Coated steel wire and manufacturing method therefor, and cord thread

Abstract

A coated steel wire, and a manufacturing method therefor, and a cord thread. The coated steel wire comprises a steel wire substrate (1) and a single-layer or double-layer coating layer, wherein the single-layer coating layer is a CuXZn coating layer (3), and the double-layer coating layer sequentially comprises, from inside to outside, a CuZn layer (2) and a CuXZn layer (3), and is expressed as a CuZn / CuXZn coating layer, or sequentially comprises, from inside to outside, a CuXZn layer (3) and a CuZn layer (2), and is expressed as a CuXZn / CuZn coating layer, and X is selected from one of samarium, lanthanum, cerium and magnesium. Compared with a traditional CuZn coating layer, the provided coated steel wire has better salt resistance, heat erosion resistance and humidity erosion resistance, and has equivalent optimum cure adhesion, but stronger adhesion and a higher adhesion retention rate in the subsequent aging process, especially salt aging.

Description

Coated steel wire, manufacturing method thereof and cord TECHNICAL FIELD

[0001] The present application relates to the technical field of steel wire product manufacturing, in particular to a coated steel wire, a manufacturing method thereof and a cord. BACKGROUND

[0002] Steel wire products are used as skeleton materials by vulcanization reaction between rubber and the coating layer of the steel wire. In the prior art, the coating layer of the steel wire is mainly brass coating. However, in actual use, if the steel wire product is in a humid and hot air environment, the brass coating will react with the steel wire under the conditions of humidity, salinity and the like, resulting in corrosion and peeling of the steel wire or the coating layer. The periodic reciprocating stress of the steel wire product or the mutual contact with other corrosive media will also accelerate the failure of the adhesion between the steel wire product and the rubber. Therefore, how to improve the corrosion resistance of the steel wire product is the key to ensuring the service life and safety of the product. SUMMARY

[0003] The present application aims to overcome the deficiencies in the prior art and provide a coated steel wire, a manufacturing method thereof and a cord. The high corrosion resistance coating layer has better salt resistance, heat corrosion resistance and humidity corrosion resistance than the traditional CuZn coating layer, and has equivalent vulcanization adhesion, but has stronger adhesion and higher adhesion retention rate during the subsequent aging process, especially salt aging.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0005] On the one hand, the present application provides a coated steel wire, comprising a steel wire base and a coating layer. The coating layer is a single-layer coating layer or a double-layer coating layer. The single-layer coating layer is a CuXZn coating layer. The steel wire coated with the CuXZn coating layer is a CuXZn coated steel wire. The double-layer coating layer comprises a CuZn layer and a CuXZn layer from inside to outside, which is represented as CuZn / CuXZn coating layer, or comprises a CuXZn layer and a CuZn layer from inside to outside, which is represented as CuXZn / CuZn coating layer. The steel wire coated with the CuZn / CuXZn coating layer is a CuZn / CuXZn coated steel wire. The steel wire coated with the CuXZn / CuZn coating layer is a CuXZn / CuZn coated steel wire. X is selected from one of samarium, lanthanum, cerium and magnesium.

[0006] Further, the content of X in the CuXZn coating layer is 0.1-1%wt of the total amount of the coating layer. The mass ratio of copper to zinc is 1.5-2.4.

[0007] Further, the content of X in the CuXZn coating layer is 0.2-0.6%wt of the total amount of the coating layer. The mass ratio of copper to zinc is 1.75-2.0.

[0008] Further, the mass ratio of copper and zinc in the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer is 1.56-2.03.

[0009] Further, the mass ratio of copper and zinc in the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer is 1.63-1.94.

[0010] Further, in the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer, the thickness of the CuXZn layer is greater than 1 / 3 of the overall plating layer thickness.

