JPH09195188A - Steel cord for reinforcing rubber and radial tire for construction vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steed cord suitable for reinforcing material for belts of radial tires of construction vehicles by enhancing extensibility and cutting through resistance against sharp extraneous matters such as stones and rocks by setting (a cord twisting pitch)/(a cord diameter) in a predetermined range. SOLUTION: A rubber-reinforcing steel cord having a (3-4)×(3-4) structure, a cord twist pitch which is 3.5-7.5 times of a cord diameter, >=4% elongation at break and a tensile strength of the wire after breaking the cord in the range of 2,000-3,300MPa by twisting 3-4 wires 1 having 0.3-0.5mm diameter to form a strand 2 and twisting the 3-4 strands. A radial tire for construction vehicles is formed by using this steel cord for reinforcing at least the outermost layer of a belt layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber-reinforcing steel cord and a radial tire for a construction vehicle.

[0002]

2. Description of the Related Art Large construction vehicles, such as dump trucks for transporting ores in open pit mines and wheel loaders, are equipped with extremely large tires having a diameter of more than 3 m in order to increase the allowable load. Conventionally, a 7 × 7 structure, a 4 × 2 structure and a 3 × 7 structure having high elongation characteristics have been generally used. However, the usage site of the above tires is a wasteland, and the rocks are exposed on the ground, and in the extremely cold forest areas, the ground is frozen and the sharpened wood pieces are scattered, so the usage conditions are very severe. . Therefore, it is desirable that the tire cord used for the belt layer has high cut resistance to rocks and frozen wood pieces and has good durability with good shear impact characteristics, but the steel cord has insufficient characteristics. It was

[0003]

As a countermeasure against this, a conventional construction vehicle tire is provided with a large diameter cord having a construction of 7 × 7 × 0.25 mm or the like to improve the cut resistance, or the cord is 4 ×. 2 x 0.35 mm configuration or 3 x 7 x 0.2
Attempts have been made to improve shear resistance and cut resistance by combining high elongation cords such as a 2 mm structure. However, a 7 × 7 × 0.25 mm configuration or 3
With the × 7 × 0.22 mm structure, the cord wire diameter is small, so in a tire using this cord, when rocks or wood chips pierce the tire, the wire strands are easily cut, and fractures of the strands propagate one after another. There was a problem with the cut resistance, because the cord often breaks early or the tire bursts early. on the other hand,
In the 4 × 2 × 0.35 mm structure, as shown in FIGS. 5 (a) to 5 (c), the cross-sectional shape perpendicular to the cord longitudinal direction changes variously in the cord longitudinal direction, and the shape is not uniform and does not function as an aggregate. As a result, the cut resistance is partially inferior, and stable cut resistance cannot be obtained. Therefore, as in the case of the conventional steel cord, there is a problem that an early cord breakage or an early tire burst occurs.

The present invention was devised in order to solve the above-mentioned problems, and its purpose is to have good shearing impact characteristics and cut resistance, especially for the ground surface of rocks and wood chips. The present invention provides a steel cord that has excellent cut penetration resistance against sharp foreign matter and durability and is suitable as a reinforcing material for tires for construction vehicles. Another object of the present invention is to provide a pneumatic radial tire having good cut penetration resistance and good durability. INDUSTRIAL APPLICABILITY The present invention is suitable as a tire reinforcing material for a vehicle for transporting ores, and a tire reinforcing material for a vehicle for transporting timber, a road grader, an earth mover, a scraper, a wagon excavator, and a tire for a large vehicle for road construction represented by mining. It is also applied to reinforcing materials.

