JPH04154401A - Radial tire for heavy vehicle - Google Patents

Abstract

PURPOSE:To improve corrosion fatigue resistance so as to enhance durability of a tire reinforced with steel cords for rubber reinforcement by providing residual compressive stress to an element wire surface layer portion of the steel cords, and also applying lubricant to an element wire surface. CONSTITUTION:In a radial tire for a heavy vehicle, at least one layer of carcass ply reinforced with steel cords arranged at substantially 90 deg. angle with respect to a tire equatorial plane is turned up from the inside to the outside around a bead core. In this constitution, the steel cords applied to the carcass ply is formed of twisted steel element wires each having a diameter of 0.4mm or less. A surface layer portion of the steel element wire is provided with residual compressive, and to the surface thereof lubricant excellent in compatibility with rubber is applied as a coating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radial tire for heavy vehicles in which the corrosion fatigue resistance of carcass plies is improved.

(Prior Art) In the past, steel cords have been frequently used as carcass ply reinforcing materials in heavy vehicle tires.

This steel cord has a diameter of 0.4m due to cold wire drawing.
It is known that residual tensile stress exists on the surface of steel wires obtained by twisting together steel wires having a thickness of less than m.

For example, according to Shigeru Yonetani's ``Generation of Residual Stress and Countermeasures J'' (published by Yokendo), there is tension residual stress in the surface layer and compressive residual stress in the center, and the larger the area reduction rate during wire drawing, the more It is stated that the amount of residual stress is large.

According to the same agency, there is a description of the relationship between residual stress due to cold working and fatigue strength, and it is also disclosed that the more the residual stress is on the compressive side, the more it contributes to improving fatigue resistance.

Also discussed is the removal and adjustment of residual stresses.

As a technique similar to these, there is JP-A-2-179333, which describes the relationship between residual tensile stress and residual compressive stress due to cold working and fatigue resistance.

All of these are related to fatigue resistance, but naturally it is thought that they behave in the same way with respect to corrosion fatigue resistance.

On the other hand, Japanese Patent Laid-Open No. 62-78291 and No. 63-132944 disclose a method of suppressing the occurrence of rust by applying mineral oil to the surface of steel wire or steel cord and improving adhesion to rubber. It is disclosed in the publication No.

(Problems to be Solved by the Invention) Steel cord wires used for reinforcing heavy vehicle radial tires are drawn with an area reduction of 90% or more, so the surface layer of the wires has Residual tensile stress exists,
As a result, corrosion fatigue resistance is impaired, resulting in a shortened tire life.

In order to solve this problem, Japanese Unexamined Patent Publication No. 57-14957
Publication No. 8 proposes a steel cord in which residual compressive stress is uniformly distributed on the surface of the steel wire, but as tires become longer lasting, it is desired to further improve the corrosion fatigue resistance of the steel cord. .

(Means for Solving the Problems) The present invention employs the following means to solve the above problems.

In other words, in a steel cord for tire brazing made by twisting together steel wires having a diameter of 0.4 mm or less,
A steel with improved corrosion and fatigue resistance, characterized in that the surface layer of the steel wire has residual compressive stress, and the surface is coated with a lubricating oil having good compatibility with rubber as a coating agent. Cord, more specifically, 0.4 mm or less obtained by cold wire drawing with a carbon content of 0.7% by weight or more and a reduction in area from final patenting of 90% or more. In the steel cord for tire braking, which is made by twisting together steel wires having a diameter of
The surface layer of the steel wire has residual compressive stress, and the surface is coated with a lubricating oil having good compatibility with rubber as a coating material.

In short, in order to manufacture steel cord for tire brazing, high-carbon steel wire with a carbon content of 0.7% or more is cold-drawn into wires with a diameter of 0.4 mm or less. By repeatedly bending and deforming the steel cord or steel wire while applying tensile force, residual compressive stress is applied to the surface layer of the steel wire. The solution is to apply a lubricating oil that has good compatibility with rubber to the surface layer of the wire when it is made into a wire or after it is made into a cord. The reason why the content of the steel cord is set to be 0.7% or more and the area reduction rate is 90% or more is because the steel cord for rubber reinforcement is required to have high strength, and in order to be put to practical use, it must have a strength of at least 250 kg/mm'. Strength is required.

On the other hand, the wire drawing process to obtain this high strength imparts a large residual tensile stress to the surface layer of the wire, which reduces the corrosion fatigue resistance.

Although the degree of residual compressive stress imparted to the surface layer of the strands of the steel cord is not particularly defined, the greater the residual compressive stress, the better the corrosion fatigue resistance.

However, processing to give a large residual compressive stress may cause scratches on the surface of the strands or cause poor flammability of the cord, so the residual compressive stress is preferably 80 mm or less.

