JP2876095B2 - Graphite electrolytic electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for electrolytic finishing used for luster finishing of metal surfaces of three-dimensional dies such as forging dies, die casting dies, and plastic molding dies. It relates to an electrode for graphite electrolytic processing.

[0002]

2. Description of the Related Art As shown in FIG. 2, in an electrolytic processing apparatus, a work 20 and an electrode 10 having an electrode surface following the processed surface of the work 20 are opposed to each other at a predetermined gap in a stationary electrolyte 30. By applying a pulsed current between the electrodes, metal ions are eluted from the surface of the work 20 and a glossy surface of the work 20 is processed.

Heretofore, graphite has been used as the electrode for electrolytic processing because graphite is easy to manufacture and does not wear out the electrode. However, since graphite originally has a porous structure, the electrolytic solution penetrates into the pores of the electrode during electrolytic processing, and after use, the electrolytic solution component becomes crystalline and precipitates out after use. And the deterioration of the working environment due to precipitates has been a problem.

On the other hand, the applicant has proposed an electrode for electrolytic processing in which a dense pyrolytic carbon film is formed on the surface of a graphite base material serving as an electrode (Japanese Patent Application No. 3-333478).

[0005]

However, when a workpiece having a complicated form is subjected to electrolytic processing, the shape of the electrode itself is also complicated, so that stress is generated due to a difference in thermal expansion between the electrode substrate and the pyrolytic carbon film. By doing so, there is a problem that the pyrolytic carbon film and the graphite substrate are liable to peel off, and the peeling causes the penetration of the working fluid from that portion, which shortens the life of the electrode. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide a graphite electrode having a pyrolytic carbon film, which is hardly peeled off and has a long life. An object of the present invention is to provide an electrode for electrolytic processing.

[0007]

That is, the above object has been achieved.
As means for achieving this, the invention described in claim 1 is based on “black
Made of graphite with a pyrolytic carbon coating formed on the surface of a lead substrate
An electrode for electrolytic processing, wherein the graphite substrate has a temperature of 20 ° C to 40 ° C.
The average coefficient of thermal expansion at 0 ° C. is 1.3 × 10 ^-6/ ℃ ~
6.0 × 10^-6/ ° C, characterized by graphite electrolysis
"Electrode for processing" is the gist of this.

[0008] Further, the invention according to claim 2 is based on a "graphite base material".
Graphite electrolytic coating with pyrolytic carbon coating
A working electrode, wherein the graphite substrate has a temperature of 20 ° C. to 400 ° C.
Average thermal expansion coefficient of 1.3 × 10 ^-6/ ° C-6.0x
10^-6/ ° C and 75 ° C measured by the mercury intrusion method.
With a diameter of ~ 75,000 Angstroms
The volume occupied by the micropores is 0.02 cc / g to 0.1.
A graphite electroforming electrode characterized by being 5 cc / g.
The pole is the gist.

[0009] The graphite base material of the graphite electrode for electrolytic processing is
It can be obtained from materials such as coal-based or petroleum-based tar, pitch, natural graphite, and artificial graphite. As a method of forming a pyrolytic carbon film on the surface of a graphite substrate, various chemical vapor deposition methods can be used. Usually, a method is used in which a graphite substrate is heated and reacted by bringing a hydrocarbon gas such as methane or propane into contact with a high-temperature graphite substrate to generate pyrolytic carbon on the surface of the graphite substrate. The pyrolytic carbon coating has a thickness of 1 as a range in which sufficient airtightness can be obtained.
0 μm or more, preferably 20 μm to 500 μm
Range is good.

[0010]

In the graphite electrode for electrolytic processing according to claim 1, the graphite substrate has an average coefficient of thermal expansion of 1.3 × 10 ^-6 / ° C.
The range is 6.0 × 10 ⁻⁶ / ° C., which corresponds to the coefficient of thermal expansion of pyrolytic carbon. For this reason, peeling of the coating due to the difference in thermal expansion between the graphite substrate and the coating of pyrolytic carbon is prevented.

[0011] In the graphite electrode for electrolytic processing according to the second aspect, the graphite base material is further measured by a mercury intrusion method.
The volume occupied by micropores having a diameter of from Angstroms to 75000 Angstroms is from 0.02 cc / g to 0.
Since it is 15 cc / g, a part of the pyrolytic carbon film enters into the pores of the graphite base material, and an anchor effect is generated, whereby the adhesion between the graphite base material and the pyrolytic carbon film is enhanced, and the film is further peeled. It becomes difficult.

