KR20020006300A - Belt Reinforced Steel Cord for Truck and Bus Radial Tires - Google Patents

Abstract

PURPOSE: A steel cord for a radial tire for reinforcing a belt and the tire are provided to reduce the weight of the tire, and to improve endurance by using a steel cord having high strength and improving rubber penetration. CONSTITUTION: A tire is regenerated and the weigh of the tire is reduced with using steel wire having tensile strength over 330kg/mm2. A core wire(1) is formed spirally with torsion stress, and surrounded by lead wires(2). The sectional area of the core wire is smaller than the sectional area of the lead wire. The flat surface is formed in the core wire with passing through a roller. The ratio of the minor axis to the major axis is formed within the ranges of 1.1-1.9. The steel cord is composed of a core wire and six lead wires. The diameter of the core wire is formed to be more than the diameters of lead wires within the ranges of 1.1-1.3. The tensile strength of a filament is more than 330kg/mm2 with drawing high carbon steel having carbon of 0.92%. The steel cord is manufactured with twisting the core wire and lead wires spirally by applying torsion stress. Rubber penetration is improved with coating the steel cord by rubber. The endurance of the radial tire is improved.

Description

Belt Reinforced Steel Cord for Truck and Bus Radial Tires

The present invention relates to a structure of a steel cord for reinforcing a belt of a tire for trucks and buses, and more particularly, to construct a steel cord by using a steel wire having a tensile strength of 330 kg / mm2 or more in order to improve weight and reproducibility of the tire. The present invention relates to a steel cord for reinforcing belts for radial tires for trucks and buses, in which a core wire is spirally formed to improve the permeability of rubber into the steel cord.

Conventional steel cords for radial tires used for trucks and buses are composed of a number of filaments as in the example of 3 × 0.20 + 6 × 0.35 to maintain mechanical strength, and the number of steel cords for use in more severe conditions We had to increase usage by increasing.

Such a conventional belt reinforcing steel cord is composed of a plurality of filaments, as described above, when the rubber cord is coated on the steel cord is not easily penetrated into the steel cord, the steel cord is corroded when the tire is used for a long time As a result, the adhesive strength with the rubber has been reduced, thereby limiting the long-term use of the tire, and in particular, the steel cord has been limited to increase the number of steel cords with low strength and large diameter. The situation is limited to use in tires.

More specifically, since the conventional steel cord for reinforcing belts of truck and bus radial tires has a tensile strength of 330 kg / mm 2 or less, it is necessary to increase the amount of steel cord used and to maintain a large number of steel cords. In order to arrange the steel cords consisting of a plurality of filaments were required.

For example, a steel cord in the form of 3 × d1 + 6 × d2 (d1: core diameter, d2: side strand diameter) is used in which three filaments are twisted in parallel in the center and six different diameter filaments are twisted on it. Cords braided in multiple layers will not penetrate the inside of the steel cord when the cord is rubberized to make a tire, resulting in corrosion due to filament wear and tear when using the actual tire. The adhesive strength of the metal quickly declined, causing the life of the steel cord to decrease.

Therefore, in order to improve the rubber penetrability, 1 × d1 + n × d2 (n: side strands) in which the diameter of the side strands is appropriately adjusted to reduce the number of filaments constituting the steel cord and easily penetrate the rubber through the side strands. Patents have been applied for tires using steel cords of the type.

However, the steel cord is not sufficiently infiltrated with rubber, so that there is a continuous void between the center core and the circumferential line around it, and this continuous void causes moisture from entering the outside when the tire is damaged. It was noted that the osmotic pressure penetrates through the continuous pores and reduces the adhesion between the steel cord and the rubber.

After that, the inventors of the present invention sought to prevent the formation of continuous voids, and finally found out that rubber permeability can be improved by discontinuous voids formed by rolling a core wire and twisting the rolled core wire.

The present invention has been made in order to improve the problems of the conventional steel cord as described above, by drawing a high carbon steel for wire rods with a carbon content of about 0.92% to develop a wire rod having a tensile strength of 330 kg / ㎡ or more, tires The purpose of the present invention is to provide a steel cord for belt reinforcement with a simplified steel cord and improved rubber permeability to reduce weight and improve reproducibility.

1 is a perspective view of a steel cord according to the present invention,

2 is a plan view of a steel cord according to the present invention.