[0011] In a second aspect, the present application provides a manufacturing method of the plating steel wire,

[0012] The manufacturing method of the CuXZn plating steel wire comprises the following steps:

[0013] Obtaining a steel wire which needs to be plated;

[0014] Plating a single metal layer on the steel wire, in the order of Cu layer, X layer and Zn layer from inside to outside;

[0015] Heating the steel wire plated with the single metal layer, so that the three-phase interfaces mutually fuse to form a CuXZn plating layer, and a plating steel wire is obtained;

[0016] The manufacturing method of the CuZn / CuXZn plating steel wire comprises the following steps:

[0017] Obtaining a steel wire which needs to be plated;

[0018] Plating a single metal layer on the steel wire, in the order of Cu layer and Zn layer from inside to outside;

[0019] Heating the steel wire plated with the single metal layer, so that the three-phase interfaces mutually fuse to form a CuZn plating layer, and a plating steel wire base is obtained;

[0020] Plating a single metal layer on the plating steel wire base, in the order of Cu layer, X layer and Zn layer from inside to outside;

[0021] Heating the plating steel wire base plated with the single metal layer, so that the three-phase interfaces mutually fuse to form a CuZn / CuXZn plating layer, and a plating steel wire is obtained;

[0022] The manufacturing method of the CuXZn / CuZn plating steel wire comprises the following steps:

[0023] Obtaining a steel wire which needs to be plated;

[0024] Plating a single metal layer on the steel wire, in the order of Cu layer, X layer and Zn layer from inside to outside;

[0025] The steel wire plated with the single metal layer is heated to make the three-phase interfaces fuse with each other to form a CuXZn plating layer, and a plating steel wire substrate is obtained.

[0026] The single metal layer is plated on the plating steel wire substrate from inside to outside in sequence of a Cu layer and a Zn layer.

[0027] The plating steel wire substrate plated with the single metal layer is heated to make the three-phase interfaces fuse with each other to form a CuXZn / CuZn plating layer, and a plating steel wire is obtained.

[0028] Further, the heating is performed by using an electrothermal process.

[0029] The electrothermal power is 3.5-4.2 kw.

[0030] The electrothermal power is 3.2-3.6 kw.

[0031] Further, in the process of plating the steel wire with the single metal layer, the residence time between plating the X layer and plating the Zn layer is ≤12 s, and the residence time of the X layer exposed to air is ≤8 s.

[0032] In a third aspect, the application provides a cord, the manufacturing material of which comprises the plating steel wire.

[0033] Further, the plating steel wire is compressed into a fine wire unit, and one or more fine wire units are twisted together in a certain direction to form a cord.

[0034] Compared with the prior art, the application has the following beneficial effects:

[0035] The plating steel wire provided by the application and the manufacturing method and the cord thereof, wherein the plating layer of the plating steel wire is a single-layer plating layer or a double-layer plating layer, the single-layer plating layer is a CuXZn plating layer, the double-layer plating layer comprises, from inside to outside, a CuZn layer and a CuXZn layer, and is represented as a CuZn / CuXZn plating layer, or comprises, from inside to outside, a CuXZn layer and a CuZn layer, and is represented as a CuXZn / CuZn plating layer, X is selected from one of samarium, lanthanum, cerium and magnesium, and by adding samarium, lanthanum, cerium or magnesium elements in the plating layer, the plating layer has better salt resistance, heat corrosion resistance and moisture corrosion resistance than a traditional CuZn plating layer, and has a comparable positive sulfurization adhesion, but has stronger adhesion and higher adhesion retention rate in a subsequent aging process, especially salt aging. BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 is a structural schematic diagram of a plating steel wire plated with a CuXZn plating layer according to an embodiment of the application;

[0037] Figure 2 is a structural schematic diagram of the plated steel wire provided by the embodiment of the present application, which is plated with CuZn / CuXZn plating layer;

[0038] Figure 3 is a structural schematic diagram of the plated steel wire provided by the embodiment of the present application, which is plated with CuXZn / CuZn plating layer;

[0039] Figure 4 is a plating layer morphology diagram of the CuLaZn plated steel wire provided by the embodiment of the present application;

[0040] Figure 5 is a plating layer morphology diagram of the CuZn plated steel wire provided by the comparative example of the present application;

[0041] Figure 6 is a corrosion morphology diagram of the CuLaZn plated steel wire provided by the embodiment of the present application in 10% salt water solution;

[0042] Figure 7 is a corrosion morphology diagram of the CuZn plated steel wire provided by the comparative example of the present application in 10% salt water solution;

[0043] Figure 8 is a corrosion morphology diagram of the CuLaZn plated steel wire provided by the embodiment of the present application eroded in 100°C hot air;

[0044] Figure 9 is a corrosion morphology diagram of the CuZn plated steel wire provided by the comparative example of the present application eroded in 100°C hot air;

[0045] Figure 10 is a corrosion morphology diagram of the CuLaZn plated steel wire provided by the embodiment of the present application eroded in 50°C / 80%RH;

[0046] Figure 11 is a corrosion morphology diagram of the CuZn plated steel wire provided by the comparative example of the present application eroded in 50°C / 80%RH.

