JP2842720B2 - Die for wire drawing and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a wire drawing die used for converting a metal into a wire.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of turning a metal into a wire by drawing a metal material through a die having a hole formed in the center. The dies for wire drawing are generally made of steel, cemented carbide, or diamond.

[0003] The metal to be drawn is Al, Au, A
Even with soft metals such as g and Cu, the inner surface of the hole of the die usually wears. When abrasion occurs on the inner surface of the hole, the cross-sectional shape of the drawn wire changes, and irregularities are formed on the surface. Therefore, when the abrasion increases, the inner surface of the hole is polished and reused, but there is a problem that the thickness of the wire becomes larger than before the polishing. Therefore, since it is desired that the die has a long life before re-polishing, it has been proposed to form a contact portion with the metal, that is, the inner surface of the hole with a material having high hardness.

[0004] Diamond is the best material for the conventional wire drawing dies, but the diamond itself is very expensive, so that it can be applied only to small dies.

Therefore, it has recently been proposed to extend the life of the die by coating the inner surface of the hole with a hard material. For example, Japanese Patent Application Laid-Open No. 61-74725 proposes coating the inner surface of a hole of a WC die with TiN.
No. 4610 discloses a diamond film or a carbon film having a hardness similar thereto by a CVD method.
Proposes to coat a hard carbon film.

[0006]

However, Japanese Patent Application Laid-Open No. 1-62213 discloses an attempt to form a diamond film on a metal substrate directly or through an intermediate layer. The bonding strength with the diamond film is insufficient even through the method, and the general CVD method requires polishing because the formed surface has irregularities due to crystals. However, if the bonding strength is low, polishing is difficult. In addition, there is a problem that the film peels during use.

In Japanese Patent Application Laid-Open No. 3-114610, since the film thickness is increased to 50 to 150 μm, the unevenness of the surface of the film is further increased, and much time and cost are required to polish the surface. Also, the described hot filament C
In the VD method, it is necessary to set a filament inside or around a die hole, and there is a problem in poor productivity and maintenance of the filament.

Further, Japanese Patent Application Laid-Open No. 3-23010 discloses a hard carbon film formed on a cemented carbide substrate, and this film is an amorphous carbon film, which is generally DLC (diamond-based).
It is a film containing a large amount of hydrogen called like-carbon, and has a hardness of about half that of crystalline diamond and is inferior in wear resistance. Further, when the drawing speed is high, the die temperature rises, and the hydrogen contained in the film escapes from the film to become graphite, which may further deteriorate the wear resistance. In addition, since the Co phase on the surface of the die is removed with hydrochloric acid as a pretreatment, the die of the substrate becomes brittle and may be damaged during wire drawing.

According to these prior arts, all of them are insufficient from the viewpoint of extending the life of the dies, and all of them can only be applied to dies having a relatively large hole diameter, and have a small hole diameter. When applied to a die, there is a problem that a film is formed only near the entrance of the hole and cannot be formed on the inner surface of the hole. In addition, it is practically impossible to place the filament inside the hole by the hot filament method, because the filament may be overheated or short-circuited when the base material is conductive.

[0010] Accordingly, an object of the present invention is to provide a wire drawing die capable of achieving excellent wear resistance and a long life for a die having a small hole diameter, and a hard die having uniformly excellent wear resistance on the inner surface of the hole. It is an object of the present invention to provide a method for producing a carbon film.

[0011]

Means for Solving the Problems As a result of repeated studies on the above object, the present inventors have found that various types of film formation in the case of forming a hard carbon film on a wire drawing die having a hole diameter of 1 mm or less. The method and the characteristics of the carbon film to be formed were examined in detail. When the film was formed under a predetermined condition by an electron cyclotron plasma CVD method, the hole diameter was 1 m.
It has been found that a hard carbon film that is uniform and has excellent wear resistance is formed on the inner surface of a hole even for a wire drawing die having a micropore diameter of not more than m.