(Explanation of reference numerals)

1 ... core, 2 ... side stranded wire.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration of the belt reinforcing steel cord according to the present invention.

First, the steel cord for belt reinforcement used in the present invention has the following features.

1) Steel cord with a structure of 1 × d _Fc + 6 × d _Fc structure consisting of one core wire (Fc) and several side strands (Fs) around it.

2) Here, the cross-sectional area A _Fc of the core wire is smaller than the cross-sectional area of the side edge A _Fc .

3) The cross-sectional area of the core wire is a method of passing the upper and lower rolling rollers as shown in Fig. 1, and there is a flat surface up and down, and the flatness ratio representing the ratio of the long diameter to the short diameter is about 1.1. It is the range of -1.9.

4) Core wires having flat top and bottom sides are twisted by applying torsional stress to form a spiral shape.

Hereinafter, the configuration of the present invention in more detail.

In steel cords of the form 1xd1 + nxd2, (d1 * 3.14) should be larger than (n * d2), generally 1.1 to 1.3 times. At this time, in order to maintain the mechanical strength, the ultimate tensile strength of the high carbon steel with a carbon content of 0.92% or more by drawing process should be composed of filaments of 330㎏ / ㎠ or more.

In addition, as shown in Figs. 1 and 2, the core wire 1 is rolled by the upper and lower rollers, and there are two or more flat surfaces, and at this time, the long diameter of the core wire 1 to the short diameter (() is reduced. The flatness ratio (f), which represents the length, should be in the range 1.1 to 1.9. The rolled core wire 1 is twisted helically by a method of applying a torsional stress, and the steel cord of the present invention is finally twisted by twisting n side strands 2 in the same manner as the conventional technique. Is made.

When rolling the steel cord thus produced, the number of arrays per 10 cm is about 25 to 70 times the cord wire diameter, and the rubber thickness is about 1.5 to 2.5 times the cord diameter. In addition, the number of belt plies used for the purpose of reinforcing radial tires for trucks and buses is generally 2 to 5 or more, and may vary depending on the use and size. Normally, the belt ply is cut in an inclined range of 15 to 65 degrees so that the upper layer and the lower layer cross each other, and the lamination method varies depending on the number of belt plies used.

For example, in a radial tire for trucks and buses using three belt plies, the first belt ply is cut at an angle of 20 degrees to 50 degrees to the right or left, and the second ply is 20 degrees to 30 degrees in the same direction as the first ply. By cutting at an angle, the third ply is cut at an angle of 20 to 30 degrees in the opposite direction to the second ply, so that when forming a tire, the second and third belt plies are stacked to cross each other.

In addition, truck and bus radial tires using four belt plies cut the first belt ply at an angle of 50 to 70 degrees to the right or to the left, and the second ply at an angle of 15 to 25 degrees in the same direction as the first ply. The third and fourth plies are cut at an angle of 15 to 25 degrees in the opposite direction to the second ply, so that when forming the tire the second and third belt plies cross each other.

First embodiment

In the steel cord of the 1 × 0.37 + 6 × 0.33 form consisting of one core wire 1 having a diameter of 0.37 mm and six side strands 2 having a diameter of 0.33 mm, the physical properties were compared with different flatness ratios of the core wires. The pitch of the core wire is 18.0 mm.

Fatigue resistance was measured under a fatigue stress of 150 kg / mm 2 using a Hunter Fatigue tester with a rotational speed of 3,600 rpm. As the flatness ratio of the core wire increased, the fatigue resistance increased because the fatigue life increased as the surface hardness increased by rolling.

The rubber penetration rate is the length of the steel cord specimen 1 inch (25.4 mm), rubberized after vulcanization and represents the time it takes for 200 ml of water to pass through the rubber coated steel cord. In other words, the longer the time it takes for the water to pass through, the more the rubber penetrates into the steel cord, which impedes the passage of water.

In addition, as shown in Table 1 below, the higher the flat ratio of the core wire, the longer the aeration time, and the higher the rubber penetration. However, when the flat ratio is 1.9 or more, the rubber penetration does not increase significantly.

