JP2000073285A - Steel cord for tire reinforcement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel cord good in penetration of a rubber into the inside thereof, capable of increasing the stiffness crossing to the tire rotation direction while decreasing the stiffness of the tire in the rotation direction, good in fatigue resistance to the compression and bending, and excellent in producing and handling workability. SOLUTION: This steel cord for tire reinforcement has a core strand 1 having nearly spiral kink having a kink pitch P1 and a kink outside diameter D1 in the miner axis direction of the cord, satisfying the equations P1=(0.1P to 0.5P), and (T-D1)/2d=(0.05 to 0.70). The core strand 1 appears between side strands 2 positioned in both sides and arranged so as to put the major axis of a nearly oval shape therebetween, nearly at the interval of pitch P1. A flat rate of the nearly oval shape (percentage of T/W) is 38-60%.

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 an automobile tire, and more particularly to a steel cord used for a steel cord.
The present invention relates to a steel code in which a total of 13 to 13 strands are twisted and the cross section of the code is substantially elliptical.

[0002]

2. Description of the Related Art In general, steel cords of this kind are used as reinforcing materials for automobile tires by being covered with a rubber material in a state where many steel cords are aligned in parallel. And
The conditions required for steel code include not only excellent mechanical strength, but also good chemical and physical adhesion to rubber materials, and the inside of steel code. And good rubber penetration. That is, in order for the steel cord to sufficiently fulfill the role of a tire reinforcing material, it is necessary to form a complete composite with a rubber material.

[0003] In particular, for tires used for heavy vehicles such as trucks and buses, steel cords having high strength and flexibility are required. One of them is a steel having a 1 + n structure. -Records have been used.

However, the conventional 1 + n steel condenser
As shown in FIG. 6, the cross-sectional structure of the cord is a close-twisted structure, and since the individual wires 7 are completely adhered to each other without any gap, the hollow portions S are scattered inside the cord. . Therefore, when a composite sheet is formed by sandwiching this steel code between two rubber sheets, the rubber material does not penetrate to the cavity S, and a complete composite with the rubber material is formed. Can not.

[0005] Therefore, when this rubber sheet is used for a tire, if the rubber coating is partially broken by a foreign substance such as a nail, moisture that has entered from the outside propagates into the cavity S, and the steel sheet is removed. Is oxidized over the entire surface. When this happens, the adhesion between the rubber and steel cord becomes weaker,
Both will peel off, and the effect of the steel cord as a reinforcing material will be very weak.

In order to solve this problem, there have been proposed a core wire 8 having a large diameter as shown in FIG. 7 or a steel cord having a core wire 9 formed as shown in FIG. Have been.

[0007]

In the steel cord shown in FIG. 7, since there is no hollow portion between the side strand and the core strand, moisture may propagate inside the steel cord. Is not
The cord diameter increases to increase the core strand diameter, and the rubber sheath
G thickens. For this reason, the weight of the tire increases, and when it is used in an automobile, the fuel efficiency deteriorates, which is not preferable. In addition, since the core strand 8 and the side strand 8a are always in contact, the fatigue value due to fretting wear is poor. Further, since the diameter of the core wire is large, the rigidity of the steel cord is increased, and there is a problem that the riding comfort is deteriorated when used in a tire.

Further, as shown in FIG. 8, a steel cord having a 1 + n configuration in which a core wire 9 is spirally shaped is such that the core wire 9 and the side wire 9a are always in contact with each other. The fatigue resistance is improved because there is no occurrence, but the rigidity of the steel cord is the same in any direction because the cross-sectional shape is a substantially circular shape. Therefore, if the rigidity is increased in order to improve the cornering performance of the tire, there is a problem that the ride quality is deteriorated. Further, the steel cord of FIG. 8 has a larger cord diameter and a thicker rubber sheet after the calendering (rubber coating step) than the cord of a close twist as shown in FIG. In addition, since the cord diameter is large, a predetermined number of steel cords cannot be embedded in the rubber sheet, and the strength of the sheet is weakened. Therefore, when this rubber sheet is used for a tire, it is necessary to increase the number of stacked sheets, and as a result, there is a problem that the weight of the tire increases. Further, from the point of view of manufacturing the steel cord, the steel cord in which the wires are neatly arranged in the space as shown in FIG. 8 is unreasonable and the twist is extremely unstable.