Examples of lubricating oils that have good compatibility with rubber include synthetic lubricants such as organic esters, and petroleum-based lubricants such as spindle oil.The rubber in which the steel cord is embedded is vulcanized on a sheet and a 1 cm square sample is prepared. A sample is cut out, immersed in a lubricating oil for 8 hours at room temperature, and the weight increase of the rubber is measured, and the lubricating oil has a rubber weight increase rate of 10% or more.

Furthermore, if the compatibility with the rubber is not good, the adhesion between the rubber and the steel cord will be inhibited and the material will not function as a rubber reinforcing material.

Rubber here refers to one or more diene rubbers such as natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber, combined with vulcanizing agents, vulcanization accelerators, anti-aging agents, adhesion aids, etc. A rubber composition in which a mixed steel cord is embedded.

(Function) Considering the factors related to the corrosion fatigue resistance of steel cord, residual stress, wire diameter, cord structure (twist pitch,
However, cord structure factors such as the wire diameter and the number of wires that make up the cord are limited by other product design aspects. Therefore, it is necessary to obtain steel cords with excellent durability using methods other than structural factors.

Now, improvements made in accordance with the prior art that improve the corrosion fatigue resistance by improving the residual stress in the surface layer of the steel cord from the tensile side to the compressive side have improved the durability of tire products, which now have a longer service life. cannot be improved, and a combination with other technological improvements is required.

Although it was known that applying mineral oil or the like to the strands of steel cord improves its adhesion to rubber, no study had been conducted on the effect on corrosion and fatigue resistance.

In the present invention, the residual stress in the surface layer of the strands is made compressive, and the above-mentioned lubricating oil is applied to the surface of the strands. We were able to obtain an improvement in corrosion fatigue resistance that had not been achieved previously.

The effect is not yet clear, so it is only a guess, but in addition to improving corrosion fatigue resistance by applying residual compressive stress to the surface layer of the strands that make up the steel cord, Applying lubricating oil suppresses fretting friction between the wires, and improves corrosion fatigue resistance by smoothing the action of the steel cord wires and reducing local deformation against repeated deformation during tire use. During the twisting process and the process of applying residual compressive stress to the surface layer of the strands, the frictional resistance between the strands is reduced, resulting in uniform deformation of the strands, improving the stranded shape of the cord and imparting corrosion resistance to steel moisture. etc. are possible.

(Example) The manufacturing method of steel cord according to the present invention is almost the same as the conventional manufacturing method, with the difference being the process of applying lubricating oil to the strands, and the process of applying lubricating oil to the strands, and the residual A step of applying compressive stress is added.

However, this process does not impede productivity, and the increase in capital equipment space is minimal.

In other words, the steel wire that has gone through the final patenting process, which controls the strength of the steel cord, is coated with a coating to improve adhesion to rubber, and then drawn to its final wire diameter to obtain the wire that makes up the steel cord. This means that they will be exposed.

The wires are then twisted together to form a steel cord using a tubular twisting machine or a puncher twisting machine. Before or after twisting, a lubricating oil with good compatibility with rubber is applied to the surface of the wires. .

The wire drawing machine is equipped with a straightening device to improve the straightness of the drawn strands, and the wire twisting machine is equipped with a straightening device to improve the straightness of the twisted steel cord. These straightening devices, for example, use rolls arranged in a staggered manner to repeatedly bend and deform the steel cord for straightening. By appropriately selecting the degree of deformation, residual compressive stress can be applied to the surface of the wire.

Test Example 1 A carbon steel wire rod with a carbon content of 0.7% is used, which is drawn to a predetermined wire diameter by dry drawing, subjected to final patenting treatment, plus plated, and wet drawn. A wire having a wire diameter of 0.23 mm was obtained using a wire drawing machine.

The residual stress of this strand is 76 mm, and a tension of 5 kg is applied to the strand, and two straightening devices with 15 11 mm rolls arranged in a staggered manner are used to straighten the strand in the upper and lower directions. Residual compressive stress was applied to the surface layer of the strand by passing the strand while repeatedly bending it in the left and right directions.

The obtained wire had a compressive residual stress of 68 mm,
Twelve strands of this wire were twisted together using a tubular twisting machine to form a cord.

When the residual stress of the drawn strand is 76 mm in tension, the residual stress of the strand formed in the cord is 60 mm tensile stress, and when the residual stress of the drawn strand is 68 mm in compression, the cord The residual compressive stress of the wire was 17 mm to 22 mm, and when the cord was passed through a straightening device with a tension of 35 kg, the residual stress of the wire constituting the cord was 43 mm.

The lubricating oil was applied to the strands before entering the twisting machine using a roller, felt, or gauze impregnated with lubricating oil.

The coating amount was 300 mg/m''.

