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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
• • 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
  • C25D11/024—Anodisation under pulsed or modulated current or potential
• • 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
• • 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
  • C25D11/14—Producing integrally coloured layers
• • 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
  • C25D11/30—Anodisation of magnesium or alloys based thereon

Definitions

• Our invention relates to improvements in the production of anticorrosive protective coatings on light metals, more particularly on aluminium and magnesium as well as their alloys.
• protective coatings of excellent quality on light metals are, according to our invcntion,-obtained by subjecting the articles to be coated in an aqueous electrolyte to the action of an alternating electric current.
• the articles of light metal serving as electrodes after some time become covered with a protective coating or film which prevents corrosion.
• the coatings or films obtained by our improved method differ according to the composition of the electrolyte, the chemical composition of the articles, their mode of manufacture and condition of surface as well as the voltage and density of the applied alternating current, the temperature of the electrolyte and the duration of the treatment.
• the articles to be coated according to our improved method are first freed from all grease in the usual manner. They are then preferably connected to a source of alternating current and immersed in the electrolyte or bath. They may, however, also be first immersed in the bath whereupon the current is switched on quickly. If desired the liquid in the bath may be agitated during the treatment. If an acid bath is employed its action is generally increased by raising the temperature of the liquid. The process may be carried through at ordinary room temperatures but preferably the temperature of the bath is kept at 40 to 50 C. or higher. The bath may be provided with a cooling device in order to regulate the temperature in case of excessive heating by the electric current.
• composition and concentration of the acid liquor or electrolyte in the bath may, according to the eflect to be obtained and according to the composition and manner of preparation of the metal, be varied within wide limits. Concentrated solutions act considerably more powerfully and require correspondingly shorter periods of treatment to obtain the same effect than diluted solutions.
• the voltages or currents may likewise vary within wide limits according to the result aimed at and according to the composition of the aluminium alloys to be treated and the electrolyte employed as well as its temperature.
• the articles After the treatment with alternating current in the acid bath, the articles are lifted out of the vat while under potential or shortly after the current has been switched off, rinsed with water and dried.
• Two strips A of duralumin are dipped into a bath at ordinary temperatures containing 0.05% of chromic acid and connected to a source of alternating current.
• the voltage is gradually raised from a low value at the start. without arcing occurring, to 100 volts and more and the strips are allowed to remain under current for After the removal of to a source of alternating current, the voltage being gradually raised from 5 volts to 40 or 50 volts.
• the sheet B is covered with a deep black protective coating 5 while the sheet A is unchanged. After removal of the sheet B from the bath any desired number of untreated sheets may be substituted for the sheet B and treated in a similar manner.
• the appearance of the coatings of the sheets B is always the same, apart from slight differences in the shades which are traceable to differences in the composition of the alloys and in the condition of the surface and the structure-of the metal.
• Two strips of duralumin are connected to a source of alternating current in a bath containing 10% of chromic acid heated to 40 C. The voltage is gradually raised to 40 to 50 volts and. the treatment is continued for about to minutes.
• One sheet A is bright, the other sheet B is covered with a pearlgrey coating.
• a fresh untreated sheet B1 is now mounted opposite the sheet A and treated in the same manner with an alternating current gradually rising to or 50 volts during one hour.
• the sheet B1 is then black while sheet A is unchanged.
• any desired number of sheets B may be treated in a similar manner.
• the protective coatings on the sheets B are uniformly black with the exception of slight variations in the shade.
• An aluminium sheet A brightly coated in diluted chromic acid is treated with alternating current opposite an untreated aluminium sheet B in an aqueous 50% chromic acid solution heated to 40 C. in such a manner that, starting with low voltages, the voltage is gradually raised to 40 to 50 volts.
• the sheet B is deep black.