SUMMARY OF THE INVENTION The present invention has been made to solve various problems of the above-mentioned various conventional steel cords.
Good rubber penetration into steel code, high rigidity in the direction perpendicular to the tire rotation direction while reducing rigidity in the tire rotation direction, good fatigue resistance to compression and bending, and manufacturing. Another object of the present invention is to provide a steel code excellent in handling workability.

[0010]

In order to achieve the above-mentioned object, a steel cord for reinforcing a tire according to the present invention has a diameter of 0.15.
6 to 13 strands each having a wire diameter of 0.1 mm to 0.40 mm, one strand being a core strand and the remaining strands being side strands, and being twisted at a time at a twist pitch P in the same direction. In a tire reinforcing steel cord having a substantially elliptical shape (major axis W, minor axis T) having a transverse section substantially in the same direction in the longitudinal direction, the core element wire is represented by the following formula (1). A) a substantially spiral shape having a custom pitch P ₁ and a custom outer diameter D _{1 in} the code minor axis direction that satisfies (2), and the core element wire is provided on both sides of the major axis of the substantial ellipse. found at substantially the pitch P ₁ interval between positions to the side strands, moreover, wherein the aspect ratio of the substantially elliptical shape (percentage of T / W) of 38% to 60%. P ₁ = 0.1 P to 0.5 P (1) (T−D ₁ ) /2d=0.05 to 0.70 (2) d: wire diameter (mm) (core wire diameter and diameter) P side strands when the side wire diameter is different _1: habit pitch (mm) T: co - de minor (mm) D _1: co - de habit outer diameter of the minor diameter direction of the core wire (Mm) The twist pitch of the steel cord is preferably about 6 to 28 mm for the reason described later. Further, the diameters of the core strand and the side strands may all be the same, but the diameter of the core strand may be slightly increased. At this time, the wire diameter d uses the wire diameter of the side strand.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The steel cord of the present invention has a substantially elliptical cross-section with a substantially same longitudinal direction and a large flattening ratio. Greatly differ in rigidity. In addition, the steel after the calendar
Since the cords are arranged substantially parallel to the longitudinal direction in the rubber sheet with the long diameter part left and right, the bending rigidity is low in the vertical direction and high in the horizontal direction. Therefore, when a tire is formed using this rubber sheet, the riding comfort is good because the rigidity in the tire rotation direction is low, and the cornering performance is enhanced because the rigidity in the direction perpendicular to the tire rotation direction is high. Can be done.

Further, since the steel cord of the present invention has a substantially elliptical cross section, almost all the steel cords are substantially parallel to the longitudinal direction with the major axis portion left and right at the time of calendaring. Therefore, the thickness of the rubber sheet corresponds to the short diameter portion of the steel cord, and the sheet can be made thin. And the number of inserted steel codes can be reduced. As a result, the weight of the tire has been reduced, and it has become possible to reduce the cost of the tire and to improve the fuel efficiency of the automobile. Further, in terms of twist stability, the twist is stable and almost the same shape even after being embedded in a rubber sheet as compared with the steel cord as shown in FIG. Excellent in work.

The twist pitch of the steel cord is 6 mm to 2 mm.
8 mm is preferred. Because if it is less than 6 mm,
This is because the bending amount is extremely increased, so that disconnection is liable to occur, and the number of twists per length of the steel cord is increased, thereby lowering productivity. Furthermore, in the present invention, since the habit pitch of the core element wire is even smaller than the twist pitch, a twist pitch of less than 6 mm is not appropriate. On the other hand, if the twist pitch of the steel cord exceeds 28 mm, the flexibility of the steel cord is lost, so that the fatigue value decreases, the twist becomes unstable, and flare is liable to occur. Not.

[0014] The wire diameter of the strand is 0.15 mm to 0.40 mm
The reason is that if it is too thin, sufficient strength cannot be obtained, and if it is too thick, the steel cord diameter becomes large. On the other hand, if the strand is made thicker, the steel cord loses its flexibility and the fatigue value becomes lower. This tendency is more remarkable in the present invention in which a strand having a small habit exists, and when the strand diameter exceeds 0.4 mm, it becomes a practical obstacle.

