KR20090073296A - Method of manufacturing steel wire for high tensile steel cord - Google Patents

Abstract

A method of manufacturing a steel wire for a high tensile steel cord is provided to prevent delamination from being generated in high speed drawing by appropriately controlling final drawing condition. A method of manufacturing a steel wire for a high tensile steel cord comprises following steps. A hot rolled wire which has the diameter of 4~7mm and consists of carbon content of 0.90 ~ 0.97 weight% and chromium content of 0.10 ~ 0.40 weight% is brass-plated through a drawing process and a thermal process. The wire plated with brass passes through multiple dices which is installed inside a wet drawing machine. The final drawing process of the wire is performed to draw the wire in a longitudinal direction of the wire. The approach angle(5) of the dice installed inside the wet drawing machine is 7~9°. The approach length is 2~4 times of the diameter of the dice. The slippage of the dice is 1~3%. The diameter of the steel wire for the steel cord is 0.1 ~ 0.4 mm. The tensile strength of the steel wire for the steel cord is 360 ~ 420 kg/mm^2.

Description

Method for manufacturing steel wire for ultra high strength steel cords {Method of Manufacturing Steel Wire for High Tensile Steel Cord}

The present invention relates to a method for producing steel wire for ultra high strength steel cord, and more particularly, in the final drawing step, drawing is carried out in the longitudinal direction of the wire rod by appropriately controlling the processing conditions so that the drawing is carried out step by step within a certain range of reduction rate. The present invention relates to a method for manufacturing a steel wire for steel cord to obtain a wire rod having a desired diameter.

Conventionally, steel cord steel wire used for reinforcement in rubber products such as tires is generally processed through steelmaking, manufacturing of hot rolled wire, drawing, heat treatment (patenting), drawing, heat treatment, coating (plating), and drawing. It is manufactured as follows.

First, one time of heat-treatment and one to two fresh processing are performed by using hot rolled wire of constant diameter (mostly 5.5 mm) made of carbon steel with carbon content of 0.6 to 0.97% by weight. A steel wire with a diameter of 0.8 to 2.0 mm is produced.

Then, in order to recover the processed internal metal structure, once again the heat-treating heat treatment is performed, and then copper plating of 0.5 to 1.5 μm thick is performed, and zinc plating of 0.3 to 1.0 μm is sequentially performed thereon. The thermal diffusion process of the method is carried out to obtain a brass plated layer. Thereafter, when the brass plated wire rod is drawn to a diameter of 0.1 to 0.6 mm, a steel wire for steel cord is introduced into the rubber product for reinforcement.

Wire rods manufactured in this way are used by twisting into various structures (1x3, 1x4, 2 + 2, 2 + 7, 3 + 6, 3 + 9 + 15, etc.), depending on the application, such as strength, modulus, heat resistance, and heat resistance. Fatigue is superior to other types of inorganic and organic fibers, and is useful for reinforcing rubber products such as tires and conveyor belts.

In the case of tire steel cord steel wire, the tensile strength of the wire should have a strength of at least 280 Kg / mm2. Generally, the tensile strength of the wire is 280 to 300 Kg / mm2. High Tensile steel cord with a strength of 320 to 340 Kg / mm 2, 360 to 380 Kg / mm 2 (Super Tensile) steel cord and 400 to 420 Kg / mm 2 (Ultra Tensile) It is classified as a steel cord.

As the present invention, if the steel cord steel wire has high strength characteristics, it can satisfy the sufficient rigidity even in a small amount compared to the existing steel cord, so that the weight and rolling resistance of the tire can be improved, thereby reducing the cost and improving fuel economy. Has a useful effect to obtain.

However, it is also important to secure the tensile strength of the ultra-high strength steel wire described above, but above all, the required characteristic of the steel cord steel wire is that there should be no disconnection phenomenon during drawing and high speed stranded wire work. In particular, in the case of the steel wire of the ultra-high strength steel cord, since the tensile strength must satisfy the strength characteristic of 380 Kg / mm2 or more, about 0.20 wt% of chromium, which is a carbon hardening element of 0.90 wt% or more, and a work hardenability reinforcing element It is common to add. However, in this case, since high alloy is added, when excessive reduction ratio (%) of high carbon steel is applied during processing (typically 96% or more), a torsional stress is applied in the twisted line process, and a delamination, which is a splitting phenomenon of the line, occurs. There is a problem, and there has been a difficulty in producing high strength steel cords.

