Abstract:
An apparatus and a method are disclosed that form an anodic oxide coating on part of the outer surface of a profile having an irregular cross-sectional shape. A partial anodizing apparatus that is used to partially anodize a profile having an irregular cross-sectional shape includes an electrolytic bath that is divided into two or more partial baths. The profile is held using the two or more partial baths so that part of the profile is situated outside the electrolytic bath to form a sealed electrolysis chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/JP2013/052135 filed on Jan. 31, 2013, and published in Japanese as WO 2014/002520 A1 on Jan. 3, 2014. This application claims priority to Japanese Application No. 2012-146843 filed on Jun. 29, 2012. The entire disclosures of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for forming an anodic oxide coating on part of a profile that is formed of a light alloy such as an aluminum alloy or a magnesium alloy. 
     BACKGROUND ART 
     A profile (e.g., extruded profile) formed of aluminum or an alloy thereof (hereinafter referred to as “aluminum alloy”) and having an irregular cross-sectional shape has been used in a wide variety of fields (e.g., building materials, vehicular parts, and daily commodities). 
     A profile formed of an aluminum alloy or the like is normally anodized in order to improve surface properties such as corrosion resistance and hardness. 
     However, since it may be unnecessary to form an anodic oxide coating over the entire surface of the profile, a method that forms an anodic oxide coating on part of the surface of the profile has been proposed. 
     For example, the Applicant of the present application proposed a method that quickly forms an anodic oxide coating on an aluminum alloy extruded profile having an irregular cross-sectional shape only within a specific range in the longitudinal direction (see JP-A-2005-68458). 
     On the other hand, the present invention was conceived to form an anodic oxide coating on part of the outer surface of a profile in a cross direction. 
     JP-A-5-25693 and JP-A-11-117092 and the like disclose a method that forms an anodic oxide coating only on the inner side of a hollow aluminum product. However, an apparatus and the like that partially anodize the outer surface of a profile having an irregular cross-sectional shape have not been proposed. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     An object of the invention is to provide an apparatus and a method that form an anodic oxide coating on part of the outer surface of a profile having an irregular cross-sectional shape. 
     Solution to Problem 
     According to one aspect of the invention, there is provided a partial anodizing method that partially anodizes a profile having an irregular cross-sectional shape using an electrolytic bath that includes a first partial bath and a second partial bath, the first partial bath having an approximately box-like shape, and being formed of an insulating material, a cathode being disposed on an inner side of the first partial bath, and the second partial bath having an approximately plate-like shape, and being formed of an insulating material, the method comprising: 
     disposing first part of the profile that does not form a design surface on the second partial bath through a seal member; 
     joining the first partial bath and the second partial bath to hold the profile so that second part of the profile is situated outside the electrolytic bath, an electrolysis chamber having inlets and outlets for an electrolyte solution being formed by joining the first partial bath and the second partial bath; and 
     discharging the electrolyte solution through the inlets. 
     The term “irregular cross-sectional shape” used herein refers to a shape other than a simple axisymmetrical cross-sectional shape (e.g., plate or cylinder). 
     The term “profile” used herein refers to a wrought product other than that having a circular cross-sectional shape. 
     Since the electrolytic bath is divided into the first partial bath and the second partial bath, and the end of the first partial bath and the end of the second partial bath can be joined (connected) either directly or through the profile to hold the profile and form the electrolysis chamber, the electrolytic bath can be formed so that the surface of part of the profile faces the electrolysis chamber. 
     Therefore, part of the profile for which an anodic oxide coating is unnecessary can be positioned outside the electrolytic bath. 
     When joining two or more partial baths into which the electrolytic bath is divided, a seal member (seal section) may be provided to at least one partial bath so that the electrolyte solution does not reach part of the profile that is not anodized. In this case, the anodizing range can be limited to the desired part (e.g., design surface) of the profile. 
     When anodizing the profile in the electrolysis chamber that is formed as described above, the profile that is formed of an aluminum alloy or the like is used as an anode, and a cathode that is situated opposite to the anode is provided in the electrolysis chamber. A voltage is applied between the anode and the cathode so that an electrolytic current flows through the electrolysis chamber to form an anodic oxide coating on the surface of part of the profile. 
     Since heat is generated during anodizing, it is necessary to cool the electrolyte solution. 
     In order to efficiently cool the electrolyte solution, and prevent a situation in which local burning occurs on the anodizing target surface of the profile, it is preferable that the electrolysis chamber have inlets and outlets for the electrolyte solution, and be provided with an electrolyte solution circulation device that collects the electrolyte solution drained through the outlets, and discharges the collected electrolyte solution through the inlets. 
     According to this configuration, the electrolyte solution can be collected when placing or removing the profile by separating the electrolytic bath into the partial baths, and it is possible to prevent a situation in which the electrolyte solution stagnates in part of the electrolysis chamber and local burning occurs on the anodizing target surface of the profile, by providing the inlets and the outlets at equal intervals. 
     In the partial anodizing method, 
     the profile is preferably anodized so that 22SJ&lt;30V is satisfied, S being a treatment area (dm 2 ) in which the profile is partially anodized, J being an electrolysis current density (A/dm 2 ), and V being a flow rate (1/min) of the electrolyte solution that is circulated through the electrolysis chamber. 
     Since the flow rate of the electrolyte solution affects removal of heat generated during electrolysis, the flow rate of the electrolyte solution that is circulated through the electrolysis chamber is controlled. 
     Advantageous Effects of the Invention 
     The outer surface of the profile can be partially anodized while providing an excellent design surface by utilizing the partial anodizing apparatus according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A to 1C  illustrate an example of the structure of an electrolytic bath according to one embodiment of the invention, wherein  FIG. 1A  is a cross-sectional view,  FIG. 1B  is a view A, and  FIG. 1C  is a view B. 