The reason why the volume occupied by the fine pores present in the graphite base material is set within the above range is that if the volume is less than 0.02 cc / g, a sufficient anchor effect cannot be obtained. This is because unevenness on the surface of the material increases, and stress concentrates on minute portions of the film to be coated thereon, and the coating is easily peeled.

[0013]

Embodiments will be described below. Example An isotropic graphite was used as a graphite base material, and as shown in FIG. 1, an electrode for electrolytic processing was formed by forming a plurality of protrusions having a size of 100 mm × 200 mm × 50 mm on an electrode surface 10 a. Was placed in a reaction furnace, heated to 1400 ° C. under reduced pressure, methane was supplied using hydrogen gas as a carrier, and an electrolytic processing electrode 10 in which a 50 μm pyrolytic carbon film 12 was formed on a graphite substrate 11 was produced. . Samples 1-3
And their physical properties are shown in Table 1.

COMPARATIVE EXAMPLE An electrode for electrolytic processing was prepared by using isotropic graphite as a graphite base material and forming a 50 μm pyrolytic carbon film on the graphite base material in the same shape and the same processing method as in the embodiment. These were designated as Samples 4 and 5, and their physical properties are shown in Table 1.

[0015] (The average coefficient of thermal expansion is an average value at 20 ° C to 400 ° C,
The micropore volume is the volume occupied by micropores having a diameter of 75 Å to 75000 Å measured by a mercury intrusion method)

Each of the samples 1 to 5 was set in an electrolytic processing apparatus, and a current density of 40 A / cm ² was used in an electrolytic solution of sodium nitrate, SKD-61 was used as a work material, and a discharge machining was performed to Rma × 30 μm in advance. Using the processed workpiece, a finishing treatment by electrolytic processing with a machining allowance of 100 μm was repeated 10 times.

As a result, with respect to Samples 1, 2, and 3, there was no peeling of the pyrolytic carbon coating and no cracks, and no precipitation of the electrolyte component crystal was observed. Sample 4
With regard to, peeling of the pyrolytic carbon film was observed, and precipitation of crystals of the electrolyte component was observed. For sample 5,
No peeling of the pyrolytic carbon film was observed, but cracks occurred, and precipitation of crystals of the electrolyte component was observed.

[0018]

As described above, according to the first or second aspect of the present invention, when a workpiece having a complicated form is subjected to electrolytic machining, a difference in thermal expansion between a pyrolytic carbon film and a graphite base material is caused. The present invention solves the conventional problem that peeling is likely to occur, and furthermore, the working fluid penetrates from the part due to the peeling, and this has caused the problem of shortening the electrode life. In this case, the pyrolytic carbon coating is prevented from peeling off from the surface of thermal expansion. In the invention according to claim 2, the pyrolytic carbon coating is further reduced from the viewpoint of the fine pore volume of the graphite base material. With a structure that enhances the adhesion of
This makes it possible to provide a long-life electrode in which the coating is hardly peeled off from the graphite electrolytic processing electrode having a coating of pyrolytic carbon on the surface.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an embodiment of a graphite electrode for electrolytic processing according to the present invention.

FIG. 2 is a front view showing the outline of the electrolytic processing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electrode 11 Graphite base material 12 Pyrolytic carbon coating

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23H 3/06

Claims (2)

(57) [Claims] 1. An electrode for electrolytic processing of graphite comprising a graphite substrate having a pyrolytic carbon film formed on the surface thereof, wherein the graphite substrate has an average coefficient of thermal expansion at 20 ° C. to 400 ° C. of 1.3.
Graphite electrochemical machining electrode which is a × 10 ^-6 /℃~6.0×10 ^-6 / ℃. 2. An electrode for electrolytic processing of graphite comprising a graphite substrate having a pyrolytic carbon film formed on the surface thereof, wherein the graphite substrate has an average coefficient of thermal expansion at 20 ° C. to 400 ° C. of 1.3.
A × 10 ^-6 /℃~6.0×10 ^-6 / ℃, and the volume occupied by fine pores having a diameter of 75 Å ～75000 angstroms as measured by mercury porosimetry is 0.02cc / g~0. An electrode for electrolytic processing made of graphite, which is 15 cc / g.