Assuming that the twist pitch of the steel cord is P, the habit pitch P ₁ of the core wire having a habit is 0.1.
Was a 1P~0.5P, when P ₁ is less than 0.1P, strands undergo extreme plastic deformation, breakage productivity is deteriorated as well as multiple, whereas, if it exceeds 0.5P However, the effect of the core element wire cannot be achieved, and the gap between the element wires decreases due to the tensile force due to the flow of the rubber at the time of molding the rubber sheet or the ironing force applied to the cord. This is because a sufficient gap does not occur between the wires. On the other hand, if it exceeds 0.5P, the steel code cannot be rolled sufficiently, and the short diameter T of the steel code cross section becomes large.
Rubber sheet thickness cannot be reduced.

Assuming that the strand diameter of the steel cord is d and the minor axis of the substantially elliptical cross section is T, the habit outer diameter D ₁ of the minor core in the minor axis direction is represented by ( TD- ₁ ) / 2d =
The reason that the range of 0.05 to 0.70 is satisfied is that, in this formula, it is practically difficult to process (T−D ₁ ) / 2d smaller than 0.05, and that there is sufficient rubber between the strands. It is better to be 0.05 or more for infiltration. If it exceeds 0.70, the effect of flattening is reduced, and the rubber sheet thickness cannot be reduced. This range is most suitable in terms of production and operation and effect.

The flatness of a substantially elliptical shape in the transverse section of the steel cord (ratio of minor axis T to major axis W, percentage of T / W)
Is set to 38% to 60%. If it is less than 38%, twisting becomes unstable, and at the same time, each wire becomes hardly bent at the long diameter end portion, and handling workability is poor and fatigue resistance is poor. . Even if the shape exceeds 60%, the twist becomes unstable and the shape becomes close to a perfect circle, so that the effect of the steel code of the present invention cannot be expected.

In the present invention, a structure is not adopted in which a core wire having a habit is not made to appear at both ends of the substantially elliptical shape and the core wire is completely disposed inside the side wire. in the both sides of the major axis shaft, until the structure as a core element wire to arrange to appear at substantially the pitch P ₁ spacing between the side strands, resulting almost monolayer at first glance to twist, steel -
The steel code of the present invention could be completed by flattening the record. Therefore, the twist is more stable than before, and a suitable gap is maintained between the strands, and a steel cord having a large flatness is obtained.

The steel cord according to the present invention is characterized in that a single wire is given a preset habit to form a core wire, a side wire is twisted around the core wire, and a roller having a flat surface is formed. −
It can be manufactured by passing through a gap and applying a considerably strong compression process. Conventionally, in such a method, it was thought that the twist of the steel cord was broken and the cord was defective. It was also found that it was easy to manufacture by applying tension and applying strong compression.

Although the steel cord of the present invention can be manufactured by a tuber type twisting machine, it is more efficient and practical to manufacture it by a buncher type twisting machine. When a buncher-type twisting machine is used, it is necessary to take into account that the twisting of the strand is different from the twisting of the steel cord in advance because of the twist.

When the tire steel cord having the above-mentioned structure is used and pressed and vulcanized by sandwiching it between two rubber sheets, the rubber easily penetrates between the wires and the rubber thickness can be reduced. Also, the bending rigidity is extremely higher in the left-right direction than in the up-down direction. At this time, the steel cord is buried in a direction in which the long side of the steel cord is in the left-right direction with respect to the sheet horizontal plane, and the steel cords are arranged substantially parallel to the longitudinal direction.

[0022]

Embodiments of the present invention will be described below. FIG. 1 is a schematic view showing a cross section of a steel code of the present invention. This steel code has a substantially spiral shape.
It comprises a core wire 1 and nine side wires 2 having the same wire diameter.

FIG. 2 is a schematic view of a steel cord according to the present invention which also comprises one core strand and eight side strands.

FIG. 3 shows a single core wire and a side wire 12 similarly.
1 is a schematic view of a steel code of the present invention composed of a book and a book.