         FIG. 2A  illustrates a state in which two partial baths are separated,  FIG. 2B  illustrates a state in which an electrolysis chamber is formed so that a profile is placed therein, and  FIG. 2C  illustrates a state in which a partially anodized profile has been removed. 
         FIG. 3A  is a cross-sectional view illustrating a state before an electrolytic bath is assembled,  FIG. 3B  illustrates a state after an electrolytic bath has been assembled, and 
         FIG. 3C  illustrates a state in which an electrolysis chamber is filled with an electrolyte solution. 
         FIG. 4A  illustrates a state in which a profile is anodized,  FIG. 4B  illustrates a state in which an electrolyte solution  20   a  is drained after anodizing, and  FIG. 4C  illustrates a state in which a profile has been removed. 
         FIG. 5  shows evaluation sample preparation conditions and evaluation results. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 1A and 4C  illustrate an example of the structure of a partial anodizing apparatus according to one embodiment of the invention. 
     An electrolytic bath  10  can be divided into a first partial bath  11  and a second partial bath  12 , the first partial bath  11  having an approximately box-like shape, and being formed of an insulating material, a cathode  13  being disposed on the inner side of the first partial bath  11 , and the second partial bath  12  having an approximately plate-like shape, and being formed of an insulating material. 
     In one embodiment of the invention, a profile  1  is held between one end  11   a  of the first partial bath  11  and the second partial bath  12 . Seal members  11   c  and  12   a  are provided to come in contact with the profile  1 . 
     An end  11   b  of the first partial bath  11  is situated opposite to the second partial bath  12  through the seal member  12   a.    
     Part of the profile  1  that does not form a design surface (i.e., a part  1   a  for which an anodic oxide coating is unnecessary) is sealed with the second partial bath  12 . 
     An electrolyte solution is introduced into an electrolysis chamber  20  through an inlet  21 , and drained through an outlet  22 . 
     The electrolyte solution drained through the outlet  22  is cooled using a cooler or the like, and re-introduced into the electrolysis chamber  20  through the inlet  21  using a circulation device such as a pump. 
     A plurality of inlets  21  are provided at equal intervals so that the electrolyte solution is uniformly discharged toward the profile  1 . A plurality of outlets  22  are provided at equal intervals between the corner of the electrolysis chamber and the inlet  21  so that the electrolyte solution does not remain at the corner of the electrolysis chamber  20 . 
     Anodizing, corrosion resistance, and the like were evaluated as described below using the electrolytic bath. 
     An aluminum alloy extruded profile was degreased, and subjected to an etching pretreatment according to a normal method. The extruded profile was then anodized in an electrolysis chamber having a given volume using a 200 g/l sulfuric acid aqueous solution as the electrolyte solution for a given time at a given current density. 
     The temperature of the electrolyte solution is preferably set to 15 to 25° C. so that a hard anodic oxide coating is not formed from the viewpoint of design. 
     As illustrated in  FIG. 2A , the profile  1  was positioned between the first partial bath  11  and the second partial bath  12  so that part of the profile  1  was situated outside the electrolytic bath, and the first partial bath  11  and the second partial bath  12  were assembled as illustrated in  FIG. 2B  (see also  FIGS. 3A and 3B ). 
       FIG. 3C  illustrates a state in which the electrolytic bath was filled with the electrolyte solution  20   a.    
     The electrolyte solution that was drained through each outlet  22  was discharged toward the profile  1  through each inlet  21  using a circulation device (not illustrated in the drawings) (see the arrows in  FIGS. 1B and 1C ). 
     The electrolysis chamber and the circulation device were connected through a pipe or the like (not illustrated in the drawings). 
     As illustrated in  FIG. 4A , a voltage was applied between the profile  1  (anode) and the cathode  13  to effect electrolysis. 
     Either direct-current electrolysis or alternating-current electrolysis may be employed. In the examples, direct current was applied. 
     As illustrated in  FIG. 4C , the electrolytic bath  10  was divided into two section after completion of electrolysis, and the profile  1  was removed. 
     An anodic oxide coating lb had been formed on part of the profile  1 . 
     The profile  1  was then washed with water, and subjected to a boiling water sealing treatment for 20 minutes. 
       FIG. 5  shows the results of a Corrodkote test performed in accordance with JIS H 8502 (“Methods of corrosion resistance test for metallic coatings”). 
     In Examples 1 and 2, a profile having a length of 250 mm was used. In Example 1, the volume of the electrolysis chamber was 0.4 l, the circulation flow rate of the electrolyte solution was 40 l/min, and the profile was anodized for 4 minutes at a current density of 10 A/dm 2 . 
     In Example 2, the profile was anodized in the same manner as in Example 1, except that the current density was set to 8 A/dm 2 . 
     In Example 3, the volume of the electrolysis chamber was 1.3 l, and a profile having the same cross-sectional shape as that of the profile used in Examples 1 and 2, and having a length of 800 mm was used. 
     The treatment conditions are shown in  FIG. 5 . 
     In Comparative Example 1, the outlets  22   a  and  22   b  were closed. In Comparative Example 2, the flow rate of the electrolyte solution was reduced. 
     In Examples 1 to 3, the profile had an excellent surface, and the corrosion ratio determined by the Corrodkote test was 10% or less. 
     In Comparative Example 1, the electrolyte solution stagnated, and local burning occurred. In Comparative Example 2, the value 30V (V: flow rate (1/min)) was smaller than the value 22SJ (S: treatment area (dm 2 ), J: current density (A/dm 2 )), and burning occurred. 
     INDUSTRIAL APPLICABILITY 
     The invention is suitable for forming an anodic oxide coating on part of an extruded profile formed of a light alloy, and various products can be produced using an extruded profile obtained by such a treatment.