[0047] In the figure, 1 is the steel wire substrate, 2 is the CuZn layer, and 3 is the CuXZn layer. DETAILED DESCRIPTION

[0048] The present application will be further described below in conjunction with the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0049] Example 1

[0050] The present embodiment provides a plated steel wire and a manufacturing method thereof, taking the CuLaZn plated steel wire as an example, the structure of which is shown in Figure 1, and the method comprises:

[0051] Obtain 2.05mm heat-treated wire;

[0052] The heat-treated wire is sequentially plated with Cu layer, La layer and Zn layer, wherein the raw materials of the La plating solution include lanthanum chloride heptahydrate and boric acid, the interface between the Cu layer, the La layer and the Zn layer is fused by electric heating with a power of 3.8 kw, and the CuLaZn plated steel wire is obtained.

[0053] The total residence time of the La layer is 8 s and the residence time exposed to air is 5 s before plating zinc. The prepared CuLaZn plated steel wire has a plating layer of 3.78 g / kg, a Cu content of 64.22%wt, a La content of 0.42%wt, and the rest is zinc, and the mass ratio of Cu / Zn is 1.82.

[0054] Example 2

[0055] The present embodiment provides a cord, specifically a CuLaZn plated steel wire cord, and the manufacturing material includes the CuLaZn plated steel wire as described in Example 1,

[0056] The CuLaZn plated steel wire of 2.05 mm is drawn in a liquid lubricated state to obtain a fine wire unit of 0.35 mm, and then two groups of fine wire units are twisted to obtain a CuLaZn plated steel wire cord with a 2+2 structure.

[0057] Comparative Example 1

[0058] The present comparative example 1 provides a CuZn plated steel wire and a manufacturing method thereof, and the method includes:

[0059] Obtaining a heat-treated wire of 2.05 mm;

[0060] The heat-treated wire is sequentially plated with Cu layer and Zn layer ， The interface between the Cu layer and the Zn layer is fused by electric heating with a power of 3.6 kw, and the CuZn plated steel wire is obtained.

[0061] The prepared CuZn plated steel wire has a plating layer of 3.84 g / kg, a Cu content of 64.54%wt, and the rest is zinc.

[0062] Comparative Example 2

[0063] The present comparative example provides a cord, specifically a CuZn plated steel wire cord, and the manufacturing material includes the CuZn plated steel wire as described in Comparative Example 1,

[0064] The CuZn plated steel wire of 2.05 mm is drawn in a liquid lubricated state to obtain a fine wire unit of 0.35 mm, and then two groups of fine wire units are twisted to obtain a CuZn plated steel wire cord with a 2+2 structure.

[0065] The coating structure and micro-morphology of the CuLaZn plated steel wire provided in Example 1 and the CuZn plated steel wire provided in Comparative Example 1 are shown in Fig. 4 and Fig. 5 respectively. As shown in Fig. 4 and Fig. 5, after the rare earth lanthanum is introduced into the coating, the coating morphology is obviously different from the CuZn morphology, the coating grains are refined, and the whole morphology presents a dendritic shape.

[0066] A consistent length of CuLaZn plated steel wire and CuZn plated steel wire is respectively taken, and the two are respectively placed in 10% brine to test the difference in corrosion resistance of the two.

[0067] Fig. 7 is a corrosion morphology diagram of CuZn plated steel wire immersed in 10% brine solution for 6h. As shown in Fig. 7, at this time, the CuZn plated steel wire surface has appeared multiple corrosion sites. Fig. 8 is a corrosion morphology diagram of CuLaZn plated steel wire immersed in 10% brine solution for 16h. As shown in Fig. 8, at this time, the CuLaZn plated steel wire surface is only slightly dull, but the whole CuLaZn plated surface has not been observed to have corrosion sites.