That is, the present invention provides a wire drawing die having a hole diameter of 1 mm or less, wherein at least the inner surface of the hole is made of diamond and amorphous carbon, the average crystal grain diameter is 1 μm or less, and 1333 ± 1 When the peak existing at 10 cm ^-1 is H ₁ and the peak existing at 1500 ± 100 cm ^-1 is H ₂ , the intensity ratio expressed as H ₂ / H ₁ is 0.35 to 20, and the surface roughness is Sa (Rma
x) is coated with a hard carbon film of 0.8 μm or less. Further, as a method of forming a hard carbon film having the above properties on the inner surface of the hole,
A carbon-containing gas is introduced into a reactor having a wire drawing die having a hole diameter of 1 mm or less under a furnace pressure of 1 torr or less, plasma is generated by microwaves, and a magnetic field is generated in a region where the plasma is generated. Is used to generate electron cyclotron resonance plasma.

Hereinafter, the present invention will be described in detail. As shown in FIG. 1, the wire drawing die of the present invention has a hole diameter a of a die hole A.
Has a micropore diameter of 1 mm or less. And
A hard carbon film is formed on the inner surface of the hole A. This hard carbon film needs to have a surface roughness Rmax of 0.8 μm or less, and if the surface roughness is larger than 0.8 μm, the cross-sectional shape of the wire changes at the time of wire drawing, or the wire surface is damaged. This is because the contact resistance with the metal at the time of processing is large, the wear of the hard carbon film is increased, and the carbon film is peeled off.

The surface roughness can usually be controlled by polishing, but it is difficult to polish the inner surface of a die or the like having a small hole diameter. Therefore, in the present invention, the hard carbon film is composed of fine crystals having an average particle diameter of 1 μm or less, and the film itself is composed of diamond and amorphous carbon. When the peak intensity existing at ± 10 cm ⁻¹ is H ₁ and the peak intensity existing at 1500 ± 100 cm ⁻¹ is H ₂ , the intensity ratio represented by H ₂ / H ₁ is 0.3.
5-20, especially 1-10. The average crystal grain size is 1
If it is larger than μm, it is difficult to control the surface roughness of the carbon film within the above range. Further, when the hard carbon film is made of only diamond, the crystallinity is enhanced, and the average grain size of the crystal is increased and the surface roughness is also increased.

In the present invention, the base material of the wire drawing die is not particularly limited. For example, in addition to ceramic materials such as silicon nitride and silicon carbide, WC-Co
A cemented carbide or a cermet containing TiC or TiCN as a main component can be used. Among them, silicon nitride is particularly preferable because of its high adhesive force.

In order to manufacture the wire drawing die, an electron cyclotron plasma CVD method (hereinafter, referred to as an ECR plasma method) is employed as a film forming method. A manufacturing method according to this method will be described with reference to FIG. In the reaction furnace 1, a wire drawing die substrate 2 having a hole diameter of 1 mm or less for forming a carbon film is provided. A microwave generator 3 for generating plasma in the reactor and an electromagnetic coil 4 for generating a magnetic field are arranged around the reactor.

When a film is formed using such an apparatus, a raw material gas containing at least carbon as a gas for forming a carbon film is supplied through a gas introduction path 5 together with a carrier gas such as hydrogen, if necessary, in a reaction furnace. At the same time, the inside of the reactor is maintained at a low pressure of 1 torr or less by introducing into the passage, and at the same time, microwaves of 2.45 GHz are introduced into the furnace by the waveguide 6. At the same time, a magnetic field of a level of about 875 gauss or more is applied by the electromagnetic coil 4. As a result, the electron has a cyclotron frequency f = eB / 2πm (m: mass of the electron,
e: charge of electrons, B: magnetic flux density), and cause cyclotron motion. When this frequency coincides with the microwave frequency (2.45 GHz), that is, the magnetic flux density B
Is 875 Gauss, electron cyclotron resonance occurs. As a result, electrons are remarkably absorbed by microwave energy and accelerated, collide with neutral molecules to cause ionization, and generate high-density plasma even at low pressure.

