JP2988593B2 - Steel cord with excellent corrosion fatigue resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord used as a reinforcing material for rubber articles such as pneumatic tires and industrial belts, and more particularly to an improvement in corrosion fatigue resistance.

[0002]

2. Description of the Related Art For example, in pneumatic tires, steel cords with high durability are required as the performance of tires becomes higher. Especially for cords used in carcass parts of tires, cord breakage directly causes tire damage,
It is important to have a long rupture life, that is, to have excellent fatigue resistance.

[0003] Normally, a steel cord used to reinforce the tire carcass portion accumulates mechanical fatigue due to repeated bending and tension fluctuation stress during tire running. On the other hand, when the tire is stored under the open-air condition, moisture invades into the rubber due to rainwater or at the time of high temperature and high humidity in summer, and is subjected to repeated fluctuating stress in a corrosive environment, thereby easily causing fatigue fracture. This corrosion fatigue fracture is accelerated and shortens the time until the cord breaks as compared with the mechanical fatigue fracture. Therefore, especially in the above-mentioned applications, a highly durable steel cord excellent in corrosion fatigue resistance is required.

Further, the cause of the corrosion fatigue failure of the steel cord used for the tire is, besides the repeated bending input and the corrosive environment according to the above-described cord, the filament of the cord is reciprocally bent so that the filaments of the cord are mutually moved and worn. A new factor due to so-called fretting wear has been added, further complicating the corrosion fatigue process.

[0005]

Heretofore, there has not been known any technique for improving the corrosion fatigue resistance of a steel cord by eliminating the above-mentioned adverse effects of fretting wear. Therefore, the present invention aims to provide a highly durable steel cord having excellent corrosion fatigue resistance.

[0006]

SUMMARY OF THE INVENTION The present invention, the pitch P ₂ of the plurality of steel filaments a plurality of steel filaments twisted in the same direction as the direction of the core around the core and the core was twisted at a pitch P ₁ in wound was a steel cord of layer twisting structure consisting of a sheath, excellent corrosion fatigue resistance of the pitch P ₁ and P ₂ and satisfies the relation 1.05P ₂ ≦ P ₁ ≦ 1.70P ₂ Steel cord.

[0007]

Next, the pitches P ₁ and P ₂ in the core and the sheath
Is described in detail below. First, the experimental results that led to the present invention will be described. Although experiments were performed on various code structures, the experimental results described below refer to typical structures, and evaluation of other code structures including this structure will be described in detail in examples described later. Fig. 1 shows the diameter of the core around three strands of 0.23mm diameter filament.
In the steel cord having a sheath in which nine 0.23 mm filaments are wound in the same direction as the core and twisted, the results of the corrosion fatigue test when the core pitch is changed for a sheath pitch of 12 mm are shown. The corrosion fatigue test
After the cord was covered with rubber, the cord that had been heated and vulcanized at 140 ° C for 40 minutes was cut into 10 cm lengths to form test specimens.
This test piece was immersed in pure water at room temperature as shown in FIG.
It was given at a speed of rpm, the number of revolutions until the test piece was broken was measured, and the evaluation was made using an index when the number of revolutions in a cord having a core pitch of 0.5 times the sheath pitch was taken as 100.

As is clear from FIG. 1, the corrosion fatigue resistance increases as the core pitch approaches the sheath pitch.
At the same pitch, the performance deteriorates rapidly, and when the core pitch exceeds the sheath pitch, it recovers rapidly, and the sheath pitch
The ratio P ₁ / P ₂ of the core pitch P _{1 to} P ₂ shows a peak around 1.05 to 1.20, and then tends to gradually deteriorate.

[0009] That is, from the results shown in FIG. 1, the ratio P ₁ / P ₂ is 0.
Is about 5, with respect to conventional coding, the corrosion fatigue life is extended considerably beyond the two times, the P ₁ / P ₂ 1.05 to
It can be seen that it should be set to the range of 1.70.

Here, the pitch of the core and the sheath is set to 1.05P ₂
The reason why the corrosion fatigue resistance is improved by setting ≦ P ₁ ≦ 1.70P ₂ is that the contact pressure between the filament of the core and the filament of the sheath falls within an appropriate range.