[0068] A consistent length of CuLaZn plated steel wire and CuZn plated steel wire is respectively taken, and the two are respectively placed in 100°C hot air to test the difference in corrosion resistance of the two.

[0069] Fig. 9 is a corrosion morphology diagram of CuZn plated steel wire eroded in 100°C hot air for 7d. As shown in Fig. 9, at this time, the CuZn plated steel wire surface is obviously darkened, and black rust spots are formed on the CuZn plated surface. Fig. 8 is a corrosion morphology diagram of CuLaZn plated steel wire eroded in 100°C hot air for 7d. As shown in the figure, at this time, the CuLaZn plated steel wire surface is only slightly dark, and no obvious black spot rust is formed.

[0070] A consistent length of CuLaZn plated steel wire and CuZn plated steel wire is respectively taken, and the two are respectively placed in a 50°C / 80% relative humidity chamber to test the difference in corrosion resistance of the two.

[0071] Fig. 11 is a corrosion morphology diagram of CuZn plated steel wire eroded in 50°C / 80% RH for 3d. As shown in Fig. 11, the CuZn plated steel wire surface is obviously darkened, and red rust appears on the steel wire surface. Fig. 10 is a corrosion morphology diagram of CuLaZn plated steel wire eroded in 50°C / 80% RH for 3d. As shown in Fig. 10, the CuLaZn plated steel wire surface is also darkened, but no rust spots are observed on the steel wire surface.

[0072] From the above corrosion resistance detection results, it can be seen that the CuLaZn plated steel wire provided by the embodiment 1 has a salt resistance obviously superior to the CuZn plated steel wire provided by the comparative example 1, after rust spots appear on the CuZn plated steel wire, the immersion corrosion time of the CuLaZn plated steel wire is prolonged by more than 3 times, but the surface rust spots cannot be observed, and the CuLaZn plated steel wire has a heat corrosion resistance and a wet corrosion resistance superior to the CuZn plated steel wire.

[0073] The CuLaZn plated steel wire provided by the embodiment 2 and the CuZn plated steel wire provided by the comparative example 2 are respectively vulcanized and cured with W, Y and Z different half steel cord rubber materials, after curing, 7d aging under 10% salt water condition, 14d aging under 100℃ hot air condition and 14d aging under 93℃ / 95% RH humid heat condition, the adhesion of the two plated layers is respectively tested, and the results are shown in Tables 1-3.

[0074] Table 1 Adhesion of CuLaZn plated cord and CuZn plated cord after vulcanization with W rubber material

[0075] Table 2 Adhesion of CuLaZn plated cord and CuZn plated cord after vulcanization with Y rubber material

[0076] Table 3 Adhesion of CuLaZn plated cord and CuZn plated cord after vulcanization with Z rubber material

[0077] From Tables 1-3, it can be clearly understood that when facing different rubber material systems, the direct vulcanization adhesion of the CuLaZn plated layer and the CuZn plated layer is basically equivalent, but in the subsequent aging process, the adhesion and adhesion retention rate of the CuLaZn plated layer are superior to those of the CuZn plated layer, especially in the experiment of 7d aging under 10% salt water condition, the adhesion retention rate of the CuLaZn plated layer is generally about 8% superior to that of the CuZn plated layer, and in the experiments of 14d aging under 100℃ hot air condition and 14d aging under 93℃ / 95% RH humid heat condition, the adhesion retention rate of the CuLaZn plated layer is generally about 3% superior to that of the CuZn plated layer.

[0078] Embodiment 3

[0079] The embodiment provides a CuZn / CuLaZn plated steel wire and a manufacturing method thereof, the structure is shown in Figure 2, and the method comprises the following steps:

[0080] obtaining a 2.05mm heat treated wire;

[0081] The CuZn / CuLaZn plated steel wire is obtained by successively plating Cu and Zn on the heat-treated wire, alloying the two by 3.9kw of electrothermal power, successively plating Cu layer, La layer and Zn layer on the CuZn coating, wherein the La-containing plating solution raw materials include lanthanum chloride heptahydrate and boric acid, fusing the interfaces between the Cu layer, La layer and Zn layer by 3.5kw of electrothermal power, and obtaining the CuZn / CuLaZn plated layer steel wire.

