JP2942880B2 - Steel wire for rubber reinforcement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber reinforcing steel wire, and more particularly to a rubber reinforcing steel wire having low tensile surface residual stress characteristics.

[0002]

2. Description of the Related Art Steel cords are widely used as reinforcing materials for rubber products such as steel radial tires, high-pressure hoses and conveyor belts. Such steel cords generally have a carbon content of 0.6%. A steel wire made of the above high carbon steel and having a diameter of 0.05 to 0.80 mm is used, and the steel wire is made of copper, brass, zinc or a main component of the outermost layer in order to improve adhesion to rubber. Is plated. In order to enhance the reinforcing effect, such a steel wire for rubber reinforcement is cold-worked, especially by a drawing method using a die,
The strength of the material is increased.

[0003] However, due to the drawing of the dies at this time, a residual stress on the tensile side generally remains on the surface of the steel wire, and in addition to the residual stress existing on the surface, a tensile or bending stress is applied to the rubber product. . For this reason, due to such repetitive stress, a fatigue phenomenon appears in the steel wire, crack generation and propagation progress, and eventually, the strength and fatigue property of the rubber reinforced product are deteriorated. For these reasons, it is considered that the lower the tensile stress remaining on the surface of the steel wire, the better, and it is desirable that the tensile stress be on the compression side if desired. From such a viewpoint, the steel wire after drawing is subjected to bending using many small-diameter rolls,
A method of reducing the residual stress by, for example, applying shot blast to the surface of a steel wire has been proposed.

However, the small-diameter roll bending method causes a decrease in physical properties such as a decrease in breaking load, and also easily damages a plating layer that imparts adhesion to rubber, which is an important property of a rubber reinforcing material. Has disadvantages. On the other hand, in the shot blast method, fine particles hit the steel wire surface,
It is unsuitable for a rubber reinforcing material since fine sand particles remain or the sand particles cause damage to the plating layer. As another treatment method, stress can be relaxed by heat treatment, but there is a problem that the plating for bonding rubber is oxidized by heating and the adhesion is hindered.

The present invention has been made by research to solve the above-mentioned problems, and it is an object of the present invention to provide a rubber having good adhesion to rubber, moderate elongation and good fatigue resistance. It is an object of the present invention to provide a rubber reinforcing steel wire which can be mass-produced relatively inexpensively.

[0006]

In order to achieve the above object, the present invention is based on a high carbon steel having a carbon content of 0.6% or more, and has a rubber reinforced rubber plating on the outermost layer thereof. In steel wire used for
The steel wire has a shaping ratio (height H / wire diameter d × 100) of 200% or more and 300% by a gear-shaped machining mechanism.
Less, shaping pitch length P (= P / wire diameter d) 4.5-2
0, has a two-dimensionally continuous wavy bent portion subjected to strong crimping, has an elongation at break of 6.0% or more, and has a residual stress on the wire surface in the circumferential direction inside the bending process.
The outer side has a low tensile or compressive side residual stress.

Hereinafter, the present invention will be described in detail. A steel wire is embedded in a rubber matrix and functions as a reinforcing material by being bonded to rubber. For this reason, high-carbon steel having a carbon content of 0.6% or more is usually made of high-carbon steel having a diameter of 3.0%. A wire drawn to 0.3 mm is used as a starting material. If the carbon content is less than 0.6%, the strength is low and the reinforcing effect is small, so that it is inappropriate. The upper limit is generally 0.7 to 0.92%, mainly on the order of 0.8%, since the uniform solid solubility limit of carbon is 1.0% or less.
This plated wire is subsequently drawn. For this wire drawing, a drawing die is used.
A plurality of stages are carried out in the cold until a predetermined diameter is reached within the range of 0 mm. By this drawing, the strength of the wire is improved and the surface is smoothed, but residual stress on the tensile side remains on the surface.