Hereinafter, the delamination phenomenon will be described in detail.

Delamination is a helical C-shaped fracture of the wire breakage that is instantaneously propagated by surface cracks in the longitudinal direction when the residual stress of the wire subjected to work deformation by the wire remains, and receives the transverse stress (twist) of the wire. It is a phenomenon that indicates a defect, and occurs mainly when the deformation of the high-carbon and high-alloy steel is large and the line surface temperature is high.

In order to solve this problem, conventionally, the total reduction ratio (area ratio between the initial wire diameter area and the final wire diameter) is made as small as possible to reduce the amount of deformation, thereby reducing the surface residual stress. In this technique, the decrease in strength due to the reduction of the total reduction rate was reduced by the addition of alloying elements, and the surface stress concentration was dispersed by proper die approach angle. In addition, the lubricant was suitably used to suppress the surface temperature increase caused by surface friction and to minimize the roughness of the die, thereby reducing the surface roughness and reducing the delamination.

However, the above conventional method has the following problems.

First, the method of reducing the total reduction rate and adding an alloy has a problem of a cost increase due to the addition of the alloy, and for the manufacture of ultra fine wires of 0.30 mm or less, the total reduction rate exceeds 96% and still causes delamination. do. In particular, it is difficult to apply this method recently due to the trend of ultra fine wire for improving tire performance of steel cords.

Second, although the surface stress concentration is dispersed to some extent by reducing the die approach angle, as the angle decreases, the die life is significantly reduced, and it is difficult to completely remove the surface stress.

Third, the method of optimizing the lubricant and reducing the surface roughness only exerts a subtle effect and does not solve the fundamental problem of delamination.

The present invention has been made to solve the above-mentioned problems in the prior art, and an object of the present invention is to control the final wire drawing conditions properly, so that no delamination occurs even when high speed wire is drawn, and the diameter is 0.1 to 0.4 mm, and the tensile strength is achieved. It is to provide a method for producing a steel wire for ultra-high strength steel cord is 360 to 420 kg / ㎜.

In order to achieve the above object, one aspect of the present invention is the drawing process and heat treatment process using a hot rolled wire having a carbon content of 0.90 to 0.97 wt%, chromium content of 0.10 to 0.40 wt% and a diameter of 4 to 7 mm After the brass plating through, the method of producing a steel wire for the steel cord comprising the step of final drawing the wire rod to be drawn in the longitudinal direction of the wire rod to pass through the multiple dies installed inside the wet wire drawing machine. To

In the final drawing step, the approach angle of the die installed in the wet drawing machine is 7 to 9 degrees, the approach length is 2 to 4 times the diameter of the die, and the slip ratio of the die is 1 to 3%, characterized in that Provided is a method for producing a steel wire for a cord.

According to one embodiment, the steel wire has a diameter of 0.1 to 0.4 mm, the tensile strength is 360 to 420 kg / mm2.

The method for producing steel wire for steel cords provided by the present invention has no delamination even with high speed drawing by optimizing the final drawing conditions, and has a diameter of 0.1 to 0.4 mm and a tensile strength of 360 to 420 kg / mm2. It can manufacture ultra high strength steel wire, and it has the effect of improving die usage and disconnection rate.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In one aspect of the present invention after using the hot-rolled wire having a carbon content of 0.90 to 0.97 wt%, a chromium content of 0.10 to 0.40 wt% and a diameter of 4 to 7 mm after brass plating through a drawing process and a heat treatment process, In the method of manufacturing a steel cord steel wire comprising the step of final drawing the wire rod to be drawn in the longitudinal direction of the wire rod to pass through the plurality of dies installed inside the wet wire drawing of the brass plated wire,

In the final drawing step, the approach angle of the die installed in the wet drawing machine is 7 to 9 degrees, the approach length is 2 to 4 times the diameter of the die, and the slip ratio of the die is 1 to 3%, characterized in that The manufacturing method of the steel wire for cords.