• This deep black coating which is obtained from a solution containing at 40 least about 40% chromic acid, is more flexible than the coating obtained according to Example 1, it is less inclined to crack so that it is, for example, very suitable as insulating layer for aluminium coils.
• the treatment is started at a voltage of about 10 volts and the voltage is gradually raised to 40 volts within the first 10 minutes, within a further 10 minutes to volts, and finally again in 10 minutes to volts and then maintained at 50 Volts during 30 minutes.
• the untreated 1 article is then covered with a grey-black protective coating.
• a sheet of pure aluminium and an article of duralumin are treated in a 2% bath of chromic acid heated to 50 C. during 1 hour at gradually increasing voltages up to 40 volts.
• the article of duralumin is then covered with a dark protective coating while the sheet of aluminium remains bright.
• any desired number of articles of duralumin or Lautal may be coated with dark protective coatings by a'similar treatment with alternating current.
• the various protective coatings produced according to the Examples 1 to 5 showed throughout a satisfactory resistance against corrosive action as was proved by continued tests in a salt water atmosphere produced by spraying or atomization.
• the peculiar phenomenon was, however, observed that the protective coatings on the two electrodes, even when using electrodes of the same material, frequently showed difierent colors. While one electrode was, for instance, covered with a light-grey or dark-grey coating, the coating of the second electrode remained frequently light or I even whitish.
• a brightly colored coating may, for instance, be precipitated previously on the article serving as a counter-electrode from a chromic acid solution diluted as far as possible and the uniformly colored protective coating may be produced on other articles by using the original aqueous chromic acid solution.
• the production of the protective coating on the counter electrode is preferably carried through in an aqueous solution of chromic acid of considerably lower concentration than that ,ess may also be carried through with alkaline baths, as shown in the Examples 12 to I4. In this case also very efiicient anticorrosive coatings are obtained.
• aqueous alkaline solutions of manganates Besides the baths stated in the examples aqueous alkaline solutions of manganates,
• niobates and similar substances may be used for the preparation of the electrolytes or as additions thereto.
• the articles treated according to our improved process are preferably covered with further protective coatings or films in order to increase their resistance to corrosion still further, such as films of grease, wax or their mixtures, and coats of oil paint, tar, asphalt and similar anticorrosion agents well known in the art.
• Our improved process is, of course, not limited to the conditions stated in the examples and it is left to the operator to vary the quality and color of the protective coatings by changing the concentration of the bath, its temperature, the duration of the treatment and the voltage of the current applied.
• the two or more electrodes consist of the same light metal or light metal alloy or of different light metals or light metal alloys.
• useful protective coatings can be produced by a proper choice of the electrolytes and by suitable operating conditions.
• a sinusoidal alternating" current should be used for our improved process. It is, however, possible to employ an alternating current the current curve of which deviates from the sinus form or an alternating current on which a direct current has been superimposed. In the examples of the process stated herein an alternating current of a frequency of 50 cycles per second has generally been used. Our improved process may. however, equally well be carried through with an alternating current, the frequency of which is less or more than 50 cycles per second. The current density may in our improved process lie between 0.4 to 1.5 amperes per square decimetre.

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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)
• Inorganic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=34577269

Family Applications (2)

Family Applications After (1)

Country Status (6)

Cited By (7)

Families Citing this family (4)

• 0
  • BE BE373447D patent/BE373447A/xx unknown
• 1929
  • 1929-09-16 DE DES93945D patent/DE600046C/de not_active Expired
• 1930
  • 1930-07-02 DE DE1930562615D patent/DE562615C/de not_active Expired
  • 1930-09-11 AT AT133115D patent/AT133115B/de active
  • 1930-09-15 FR FR702266D patent/FR702266A/fr not_active Expired
  • 1930-09-16 US US482368A patent/US1923539A/en not_active Expired - Lifetime
• 1931
  • 1931-06-24 GB GB18313/31A patent/GB371213A/en not_active Expired
• 1932
  • 1932-12-10 FR FR42676D patent/FR42676E/fr not_active Expired
  • 1932-12-12 GB GB35223/32A patent/GB390110A/en not_active Expired
  • 1932-12-13 US US646978A patent/US1936058A/en not_active Expired - Lifetime

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