JPH08132128A - Manufacture of high tensile strength steel wire for reinforcing rubber - Google Patents

Abstract

PURPOSE: To provide the excellent tensile strength and toughness (torsion characteristic) by executing a prescribed reversal drawing and the finish drawing in drawing the high carbon steel wire. CONSTITUTION: In the drawing operation, the plain carbon steel wire of 0.8-1.05% C is used, and the wire is first drawn to a prescribed intermediate diameter, and the dry drawing is achieved after the heat treatment, the plating and the plating diffusion treatment. Then, the wet drawing is achieved to the target wire diameter to obtain the plated scale wire of >=3800MPa. The wet drawing process is divided into two processes, and the reversal drawing is achieved by the times less than one half of the total drawing times in the second process where the temperature of the lubricating oil is made below 35 deg.C, and the finish drawing is achieved using the double dies of the skin pass section reduction ratio of 1.2-3.9%. The dies to be used are preferably have sintered diamond nib where the approach angle (2α) is 8-10 deg. and the bearing is 0.25-0.35d. Generation of delamination can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high tensile strength steel wire suitable for a rubber reinforcing steel cord.

[0002]

2. Description of the Related Art Steel cords are used as reinforcing materials for rubber products represented by tires, high-pressure hoses, etc. Generally, the steel cords have a brass-plated surface with a diameter of 0. .10 to 0.4
It is obtained by twisting a plurality of 5 mm steel wires. Therefore, such plated steel wire is required to have excellent tensile strength, and particularly for radial tires, in order to realize weight reduction, tensile strength is 380
A high tensile strength of 0 MPa or more is required. As a method for producing a plated steel wire having such characteristics,
In addition to a method of making the wire material itself a special component composition, there is a method of devising manufacturing conditions, that is, heat treatment and wire drawing conditions. As an example of the latter, Japanese Patent Laid-Open No. 62-192532 discloses heat treatment conditions before wire drawing. Is proposed. By the way, the steel wire with plating is subjected to twisting process during cord manufacturing as described above, and is also subjected to various external forces such as tensile stress, compressive stress and shear stress while embedded in rubber. At the same time, it is necessary to have good toughness. This toughness was generally evaluated with a twist value of a certain value or more, but even if the twist value was good, there were cases where the wire was broken when twisted to obtain a cord. That is, the wire sometimes deteriorates in toughness at a time when the total area reduction rate is lower than the total area reduction rate at which the twist value extremely decreases. This is a phenomenon called delamination, in which fine cracks are generated inside the wire during the twisting of the wire, and the twisting torque becomes unstable as shown in FIG. Therefore, as a steel wire for rubber reinforcement, it is required to have a high tensile strength and toughness in which delamination does not easily occur. Was actually difficult.

The present invention was devised to solve the above-mentioned problems, and the purpose thereof is to use a plain carbon steel wire rod and to obtain a tensile strength of 3800M.
It is an object of the present invention to provide a method capable of producing a steel wire having a high tensile strength of Pa or more and having a characteristic that delamination does not easily occur.

[0004]

In order to achieve the above object, the present invention uses a plain carbon steel wire rod having a C content of 0.80 to 1.05%, which is drawn to a predetermined intermediate diameter and heat treated. After applying plating and plating diffusion treatment, dry wire drawing is performed,
Then, a wet drawing is performed to a target wire diameter to obtain a steel wire with plating of 3800 MPa or more, wherein the wet drawing step is divided into two steps, and a total drawing in the latter half step is performed at a lubricating liquid temperature of 35 ° C. or less. Reverse drawing is performed less than half of the number of lines, and finish drawing is performed with a skin pass reduction ratio of 1.2 to 3.9.
It is a method of performing with a double die of%. In the wet drawing process, the approach angle (2
α) is 8-10 °, bearing is 0.25-0.35d
It is preferred to use the sintered diamond nibs of.