Furthermore, the P ₁ exceeds 1.70P _2, elongation of the core is small with respect to the tensile input to the code, since the balance of a strong sharing between the core and the sheath collapses, the cord strength is lowered It is effective to set P ₁ ≦ 1.70P ₂ because core quality is lost and code quality is degraded.

[0012]

[Example] (A) A structure in which three filaments having a diameter of 0.23 mm are twisted into three cores, and nine filaments having a diameter of 0.23 mm are wound around the core at a pitch of 12 mm in the same direction as the core. (B) A structure in which two filaments having a diameter of 0.24 mm are formed into a stranded core, and 7 to 8 filaments having a diameter of 0.225 mm are wrapped around the core at a pitch of 12 mm in the same direction as the core. In, the twist pitch of the core is 4-20mm
Steel cords having different core pitches were manufactured, and those having a core twist pitch of 13 mm or more and 20 mm or less were defined as invention examples, and those having a core twist pitch of 12 mm or less were defined as comparative examples. The steel cord thus obtained was coated with a sheet of unvulcanized rubber 0.8 mm thick and vulcanized at a temperature of 140 ° C for 40 minutes at a pressure of ²⁰ kgf / mm2 for a corrosion fatigue test. Provided. As shown in FIG. 2, the corrosion fatigue resistance is measured by immersing a test portion of a steel cord 1 in pure water 2 at room temperature and repeatedly rotating and bending the steel cord 1 with a surface strain of 0.4% until the fracture occurs. The test was repeated four times, the average value was determined, and evaluation was performed using an index when the average value of the code of No. 2 was set to 100. The evaluation results are shown in Tables 1-4 together with the specifications of each steel cord.
Shown in

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

It can be seen from the table that the life of the steel cord according to the present invention is extended to 2 to 4 times that of the conventional example.

Further, the steel cord having the above structure (A) was subjected to a drum test with water. That is, each steel cord is covered with a sheet-like rubber and cut and processed, and six types of carcass plies having a cord-implantation number of 30.2 / 5 cm are prepared, and each carcass ply is applied to an area divided into six in the circumferential direction of the tire. And follow the general structure, 10.0
0 A radial tire of R20 size was created. The thus obtained tire is closed after sealing the rubber layer (inner liner) inside the tire, filling 300 cc of water, and then closing the carcass at a speed of 60 km / h at a tire internal pressure of 7.25 kgf / cm ² . When the car was driven on the drum until the cord broke, the carcass ply was broken after traveling 14700 km and was unable to run. Next, disassemble the broken tire,
Six types of carcass plies were taken out, the number of broken filaments constituting the sheath of the cord in each carcass ply was examined, and the strength (maximum tensile load) of each cord was measured. Regarding the test results, the ratio of the total number of broken filaments of the sheath to the total number of filaments of the sheath of all cords is defined as the sheath breaking ratio, and the ratio of the measured cord strength to the cord strength before tire molding is the strong retention rate. Are shown in Table 5 together with the specifications of the steel cord. The indications in the tables are the same as in Tables 1-4.

[0019]

[Table 5]

[0020]

According to the present invention, it is possible to improve the corrosion fatigue resistance of a steel cord and to provide a steel cord most suitable for tires, industrial belts, and the like in which moisture is likely to enter.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between core pitch and corrosion fatigue life with respect to sheath pitch.

FIG. 2 is a schematic view showing a method for evaluating the corrosion fatigue resistance of a steel cord.

[Explanation of symbols]

 1 Steel cord 2 Pure water

Continuation of front page (72) Inventor Naohiko Obana 800 Shimonakano, Kuroiso City, Tochigi Prefecture Bridgeton Bekaert Steel Code Co., Ltd. Tochigi Plant (56) References Japanese Patent Laid-Open No. 50-29855 Showa 64-33288 (JP, A) Actually open Showa 64-45196 (JP, U)

Claims (1)

(57) [Claims] 1. Pitch a plurality of steel filaments
A steel cord of the layer twisting structure consisting of a sheath wound at a pitch P ₂ a plurality of steel filaments twisted in the same direction as the direction of the core around the twisted core and the core is P _1, the pitch P ₁ and steel cord P ₂ is excellent in corrosion fatigue resistance which satisfies the relationship _{1.05P 2 ≦ P 1 ≦ 1.70P 2} .