As a countermeasure against this tensile surface residual stress, the present invention basically applies crimping to a drawn linear wire having a residual stress distribution on the tensile side, as shown in FIG. Dimensionally continuous wavy bends 1,1
Is formed. A steel wire having such wavy bent portions 1 and 1 can follow a certain degree of elongation in rubber, and has a compressive stress distribution in the wire circumferential direction, that is, a bent outer side, and a tensile strength in the inner side. Has a stress distribution of That is, when a steel wire is subjected to a tensile stress, a larger tensile stress acts on the inside of the bend than on the outside, so that such a portion becomes a starting point of fatigue, and fracture from the outside is reduced. Based on this, the inventors paid attention to crimping, and wondered whether it would be possible to produce wires with low residual stress on the tensile side or on the compressive side, both inside and outside of the bent wire. As a result of the intensive research, as a trial, a wire was passed through a processing mechanism having gear-shaped irregularities, and the shaping rate (H /
d × 100) was subjected to a 130% crimping process.

However, when the crimped wire was examined for the stress state in the bent portion, the elongation at break, which is an important physical property of the rubber reinforcing material, was reduced by 2.5% even with the above-described weak processing. Although the above can be achieved, an ideal result was not obtained for the surface residual stress. Then, the reason why the effect of improving the surface residual stress was not obtained under the above conditions was examined. As a result, under the above conditions, since the shaping ratio is a weak crimping process with a small shaping ratio, only a loose simple bending process is performed between the tooth molds 200, 200, and 300 as shown in FIG. It is considered that when the wire W left the tooth form, an elongation behavior as shown by an arrow in FIG. 6 occurred. Therefore, the crimping process for the wire manufactured by the cold drawing process is performed with the shaping ratio (H
/ D × 100) from 130 to 320.
The correlation between the shaping ratio and the stress state of the bent part was examined and analyzed, and the optimum processing conditions for crimping were determined in consideration of elongation at break as one of the important physical properties of rubber reinforcing materials.

As a result, the shaping ratio (H / d × 100) is 2
It has been found that when crimping is performed at a rate of 00% or more, the surface residual stress in the circumferential direction of the wire is rearranged, and low tensile strength and residual stress on the compression side can be left outside or inside the bending process. The surface residual stress is based on the value obtained from the (220) crystal spacing of α-Fe, particularly the X-ray diffraction method. To be more specific, 100 to 200 μm
X-rays are radiated only to a small part called φ, and 2θ and SIN ² ψ
According to the diagram, the SIN ²ら れ る value obtained from the linear portion is 0.1 to
In this method, the stress is obtained by a gradient in the range of 0.5, and this method enables accurate and quantitative measurement of a residual stress of 10 μm from the surface toward the center of the wire.

FIGS. 2 to 4 show a method of performing such a high crimping process by increasing the shaping ratio. The wire W is provided with the radiused edges 20 of the two first tooth forms 2 and 2.
The second tooth form 2 is engaged with the first tooth forms 2, 2, and is processed by contacting the four points of the rounded edges 30, 30 on both ends of the second tooth form 3. Clearance with 2 tooth mold 3
(Backlash) 4 is intentionally set to be large. In this case, since the gap 4 between the first and second tooth molds 2 and 2 and the second tooth mold 3 is large, the wire W is easily drawn into the tooth mold at the time of processing, and therefore, as shown in FIG. The bending radius R is smaller than in the case where the shaping ratio is small, and the bent portion 10 is buckled. At this time, the edges 30 with rounded ends on both sides of the second tooth mold 3 try to spread the angle θ between the right side portions 100 from the inside of the bent portion 10 as shown by the arrow in FIG. Thereby, the bending section 1
0, when the wire W leaves the tooth form, a movement (spring-back phenomenon) is generated, as shown in FIG. 4, so that the outside of the bent portion 10 has a low tension and the inside has a residual stress on the compression side. As shown.