Comparison of properties of core wire flatness ratio of 1 × 0.37 + 6 × 0.33 steel cord Core fertilizer properties Flat ratio 1.0 1.3 1.6 1.9 2.5 Long diameter / short diameter 0.37 / 0.37 0.40 / 0.31 0.44 / 0.27 0.46 / 0.24 0.50 / 0.20 Fatigue Resistance-Hunter Kcycles 9.6 10.7 12.2 14.5 18.4 Rubber Penetration-Aeration Time Sec 59 77 85 90 91 Machining Energy-ΔT Kgf 0 2.4 4.9 7.4 9.2

In Table 1, the processing energy shows the additional drawing force required to roll the core wire, and the higher the flat ratio, the more required the processing energy, and it is advantageous to keep the flat ratio as low as possible within the preferred range. Therefore, excessively high flatness ratio causes an increase in the power ratio and wear of the rollers, which causes the processing cost to increase.

As a result, the increase in the flatness ratio of the core wire improves fatigue resistance and rubber permeability, but when the flatness ratio is increased to 1.9 or more, the rubber permeability is almost unchanged and only the processing energy increases, so the flatness ratio of 1.9 or less can be practically applied.

Next, the physical properties were compared while changing the spiral pitch of the core wire in the second embodiment.

In the following Table 2, the flatness ratio of core wire is rolled to 1.3 in 1 × 0.37 + 6 × 0.33 cord, and twisted spirally by applying torsional stress to the rolled core wire. Compare with each other.

Comparison of Physical Properties of Spiral Pitch of Steel Cord Core Wires of 1 × 0.37 + 6 × 0.33 Helix Pitch Comparison Flat core without spiral 12 mm 18 mm 22 mm Fatigue Resistance-Hunter Kcycles 9.6 16.3 12.1 10.5 Rubber Penetration-Aeration Time Sec 59 88 86 83

As can be seen from the table, the fatigue resistance and the rubber penetration property of the flat cores not twisted by the spiral were very low, but the fatigue resistance and the rubber permeability increased when the flat cores were twisted into the spiral.

In addition, in the case where the core wire is spiraled, the smaller the pitch is, in general, the lower the pitch. However, the excessively small pitch does not improve fatigue resistance and rubber permeability, but increases the processing cost for applying torsion stress, so the pitch ranges from 5.0 to 22.0 mm. Proper

According to the present invention, a 1 × 0.37 + 6 × 0.33 SHT steel cord having a spiral pitch of 18 mm and a flatness ratio of 1.4 was applied to radial tires for trucks and buses of the 11.00R20 standard. The tire of the present invention is composed of four belts, the first belt at the right angle of 65 degrees, the second belt at the right 22 degrees, the third belt at the left 22 degrees, the fourth belt at the left 22 degrees Each was laminated and molded.

The first and fourth belt plies were loaded with 40 steel cords per 10 cm and the second and third belt plies embedded with 55 steel cords per 10 cm in rubber, respectively, and the rolling thickness of the rubber was 1.9 mm.

Tires produced according to the present invention have improved indoor running durability by at least 10% compared to tires produced by the prior art.

According to the steel cord for reinforcing the belt of the present invention having the above object and configuration, by using a steel cord having high strength and excellent rubber permeability, there is an effect of reducing the weight of the radial tire for trucks and buses and improving reproducibility and durability.

Claims (4)

In a steel cord for reinforcing the belt ply, which is composed of one core wire (F _C ) and several side strands (F _S ) around it in a radial tire for trucks and buses composed of two or more belt plies, The core wire 1 is a steel cord having a shape of 1 × d _Fc + n × d _Fs in a state in which at least one flat surface is present by a rolling roller, and the core wire 1 is twisted spirally by torsional stress. Steel cords for belt reinforcement of radial tires for trucks and buses. A radial tire for trucks and buses using the belt reinforcing steel cord, wherein the number of steel cords is 25 to 70 times the cord diameter per 10 cm, and the thickness of the rubber is 1.5 to 2.5 times the cord diameter. The method of claim 1, The flattening ratio of the core wire (1) is in the range of 1.1 to 1.9, and the spiral pitch of the core wire (1) is in the range of 5 to 22. The steel cord for belt reinforcement of radial tires for trucks and buses. The method according to claim 1 or 3, The steel cord is a belt cord reinforcing steel cord of the radial tire for trucks and buses, characterized in that the tensile strength of 330kg / ㎠ or more.