The temperature of the substrate at this time is set to 150 to 12
By maintaining the temperature at 00 ° C., a carbon film can be formed on the substrate surface.

In the present invention, when a hard carbon film having the above-mentioned predetermined characteristics is formed, the substrate temperature is set to about 150 ° C. to 800 ° C., the source gas concentration is set to about 10% to 60%,
The furnace pressure may be set in the range of 1 × 10 ⁻³ torr to 1 torr.

As the carbon-containing raw material gas used in the above-mentioned production method, in addition to hydrocarbon gas such as methane, ethane and propane, C _x H _Y O _Z (x, y and z are each 1)
Organic compounds and gases such as CO and CO ₂ as described above can also be used.

The mixing ratio and type of these gases have no effect on the effect of the present invention regardless of any of the known methods disclosed in JP-A-60-19197 and JP-A-61-183198. Has no effect.

[0022]

The uniformity of the film thickness generated with respect to the shape of the substrate during film formation depends on the plasma density during film formation and the thickness of the plasma sheath formed on the surface of the substrate when the substrate is placed in the plasma. However, under low pressure deposition conditions, the higher the plasma density, the smaller the thickness of the plasma sheath, and the smaller the thickness of the plasma sheath, the more uniformly the plasma sheath is formed on a substrate having a complicated surface shape. Can be.

In the conventional microwave plasma CVD method in which plasma is generated by microwaves to form a carbon film on a predetermined substrate surface, the pressure inside the furnace is high and the plasma density is low, so that the plasma sheath is thick, In addition, a sheath is not formed on the inner surface of a small die having a hole diameter of 1 mm or less, and it is difficult to uniformly generate a carbon film.
In the high-frequency plasma CVD method, the sheath portion fluctuates with time, and a thick sheath is formed regardless of the plasma density. Therefore, it is difficult to form a uniform film. Even in the hot filament method, a uniform film cannot be formed on the surface of a substrate having a complicated uneven shape such as the inner surface of a die hole.

On the other hand, according to the present invention, the plasma density at the time of film formation can be increased in a very low pressure range of 1 torr or less, and the plasma generated near the substrate by electron cyclotron resonance can be increased. The density can be increased ten times or more as compared with the ordinary plasma CVD method. This makes it possible to reduce the thickness of the plasma sheath on the surface of the substrate during film formation, and to form a uniform carbon film on the inner surface of the hole of a die having a small hole diameter.

Further, by forming a film in which diamond and amorphous carbon are mixed by such a method, the crystallinity of the carbon film is relaxed, the surface roughness after film formation is small, and the carbon film is excellent in wear resistance. Does not require polishing processing of the film in particular, and no welding of soft metal occurs,
The life of the die can be extended.

Further, the hard carbon film of the present invention has the advantage that the resistance at the time of metal extraction is low due to the low coefficient of friction, and it is difficult to generate heat even if the extraction speed is increased. Even if there is any wear, the dice having the same life can be regenerated by coating the carbon film again to the original pore diameter on the dice having a long life.

[0027]

EXAMPLE Using a device as shown in FIG. 2, a disk substrate made of cemented carbide having a diameter of 40 mm and a surface roughness Rmax of 0.1 μm was set in a reactor, and ECR plasma CV was used.
According to Method D, a magnetic field having a maximum intensity of 2 kGauss was applied, and a film was formed on the surface of the substrate under the conditions of a microwave output of 3.0 kW, a substrate temperature of 650 ° C., and a furnace pressure of 0.3 torr. The reaction gas is methane gas, C
O ₂ and hydrogen gas at 54 sccm and 36 sccm respectively
and a mixture at a flow rate of 210 sccm. Under these conditions, the carbon film was formed so as to have a thickness of about 6 μm.

