STEEL CORD FOR RUBBER ENHANCEMENT AND MANUFACTURING METHOD THEREFOR

Abstract

The present invention relates to a steel cord for rubber reinforcement wherein a steel wire for steel cord has a plating layer of a ternary or quaternary alloy.

The steel wire for the steel cord of the present invention comprises a plating layer of Cu-M-Zn (M is one or two elements of Co, Ni, Cr, Mo, Al, In, or Sn) and has a concentration gradient in which the M content ratio in a region from the surface to ¼ of the plating layer is 40% or more compared with the M content ratio in the entire region of the plating layer, and the steel cord for rubber reinforcement is obtained by a manufacturing method comprising: performing sequential plating on a surface of a steel wire in the order of Cu.fwdarw.M.fwdarw.Zn; performing a primary diffusion, for concentration gradient of M, by subjecting the sequentially plated steel wire to high-frequency induction heating using 1-500 MHz; and performing a secondary diffusion, following the primary diffusion, by medium-frequency induction heating using 10-500 KHz.

Claims

1. A steel cord for rubber reinforcement, comprising at least one strand of a plated steel wire, wherein the steel wire comprises a plating layer of Cu-M-Zn (M is one or two elements of Co, Ni, Cr, Mo, Al, In, or Sn) and has a concentration gradient in which the M content ratio in a region from the surface to ¼ of the plating layer is 40% or more compared with the M content ratio in the entire region of the plating layer.

2. The steel cord for rubber reinforcement of claim 1, wherein the plating layer has a concentration gradient in which the M content ratio in a region from the surface to ½ of the plating layer is 20% or more compared with the M content ratio in the entire region of the plating layer.

3. The steel cord for rubber reinforcement of claim 1, wherein M is Co.

4. The steel cord for rubber reinforcement of claim 1, wherein the total content of M in the plating layer is 0.5-20 wt %.

5. The steel cord for rubber reinforcement of claim 4, wherein the proportion of Cu in Cu and Zn excluding M in the plating layer is 60-70 wt %.

6. The steel cord for rubber reinforcement of claim 1, wherein the diameter of the steel wire is 0.1-0.4 mm and the average thickness of the plating layer is 0.1-0.4 μm.

7. The steel cord for rubber reinforcement of claim 1, wherein the ZnO content in the surface of the plating layer is 35-50 mg/m.sup.2.

8. A method for manufacturing a steel cord for rubber reinforcement, the method comprising: performing sequential plating on a surface of a steel wire in the order of Cu.fwdarw.M.fwdarw.Zn (Mn is one or two elements of Co, Ni, Cr, Mo, Al, In, or Sn); performing a primary diffusion, for concentration gradient of M, by subjecting the sequentially plated steel wire to high-frequency induction heating using 1-500 MHz; and performing a secondary diffusion, following the primary diffusion, by medium-frequency induction heating using 10-500 KHz.

9. The method of claim 8, wherein the steel wire subjected to the primary diffusion and the secondary diffusion has a concentration gradient in which the M content ratio in a region from the surface to ½ of the plating layer is 20% or more compared with the M content ratio in the entire region of the plating layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a cross-sectional view of a ternary alloy plating layer of a steel wire for a steel cord according to the present invention.

[0046] FIG. 2 is a graph showing the Co content in a region from the surface to ¼ of the plating layer in a Co containing product.

[0047] FIG. 3 is a graph showing the Co content in a region from the surface to ½ of the plating layer in a Co containing product.

[0048] FIG. 4 shows the steam aging adhesion index of the steel cord according to the Co content in rubber.

MODE FOR CARRYING OUT THE INVENTION

[0049] The manufacturing method including the above-described objects and technical features of the present invention can be understood more detail through the following examples. The present examples are included in desirable examples provided for understanding of the present invention, and the protection scope of the present invention is not limited or restricted by the examples.

[0050] First, a steel wire for a steel cord, having a wire diameter of 1.75 mm, was prepared. The surface of the steel wire was subjected to sequential plating in the order of Cu.fwdarw.M.fwdarw.Zn to form a ternary alloy plating layer having a section as shown in FIG. 1. Co as a third element was used in a varied content within a range of 1-20%. A plurality of samples of examples and comparative examples shown in Table 1 below were prepared by varying the contents of three alloy elements constituting the plating layer.

[0051] In order to investigate the adhesive characteristics and drawing workability behavior according to the Co content and the concentration gradient in the surface portion, the samples were subjected to induction heating diffusion. In order to give a concentration gradient of Co to the plating layer of each sample, each sample was subjected to induction heating diffusion twice using different frequencies by using a skin effect of the inductive heating diffusion.

[0052] First, primary induction heating was carried out using a high frequency of 500 MHz such that diffusion occurs in the surface of the plating layer, that is, only a Co—Zn plating layer, and then secondary induction heating was carried out using a medium frequency of 30 KHz such that diffusion occurs in the entire region of the plating layer, that is, a Cu—Co—Zn plating layer. The measured diffusion temperature of the plating layer was 420° C. and the diffusion time was 5 s for the primary induction heating and 10 s for the secondary induction heating, so that a concentration gradient with respect to the Co content ratio was configured such that the Co content ratio was high in the surface portion of the plating layer and the Co content ratio was reduced closer to the substrate steel.

