ELECTROLYTIC APPARATUS AND SURFACE TREATMENT METHOD USING THE SAME

Abstract

An electrolytic apparatus that is used for a workpiece having an irregular cross-sectional shape, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof, the electrolytic apparatus includes a mounting section that closes a lower opening of the workpiece, a holding section that closes an upper opening of the workpiece, and an electrode that is placed inside the workpiece, the electrode having a hollow cross-sectional shape, and having a plurality of jet orifices for discharging an electrolyte solution respectively toward the plurality of recesses of the workpiece, and the mounting section and/or the holding section having a plurality of drain outlets that are provided respectively corresponding to the plurality of recesses of the workpiece.

Description

BACKGROUND

The present invention relates to an electrolytic apparatus that may suitably be used to treat the inner surface of a workpiece having an irregular hollow cross-sectional shape, and a surface treatment method using the same.

A number of pieces of surface treatment apparatus for treating only the inner surface of a workpiece having a hollow section have been proposed.

For example, Japanese Patent No. 4886555 discloses an inner surface treatment apparatus for a cylindrical member. According to the inner surface treatment apparatus, the upper opening and the lower opening of the cylindrical member are closed, a treatment solution is discharged from a liquid jet tube toward the inner surface of the cylindrical member, and part of the treatment solution is made to overflow. The inner surface treatment apparatus includes a liquid detection sensor that detects the presence or absence of overflow.

JP-A-11-117092 discloses an anodizing and coating apparatus that anodizes the cylinder inner surface of a cylinder block.

The Applicant of the present application proposed an anodizing apparatus that is configured so that a hollow electrode is placed in a hollow section of a workpiece, and an electrolyte solution jet port is provided that discharges an electrolyte solution from the hollow section of the electrode toward the inner surface of the workpiece in a direction diagonal to the tangential direction of the electrode (JP-A-2005-314751).

However, such a known surface treatment apparatus is designed to be applied to a workpiece having a circular cross-sectional shape, and cannot uniformly treat the inner surface of a workpiece having a hollow section, and having a plurality of protrusions and a plurality of recesses that are formed on the inner surface thereof.

SUMMARY

An object of the invention is to provide an electrolytic apparatus for uniformly treating the inner surface of a workpiece having a hollow section, and having a plurality of protrusions and a plurality of recesses that are formed on the inner surface thereof, and a surface treatment method using the same.

According to one aspect of the invention, there is provided an electrolytic apparatus that is used for a workpiece having an irregular cross-sectional shape, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof, the electrolytic apparatus comprising:

a mounting section that closes a lower opening of the workpiece;

a holding section that closes an upper opening of the workpiece; and

an electrode that is placed inside the workpiece,

the electrode having a hollow cross-sectional shape, and having a plurality of jet orifices for discharging an electrolyte solution respectively toward the plurality of recesses of the workpiece, and

the mounting section and/or the holding section having a plurality of drain outlets that are provided respectively corresponding to the plurality of recesses of the workpiece.

According to another aspect of the invention, there is provided a surface treatment method that utilizes the electrolytic apparatus as defined in claim 1, the surface treatment method comprising:

closing a lower opening of a workpiece having an irregular cross-sectional shape using the mounting section, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof;

closing an upper opening of the workpiece using the holding section;

connecting the electrode and the workpiece to a power supply for electrolysis; and

discharging an electrolyte solution from the plurality of jet orifices of the electrode respectively toward the plurality of recesses of the workpiece to effect electrolysis while discharging the electrolyte solution from the plurality of recesses of the workpiece through the plurality of drain outlets provided to the mounting section and/or the holding section.

The term “electrolytic apparatus” used herein refers to an apparatus that effects surface treatment using an electrolyte solution through electrolysis. The term “electrolytic apparatus” used herein includes an apparatus that effects anodizing using an electrolyte solution of aluminum, an alloy thereof, magnesium, an alloy thereof, titanium, or an alloy thereof, and an apparatus that effects electroplating using a plating solution as an electrolyte solution.

The workpiece to which the invention is applied has a hollow section that is formed therethrough from one end to the other end, and has a plurality of protrusions and a plurality of recesses that are formed on the inner surface thereof (inside the hollow section) (i.e., the inner surface of the workpiece has an irregular cross-sectional shape).

When a plurality of protrusions and a plurality of recesses are formed on the inner surface of the workpiece (inside the hollow section), the electrolyte solution does not uniformly flow over the inner surface of the workpiece when the electrolyte solution is merely discharged from the hollow electrode placed inside the workpiece.

The plurality of protrusions and the plurality of recesses are formed on the inner surface of the workpiece so that the value “H/D” is within the range of 0.05 to 0.4 (where, H is the height from the bottom of the recess to the top of the protrusion, and D is the diameter of an inscribed circle that is inscribed to the bottom of the recess).

The term “recess” used herein excludes a recess that is formed on each side or around a protrusion having a value “H/D” of less than 0.05.

According to one aspect of the invention, since the electrolyte solution is discharged toward the plurality of recesses formed on the inner surface of the workpiece, and a plurality of drain outlets are provided respectively corresponding to the plurality of recesses, the electrolyte solution flows over the entire inner surface of the workpiece, and local burning due to electrolysis can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of the structure of an electrolytic apparatus (anodizing apparatus) according to one embodiment of the invention, and FIG. 1B illustrates an example of the shape of a hollow section of a workpiece, and the arrangement of a jet orifice and a drain outlet.

FIGS. 2A and 2B illustrate an example of the arrangement of a jet orifice and a drain outlet, wherein FIG. 2A illustrates a case where one drain outlet is provided, and FIG. 2B illustrates a case where one jet orifice is provided.