When the plasma density and the electron temperature at this time were measured with a Langmuir probe, the plasma density (np) was 4 × 10 ¹¹ cm ⁻³ and the electron temperature (Te) was 4e.
V. Note that the thickness of the plasma sheath was calculated to be 70 μm or less from np and Te.

When the obtained carbon film was analyzed by Raman spectroscopy of the film surface, a diamond peak and a slight amorphous carbon peak were observed, and two phases of diamond and amorphous carbon were observed. It turned out to be a structure.
The Raman spectroscopy was performed by narrowing an 488 nm Ar laser beam to a beam diameter of about 1 μm. Peak intensity ratio is 110
Pull the hatched between positions 0 cm ^-1 and 1700 cm ^-1, which performs curve fitting process each peak as the baseline as the Lorentz type, after peak separation, obtains the height of each peak was calculated the ratio . In addition, when the surface roughness was evaluated by a stylus type surface roughness meter, it was Rmax 0.3 μm or less.

In order to evaluate the sliding characteristics of this film, the cemented carbide disk on which the carbon film was formed and the tip portion had a radius of curvature R
= 4.763 mm, and a sliding test was performed by a pin-on-disk method. The sliding conditions were a load of 19.6 N, a sliding speed of 2 m / sec, room temperature, air,
The test was performed continuously for about 45 hours without lubrication. By this test, the friction coefficient and the specific wear amount were evaluated. For comparison, a similar sliding test was performed on a cemented carbide disk having no carbon film.

FIG. 3 shows how the friction coefficient changes with the sliding characteristics (distance). The friction coefficient of the cemented carbide disk not coated with the carbon film varies between 0.6 and 0.8, and the dispersion is large. On the other hand, it can be seen that the disk on which the carbon film is formed according to the present invention shows a low friction coefficient of 0.1 or less from the initial stage of sliding, and there is almost no variation. When the sliding trace was observed, the disc not covered had a trace scraped off with a pin and had a depth of about 5 μm. Further, it was observed that aluminum was adhered to the entire sliding mark. In contrast, discs coated with carbon film are hardly scraped off with aluminum pins,
The depth was about 2 μm, and almost no aluminum welding was observed. FIG. 4 shows the results of measuring the sliding marks with a surface roughness meter. The specific wear of the carbon film and the cemented carbide can be estimated from the cross-sectional area of the sliding trace obtained in this manner. As a result, the weight loss of the aluminum pin was 0.012 g and the specific wear amount was 2.0 × 10 ⁻¹⁷ m ² / N in the disk with the carbon film formed thereon, whereas the disk without the carbon film formed the disk with the specific wear amount of 2.0 × 10 ⁻¹⁷ m ² / N. The weight loss of the aluminum pin is 0.096 g, and the specific wear is 2.0 × 10 ⁻¹⁵ m ² /
N, and it was found that the carbon film formed by the above method had abrasion resistance 100 times that of the cemented carbide.

Next, the inner surface of the hole is made to have a surface roughness Rmax of 0.1 μm.
The above carbon film was formed in a thickness of 2 μm on the inner surface of a hole of a silicon nitride aluminum wire drawing die having a hole diameter of 0.4 mm, which was mirror-finished to a diameter of 0.4 mm or less. At the time of film formation, the dice were floated and held from the substrate holder in order to improve the gas flow, and portions not requiring coating were masked with a metal plate so that the carbon film was not coated. The die after film formation had a smooth surface and was uniformly coated with a hard carbon film without peeling. The dies of the same lot were broken, and the surface roughness of the carbon film was measured. The Rmax was 0.3 μm, which sufficiently satisfied the specifications of the dies. When the film thickness distribution was examined by SEM, it was confirmed that the film thickness was almost uniform within ± 10%.

When a die having a diameter of 0.4 mm was drawn using this die, it was possible to draw a wire having a length of 400,000 m. For comparison, when wire drawing was performed in the same manner using a conventional die of the same shape made of cemented carbide, the wire was 80,000 m drawn and deteriorated due to wear.

