Anodising Process
CURRENT ANODISING PROCESSES
Sulphuric Acid. Is the predominant Anodising 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 coloured with deposited metals (two-step). Offers a wide array of applications. Most anodisers use this method, although other acids are available for specialty purposes.
Organic acids. These integral one-step processes employ 90-100 g/litre solutions of organic acids, containing a small amount of sulphuric 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.
Here is a detailed description of the processes used - and the results obtained - for six Anodising colour systems:
 Surface Coating
Working method
Pre treatment
Grounding
(Chromatising)
Colour Coating
Curing of lacquer coat
Structure
Grip coat ca. 1 pm of Al oxide hydrates. Al-Cr phosphates
Lacquer coat 30-80 pm organ. polymers
Colour pigments distributed in lacquer coat
Shades
Unlimited, including white; various degrees of gloss
Appearance of surface
Metallic character of the Aluminium 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 Anodised aluminium, flaking of lacquer coat possible
Colour 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 Colouring
Working method
Pre-treatment
Anodising(special alloy + organic acid)
Sealing*
Structure
Colouring matter distributed in hard Al oxide, inseparably bound to the aluminium; anodic film thickness 15-40 pm
Shades
Brown, bronze, grey, slate; no special colours; no white
Appearance of surface
Metallic character of the Aluminium 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
Main applications
Buildings with a highly representative character
 Organic Dying
Working method
Pre-treatment
Anodising(no special alloy)
Dyeing (with highly-fast organic dyes, without current)
Sealing*
Structure
Colouring matter (org. dye) in most cases incorporated throughout the coating, which is inseparably bound to the aluminium; minimum anodic film thickness 20pm
Shades
Spectral colours; deep yellow, d. red, d. blue, d. turquoise, d. black; no brown, bronze or gray tones
Appearance of surface
Metallic character of the Aluminium retained; high brilliance
Overall resistance
Very good
Chemical stress
Sensitive to alkaline construction materials
Mechanical stress
Like normal electrolytic dyeing; no flaking
These coats are considerably harder than surface coatings
Colour repairs
Impossible without dismantling (but alien retouching possible on the building)
Main applications
Buildings with a highly representative character and a distinctive colourful appearance
 Inorganic Dyeing
Working method
Pre-treatment
Anodising(no special alloy)
Dyeing (with highly-fast, inorganic dye salts, without current 1- or 2- bath)
Sealing*
Structure
Colouring matter (heavy metal oxide hydrates; Fe, Co, Mn) incorporated in outer region of coating; minimum anodic film thickness 20 pm
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 dyeing; no flaking
These coats are considerably harder than surface coatings
Colour repairs
Impossible without dismantling (but alien retouching possible on the building)
Main applications
Buildings with high requirements as to appearance (metallic character)
 Electrolytic Colouring
Working method
Pre-treatment
Anodising(no special alloy)
Dyeing with metal salts and A.C.
Sealing* or Coating with colourless lacquer, then curing
Structure
Colouring matter at base of pores consists of metals in highly dispersed
form inseparably bound to the aluminium; minimum anodic coat thickness 20 pm
Shades
Brown, bronze, gray, slate, black, pink, burgundy, no spectral colours, no white
Appearance of surface
Metallic character of the Aluminium retained
Overall resistance
Outstanding, no chalking
Chemical stress
Sensitive to alkaline construction materials
Mechanical stress
Slightly less hard than colour-Anodised coats; no flaking
These coats are considerably harder than surface coatings
Colour repairs
Impossible without dismantling (but alien retouching possible on the building)
Main applications
Building with high requirements as to appearance (metallic character
 Electrolytic Colouring Combined With Organic Dyeing
Working method
Pre-treatment
Anodising(no special alloy)
Dyeing with highly-fast organic or inorganic dyes
Sealing* (Nt)
Structure
One colouring matter at base of pores, the other incorporated in the coating; min. anodic coat thickness 20 pm
Shades
Virtually unlimited, muted shades, no white
Appearance of surface
Metallic character and surface appearance of the Aluminium retained
Overall resistance
Outstanding, no chalking
Chemical stress
Sensitive to alkaline construction materials
Mechanical stress
Like normal electrolytic dyeing; no flaking
These coats are considerably harder than surface coatings
Colour 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
|