In order to evaluate the characteristics of the steel cord of the present invention, the number of strands N, the twist pitch P, the habit pitch P ₁ of the core strand, the outer diameter D ₁ , the steel cord cross section Examples 1 to 4 are steel codes in which the minor axis T and the major axis W of the elliptical shape are changed within the range of the present invention, and the numerical values of any of the constituent elements are within the scope of the present invention. The steel code having the cross section shown in FIG. 7 is referred to as Comparative Example 1 and the steel code having the cross section shown in FIG.
A steel cord having a cross-sectional shape as shown in Fig. 1 was used as a conventional example 2, and the rubber penetration rate, fatigue resistance, rigidity ratio and handling workability of each steel code were evaluated. The result as shown in FIG. Test conditions and evaluation methods for each item shown in Table 1 are as follows.

Rubber penetration rate: Each steel cord was embedded in rubber while applying a tensile load of 5 kg, and after vulcanization, the steel cord was taken out of the rubber and the steel cord was removed.
The cord was disassembled to observe a certain length of the strand, and the ratio of the observed length to the length of the trace in contact with the rubber was expressed in%. In the table, the larger the value, the better the rubber penetration rate.

Fatigue resistance: A three-point pulley using a composite sheet in which a plurality of steel cords are embedded in a rubber sheet.
The number of repetitions until the embedded steel cord breaks through fretting wear, buckling, etc., was determined by testing with a bending fatigue tester, and the twisted steel of the conventional example 2 was obtained.
The index was expressed as an index with the value of the record being 100. In the table, the larger the value, the better the fatigue resistance.

Stiffness ratio: As shown in FIG. 4 (a), "5 steel cords 3 having a 100% modulus of 35 kg
The steel sheet 4 was embedded in a row so that the longitudinal direction of the cross section of the steel code was horizontal with respect to the rubber sheet 4 of / cm2. "
As shown in FIG. 4 (b), a test piece 5 and "five steel cords 3
The test piece 6 was buried in parallel so that the longitudinal direction of the cross-section of the record was vertical. "As shown in FIG. 5, the test piece 5 or 6 was spanned with a span Sp = 20 mm.
On the three-point bending tester, which was set as follows: "Load G when test piece 5 was held down by 5 mm" / "Test piece 6"
The weight G when 5 mm is held down was defined as the rigidity ratio.

That is, the rigidity ratio was defined as "the bending rigidity of the steel cord in the minor axis direction" / the bending rigidity of the steel cord in the major axis direction. In the table, a smaller value indicates a difference in bending stiffness. The test piece 5 or 6 had a thickness of 4 mm, a width of 15 mm, and a length of 100 m.
m.

Handling operability: A sample having good operability was rated as “〇”, a sample with poor operability was rated as “x”, and a sample with an intermediate level was rated as △.

[0031]

[Table 1]

The following points are evident from Table 1. In Comparative Example 1, P _{1 of} the core strand was larger than the upper limit of the present invention, and (T
-D ₁ ) / 2d is larger than the upper limit of the present invention, and the flattening rate of the substantially elliptical shape of the code cross section is larger than the upper limit of the present invention. That is, the core wire has a large habit pitch, and the flatness is a steel code larger than the upper limit of the present invention.
This steel cord has a small gap between the wires, is inferior in rubber penetration, and has a slightly inferior rigidity ratio.

In Comparative Example 2, the value of (T−D ₁ ) / 2d is in Comparative Example 1 although P1 of the core wire falls within the range of the present invention.
In this case, the upper limit is larger than the upper limit of the present invention, and the flattening rate is higher than the upper limit. This steel
Is inferior to rubber intrusion compared to Comparative Example 1,
Both rigidity ratio and handling workability are not good.

In Comparative Example 3, both P ₁ and D ₁ of the core wire are largely out of the range of the present invention, and the flattening rate is almost the same as that of Comparative Example 2. This steel code was a poorer result than Comparative Example 2.

The steel cord of Conventional Example 1 does not have a sufficient rubber penetration rate, lacks flexibility due to a thick core wire, is inferior in fatigue resistance, and has a large cord diameter so that a rubber sheet cannot be used. Problems such as thickening occurred.

The steel cord of Conventional Example 2 has a substantially circular cross section, not an elliptical cross section. For this reason, rubber
When the steel cord is sandwiched between the rubber sheets, the thickness of the rubber sheet cannot be reduced. Also, rubber penetration, fatigue resistance, rigidity ratio and handling workability are inferior to those of the steel cords of Examples 1 to 4.