FIG. 3 illustrates a thickness measurement target part.

FIG. 4 shows an electrolytic condition and quality evaluation results.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1A and 1B illustrate an example of the structure (configuration) of an electrolytic apparatus according to one embodiment of the invention.

An electrolytic apparatus 10 includes a mounting section 11 that closes the lower opening of a workpiece W, and a holding section 12 that closes the upper opening of the workpiece W, and is configured so that the workpiece W can be removed by moving one of the holding section 12 and the mounting section 11 vertically relative to the other.

Although FIG. 1A illustrates an example in which the workpiece W placed on the mounting section 11 is held by the holding section 12 from the upper side, the workpiece W may be placed to have the openings on the right side and the left side, and either side (i.e., the right side or the left side) of the workpiece W may be held by the mounting section 11 and the holding section 12.

A seal member 11a is provided between the mounting section 11 and the edge of the lower opening of the workpiece W, and a seal member 12a is provided between the holding section 12 and the edge of the upper opening of the workpiece W in order to prevent a situation in which an electrolyte solution leaks through the opening of the workpiece W.

In one embodiment of the invention, a hollow electrode 14 is disposed through the holding section 12, and a voltage is applied between the electrode 14 and the workpiece W from a power supply 16 through wiring members 16a and 16b.

As illustrated in FIG. 1B, the workpiece W has a cross-sectional shape in which an opening is formed therein in the vertical direction, and four protrusions 21 to 24 are formed on the inner surface thereof so that four recesses 31 to 34 are formed.

The number of protrusions is not particularly limited as long as two or more protrusions are formed. In one embodiment of the invention, the protrusions are formed in the vertical direction from the upper end to the lower end of the workpiece W. Note that the protrusions may be partially formed in the vertical direction.

Four jet orifices 15a to 15d are provided so that the electrolyte solution is discharged from the hollow electrode 14 toward the recesses 31 to 34 of the workpiece W, and four drain outlets 13a to 13d are provided respectively corresponding to the recesses 31 to 34 so that the electrolyte solution is discharged from the recesses 31 to 34.

In FIGS. 1A and 1B, the flow of the electrolyte solution is schematically indicated by each arrow.

The electrolyte solution discharged through the drain outlets is supplied to the electrode through a circulating pump and a temperature controller.

The inner surface of the workpiece illustrated in FIG. 3 that was formed of an aluminum alloy was anodized using the electrolytic apparatus illustrated in FIGS. 1A and 1B, and the results were evaluated (see below).

The workpiece was anodized using an electrolytic apparatus in which four jet orifices and four drain outlets were provided (Examples 1 to 4), an electrolytic apparatus in which four jet orifices and one drain outlet were provided (Comparative Example 1) (see FIG. 2A), or an electrolytic apparatus in which one jet orifice and four drain outlets were provided (Comparative Example 2) (see FIG. 2B).

The diameter D of an inscribed circle inscribed to the bottom of the recess of the workpiece W was about 80 mm, and the height H of the protrusion of the workpiece W was about 15 mm.

The workpiece W was subjected to a pretreatment (e.g., degreasing) according to a common procedure, and then anodized. A sulfuric acid aqueous solution (concentration: 200 g/L) was used as the electrolyte solution (temperature: 10° C.). The electrolyte solution was discharged from the jet orifice of the electrode, discharged through the drain outlet, and circulated using a circulating pump.

The anodized workpiece W was washed with hot purified water (70° C.) for 3 minutes, and the thickness of the measurement target parts a to d of the workpiece W illustrated in FIG. 3, and the hardness of the coating were measured.

FIG. 4 (table) shows the electrolytic condition (current density), the flow rate of the electrolyte solution, and the quality evaluation results.

Note that the thickness of the workpiece W was measured using an eddy current thickness gauge, and the hardness of the coating (cross section) was measured using a micro Vickers hardness tester (load: 25 g).

As shown in FIG. 4, the measurement target parts a to d had a uniform thickness, and the coating had a uniform hardness in Example 1 (current density: 1 A/dm² (normal coating-forming condition)) and Examples 2 to 4 (current density: 27 or 40 A/dm² (hard coating-forming condition)).

In contrast, the coating was burned (i.e., a normal coating could not be obtained) in Comparative Examples 1 and 2.

Although only some embodiments of the invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within scope of this invention.

Claims

1. An electrolytic apparatus that is used for a workpiece having an irregular cross-sectional shape, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof, the electrolytic apparatus comprising:

a mounting section that closes a lower opening of the workpiece;

a holding section that closes an upper opening of the workpiece; and

an electrode that is placed inside the workpiece,

the electrode having a hollow cross-sectional shape, and having a plurality of jet orifices for discharging an electrolyte solution respectively toward the plurality of recesses of the workpiece, and

the mounting section and/or the holding section having a plurality of drain outlets that are provided respectively corresponding to the plurality of recesses of the workpiece.

2. A surface treatment method that utilizes the electrolytic apparatus as defined in claim 1, the surface treatment method comprising:

closing a lower opening of a workpiece having an irregular cross-sectional shape using the mounting section, the workpiece having a hollow section that is formed vertically therethrough, and having a plurality of protrusions and a plurality of recesses that are formed on an inner surface thereof;

closing an upper opening of the workpiece using the holding section;

connecting the electrode and the workpiece to a power supply for electrolysis; and

discharging an electrolyte solution from the plurality of jet orifices of the electrode respectively toward the plurality of recesses of the workpiece to effect electrolysis while discharging the electrolyte solution from the plurality of recesses of the workpiece through the plurality of drain outlets provided to the mounting section and/or the holding section.