[0005]

According to the present invention, the steel wire after the final heat treatment plating is dry-drawn and then wet-drawn. As the wet wire drawing conditions at this time, the lubricating liquid temperature is set to 35 ° C. or lower. Then, the wire is once wound between 70 to 99.8% of the total area reduction rate of wet drawing, and then the reverse drawing is restarted to restart the wire drawing from the tail of the wound part. Go over and over to finish to the specified wire diameter. The reverse drawing has the effect of re-increasing the ductility of the wire whose ductility has been reduced by the wire drawing process and the effect of relieving the residual stress of pulling on the surface of the wire.As a result, the toughness of the pulled wire is increased and delamination is prevented can do. Further, in the present invention, a double die in which dies are connected in series is used as a finishing die, and the final die of this double die is used as a skin pass, and the area reduction ratio is 1.2.
Draw up to 3.9%. Such double-die skin-pass wire drawing can reduce the residual stress of wire surface tension accumulated during wire drawing and reduce it to almost zero.Therefore, properly prevent delamination during twisting. Further, by using it in combination with the above-mentioned reverse drawing, it is possible to further improve the toughness when the wire is pulled up.

The present invention will be described below with reference to the accompanying drawings.
In the present invention, the amount of C as a raw material is 0.80 to
Using 1.05% plain carbon steel wire, the surface is reduced to a predetermined intermediate diameter by primary drawing and secondary drawing, and heat treatment and plating are performed. Then, this plated intermediate diameter steel wire is subjected to dry drawing and then wet drawing to a target diameter.
A plain carbon steel wire as a raw material has a chemical composition such that the C content is 0.80 to 1.05% by weight and Si:
0.15 to 0.35%, Mn: 0.3 to 0.9% The balance is iron and inevitable impurities, and the diameter is 4.0.
The one having a size of up to 5.5 mm is used. Lower limit of C amount is 0.8
The reason why 0% is set is that sufficient strength cannot be obtained with a carbon amount below this range, and the upper limit is 1.05% because the required toughness cannot be obtained with a carbon amount above this range. is there. For the primary wire drawing, pickling and coating are performed in the same manner as usual, and the diameter is 3.00 after 4 to 5 times.
Reduce the surface to about 3.50 mm. At this stage, if necessary, patenting and coating treatment
Draw secondary wire about 5 times. As a result, the wire diameter of 2.00
Obtain an intermediate wire of 2.60 mm.

Then, the final heat treatment / plating / plating diffusion process is performed. FIG. 1 schematically shows an example of this step, 1 is a raw material wire bobbin, 2 is a winding bobbin,
Between the raw material wire bobbin 1 and the winding bobbin 2,
A heating furnace 3, a patenting furnace 4, a water cooling mechanism 5, a plating pretreatment device 6, a Cu plating tank 7, a Zn plating tank 8 and a thermal diffusion furnace 9 are arranged. Patenting furnace 4
Although a fluidized bed type is preferable as the above, a molten lead type or a molten salt type may be used. In this example, an adjusting cooling device 10 is provided continuously or separately on the outlet side of the heat diffusion furnace 9,
A water cooling mechanism 11 is arranged downstream of this. The intermediate-diameter wire W is paid out from the raw material wire bobbin 1 and is, for example, 900 to 960 ° C. in a heating furnace 3 of a gas direct fire type or the like.
To be heated. This forms a uniform austenite phase. Then, the intermediate diameter wire W is fed into the patenting furnace 4, where it is quenched to 480 to 560 ° C.,
Perlite is transformed. When this pearlite transformation is completed, the water cooling mechanism 5 rapidly cools to room temperature.