In the drawing process performed to obtain a desired diameter of the steel cord manufacturing process, the steel wire is drawn through the die as shown in FIG. The die consists of a tip through which the actual steel wire passes and a case surrounding the tip, and the tip is divided into four parts, specifically, a bell and an actual steel wire that facilitates the introduction of lubricant. Approach that reduces the cross-sectional area of steel wires and causes friction with the bearing, bearings that determine the actual wire diameter, and back relief to prevent the die strength and fresh steel wires from tensioning due to tension when drawing It consists of).

The shape of the die is determined and used in the most suitable form according to the material and the wire diameter of the wire to be drawn. In addition, die tips of various materials are used depending on the application, but generally used in a steel cord manufacturing process are alloy die tips obtained by sintering tungsten carbide (WC) powder at a high temperature. In general, the conventional alloy die tip has an approach angle of 10 to 12 degrees, the approach length is 1 to 8 times the die diameter, the bearing length is about 0.1 times to 0.6 times the wire diameter, and the angle of the back relief is 30 degrees to 120 degrees. It is suitably determined and used within the range.

In the present invention, the die approach angle is preferably 7 to 9 degrees. If the angle of approach is less than 7 degrees, the die life is considerably reduced as the angle becomes too small, and the tensile stress in the center of the steel wire is excessively concentrated, which is likely to cause breakage, and if the angle of approach exceeds 9 degrees Too large an effect of dispersing the surface stress of the wire can be reduced.

In addition, the approach length is preferably 2 to 4 times the die diameter. If the approach length is less than 2 times the die diameter, the steel wire and friction area become too short, so the stress is concentrated on the surface, and it is difficult to obtain the desired wire diameter.If the approach length exceeds 4 times the die diameter, it acts as a lubrication when drawing. Since the inflow of the wet lubricating fluid becomes difficult, the disconnection phenomenon and the wear of the dies occur quickly.

And it is preferable to make die slip ratio into 1 to 3%. This is to introduce the die slip ratio concept in consideration of both the die reduction rate and mechanical reduction rate in wet drawing, and to set an appropriate die slip rate range, for example, as shown in Equation 1 below. If the die slip ratio is less than 1%, the wire diameter of the steel wire becomes larger than the die diameter and the die wears out quickly.If the die slip ratio exceeds 3%, the wire diameter of the steel wire becomes smaller than the die diameter. It is highly likely to cause shortage of wire diameter and disconnection due to excessive force.

[Equation 1]

i-th Dies slip ratio = 1- (1-r _{i +1} ) / (1-R _{i +1} )

(In the above formula, r _{i +1} : i + 1 th die reduction rate, R _{i +1} : i + 1 th machine reduction rate.)

Hereinafter, although an Example etc. demonstrate this invention further more concretely, the scope of the present invention is not limited by the Example etc. which are described below.

In the following examples and comparative examples, the bearing length was 0.3 times the wire diameter, the back relief angle was equally applied to 90 degrees.

Example  One

As shown in Table 1, using a hot rolled wire having a diameter of 5.5 mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt%, the wire with a diameter of 1.50 mm of brass plated was drawn to a diameter of 0.25 mm. At this time, a die having an approach angle of 8 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 2%. After the final drawing was made to prepare a steel wire for ultra-high strength steel cord of the present invention, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  One

In a conventional method, a hot rolled wire having a diameter of 5.5 mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt% was drawn to a diameter of 0.25 mm with a brass plated diameter of 1.50 mm. At this time, a die having an approach angle of 4 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 2%. After the final drawing was made to prepare a steel wire for ultra-high strength steel cord of the present invention, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  2

In another conventional method, a hot rolled wire of 5.5 mm in diameter having a carbon content of 0.90 wt% and a chromium content of 0.20 wt% was drawn to a diameter of 0.25 mm in a brass plated diameter of 1.50 mm. At this time, a die having an approach angle of 12 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 2%. After the final drawing was made to prepare a steel wire for ultra-high strength steel cord of the present invention, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  3