[0082] The total residence time of the La layer from plating La to plating Zn is 8s, and the residence time exposed to air is 5s. The plated layer gram weight of the prepared CuZn / CuLaZn plated layer steel wire is 3.69g / kg, the Cu content is 65.20%wt, the La content is 0.31%wt, the rest is zinc, and the mass ratio of Cu / Zn is 1.78.

[0083] Example 4

[0084] The present embodiment provides a cord, in particular a layered plated layer steel wire cord, the manufacturing material including the CuZn / CuLaZn plated layer steel wire as described in Example 3,

[0085] The CuZn / CuLaZn plated layer steel wire of 2.05mm is drawn in a liquid lubricated state to obtain a fine wire unit of 0.35mm, and then two groups of fine wire units are twisted to obtain a layered plated layer steel wire cord with a 2+2 structure.

[0086] Example 5

[0087] The present embodiment provides a CuLaZn / CuZn plated layer steel wire and a manufacturing method thereof, the structure of which is shown in FIG. 3, and the method includes:

[0088] Obtaining a heat-treated wire of 2.05mm;

[0089] The Cu layer, La layer and Zn layer are successively plated on the heat-treated wire, and the three are alloyed by 4.1kw of electrothermal power, wherein the La-containing plating solution raw materials include lanthanum chloride heptahydrate and boric acid, the Cu layer and Zn layer are successively plated on the CuLaZn coating, and the interface between the Cu layer and Zn layer is fused by 3.4kw of electrothermal power, thereby obtaining the CuLaZn / CuZn plated layer steel wire.

[0090] The total residence time of the La layer from plating La to plating Zn is 8s, and the residence time exposed to air is 5s. The plated layer gram weight of the prepared CuLaZn / CuZn plated layer steel wire is 3.71g / kg, the Cu content is 63.80%wt, the La content is 0.28%wt, the rest is zinc, and the mass ratio of Cu / Zn is 1.84.

[0091] Example 6

[0092] The embodiment provides a cord, in particular a layered plated steel cord, and a manufacturing material including a CuLaZn / CuZn plated steel wire as described in Embodiment 5,

[0093] The CuLaZn / CuZn plated steel wire with a diameter of 2.05 mm is drawn in a liquid lubrication state to obtain a fine wire unit with a diameter of 0.35 mm, and then two groups of the fine wire units are twisted to obtain a layered plated steel cord with a 2+2 structure.

[0094] The cords of Embodiments 4 and 6 and the cord of Comparative Example 2 are respectively subjected to corrosion on the cord surface in 10% brine, 100°C hot air and 50°C / 80% RH environment medium, and the corrosion resistance comparison results are shown in Table 4 below. The plated layer adhesion is tested after vulcanization and curing of the W semi-steel cord rubber, and after aging in 10% brine for 7 days, aging in 100°C hot air for 14 days and aging in 93°C / 95% RH humid heat for 14 days, and the results are shown in Table 5. The layered plated cord in Table 4 is superior to the CuZn cord in terms of salt resistance, humidity resistance and heat resistance, and also shows that the anti-corrosion ability of the cord containing La is obviously superior to that of CuZn. The layered plated cord and the CuZn cord in Table 5 are both superior to the CuZn cord in terms of adhesion in the semi-steel W rubber, and especially show better performance in salt aging resistance. The adhesion retention rate is still between 81% and 87% after aging in 10% brine for 7 days, and the addition of La obviously slows down the adhesion decay after salt water corrosion.

[0095] Table 4 Comparison of corrosion resistance of layered plated cord and CuZn plated cord

[0096] Table 5 Comparison of adhesion of layered plated cord and CuZn cord in W rubber

[0097] The embodiments of the present application are described above with reference to the drawings; however, the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative rather than limiting. Those skilled in the art can make many modifications to the present application under the guidance of the present application without departing from the purpose of the present application and the scope protected by the claims, and all of these are within the protection scope of the present application.

