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Current Anodizing Processes

Current Anodizing Processes

Sulfuric Acid is the preferred method among anodizers

Sulfuric Acid. The predominant anodizing process today. Coatings 0.1-1.0 mil thick formed in a 15 pct. solution, 12asf, 18-24 volts, 70F for 10-60 min. This coating is usually organically dyed or colored with deposited metals (two-step). Offers a wide array of applications. Most anodizers use this method, although other acids are available for specialty purposes.

Organic acids. These integral one-step processes employ 90-100 g/liter solutions of organic acids, containing a small amount of sulfuric acid (for increased conductivity). Operating conditions: 70-80F, 24asf, voltage up to 75; produces amber, bronze and black coatings. The resulting oxide coating is light-fast and weather resistant.

Six Anodizing Processes

The processes used and the results obtained for six anodizing color systems are detailed below.

Use the following number key for the illustrations:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Surface Coating

Working method

  • Pretreatment
  • Grounding
    (Chromatizing)
  • Color Coating
  • Curing of lacquer coat
Structure
  • Grip coat ca. 1碌m of Al oxide hydrates. Al-Cr phosphates
  • Lacquer coat 30-80碌m organ. polymers
  • Color pigments distributed in lacquer coat
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Shades
  • Unlimited, including white; various degrees of gloss
Appearance of surface
  • Metallic character of the aluminum lost, pigments cover underlying surface
Overall resistance
  • Good, depending on binder type and pigment quality; chalking observable in most cases
Chemical stress
  • Very good resistance to alkaline construction materials and corrosion influences
  • May show chalking after a few years.
Mechanical stress
  • Less resistant than anodized aluminum, flaking of lacquer coat possible
Color repairs
  • Possible without dismantling, but with limitations;
  • Shade/gloss is a problem
  • Adhesion of repair lacquer may vary
Main applications
  • Buildings with a normal to high representative character


Integral Coloring
Working method
  • Pretreatment
  • Anodizing (special alloy + organic acid)
  • Sealing*
Structure
  • Coloring matter distributed in hard Al oxide, inseparably bound to the aluminum; anodic film thickness 15-40碌m
Shades
  • Brown, bronze, gray, slate; no special colors; no white
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Appearance of surface
  • Metallic character of the aluminum retained
Overall resistance
  • Outstanding, virtually unlimited durability, no chalking
Chemical stress
  • Sensitive to alkaline construction materials
Mechanical stress
  • Extremely resistant; no flaking
  • These coats are considerably harder than surface coatings
Color repairs
  • Impossible without dismantling (but alien retouching possible on the building)
Main applications
  • Buildings with a highly representative character

Organic Dyeing
Working method
  • Pretreatment
  • Anodizing (no special alloy)
  • Dyeing (with highly-fast organic dyes, without current)
  • Sealing*
Structure
  • Coloring matter (org. dye) in most cases incorporated throughout the coating, which is inseparably bound to the aluminum; minimum anodic film thickness 20碌m
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Shades
  • Spectral colors; deep yellow, d. red, d. blue, d. turquoise, d. black; no brown, bronze or gray tones
Appearance of surface
  • Metallic character of the aluminum retained; high brilliance
Overall resistance
  • Very good
Chemical stress
  • Sensitive to alkaline construction materials
Mechanical stress
  • Like normal electrolytic dyeings; no flaking
  • These coats are considerably harder than surface coatings
Color repairs
  • Impossible without dismantling (but alien retouching possible on the building)
Main applications
  • Buildings with a highly representative character and a distinctive colorful appearance

Inorganic Dyeing
Working method
  • Pretreatment
  • Anodizing (no special alloy)
  • Dyeing (with highly-fast, inorganic dye salts, without current 1- or 2- bath)
  • Sealing*
Structure
  • Coloring matter (heavy metal oxide hydrates; Fe, Co, Mn) incorporated in outer region of coating; minimum anodic film thickness 20碌m
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4
- Lacquer coating
5- Coloring matter

Shades
  • Pale to dark bronze and gold tones, muted
Appearance of surface
  • Metallic character retained; anodic film somewhat duller, especially with gold tones
Overall resistance
  • Very good
Chemical stress
  • Sensitive to alkaline construction materials
Mechanical stress
  • Practically as with absorptive dyeings; no flaking
  • These coats are considerably harder than surface coatings
Color repairs
  • Impossible without dismantling (but alien retouching possible on the building)
Main applications
  • Buildings with high requirements as to appearance (metallic character)

Electrolytic Coloring
Working method
  • Pretreatment
  • Anodizing (no special alloy)
  • Dyeing with metal salts and A.C.
  • Sealing* or
  • Coating with colorless lacquer, then curing
Structure
  • Coloring matter at base of pores consists of metals in highly dispersed form inseparably bound to the aluminum; minimum anodic coat thickness 20碌m
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Shades
  • Brown, bronze, gray, slate, black, pink, burgundy, no spectral colors, no white
Appearance of surface
  • Metallic character of the aluminum retained
Overall resistance
  • Outstanding, no chalking
Chemical stress
  • Sensitive to alkaline construction materials
Mechanical stress
  • Slightly less hard than color-anodized coats; no flaking
  • These coats are considerably harder than surface coatings
Color repairs
  • Impossible without dismantling (but alien retouching possible on the building)
Main applications
  • Building with high requirements as to appearance (metallic character)

Electrolytic Coloring Combined With Organic Dyeing
Working method
  • Pretreatment
  • Anodizing (no special alloy)
  • Dyeing with highly-fast organic or inorganic dyes
  • Sealing* (Nt)
Structure
  • One coloring matter at base of pores, the other incorporated in the coating; min. anodic coat thickness 20碌m
Shades
  • Virtually unlimited, muted shades, no white
KEY:
1- Aluminum metal
2- Chromate coating (as grip for lacquers)
3- Aluminum oxide coating (as color anchor in anodizing process)
4- Lacquer coating
5- Coloring matter

Appearance of surface
  • Metallic character and surface appearance of the aluminum retained
Overall resistance
  • Outstanding, no chalking
Chemical stress
  • Sensitive to alkaline construction materials
Mechanical stress
  • Like normal electrolytic dyeings; no flaking
  • These coats are considerably harder than surface coatings
Color repairs
  • Impossible without dismantling (but alien retouching possible on the building)
Main applications
  • Buildings with high requirements as to appearance (metallic character)

*Sealing = Closing the pores