Such characteristics can be obtained only when the shaping ratio is 20
If the shaping ratio is less than 0%, the surface residual stress characteristics are insufficient. However, if the shaping ratio is excessively high, the effect of improving the residual surface stress is sufficiently satisfied, but the elongation is too large to function as a rubber reinforcing material, which is not suitable. Therefore, the upper limit shaping ratio is less than 300%. is there. It is appropriate that the shaping pitch length P is 4.5 to 20 in wire diameter magnification (P / d). The reason is,
If the wire diameter ratio is less than 4.5, the tooth mold used for crimp molding becomes dense, and there is a problem that it is difficult to remove the radius of the portion where the tooth mold contacts the wire, which is not practical. Also,
This is because if the wire diameter magnification is 20 or more, the wire has an unnatural bend before crimping, which remains after crimping.

[0013]

Next, an embodiment will be described. High carbon steel (C:
0.82%, Si: 0.2%, Mn: 0.45%, P: 0.01%, S: 0.005% balance iron and unavoidable impurities) 1. 70 mmφ wire is copper, zinc plated by diffusion plating method and then heat treated The plating layer was alloyed to obtain 63.5% Cu and the amount of adhesion was 4.
0 g / kg of plating was applied. The wire was drawn to a small diameter sequentially using a drawing die, and 0.30 m
An mφ wire was obtained. The straight wire thus obtained was subjected to crimping using a pair of tooth molds having a center distance of 100 mm, tooth shape: parallel teeth, 98 teeth, and a tooth height of 1.5 mm, and crimping the wire diameter ratio of the pitch (P / d): At 12, the shaping rate was changed as described below, and the measurement of the residual stress distribution and the elongation at break of the bent portion of each wire were performed. The residual stress was determined from the 200-crystal spacing of α-Fe by X-ray diffraction. Table 1 shows the results.

[0014]

[Table 1]

From Table 1, it can be seen that the shaping rate is 200% or more,
By setting it to less than 300%, it has a good elongation at break of 6.0 to 15%, and the surface residual stress can be set to a low tension or compression even outside or inside the bent portion. You can see that there is.

[0016]

As described above, according to the present invention,
Based on high carbon steel with a carbon content of 0.6% or more, the outermost layer is provided with a plating that imparts rubber adhesiveness, and the steel wire used for rubber reinforcement is shaped by a gear-shaped machining mechanism (shape height). H / wire diameter d × 100) 200%
It is strongly crimped at a shaping pitch length P (= P / wire diameter d) of 4.5 to 20 and has a two-dimensionally continuous wavy bent portion, and the elongation at break is less than 300%. 6.0%
As described above, due to the springback phenomenon at the time of strong crimping by the gear-shaped machining mechanism, the residual stress on the wire surface becomes low tensile or compressive residual stress both inside and outside of the bending in the circumferential direction. Therefore, it is possible to obtain a rubber reinforcing wire that has good adhesion to rubber and has appropriate elongation and good fatigue resistance.
In addition, an excellent effect is obtained in that such characteristics can be mass-produced relatively inexpensively.

[Brief description of the drawings]

FIG. 1 is an enlarged side view showing one embodiment of a steel wire for rubber reinforcement according to the present invention.

FIG. 2 is an explanatory view showing a crimping state according to the present invention.

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is an explanatory view showing a state of a bent portion immediately after leaving a machining tooth mold.

FIG. 5 is an explanatory view showing a crimping state outside the condition range of the present invention.

FIG. 6 is an explanatory view showing a state of a bent portion immediately after the processing tooth form is released in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wavy bending part 10 Machining part H The height of the peak of a wavy bending part d Wire diameter P Shaping pitch length

Claims (1)

(57) [Claims] 1. A steel wire used for reinforcing rubber having a carbon content of 0.6% or more as a base and having a plating for imparting rubber adhesiveness to an outermost layer thereof, wherein the steel wire is a gear wheel. Forming ratio (height H / wire diameter d × 100) is 200% or more 30 by the shape processing mechanism
Less than 0%, shaping pitch length P (= P / wire diameter d) 4.5
-20, having a two-dimensionally continuous wavy bent portion subjected to strong crimping, having an elongation at break of 6.0% or more, and having a residual stress on the wire surface in the circumferential direction of the bending process. A steel wire for rubber reinforcement characterized in that both inside and outside have low tensile or compressive residual stress.