In another conventional method, a brass plated wire rod having a diameter of 1.50 mm was drawn to a diameter of 0.25 mm using a hot rolled wire having a diameter of 0.9 mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt%. At this time, a die having an approach angle of 8 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 2%. After the final drawing was made to prepare a steel wire for ultra-high strength steel cord of the present invention, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  4

In another conventional method, a 1.50 mm diameter brass plated wire was drawn to a diameter of 0.25 mm using a hot rolled wire having a diameter of 5.5 mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt%. At this time, a die having an approach angle of 8 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 2%. After producing the steel wire for ultra-high strength steel cord of the present invention subjected to the final drawing, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  5

In another conventional method, a brass plated diameter 1.50 mm wire was drawn to a diameter of 0.25 mm using a hot rolled wire of 5.5 mm in diameter with a carbon content of 0.90 wt% and a chromium content of 0.20 wt%. At this time, a die having an approach angle of 8 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 0%. After producing the steel wire for ultra-high strength steel cord of the present invention subjected to the final drawing, the results of evaluating the physical properties are shown in Table 1 below.

Comparative example  6

In another conventional method, a 1.50 mm diameter brass plated wire was drawn to a diameter of 0.25 mm using a hot rolled wire having a diameter of 5.5 mm having a carbon content of 0.90 wt% and a chromium content of 0.20 wt%. At this time, a die having an approach angle of 8 degrees and an approach length twice the die diameter was used, and the die slip ratio was adjusted to 5%. After producing the steel wire for ultra-high strength steel cord of the present invention subjected to the final drawing, the results of evaluating the physical properties are shown in Table 1 below.

Physical property measurement method used in the present invention is as follows.

1) Tensile Strength (Kg / ㎡)

Instron tensile tester (1 Ton, model name: Instron 4201, measuring conditions: measured using ASTM E8M).

2) Die usage (Kg / ea)

The amount of wire produced per die was evaluated in the final drawing process.

3) Disconnection rate (times / ton)

Final drawing process The number of times the wire was cut during 1 ton production was evaluated.

TABLE 1

division Approach angle (degrees) Approach length (mm) Dice slip rate (%) Die usage (kg / ea) Final wire rod Tensile Strength (kg / ㎠) Delamination occurrence Disconnection rate (times / ton) Example 1 8 2D 2 155 375 Not Occurred 0.1 Comparative Example 1 4 2D 2 50 375 Not Occurred 0.6 Comparative Example 2 12 2D 2 - 380 Occur Not fresh Comparative Example 3 8 1D 2 - 380 Occur Not fresh Comparative Example 4 8 6D 2 60 375 Not Occurred 0.5 Comparative Example 5 8 2D 0 - 380 Occur Not fresh Comparative Example 6 8 2D 5 50 375 Not Occurred 0.1

* Note 2D = 2 times the die diameter

In the above, the present invention has been described in detail only with respect to the described embodiments, but it will be apparent to those skilled in the art that various changes and modifications can be made within the technical scope of the present invention. And modifications are within the scope of the claims.

1 is a cross-sectional view of a model showing a general form of a die tip for steel cord production.

<Explanation of symbols>

1: Bell

2: Approach

3: Bearing

4: Back Relief

5: approach angle

Claims (2)

After the copper plating using a hot-rolled wire having a carbon content of 0.90 to 0.97 wt%, a chromium content of 0.10 to 0.40 wt% and a diameter of 4 to 7 mm through drawing and heat treatment, the brass plated wire was In the method of manufacturing a steel cord steel wire comprising the step of final drawing the wire rod to be drawn in the longitudinal direction of the wire rod to pass through a plurality of dice installed inside the wet drawing machine, In the final drawing step, the approach angle of the die installed in the wet drawing machine is 7 to 9 degrees, the approach length is 2 to 4 times the diameter of the die, and the slip ratio of the die is 1 to 3%, characterized in that Method for producing steel wire for cords. The method of manufacturing a steel cord steel wire according to claim 1, wherein the steel cord steel wire has a diameter of 0.1 to 0.4 mm and a tensile strength of 360 to 420 kg / mm 2.

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