Next, the intermediate diameter wire W is subjected to electrolytic pickling by removing the oxide film on the surface thereof in the plating pretreatment device 6. These conditions are the same as usual. And then C
By passing through the u plating bath 7 and the Zn plating bath 8, Cu plating and Zn plating are applied in layers on the surface. Cu plating and Zn plating are sufficient under normal conditions. Next, the plated intermediate diameter wire W is heated in the thermal diffusion furnace 9. As the heat diffusion furnace 9, a fluidized bed type heat diffusion furnace is preferably used. The intermediate diameter wire W with plating is 5 to 480 to 560 ° C.
Reheat for 15 seconds. By this reheating, the solid solution carbon in the ferrite of the structure of the plain carbon steel wire W becomes diffusible. The lower limit of the reheating temperature is 480 ° C., and the temperature lower than this limit cannot effectively diffuse the heat of the two-layer plating. If the temperature exceeds the upper limit of 560 ° C, cementite re-dissolves and the tensile strength decreases, so it must be avoided.

The intermediate diameter wire W with diffusion plating then enters the adjusting cooling device 10 where it is gradually cooled under predetermined conditions.
As the adjustment cooling device 10, for example, a tunnel furnace with a heater or a warm air oven is used, and the intermediate diameter wire W with diffusion plating is cooled to a temperature of 400 ° C. or lower, preferably 300 ° C. or lower (however, room temperature or higher), and a cooling rate of 25 to 25 ° C. It is cooled at 50 ° C / sec. By the reheating and the slow cooling, the carbon solid-dissolved in the ferrite matrix of the steel wire structure is precipitated on the cementite, thereby improving the working limit of the wire. If the cooling rate is 25 ° C./sec or less, the total line length becomes too long, and if the temperature exceeds 50 ° C./sec, the solid solution carbon in the ferrite is insufficiently precipitated. And the above 400
After being gradually cooled to a temperature of not higher than 300 ° C., preferably not higher than 300 ° C., it is rapidly cooled to room temperature by the water cooling mechanism 11 and wound on the winding bobbin 2.

The intermediate diameter wire with diffusion plating wound as described above is then dry-drawn to a surface reduction rate of 88 to 93% by drawing 10 to 14 times. It is not the wet drawing of the intermediate diameter wire W with diffusion plating to the target diameter immediately but the dry drawing to the predetermined diameter within the range of 89.5 to 93.9% of the target diameter. This is because, in order to maintain the toughness of No. 1, the dry wire drawing having a low friction coefficient is introduced to suppress the deterioration of the toughness. Although the wire drawing machine is not shown, dies are arranged at a predetermined interval between the payoff on the entrance side and the winding machine on the exit side, and an idler consisting of a drawing block and a pair of rolls is arranged on the downstream side of each die, The drawing block is rotated at high speed to continuously pull the intermediate diameter wire with diffusion plating. The wire is spirally wound on the block surface from the large diameter side of the drawing block,
It is guided to the next die from the exit side in a state of being wound 0 to 120 times. The wire drawing conditions at this time are such that an alloy die is used as the die and the wire speed is 200 to 600 m / min.

When the linear velocity is less than 200 m / min, the productivity is low, and when the linear velocity is higher than 600 m / min, the wire becomes brittle at this point, which is not suitable. The die has an approach angle (2α) of 8 to 10 ° and a bearing of 0.25 to 0.25.
0.35d (d is wire diameter) is suitable. The reason for this is that the tensile strength of the wire increases and the toughness is maintained,
If the approach angle is less than 8 °, the pulling resistance becomes too high, and if the approach angle is greater than 10 °, the tensile strength of the wire is low and the toughness deteriorates, which is not possible. The wire die outlet temperature is preferably 170 ° C. or lower. This is to prevent strain aging, and this can be realized by a method of arranging a spray nozzle inside the drawing block so that a large amount of cooling water acts on the inner surface of the block.

The thin wire with diffusion plating wound after the dry wire drawing step in this manner is drawn to a target diameter by a wet wire drawing machine. In this wet drawing process, the present invention adopts the following conditions. (1) The die uses a sintered diamond nib with an approach angle (2α) of 8 to 10 ° and a bearing of 0.25 to 0.35d (d is the wire diameter). (2) The number of drawing is 8 to 14, and the drawing process of the latter half is performed once or more and less than half by reverse drawing. (3) The final drawing is done with a double die, and the skin pass reduction ratio is about 1.2 to 3.9%. (4) Linear velocity is 100-500m / min, lubricant temperature is 3
Control below 5 ° C.