Table 1 shows the results of examining the effects on corrosion fatigue resistance by varying the presence or absence of this lubricating oil, the type of lubricating oil, and the amount of residual stress in the surface layer of the steel cord strands.

The presence or absence of lubricating oil and the amount of lubricating oil applied were expressed in units of weight (mg) of lubricating oil attached per rn' surface area of the strands constituting the steel cord.

Organic esters are used as lubricants here, but
Such an organic ester refers to an ester obtained by the reaction of an organic acid and an organic alcohol, and the organic ester specifically used is a lubricating oil synthetic base and has the trade name "KAOLUBE 190J" (manufactured by Kao Corporation). .

The outline of the measurement method for each test shown in Table 1 is as follows.

(1) Amount of residual stress in the surface layer of the wire The steel cord to be measured was cut 10 cm lengthwise, the rubber was removed and the twist was loosened to form individual wires, and the plus plating was removed using an aqueous ammonium persulfate solution. After covering the half circumference of the wire in the longitudinal direction with lacquer to prevent it from being etched, the wire was etched with 50% nitric acid by volume at 50°C. And so. If the wire was bent before etching, the difference in the amount of bending before and after etching was determined and used as the amount of residual stress.

To determine whether the residual stress was compressive or tensile, it was determined that the wire bent toward the etched side was compressive, and the wire bent toward the lacquered side was determined to be tensile.

(2) Corrosion fatigue resistance (degree of decline) A 1000R20 ribbed tire was made using each cord for braking, and the internal pressure was 7.25/cm” and the load was 2425 kg.
/ I drove it 200,000 km under the conditions of this book.

The carcass cord has a strand structure of 1 x 12, a core wire diameter of 0.24 mm, a sheath wire diameter of 0.225 mm, a number of threads of 9.6 Ends/Inch, and a wire length of 0.005 mm with respect to the equatorial plane of the tire.
I typed it in.

Rubber cord 1 taken out from the tire after such running
As shown in Figure 2, pulley 2 of 3 with a diameter of 40 mm
A tensile load was applied to the weight 4 corresponding to 10% of the breaking load of the new cord via the fixed pulley 3, and the pulley 3 was repeatedly moved 20 cm from side to side to give repeated bending strain to the cord as shown in the figure. cause the cord to break due to fatigue,
The number of repetitions leading to cord breakage was determined as the average number of times of breakage of 10 cords.

The corrosion fatigue resistance shown in Table 1 is expressed as an index value, with the above values set as 100 for the control tire of Comparative Example 2, and the larger the value, the better the corrosion fatigue resistance.

Test Example 2 Corrosion resistance was achieved by changing the residual stress by adjusting the tension and degree of repeated bending of the strands passing through the straightening device of the wire drawing machine and the tension and degree of repeated bending of the steel cord passing through the straightening device of the stranding machine. Fatigue properties were investigated. The steel cord used was 1×12, and the core wire diameter was 0.2.
The diameter of the sheath wire is 0.225 mm.

The results are shown in Figure 1.

It can be seen that as the residual compressive stress of the steel wire increases, the corrosion fatigue resistance due to the application of lubricating oil is improved.

(Effects) As mentioned above, the steel cord for rubber reinforcement of the present invention can significantly improve corrosion fatigue resistance by applying residual compressive stress to the surface layer of the wire and applying lubricating oil to the surface of the wire. The durability of the tire reinforced with steel cords provided by the present invention is significantly improved, and the present invention has excellent effects.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between residual compressive stress in the surface layer of steel cord wire and corrosion fatigue life, and Figure 2 is a conceptual diagram of a test device for evaluating the degree of decline in corrosion fatigue resistance of steel cord. be.

Claims (2)

[Claims] (1) A radial tire for a heavy vehicle comprising at least one carcass ply reinforced with steel cords arranged at an angle of substantially 90° to the tire equatorial plane and wound around a bead core from the inside to the outside. The steel cord applied to the carcass ply is made by twisting together steel wires having a diameter of 0.4 mm or less, and the surface layer of the steel wires has residual compressive stress, and the surface is coated with rubber as a coating material. A radial tire for heavy vehicles characterized by being coated with a lubricating oil with good compatibility. (2) A radial tire for a heavy vehicle comprising at least one carcass ply reinforced with steel cords arranged at an angle of substantially 90° to the tire equatorial plane and wound around a bead core from the inside to the outside. The steel cord used as carcass ply cord has a carbon content of 0.
7% by weight or more, reduction in area from final patenting to 90%
0% or more obtained by cold wire drawing
．． It is made by twisting steel wires having a diameter of 4 mm or less, the surface layer of the steel wires has residual compressive stress, and the surface is coated with a lubricating oil that has good compatibility with rubber. A radial tire for heavy vehicles characterized by a coated tire.