In the above test, wire drawing was performed in the same manner as described above, except that the hard carbon film was coated under various conditions. Note that the wire drawing was performed with copper in addition to aluminum. Samples No. 1 to No. 11 were all formed by the ECR plasma CVD method.
Is a conventional microwave plasma CVD method, and a sample No. 14 is formed by placing a filament below the die by a hot filament method. The results are shown in Table 1.

[0035]

[Table 1]

According to Table 1, samples Nos. 1 to 5 satisfying the conditions of the present invention were several times as many as the conventional hard metal dies (sample No. 12) in drawing aluminum and copper wires. It can be seen that the life is obtained. Samples Nos. 6 and 7 had surface roughness Rmax greater than 0.8 μm, so that the same characteristics as samples Nos. 1 to 5 could not be obtained unless mirror-finished by the skiff method.

In Samples Nos. 6 and 711, in which the ratio of H ₂ / H ₁ was smaller than 0.35, the crystallinity of the film was high, the particles constituting the film were large, and the surface roughness of the film was high. Has grown. In the case of sample No. 10 having a ratio of more than 20, the die life was slightly improved as compared with the conventional sample No. 12, but the film was worn.

For comparison, a sample No. 13 and a hot filament C by microwave plasma CVD were used for comparison.
In the sample No. 14 by the VD method, although the film itself was made of diamond, the film was formed only on the outer surface of the die and the portion near the outer surface of the hole inner surface, and no carbon film that could be used as a die was formed on the inner surface. Was.

[0039]

As described above in detail, according to the present invention, it is possible to uniformly form a carbon film which is harder than a wire drawing die having a small hole diameter and has a small surface roughness after film formation. In the wire drawing of a soft metal such as Al or Cu, the life of the die can be extended without causing welding or the like to the die.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a wire drawing die of the present invention.

FIG. 2 is a schematic view of a film forming apparatus used in the present invention.

FIG. 3 is a diagram showing a change in a friction coefficient with respect to a sliding time (distance).

4A and 4B are diagrams showing the surface roughness of a sliding mark, in which (a) shows a hard carbon film formed on a cemented carbide surface, and (b) shows only a cemented carbide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction furnace 2 Substrate 3 Microwave generator 4 Electromagnetic coil 5 Gas introduction furnace A Die hole a Dice hole diameter

Continuation of the front page (56) References JP-A-3-23010 (JP, A) JP-A-3-114610 (JP, A) JP-A-2-155520 (JP, A) JP-A-2-232106 (JP) JP-A-3-153874 (JP, A) JP-A-5-123908 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21C 1/00 B21C 3/00 C04B 41/00 C23C 16/00

Claims (2)

(57) [Claims] 1. A drawing die having a pore size of 1 mm or less, comprising at least the inner surface of a hole made of diamond and amorphous carbon, having an average crystal grain size of 1 μm or less, and having a mean particle size of 1333 ± 10 cm ^-1 in Raman spectroscopy. The peak present is H ₁ , the peak present at 1500 ± 100 cm ⁻¹ is H
_The intensity ratio represented by H ₂ / H ₁ is 0.35 to 20 and the surface roughness (Rmax) is 0.8 μm.
A wire drawing die coated with the following hard carbon film. 2. A carbon-containing gas is introduced into a reaction furnace in which a wire drawing die having a hole diameter of 1 mm or less is installed at a furnace pressure of 1 torr or less, and plasma is generated by microwaves. An electron cyclotron resonance plasma is generated by applying a magnetic field to a region where the plasma is generated, and the inner surface of the hole of the wire drawing die is substantially composed of diamond and amorphous carbon. The peak existing at 1333 ± 10 cm ⁻¹ in Raman spectroscopy at 1 μm or less was H ₁ , 1
When the peak existing at 500 ± 100 cm ^-1 is H ₂ , the intensity ratio represented by H ₂ / H ₁ is 0.35 to 20 and the surface roughness (Rmax) is 0.8 μm or less. A method for producing a wire drawing die, wherein the die is coated with a carbon film.