More specifically, FIGS. 2 and 3 schematically show this wet wire drawing process. 13a is a wet wire drawing portion for front drawing, 13b is a wire drawing portion for reverse drawing, and each wire drawing is shown. Part 13
Lubricating liquid tanks 130a and 130b are provided in a and 13b, and a normal steel cord lubricant is added to the water to a concentration of 1
The lubricating liquid 14 having 0 to 30% dissolved therein is contained. In each of the lubricating liquid tanks 130a and 130b, a pair of capstans 1 are arranged in parallel so as to be immersed in the lubricating liquid 14, respectively.
5, 15 'are rotatably mounted horizontally, and the capstan 15' on the downstream side is driven by a variable speed motor (not shown). A plurality of front drawing dies 17 are provided between the pair of capstans 15 and 15 'of the front drawing wire portion 13a, and between the pair of capstans 15 and 15' of the reverse drawing wire portion 13b. Is provided with at least one reverse drawing die 18 which is less than the number of dies for the drawing wire portion for front drawing, and the wires hooked in the grooves of the capstans 15 and 15 'are sequentially passed through the dies. It is designed to be pulled out by. The wet drawing part 13 for front drawing
Upstream of a, reel 1 of thin wire W'with diffusion plating
9, and a take-up reel 20 is arranged downstream of the wet drawing part for front drawing via a traverser 200. The wet drawing part 13 for front drawing is provided on the upstream side of the drawing part 13b for reverse drawing.
The take-up reel 20 of a is provided as a pay-off side reel, and the take-up reel 25 of the plated tensile strength wire W ″ as the final product is provided on the downstream side.

FIG. 4 shows one front drawing die of the front drawing wire portion 13a. FIG. 5 shows a finishing die 18 'of the reverse drawing wire portion 13b.
a and the skin pass die 18b are arranged in close proximity to each other in series, and the predetermined surface reduction rate is divided into two parts. In each of the dies, a die 23 containing a nib 22 made of sintered diamond is fixed to the die holder 21, and the angle (2α) of the approach portion 220 of the nib 22 is 8 to 10.
°, the size of the bearing portion 221 is 0.25 to 0.35d
Has become. Explaining the reasons for limitation, the reason why sintered diamond is used as the nib is to prevent the die diameter from increasing and the skin pass area reduction rate from changing due to friction. Further, the approach angle is limited because the pulling resistance is high when the angle is less than 8 ° and the toughness of the wire deteriorates when the angle is 10 ° or more. The reason for limiting the bearing size is that if the bearing is long, the contact area with the wire becomes large and the heat generation of the wire becomes high.

The reason why the number of times of wet wire drawing is set to 8 to 14 is because the toughness of the wire is taken into consideration. If the number of times is less than the lower limit, the area reduction rate per pass becomes too large and the toughness of the wire deteriorates. To do. Further, if the number of times exceeds the upper limit, the number of times of drawing becomes too large, and the toughness of the wire deteriorates. The reduction rate of each time by the die should be as low as the latter stage, but not only this, but as the finishing die 18 ',
A normal die 18a and a skin pass die 18b are used. This is to prevent delamination by releasing the residual tensile stress of the surface of the wire to almost zero. However, the skin bath reduction ratio by the skin pass die 18b at the finish reduction ratio is 4.
If it is too large, such as 0% or more, the residual stress relaxation effect is small. Conversely, if it is too small, such as 1.1% or less, the amount of processing is too small and the residual stress relaxation effect is small. Most preferably, it is 1.2 to 3.9%, and delamination can be accurately prevented.