[0005]

In order to achieve the above object, the present invention provides a steel cord of (3-4) × (3-4) construction, in which the wire diameter of the cord is 0.3- 0.5m
m, the tensile strength of the wire after the cord is disassembled is 2000 to 3
300 MPa, cord twist pitch is 3.5 to the cord diameter
It is a steel cord that is 7.5 times larger. Furthermore, the elongation at break is preferably 4% or more. Further, the present invention is a pneumatic radial tire using the steel cord having the above-mentioned structure in at least the outermost belt layer.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION To explain the reasons for limitation, firstly, the present invention uses a cord construction of 3 × 3, 3 × 4, 4 × 3 or
The form is any one of × 4. FIG. 1 shows a 4 × 3 configuration (first embodiment), in which three strands 1, 1, 1 are twisted into one strand 2 and four strands 2 are twisted together. 1 (a) and 1 (b) show cross sections at different positions in the longitudinal direction, and the code cross-sectional shapes are the same. FIG. 2 shows a 3 × 4 configuration (second mode), in which four strands 1, 1, 1, 1 are twisted together to form a strand 2,
Three strands 2 are twisted together. FIG.
As is clear from (a) and (b), the cord cross-sectional shape is the same at different positions in the longitudinal direction. FIG. 3 shows a 4 × 4 configuration (third aspect) in which four strands 1, 1, 1, 1 are twisted together to form a strand 2, and four strands 2 are twisted together. Also in this case, the cord cross-sectional shape is the same at different positions in the longitudinal direction as shown in FIGS.
As described above, the cord structure of the present invention has a stable shape because the cross section of the cord is uniform even at different positions in the cord longitudinal direction, and the entire cord is compact and functions integrally. Therefore, the shear impact resistance becomes extremely high. Also, since the cord shape is stable in the longitudinal direction, stable cut resistance can be obtained over the entire length.

The present invention employs the following conditions in the first to third aspects and the 3 × 3 code structure (not shown). The wire diameter of the strand 1 is 0.30 to 0.50 mm. The tensile strength of the wire after the cord is disassembled is 2000-330
It is set to 0 MPa. The cord twist pitch P is 3.5 to 7.5 times the cord diameter D. Explaining the reasons for these limitations, the wire diameter d of the wire 1 is 0.3.
If it is less than 0 mm, the strength required for reinforcement is lowered, and a broken wire cross-section is likely to occur, which is not suitable. However, if the wire diameter d of the strand 1 exceeds 0.50 mm, the cord diameter becomes large and the rigidity becomes too high, and the belt layer in which the cord is embedded becomes thick, which is also inappropriate. A more preferable wire diameter range is 0.32 to 0.45 mm. By thickening the wire diameter within a predetermined range in this way, the wire 1 becomes less likely to break even if rocks, wood chips, etc. are struck by the tire,
The propagation phenomenon of wire breakage is less likely to occur. The strands are not limited to all having the same diameter, but may be different within the above range. The tensile strength of the wire is defined in order to secure the strength and toughness. When it is less than 2000 MPa, the strength is insufficient, and when it exceeds 3300 MPa, it is unsuitable because it becomes brittle due to the decrease in toughness.

The reason why the cord twist pitch P is made smaller in relation to the cord diameter D is that the elongation at break of the cord is secured to be 4% or more to increase the shear shock resistance and the cut penetration resistance against rocks and wood chips. This is to improve. Here, the cord diameter means the circumscribed circle diameter of the cord. If the twist pitch of the cord is less than 3.5 times the cord diameter, it is not suitable because the strength utilization factor of the wire decreases, and the cord diameter is 7.5. If the twist pitch exceeds twice, the elongation at break of the cord becomes small, which is also unsuitable. By satisfying the above conditions, the cut resistance and the durability can be improved by the synergistic effect of the cord configuration without impairing the strength and the toughness. In any of the embodiments, the surface of the strand is coated with a surface such as brass plating to improve the adhesiveness with the rubber matrix.

[0009]

Next, examples of the present invention will be described. Samples 1 to 13 in Table 1 show examples of the steel cord of the first embodiment. Samples 14-25 in Table 2 show examples of steel cords of the second aspect, and Samples 26-3 in Table 3
7 shows an example of the steel cord of the third mode.
The ratios 1, 2, 3 and 4 show comparative examples. In Tables 1 to 3, “shear impact properties” are measured using a Charpy impact tester, and as shown schematically in FIG.
A method in which the weight 5 is dropped in a pendulum shape from a predetermined position A with a point a as a fulcrum, the sample cord cd attached to the predetermined position B is sheared and ruptured, and the position where the sample cord cd is swung up to the opposite side by the pendulum motion at that time is detected. , The angle θ between the extension line of the position A and the swing-up position C is measured to calculate the shear shock absorption energy. In Tables 1 to 3, the shear shock absorption energy is converted as per unit mass, and the shear shock absorption energy per unit mass of the conventional example 3, that is, the steel cord having a configuration of 4 × 2 × 0.35 mm is 1.
It is set to 00 and is displayed as an index. Further, "repeated shear impact property" means cut resistance, and similarly, using a Charpy impact tester, a weight with a wedge-shaped tip and a predetermined weight is shaken down from position A, and the number of repeated drops until breakage is read. In the same manner, the value per unit mass of Conventional Example 3 is set to 100 and is indexed.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