Claims

1. A coated steel wire, characterized in that: The steel wire includes a steel wire base and a plating layer, the plating layer is a single-layer plating layer or a double-layer plating layer, the single-layer plating layer is a CuXZn plating layer, the steel wire plated with the CuXZn plating layer is a CuXZn plating layer steel wire, the double-layer plating layer is sequentially a CuZn layer and a CuXZn layer from inside to outside, represented as a CuZn / CuXZn plating layer, or sequentially a CuXZn layer and a CuZn layer from inside to outside, represented as a CuXZn / CuZn plating layer, the steel wire plated with the CuZn / CuXZn plating layer is a CuZn / CuXZn plating layer steel wire, the steel wire plated with the CuXZn / CuZn plating layer is a CuXZn / CuZn plating layer steel wire, and X is selected from one of samarium, lanthanum, cerium and magnesium.

2. The coated steel wire according to claim 1, characterized in that: The content of X in the CuXZn plating layer is 0.1-1%wt of the total content of the plating layer, and the mass ratio of copper to zinc is 1.5-2.

4.

3. The coated steel wire according to claim 2, characterized in that: The content of X in the CuXZn plating layer is 0.2-0.6%wt of the total content of the plating layer, and the mass ratio of copper to zinc is 1.75-2.

0.

4. The coated steel wire of claim 1, wherein: The mass ratio of copper to zinc in the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer is 1.56-2.

03.

5. The coated steel wire according to claim 4, characterized in that: The mass ratio of copper to zinc in the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer is 1.63-1.

94.

6. The coated steel wire according to claim 1, characterized in that: In the CuZn / CuXZn plating layer and the CuXZn / CuZn plating layer, the thickness of the CuXZn layer is greater than 1 / 3 of the thickness of the whole plating layer.

7. A manufacturing method of the plating layer steel wire according to any one of claims 1-6, characterized in that: The manufacturing method of the CuXZn plating layer steel wire comprises the following steps: obtaining a steel wire needing plating; plating a single metal layer on the steel wire, sequentially from inside to outside, a Cu layer, an X layer and a Zn layer; heating the steel wire plated with the single metal layer, so that the three-phase interfaces are fused with each other, a CuXZn plating layer is formed, and a plating layer steel wire is obtained; The manufacturing method of the CuZn / CuXZn plating layer steel wire comprises the following steps: obtaining a steel wire needing plating; plating a single metal layer on the steel wire, sequentially from inside to outside, a Cu layer and a Zn layer; heating the steel wire plated with the single metal layer, so that the three-phase interfaces are fused with each other, a CuZn plating layer is formed, and a plating layer steel wire base is obtained; plating a single metal layer on the plating layer steel wire base, sequentially from inside to outside, a Cu layer, an X layer and a Zn layer; heating the plating layer steel wire base plated with the single metal layer, so that the three-phase interfaces are fused with each other, a CuZn / CuXZn plating layer is formed, and a plating layer steel wire is obtained; The manufacturing method of the CuXZn / CuZn plating layer steel wire comprises the following steps: obtaining a steel wire needing plating; plating a single metal layer on the steel wire, sequentially from inside to outside, a Cu layer, an X layer and a Zn layer; heating the steel wire plated with the single metal layer, so that the three-phase interfaces are fused with each other, a CuXZn plating layer is formed, and a plating layer steel wire base is obtained; plating a single metal layer on the plating layer steel wire base, sequentially from inside to outside, a Cu layer and a Zn layer; heating the plating layer steel wire base plated with the single metal layer, so that the three-phase interfaces are fused with each other, a CuXZn / CuZn plating layer is formed, and a plating layer steel wire is obtained.

8. The manufacturing method of the plating layer steel wire according to claim 7, characterized in that: The heating is performed by using an electric heating process; The power of the electric heating is 3.5-4.2kw when the steel wire is heated to coat the single metal layer; The power of the electric heating is 3.2-3.6kw when the plated steel wire substrate is heated to coat the single metal layer.

9. The method of claim 7, wherein: The residence time between coating X layer and coating Zn layer is less than 12s, and the residence time of X layer exposed to air is less than 8s.

10. A cord characterized by: The manufacturing material comprises the plated steel wire as claimed in any one of claims 1-6; the plated steel wire is compressed into a fine wire unit, and one or more fine wire units are twisted together in a certain direction to form a cord.

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