Further, in the present invention, reverse drawing is also used in order to prevent delamination. The reason for this is that the residual stress on the wire surface becomes too large on the pulling side and the delamination occurs during the twisting process only by pre-drawing, but reverse drawing reduces the residual stress on the wire surface and prevents delamination. Because it is done. This reverse drawing is performed in the latter half of the wet drawing process and once or more and less than half. In terms of the relationship with the area reduction rate, it is a stage of 70 to 99.8% of the total area reduction rate of wet drawing, and as a reverse drawing method, when the area reduction rate is reached, As described above, the winding reel 20 may be wound once, the winding reel 20 may be attached to the reverse drawing wire portion 13b, and wire drawing may be performed from the tail portion.

Further, the linear velocity in wet drawing is 50 to 300 m /
The reason why the temperature is set to min and the lubricating liquid temperature is set to 35 ° C. or lower is
This is to prevent the occurrence of delamination by controlling the wire temperature. For this reason, as shown in FIG. 3, a circulation pump 140 and a cooler 141 are provided outside the tank, and the lubricating liquid is forcibly removed by forcibly extracting the lubricating liquid from the tank and returning it to the tank. 35 ° C or less during operation, preferably 30 to 3
The temperature is controlled to 5 ° C. This allows the wire temperature to rise to 150 ° C. or lower in combination with the linear velocity.

[0018]

EXAMPLES Examples of the present invention will be described below. 1) A brass-plated steel wire for tire cord was manufactured according to the present invention. As the raw material wire, a plain carbon material having a diameter of 5.5 mm was used. Its composition is C: 0.8
4%, Si: 0.22%, Mn: 0.50% The balance is iron and inevitable impurities. The raw material wire was pretreated and primary drawn by drawing 5 times to a diameter of 3.45 mm. After patenting, secondary drawing was performed by drawing 5 times to a diameter of 2.35 mm.
This intermediate diameter wire was subjected to heat treatment, plating and plating diffusion treatment. The conditions were first heating to 950 ° C. in a gas direct-fired heating furnace, followed by quenching in a fluidized-bed patenting furnace at 500 ° C., followed by water cooling immediately after completion of pearlite transformation. The tensile strength at this time was 132 kgf / mm ² . Then, after descaling and electrolytic pickling, two layers of Cu and Zn were plated by passing through a Cu bath and a Zn bath. The plating has a Cu content of 64.0% and an adhesion amount of 4.1 g / kg. Then, it was reheated in a fluidized bed type diffusion furnace and reheated to improve heat diffusion and drawing workability. The furnace temperature was set to about 600 ° C. and was held for 30 seconds. Then, subsequently, it was gradually cooled (cooling rate 37.5 ° C./sec) to 250 ° C. over 8 seconds in an attached hot stove type box, then water-cooled to room temperature and wound up.

2) Then, the diameter was reduced to 0 by a continuous dry wire drawing machine.
Dry drawing was performed up to 70 mm (area reduction rate: 91.1%). The die used was an alloy die with an approach angle of 10 ° and a bearing of 0.30d, and the drawing was performed 11 times at a linear velocity of 400 m / min. Then, a brass-plated steel wire having a finished diameter of 0.28 mm was obtained by the wet drawing machine shown in FIGS. 2 and 3. A normal wet lubricating liquid having a concentration of 10% was used as the lubricating liquid, and the liquid temperature was kept at 32 ° C. by a cooling circulation system. The die used in this step was an approach angle of 10 °, a bearing of 0.30 d, and drawing was performed 11 times at a linear velocity of 60 m / min. Six times of these were performed by pre-drawing (74.7% of the total area reduction rate of the wet drawing part), the wire that had been pre-drawn was wound up on a reel, and the reel was paid off for a wet drawing machine for reverse drawing. It was attached to the side and reverse-drawn 5 times. Finally, it was introduced into a finishing die (double skin pass die) and reverse-drawn with a surface reduction rate of 11%. At this time, the area reduction rate by the normal die was 9.0%, and the area reduction rate by the skin pass die was 2.0%. During the process, the wire temperature was kept below 150 ° C and the rising wire temperature was 135 ° C.

