Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing

Definitions

• Anodizing is a process in which an aluminum oxide film is formed on the surface of aluminum or an aluminum alloy for protection against corrosion and for decorative effects.
• the part is made the anode and is immersed in an electrolytic bath such as sulfuric, oxalic or chromic acid through which direct current is passed.
• an electrolytic bath such as sulfuric, oxalic or chromic acid
• the film formed by anodizing is characterized as an aluminum oxide film, it may also contain aluminum hydroxides (Al O -XH O).
• Anodizing is unique in the sense that the film is formed from the outside of the surface inwardly instead of being built up or deposited on the surface as in a plating operation.
• Hard anodizing is an anodizing process in which a relatively thick aluminum oxide surface is formed on the part, such surfaces being approximately .001" to .008" thick. They are known in the trade as Alumilite Nos. 225, 226, 725 or 726, Martin Hard Coat and Sanford Process Hard Coat.
• this aluminum oxide layer is extremely hard and highly stressed, it is liable to craze and crack, particularly when subjected to thermal shock. When this happens, the serviceability and corrosion resistance of the surface is seriously affected.
• the thinner decorative anodized surfaces are often sealed by immersing the part in hot water with a small amount (5 to of potassium dichromate or the like. This is known as hot water sealing. Thick hard anodized surfaces cannot be hot water sealed because they cannot withstand the thermal shock and for this reason it is generally specified that such surfaces cannot be heated for any purpose without causing serious crazing and cracking in the surface.
• the minimum heating ice time is one-half hour.
• the heating should be primarily by convection. Non-uniform heating, such as by contact with hot metal surfaces, is to be avoided. It is not necessary to control the atmosphere in the heating oven. I can use either a gas or an electric oven.
• the parts must be thoroughly dry before heating. After the part has been brought up to the temperature of 200 F., the oven is turned off and the part is gradually cooled. Larger parts may be removed from the oven and cooled in the room atmosphere. Rapid cooling of the part is to be avoided. After this treatment, the part can be heated rapidly up to about 200 F. and subjected to thermal shock (i.e., rapid cooling) without ill effects.
• the part can be heated slowly to F. and then maintained at that temperature for at least 20 minutes. It may be necessary, however, to maintain the part at that temperature for a longer period of time depending upon the size of the part and other variables which trial and error will quickly resolve. Thereafter, the part is treated as described above.
• I can, of course, compromise between the two forms of the invention and, for example, hold the part at F. for at least 10 minutes. As already stated, however, I prefer to heat the part slowly up to 200 F. and then gradually cool it off. This eliminates a holding period at a lesser temperature.
• EXAMPLE I A former part for fabricating paper and polyethylene bags was hard anodized in an Alumilite No. 225 system.
• the former was made out of a 6061 aluminum alloy.
• the former was placed in an electric oven without any atmospheric control and gradually heated from room temperature to 200 F. It took 30 minutes to heat the former from room temperature to 200 F. At the end of 30 minutes, the oven was turned off and allowed to cool gradually back to room temperature. Then the former was again heated, this time up to 400 F. It was removed from the oven and promptly treated with finely divided Teflon particles at below room temperature in accordance with my co-pending application previously identified. This shock did not craze the surface at all. The former then was subjected to its regular use.
• a method of treating a hard anodized surface to make it resistant to thermal shock comprising the steps of anodizing an aluminum surface, thoroughly drying the surface at room temperature and then uniformly and gradually heating it up over a periodof not less than 30 minutes to at least 150 F. but not more than 212 F. and holding it at that temperature for a period of minutes ranging ininverse proportion from 20 to 150 F.
• a method of treating a hard anodized surface to make it resistant to thermal shock comprising the steps of anodizing an aluminum surface, thoroughly drying the surface at room temperature, gradually and uniformly heating it up to about 200 F. in not less than about 30 minutes, gradually cooling it back to room temperature, slowly heating it up to at least about 400 F. and then cooling it back to room temperature.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Laminated Bodies (AREA)
• Heat Treatment Of Articles (AREA)
• Chemical Treatment Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (6)

Cited By (6)

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Citations (5)

• 1966
  • 1966-07-13 US US564738A patent/US3488262A/en not_active Expired - Lifetime
• 1967
  • 1967-06-29 GB GB29998/67A patent/GB1139013A/en not_active Expired
  • 1967-07-03 SE SE10303/67A patent/SE334079B/xx unknown
  • 1967-07-07 BE BE701076D patent/BE701076A/xx unknown
  • 1967-07-07 DE DE1967F0052893 patent/DE1621078B2/de active Granted
  • 1967-07-07 NL NL6709471A patent/NL6709471A/xx unknown

Patent Citations (5)

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