The steel cords of Examples 1 to 4 do not have the above-mentioned drawbacks and have a low rigidity ratio. When used in tires, they deform according to the force from the road surface and have a comfortable ride. And it is hardly deformed at the time of cornering.

[0038]

The steel cord for reinforcing a tire according to the present invention is constituted as described above and has the following effects. Steel code is applied over almost the entire area in the longitudinal direction.
Because there is no hermetically closed cavity in the inside of the door and the minor axis of the cross-sectional shape is extremely small (so-called thin)
Good rubber penetration into the interior of the record. Since the thickness of the rubber sheet when it is embedded in rubber to form a sheet can be extremely reduced, the weight of the tire can be reduced, and the cost of the tire can be reduced and the fuel efficiency of the automobile can be improved. The rigidity in the tire rotation direction can be reduced, so that the riding comfort can be improved. On the other hand, the rigidity in the direction orthogonal to the tire rotation direction can be increased, so that the cornering performance can be enhanced. A core wire having a small habit does not appear at both ends of the major axis of a substantially elliptical cross section, and is located substantially at the center, and has a substantially pitch P ₁ between the side wires located on both sides of the major axis.
Since they appear at intervals, the shape as a steel code is very stable, and the penetration of rubber into the inside becomes very good. Since there is no wire in a state like a core wire and all wires have a structure like a single-layer twist, fatigue resistance is improved. Conventional tuber type and buncher type can be manufactured with any stranded wire machine and there is no trouble such as poor twisting.
Excellent handling workability.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a tire reinforcing steel cord of the present invention. It is the schematic which shows the cross section of a 1 + 9 structure.

FIG. 2 shows an embodiment of a tire reinforcing steel cord of the present invention. It is the schematic which shows the cross section of a 1 + 8 structure.

FIG. 3 shows an embodiment of a tire reinforcing steel cord of the present invention. It is the schematic which shows the cross section of a 1 + 12 structure.

4A and 4B are diagrams showing test pieces used for a three-point bending test. FIG. 2A is a schematic view of a test piece for measuring bending rigidity in a short diameter direction, and FIG. It is the schematic of the test piece for bending rigidity measurement.

FIG. 5 is an explanatory view showing a three-point bending test method.

FIG. 6 is a sectional view of a conventional steel cord having a 1 + 6 structure of a close twist.

FIG. 7: Conventional close twisted 1+ with a large core strand diameter
It is sectional drawing of the steel code of 6 structures.

FIG. 8 is a cross-sectional view of a conventional 1 + 6 steel code in which a core wire is provided with a small spiral in a substantially spiral shape.

[Explanation of symbols]

1 ... Core wire 2 ... Side Element Wire 3 ... steel - Turkey - de 4 ... Gomushi - DOO 5,6 ... test pieces - scan d ... wire diameter D ₁ ... habit outer diameter W of the core wire ... steel - Turkey - Major diameter of cross section of steel T: minor diameter of horizontal cross section of steel cord S: cavity

Claims (1)

[Claims] 1. Twist to 13 strands having a wire diameter of 0.15 mm to 0.40 mm, one as a core strand, the other strands as side strands, and a twist pitch P in the same direction. In a steel cord for reinforcing a tire, the steel cord having a substantially elliptical shape (major axis W, minor axis T) having substantially the same cross-section in the longitudinal direction. pitch P ₁ and co habit of wire satisfies the following formula (1) (2) - has a habit de substantially spiral habit outer diameter D ₁ of the minor axis and the core wire is the generally elliptical the found at substantially the pitch P ₁ spacing between the side strands positioned on both sides of the major axis shaft, yet the substantially flat of elliptically shaped (T / W of the percentage) 38% 6
Tire reinforcing steel characterized by being 0%
De P ₁ = 0.1P to 0.5P (1) (T-D ₁ ) /2d=0.05 to 0.70 (2) d: Element wire diameter (mm) (core element wire diameter P ₁ : habit pitch (mm) T: code short diameter (mm) D ₁ : habit outside of core wire in the code short diameter direction Diameter (mm)