Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/16—Polishing
  • C25F3/18—Polishing of light metals
  • C25F3/20—Polishing of light metals of aluminium

Definitions

• nforcing bath serves to protect the burfiiishcd metal with a transparent film of oxide.
• the steps in the treatment may for example include: 1) Thorough mechanical bufling;
• My present invention is more especially concerned with the electrolytic burnishing step. While a number of suitable baths are already known some of which are employed on a commercial scale, in practice they all show serious shortcomings. Thus some of the known baths are only satisfactory when operated in connection with high-purity aluminum, whereas others on the other hand are successful only when used on aluminum alloys; inmost cases moreover the operating temperature-of known baths is high, being close to 100 C. Another drawback of a number of known baths is that the current density usable therein is too low to permit a rapid burnishing process. Then again, they may require a thorough mechanical bufiing treatment prior to the electrolysis treatment.
• an electrolyte for electrolytic burnishing of aluminum and its alloys which comprises as main constituents nitric acid and water.
• the bath may contain only nitric acid and water.
• I have obtained satisfactory results by adding to the nitric bath an acid or a mixture of acids having a high alumina-dissolving capacity.
• horic acid to the nitric bath.
• nitric acid content within an approximate range from 5% to when a nitric bath is used without any added acid or mixed acids:
• compositions when only phosphoric acid is added to the nitric bath, the following approximate ranges of compositions are preferably maintained:
• Nitric acid from 35% to 45%
• Phosphoric acid from 8% to 24%
• Chromic acid from 3% to 10% Water as required to make
• percentages are by weight and the acids used are assumed to be anhydrous. In practice we may use:
• Nitric acid at 36 Baum, specific gravity d 1.332, containing 52% by weight of nitric acid.
• Nitric acid at 40 B., specific gravity d 1.383, Con ining by weight of nitric acid; this type of acid is used where the bath contains over 52% nitric acid.
• Nitric acid at 42 B.. specific gravity d 1.41, containing 92.76% by weight nitric acid; this is used where the bath contains over 62% nitric acid. ,m.
• Phosphoric acid-"'at 59 l3., specific gravity d 1.691, containing .Bflfhby weight phosphoric acid.
• the following preferred operative conditions are em- 3 ployed when using the improved electrolysis bath:
• the bath is operated at surrounding temperature.
• the temperature is mamtained under 20 C.
• the current density may be varied in the range of from about 90 to about 450 amperes per square foot with a corresponding time range of from about to about one or two minutes, according to the current density and the initial surface condition of the articles.
• the cathode used in the improved bath is an aluminum or a graphite cathode.
• the tanks or containers containing the bath may be made of stainless steel, various plastics, ebonite-coated iron or generally any suitable materials impervious to the 'acids used in my process. Coolin means should be provided, since heat is rapidly evolved in the bath and, as stated, the temperature thereof should not exceed about C. in operation.
• the steps prior to and the steps subsequent to the bumishing step may be accomplished in any of the well-known ways.
• a substance such as trichloroethylene or the like may be used.
• I may use, for example, a, bath of the following composition:
• the reenforcing treatment may comprise an anodic oxidisation in an aqueous bath containing 20% of its weightof 36 B. sulphuric acid. This bath may be used at a temperature of about 20 C. with a current density of about 13.8
• the bath of this example is particularly suit able for high purity aluminum.
• the time of treatment is from about 10 to 15 minutes, with strong agitation throughout.
• the bath of this example is especially suitable for high-purity aluminum.
• Phosphoric acid 14 Chromic acid: 5 Water: 40 Conditions of operation:
• the articles to be burnished do not require to be subjected prior to burnishing to a thorough mechanical buffing. since the bath is effective to produce in addition to burnishing, a slight polishing or buffing effect. It is merely necessary to effect a rough mechanical polish in order to remove the coarser asperities from the surface, such as scratches and surface irregularities found in metal castings direct from the foundry.
• the substances used in the composition of the bath are widely available, and may be handled without any exceptional precautions.
• the bath is applicable for burnishing both aluminum of high purity and of ordinary grades, as well as aluminum base alloys.
• aluminum alloys containing copper (such as duralumin) magnesium such as aluminum alloys containing from 3 to 5% magnesium
• magnesium and silicon containing alloys such as almasilium
• aluminum alloys containing magnesium and zinc A handsome burnish may also be obtained on aluminum alloys of the moldable type, such as those containing from 3 to 5% magnesium, the alloy known as A. P. M. (4.2% Cu, 0.184140% Mg, (LN-0.35% Ti), the alloy known as Y (35-45% Cu, l.2-1.8% Mg, 1.7-2.3% Ni) and others.
• a method for electrolytically polishing and brightening articles consisting at least for the major part of aluminum, the step of effecting the electrolytic polishing and brightening treatment at a temperature below 20 C. in an electrolysis bath containing 30 to 45% by weight of nitric acid and a significant amount of at least one member of the group consisting of phosphoric and chro'mic acids, the total of the acids ranging between 43 and 79% by weight, the balance being water.
• a method for electrolytically polishing and brightening articles consisting at least for the major part of aluminum
• the step of effecting the electrolytic polishing and brightening treatment under a current tension of 3 to 7 volts and at a current density of 10 to 50 amperes per square decimeter, and at a temperature below 20 C. in an electrolysis bath containing to 45% by weight of nitric acid and a significant amount of at least one member of the group consistin of phosphoric and chromic acids, the total of the acids ranging between 43 and 79% by weight, the balance being water.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)
• Chemical Treatment Of Metals (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

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Publications (1)

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Cited By (7)

Citations (3)

• 0
  • FR FR961236D patent/FR961236A/fr not_active Expired
• 1949
  • 1949-01-07 GB GB454/49A patent/GB659893A/en not_active Expired
  • 1949-01-11 US US70364A patent/US2553937A/en not_active Expired - Lifetime
• 1950
  • 1950-06-06 DE DEC1144A patent/DE825030C/de not_active Expired

Patent Citations (3)

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