal direction, and the air impermeability will cause air to accumulate frequently. It is from. In addition, when there are five cores, the area of the gap formed in the center of the core becomes too large for rubber to enter, and as a result, more air passes through than necessary, making it more likely to rust. Therefore, in this invention, the number of cores is 3 to 4 as a means to maintain appropriate air permeability. In the case of a two-layer steel cord with all strands having the same diameter, the maximum number of strands that can be arranged around a core consisting of n strands can be calculated geometrically, and is calculated as the number of core strands + 6. Become. Normally, a structure in which the number of core strands is +6 has been used for the purpose of increasing the strength per unit area of the cross section surrounded by the circumscribed circle of the steel cord as much as possible and making it compact. When there are three cores, 3 as shown in Figure 4.
It becomes a structure of +9. In the case of the 3+9 structure, as described above, the side wires are close to each other and the space between them is narrow, so there is insufficient penetration of rubber into the steel cord, and the side wires come into contact with each other and wear out, resulting in poor durability. Poor fatigue properties. The steel cord used in this invention has a 3+8, 4+9 structure in which the number of side strands is reduced by one from the core + 6 of the general structure, and gaps are provided between the strands for the rubber to enter without disturbing the spacing. will be adopted. In the case of a steel cord with a core + 4, in which the number of side strands is reduced by 2 from the standard structure, the side strands are concentrated in one place, creating areas where the strands are close together and areas where the strands are large, resulting in poor fatigue resistance. In addition, since the strength per unit area of steel cords is low, in order to maintain the preset tire strength, it is necessary to increase the number of cords to compensate for the decrease in strength, and the number of adjacent steel cords in the reinforcing layer must be increased. As the distance between the cords becomes narrower, there is not enough rubber to relieve the shear stress acting between the steel cord and the surrounding rubber, making separation more likely to occur. Incidentally, in the case of a structure in which the number of side strands is two less than the above-mentioned general structure, the cause of the phenomenon in which the side strands are biased has not been clarified, but it is thought to be as follows. When manufacturing steel cord, pre-shaped strands are twisted together, but in a cord with one fewer strand, adjacent strands interfere with each other and there is no movement in the upper circumferential direction of the core, but when there are two fewer strands, To〓
Because the gap is wide, adjacent strands do not interfere with each other and can easily move in the circumferential direction. Therefore, in the process of pressing a rubber sheet between the parallelly arranged steel cords to form a steel cord reinforcement layer, the strands are As one of the wires moves and the gap becomes larger, it is presumed that the total pressure acting on that part also increases, pushing the strands to the side and concentrating them in one place. [Function] Since the present invention is as described above, the intrusion of rubber into the inside of the steel cord is moderately improved, and unlike the conventional tire, which is based on zero air permeation caused by excessive intrusion of rubber. Poor air accumulation and the resulting separation during short-term running are eliminated, and contact wear between wires due to excessive air permeation, fatigue, and rusting that occur as a result of insufficient rubber penetration are eliminated. Furthermore, since the twisting direction is the same, the contact pressure between the core and side strands is also reduced, reducing fatigue due to abrasion. Furthermore, since the bending rigidity is uniform in the longitudinal direction, extreme fatigue does not occur. In short, during tire vulcanization, there was no problem with air pockets, and the rubber penetrated into the inside of the cord while maintaining ventilation, thereby preventing fatigue and rust, and improving durability. It can be a long-life radial tire. [Examples] Example 1 Four types of steel cords shown in Table 1 were made. A is a steel cord having a core 1 and side 2 layers of 3+8 structure as shown in Fig. 1, B, C,
D is shown in FIG. 4, FIG. 3, and FIG. 6, respectively.
3+9, 2+7, 5 according to conventional example or comparative example
It is a steel cord with a core 6 and side 7 layers of +6 construction. Note that FIG. 2 shows a steel cord with a 4+8 structure, which is a conventional cord in which gaps are provided between side strands.

[Table] The amount of air flowing through the steel cord was measured.
Next, prototype 11R22.5 radial tires were made using the above code for the ply, Example TA, Comparative Example TB,
Performed prescribed tests as TC and TD. The results are as follows. The results are based on the value of comparative example TB.
Expressed as an index of 100.

[Table] As is clear from the table, in the tire according to the example using code A, the steel cord maintains appropriate air permeability and appropriate rubber penetration is obtained, so air during tire manufacturing is There are fewer defects due to pooling, so it has great separation and durability in drum tests, and has excellent fatigue resistance. On the other hand, in the comparative tire TB using code B, the gap between the side strands of the cord is narrow and there is little rubber intrusion, so separation occurs early, and the strength retention ratio decreases due to contact abrasion between the strands. small. The comparative example tire TC using code C had poor uniformity in the drum separation test because the code had some parts with different bending rigidities and lacked uniformity. Codes D and E have a larger number of side wires than the general structure, so the wires are biased,
Comparative tire TD using this tire has insufficient rubber penetration and is inferior in the drum separation test and strength retention ratio, while TE has good rubber penetration, but has low strength and requires a large number of ends. The steel cord is crowded inside the drum, and the drum separation test is inferior. Example 2 Next, the ply material of Example 1 was applied to Cheeha, and a 11R22.5 tire was produced and tested. The results are shown in Table 3.

【table】

[Table] As is clear from the table, tire CC uses steel cord C, and as a result of excessive rubber infiltration, air pockets occur during tire vulcanization, and the bead separation Shion,
Deterioration of durability is observed. Also, as with tire CD, undesirable results occur when the air permeation is too large. In contrast, the tire according to the example
CA has a favorable value in terms of durability. Example 3 Next, a study was conducted on cords different from those used in Examples 1 and 2, in which the diameter etc. were changed. The steel cords are those shown in Table 4.

[Table] Next, we reinforced this cord to the belt of a 1200R24 radial tire and tested it. The results are shown in Table 5.

【table】

〔Effect of the invention〕

As described above, the steel cord according to the present invention is
It has appropriate air permeability, the penetration of rubber into the inside of the cord is also appropriate, the contact pressure between the core and side strands is low, and there is little abrasion, so during tire vulcanization,
This resulted in a tire that did not cause air trap defects, was able to prevent fatigue and rust, and had excellent shape stability, strength, and a longer lifespan compared to conventional tires.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a steel cord used in an embodiment of a radial tire according to the present invention, FIGS. 2 to 5 are sectional views showing an example of a conventional steel cord, and FIG. 6 is a comparative example. FIG. 1...Core, 2...Side, 3...Steel cord,
4... Core strand, 5... Side strand.

Claims (1)

[Claims] 1 All the strands have the same diameter, and a core made of 3 or 4 strands twisted together, and around the core, 5 more strands than the number of core strands, in the same direction as the core, 2 of the core. A radial tire characterized by having at least one of a carcass, a belt, and a cheerer reinforced with a double-pitch steel cord on the twisted side.