[Table 3]

As is clear from Tables 1 to 3, the steel cord of Conventional Example 1 (7 × 7 × 0.25 + 0.15 structure) has a small strand diameter, and the ratio of the cord twist pitch to the cord diameter ( P / D) is too large and the elongation at break is low. Therefore, although the shear impact property per cord is good, the shear impact property per unit mass and the repeated shear impact property are greatly inferior. In addition, since the cord diameter is large, the number of hammers in the tire is small, and the shear impact characteristics when used in a tire for construction vehicles are poor. It should be noted that "+0.15" in Conventional Example 1 means that a strand having a diameter of 0.15 mm was wrapped around the outer circumference in a state where the strands were twisted together. Conventional example 2 (3 x
7x0.22mm structure) has a small wire diameter, so code 1
The shear impact properties per book, the shear impact properties per unit mass, and the repeated shear impact properties are greatly inferior. In Examples 1 to 37 according to the present invention, the cord composition, the filament diameter, and the cord twist pitch / cord diameter ratio (P / D) are in the proper ranges, so that the elongation, the shear impact characteristic per cord, the unit mass Shear impact properties and repeated shear impact properties are all good. In Comparative Example 1, since the strand diameter is too large, the shear impact property is inferior. In Comparative Example 2, since the relationship (P / D) between the cord diameter and the twist pitch is inadequate, the shear impact property is also inferior. In Comparative Example 3, the wire diameter is too small and the cutting strength is poor. In Comparative Example 4, the cut resistance is inferior because the relationship (P / D) between the cord diameter and the twist pitch is inappropriate.

[0014]

According to the first aspect of the present invention described above, the cord twist structure is stable, the strand diameter is set thick in a certain range, and the cord twist pitch / cord diameter is set. By obtaining a high elongation as the predetermined range, it is possible to obtain an excellent effect that the cut resistance and durability against sharp foreign matter such as rocks and wood chips can be improved. According to claim 3, the claim 1
By using the steel cord of (1) in at least the outermost belt layer, the excellent effect that the cut penetration resistance and the durability can be remarkably improved in a large radial tire for construction vehicles can be obtained.

[Brief description of the drawings]

1A and 1B are cross-sectional views schematically showing a first embodiment of a steel cord according to the present invention in a state of being cut at different positions in the cord longitudinal direction.

2 (a) and 2 (b) are sectional views schematically showing a second embodiment of the steel cord according to the present invention in a state in which it is cut at different positions in the cord longitudinal direction.

3 (a) and 3 (b) are cross-sectional views schematically showing a third embodiment of the steel cord according to the present invention in a state of being cut at different positions in the cord longitudinal direction.

FIG. 4 is an explanatory view schematically showing a test method for shearing impact characteristics in the present invention.

5 (a), (b) and (c) are cross-sectional views showing changes in the cross-sectional shape of the conventional steel cord in the longitudinal direction.

[Explanation of symbols]

 1 strand 2 strands d strand diameter P cord twist pitch D cord diameter

Claims (3)

[Claims] 1. A steel cord having a structure of (3-4) × (3-4), and a diameter of a wire constituting the cord is 0.3-0.5.
mm, the tensile strength of the wire after cord disassembly is 2000-
3300MPa, cord twist pitch is 3.5 of cord diameter
~ 7.5 times the steel cord for rubber reinforcement. 2. The steel cord for rubber reinforcement according to claim 1, which has an elongation at break of 4% or more. 3. A radial tire for a construction vehicle, wherein the steel cord according to claim 1 or 2 is used in at least the outermost belt layer.