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
  • C25D11/24—Chemical after-treatment

Definitions

• the present invention relates to a method of providing aluminum with a flexible oxide coating. More particularly, it is concerned with a method of treating anodically oxide-coated aluminum surfaces to render the oxide coating more flexible.
• a primary object of the present invention is to provide a process for rendering more flexible the surfaces of anodized aluminum, that is, the oxide coatings obtained by anodically treating an aluminum surface.
• a further object of the invention is to provide a more flexible aluminum oxide coated magnet wire.
• the present invention is based on the discovery that the above and further objects, which will become apparent from the following description of the invention, can be attained by subjecting the anodically formed oxide coating on an aluminum surface to an immersion in an aqueous solution of oxalic acid. More particularly, it has been found that when an anodized aluminum wire is immersed for a short time in a hot solution of oxalic acid the anodically formed oxide coating on the wire becomes more flexible, that is, less brittle and this improved flexibility characteristic is also possessed by the oxide coated wire after coating with any of the usual organic enamels such as the silicone resin enamels.
• the flexing treatment of the present invention is carried out by immersing the oxide-coated conductor in an aqueous oxalic acid solution containing from about 2.5 to oxalic acid for a time ranging from about 30 to 120 seconds.
• the oxalic acid bath is maintained at a temperature of at least 80 C. and preferably at a temperature of from about 84 to 95 C.
• Numerous experiments have shown that the desired increase in flexibility is obtained only by the use of an aqueous solution of oxalic acid at the more elevated temperatures. For example, neither hot water alone nor a butyl alcohol solution of oxalic acid will give the desired results.
• the flexing treatment of the present invention gives best results when employed on the coatings obtained by subjecting an aluminum or aluminum-surfaced wire to electrolytic treatment in an oxalic acid solution.
• a dilute solution of oxalic acid containing for example from about 1 to 10% oxalic acid is used.
• Anodiza'tion of the aluminum is preferably carried out at a high current density ranging from about 159 to 450 amps. per sq. ft. and the wire is subjected to the anodizing treatment from about 1 to 3 minutes.
• the thickness of the anodic oxide coating depends of course upon the current density and time of treatment in the bath. In general, the oxalic bathshould be at a temperature of from room temperature up to about 50 C.
• both the anodizing treatment and the flexing treatment can be carried out in one continuous operation.
• the aluminum wire can be unwound from a feed spool and after being cleaned by passing through a bath composed of ethyl alcohol and ethylene dichloride to remove any traces of grease or die lubricant on the aluminum surface, the wire is run through wipers to remove the excess solvent from the wire, It is then dried and passed into the anodizing bath where an oxide coating is anodically formed due to the combined action of the electric current and the oxidizing agent, that is. the oxalic acid, As the wire leaves this bath, it is found that the oxide coating thereon is quite brittle.
• the oxide coating becomes somewhat thinner and considerably more flexible.
• the decrease in thickness of the coating is not, however, responsible for the increased flexibility since the coating of the same thickness obtained merely by anodic oxidation of the wire is much more brittle than that obtained by immersing a thicker coating in the flexing bath.
• a 32 mil diameter aluminum wire was anodized in a 5% aqueous solution of oxalic acid using a current density of 240 amperes D, C. per sq. ft., an immersion time of seconds and a bath temperature of 50 C.
• the anodically coated wire as obtained from the anodic treating bath had a flexibility equivalent to about 10% elongation of the coating.
• this anodized wire was passed through a bath of pure water at 94 C., no improvement in the flexibility characteristics was noted.
• the anodized wire was run through flexing baths respectively containing 2.5, 5, 7.5 and 10 percent oxalic acid at 94 C. a decrease in the thickness of the oxide film was noted although the decrease was substantially the same for all concentrations of the bath from 2.5% to 10% oxalic acid.
• the percent elongation of the coating without cracking steadily increased as the concentration of the baths increased from to oxalic acid. An even greater increase in flexibility was obtained as the concentration was approached.
• Oxide-coated aluminum wire having very good flexibility was obtained under the following conditions.
• a .002 diameter wire of aluminum moving at a speed of 4-. feet per minute was passed through a 5 foot anodizing bath composed of a 5% aqueous solution of oxalic acid at 50 C. and then through a 3 foot flexing bath composed of a 5% solution of oxalic acid in water and thereafter washed and dried.
• Currents of from 10 to 14 amperes were employed in the anodizing bath.
• the flexing bath was maintained at a temperature of 84 C.
• the resultant wire was coated. with an exceedingly flexible oxide coating which showed no signs ofcracking under a 'Z-pcwer microscope when flexed to an elongation of 50%.
• the thickness of the oxide film ranged from about .06 to .11 mil.
• steps which comprise anodizing an aluminum-surfaced conductor in a 5% oxalic-acid solution in water at a current density of about 240 amps. per sq. ft. for about '75 seconds and thereafter passing the anodized conductor through a flexing bath consisting of an aqueous solution of oxalic acid containing from about 2.5 to 10% oxalic acid, said solution being held at a temperature of from about 84 to 94 C., said anodized conductor being immersed in said flexing bath for about /2 to 2 minutes.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Processes Specially Adapted For Manufacturing Cables (AREA)
• Insulated Conductors (AREA)
• Organic Insulating Materials (AREA)
• Insulating Bodies (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

Country Status (4)

Cited By (9)

Citations (1)

• 0
  • BE BE517662D patent/BE517662A/xx unknown
• 1952
  • 1952-02-15 US US271848A patent/US2665243A/en not_active Expired - Lifetime
• 1953
  • 1953-02-04 GB GB3169/53A patent/GB725681A/en not_active Expired
  • 1953-02-13 FR FR1079038D patent/FR1079038A/fr not_active Expired

Patent Citations (1)

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