3) The wire obtained as described above has a tensile strength of 4085 MPa and 100 d
The twist value was 31 times. Moreover, when the number of twists-torque (twisting speed 30rppm) at this time was measured by a twist-torque tester, delamination did not occur.
For comparison, the result of wet drawing with a die approach angle of 12 ° and the other conditions described above shows a tensile strength of 3960.
When the MPa was 25 and the number of twists was 25, delamination was unacceptable, and there were frequent disconnections during wire drawing. In addition, the number of times of pre-drawing was set to 5 (67% of the total area reduction rate of the wet drawing part), the number of times of reverse drawing was set to 6 and the results of wet drawing under the other conditions were the tensile strength of 4079 MPa and twisting. The number of times was 20 and the delamination failed. In addition, the result of wet drawing with a reduction rate of 4.0% in the skin pass die of the finishing die and the other conditions above is the tensile strength of 3995MP.
a, the number of twists was 22 and the delamination was unsuccessful. As a result of wet drawing with a reduction rate of 1.0% in the skin pass die of the finishing die and the other conditions described above, the tensile strength was 3981 MPa, the number of twists was 23, and delamination was unsuccessful. As a result of wet drawing with the lubricating liquid temperature set to 50 ° C. and the other conditions set forth above, the tensile strength was 4085 MPa, the number of twists was 21, and the delamination was unsuccessful. This is because the wire temperature became higher than 150 ° C. From the above, it is clear that high tensile strength characteristics and anti-delamination characteristics can be obtained by the synergistic effect of reverse drawing of predetermined conditions, double die with predetermined surface reduction ratio, predetermined die approach angle, and lubricating liquid temperature conditions. is there.

Example 2 Heat treatment, plating, and plating diffusion were carried out with a diameter of 2.45 mm, and the other conditions were the same as in Example 1, and the wire was drawn under the same conditions. The tensile strength was 4189 MPa, the number of twists was 29 times (100d), and the delamination passed A good product was obtained.

[0022]

According to the present invention described above, a plain carbon steel wire rod is used and the tensile strength is 3800.
An excellent effect is obtained in that a steel wire for rubber reinforcement having a high tensile strength of MPa or more and having a characteristic that delamination does not easily occur can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a heat treatment / plating / plating diffusion step of the present invention.

FIG. 2 is a plan view schematically showing a wet wire drawing step in the present invention.

FIG. 3 is a cross-sectional view of the front drawing wire portion and the reverse drawing wire portion in FIG.

FIG. 4 is a cross-sectional view showing a front drawn wire state.

FIG. 5 is an enlarged sectional view showing a finish wire drawing state.

FIG. 6 is a diagram showing a torque-twisting relationship of a plated steel wire.

[Explanation of symbols]

 13a Front drawn wire portion 13b Reverse drawn wire portion 14 Lubricating liquid 18 'Finishing die 18a Normal die 18b Skin pass die

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C08J 5/04 CEQ C22C 38/00 301 Y

Claims (2)

[Claims] 1. A plain carbon steel wire rod having a C content of 0.80 to 1.05% is drawn, and the wire is drawn to a predetermined intermediate diameter, subjected to heat treatment, plating and plating diffusion treatment, and then dry drawn. Then, wet drawing to the target wire diameter and then 3800MP
A method for obtaining a steel wire with a plating of a or more, wherein the wet wire drawing step is divided into two steps, and a lubricating liquid temperature of 35
In the latter half of the process below ℃, reverse drawing is performed less than half of the total number of wire drawing operations, and finish drawing is performed with a skin pass area reduction ratio of 1.2 to
A method for producing a high-strength steel wire for rubber reinforcement, which is characterized by being performed with a double die of 3.9%. 2. A die having an approach angle (2α) of 8 to 1
The method for producing a high tensile strength steel wire for rubber reinforcement according to claim 1, which is carried out using a sintered diamond nib having a bearing of 0.25 to 0.35d at 0 °.