[0053] In Table 1 below, the sample of Comparative Example 1 was a conventional brass plated steel wire containing no Co, and was prepared to compare adhesion with ternary alloy plating layers containing Co. The sample of Comparative Example 2 was prepared to investigate whether the concentration gradient of the Co metal element is obtained by high-frequency diffusion. Sequential plating of Cu—Co—Zn was carried out such that the Co content was 5 wt %, and then only primary induction heating was carried out using a medium frequency of 30 KHz while the diffusion temperature was 420° C. and the diffusion time was 15 s.

[0054] The 1.75 mm-diameter samples obtained through such a procedure were drawn into a diameter of 0.3 mm through wet drawing, and thereafter, three wire strands of the same steel wire sample were joined to manufacture a 3×0.30 steel cord.

[0055] In order to investigate the Co %, Cu %, and adhesive amount in the plating layer of a steel wire for a steel cord, ICP was used, and in order to analyze the Co % in regions from the surface to ¼ and ½ of the plating layer, each plated wire was immersed in a 25% brass striper solution for a calculated time, to dissolve a portion of the surface of the plating layer, wherein the time for immersion was obtained from the following calculation equation. In addition, the Co content at each position was analyzed to check a concentration gradient.

[0056] (1) The time for immersion to dissolve a region from the surface to ¼ of the plating layer (s)=CW/4*(80.186*D−21.862) [0057] (1) The time for immersion to dissolve a region from the surface to ½ of the plating layer (s)=CW/2*(80.186*D−21.862)

[0058] * C/W: total plating adhesive amount (g/kg), D: wire diameter (mm)

[0059] The plated steel wire samples obtained from the manufacturing process were subjected to wet drawing to evaluate drawing workability, and rubber products having steel cords embedded therein manufactured using these steel wire samples were evaluated for initial and damp-heat aging adhesiveness according to the Co content change.

TABLE-US-00001 TABLE 1 Comparative Comparative Example Example Example Example Example Example Classification Example 1 Example 2 1 2 3 4 5 6 Induction Primary 30 KHz 30 KHz 5000 MHz 500 MHz 500 MHz 500 MHz 500 MHz 500 MHz heating Secondary — —  .sup. 30 KHz .sup. 30 KHz .sup. 30 KHz .sup. 30 KHz .sup. 30 KHz .sup. 30 KHz frequency Cu/(Cu + Zn) 62 62 62 62 62 62 62 62 Zn/(Cu + Zn) 38 38 38 38 38 38 38 38 Co/(Cu + Zn + Co in entire — 5 1 3 5 7 10 20 Co) layer Co in region — 5 1.4 4.2 7 9.8 14 28 from surface to ¼ Co in region — 5 1.2 3.6 6 8.4 12 24 from surface to ½ Drawing workability ⊚ Δ ◯ ◯ ◯ ◯ ◯ ◯ Adhesive Initial ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ characteristics Damp-heat X Δ ◯ ◯ ⊚ ◯ ◯ ◯ aging

[0060] Drawing Workability and Adhesive Characteristics by Alloy Composition of Plating Layer and Diffusion Heating Process

[0061] As shown in Table 1 above, in Comparative Example 2 in which only primary diffusion after sequential plating was carried out, the Co concentration was 5%, uniform over the entire region of the plating layer, but Examples 1 to 6 in which diffusion was carried out twice using different induction heating frequencies showed concentration gradients in which the Co contents in the regions from the surface to ¼ and ½ depth of the plating layer were 40% or more and 20% or more compared with the total Co content, respectively. FIG. 2 is a graph showing the Co content in the region from the surface to ¼ of the plating layer in Examples 1-6, and FIG. 3 is a graph showing the Co content in the region from the surface to ½ of the plating layer in Examples 1-6.

[0062] As shown in the measurement results of drawing workability and adhesive characteristics in Table 1, the drawing workability and damp-heat aging adhesion were excellent in Examples 1-6 having concentration gradients rather than when Co was uniformly distributed over the entire region of the plating layer (Comparative Example 2).

[0063] In addition, when comparing steel cord products composed of steel wires of ternary alloy plating layers (Examples 1-6) with the general brass plated steel cord (Comparative Example 1), the initial adhesion was similar, but the damp-heat aging adhesion was significantly excellent in the products of the examples, and especially, a greatest improvement effect was shown when the Co content was 5 wt %.

[0064] Table 2 below shows the results of measuring the change in steam aging adhesion according to the Co content in rubber when the steel cord of Example 3 (Co 5 wt %) on Table 1 above was embedded in the rubber with a varied Co content in the rubber. The adhesion data were expressed as an index on the basis of the adhesion value of Comparative Example 1 (brass plated steel cord) on Table 1 above.

TABLE-US-00002 TABLE 2 Co content in rubber Steam aging adhesion Classification (ppm) index A 1157 145 A(Co-free) 0 333 B 960 145 B(Co-free) 0 161 C 1062 206 D 1195 141 E 1559 106 F 1061 250 G 703 195 H 2094 89 I 1282 110

[0065] Adhesion Index According to Co Content in Rubber

[0066] As shown in Table 2 above, as the steam aging adhesion according to the Co content in rubber, the smaller the Co content in the rubber, the greater the adhesion enhancement effect, for the same type of ternary alloy steel cords, and a greater adhesion enhancement effect was shown in the absence of Co for the same kind of rubbers.

[0067] FIG. 4 is a graph showing the measurement results of Table 2 above. Through the measurement results, the aging of tires can be prevented by varying the Co content and the concentration gradient in steel cord products according to the kind of rubber, and the steel cords formed of ternary alloy plated steel wires can be used to exhibit adhesive characteristics in substitution for a role of the cobalt compound in tire rubber, and it is therefore expected that environmentally preferable tires free of cobalt can be realized.