What is Anodising?

Anodising is an electrochemical process used to create a protective film of aluminium oxide on the surface of aluminium quoting information or sheet. As the aluminium oxide film is created from the aluminium itself, it is integral to the aluminium and cannot crack or peel.

Anodising is translucent giving the aluminium a deep metallic lustre and is extremely durable and continues to stand the test of time.
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Benefits of Anodising

The unique anodised finish is the only one in the metals industry that satisfies each of the factors that must be considered when selecting a high-performance aluminium finish:
Since the anodising process is a reinforcement of a naturally occurring oxide process, it is non-hazardous and produces no harmful or dangerous by-products.
Anodising enhances aluminium and its environmental virtues. Anodising uses the base metal – the aluminium alloy – to create a thin, extremely strong and corrosion-resistant finish. The anodised surface is very hard and thus preserves and extends the life of the aluminium product.
In contrast to anodising, coatings – paint, for example – can dramatically reduce the ability to recycle the aluminium and can increase costs. Paints, plastics, and plating rely on problematic materials in their production that can compromise green objectives. Anodising, on the other hand, is “recycle-neutral” with minimal use of such materials as volatile organic compounds and heavy metals.
  • Durability:
    Most anodised products have an extremely long life span and offer significant economic advantages through maintenance and operating savings. Anodising is a reactive finish that is integrated with the underlying aluminium for total bonding and unmatched adhesion.
  • Ease of Maintenance:
    Cleaning with mild soap and water will usually restore an anodised surface to its original appearance. Mild abrasive cleaners can be used for more difficult deposits.
  • Health and Safety:
    Anodising is a safe process that is not harmful to human health. An anodised finish is chemically stable, will not decompose, and is non-toxic.
  • Cost:
    An initial finishing cost combined with lower maintenance costs for greater long-term value.
  • Aesthetics:
    Anodising allows the aluminium to maintain its metallic appearance.

Benefits of Anodising

The unique anodised finish is the only one in the metals industry that satisfies each of the factors that must be considered when selecting a high-performance aluminium finish:
Since the anodising process is a reinforcement of a naturally occurring oxide process, it is non-hazardous and produces no harmful or dangerous by-products.
Anodising enhances aluminium and its environmental virtues. Anodising uses the base metal – the aluminium alloy – to create a thin, extremely strong and corrosion-resistant finish. The anodised surface is very hard and thus preserves and extends the life of the aluminium product.
In contrast to anodising, coatings – paint, for example – can dramatically reduce the ability to recycle the aluminium and can increase costs. Paints, plastics, and plating rely on problematic materials in their production that can compromise green objectives. Anodising, on the other hand, is “recycle-neutral” with minimal use of such materials as volatile organic compounds and heavy metals.

Durability

Most anodised products have an extremely long life span and offer significant economic advantages through maintenance and operating savings. Anodising is a reactive finish that is integrated with the underlying aluminium for total bonding and unmatched adhesion.

Ease of Maintenance

Cleaning with mild soap and water will usually restore an anodised surface to its original appearance. Mild abrasive cleaners can be used for more difficult deposits.

Health and Safety

Anodising is a safe process that is not harmful to human health. An anodised finish is chemically stable, will not decompose, and is non-toxic.

Cost

An initial finishing cost combined with lower maintenance costs for greater long-term value.

Aesthetics.

Anodising allows the aluminium to maintain its metallic appearance.

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ANODISERS

What is the Purpose of Anodising?

The purpose of anodising is to form a layer of aluminium oxide that will protect the aluminium beneath it. The aluminium oxide layer has much higher corrosion and abrasion resistance than aluminium.
The anodic oxide structure originates from the aluminium substrate and is composed entirely of aluminium oxide. This aluminium oxide is not applied to the surface like paint or plating, but is fully integrated with the underlying aluminium substrate, so it cannot chip or peel. It has a highly ordered, porous structure that allows for secondary processes such as colouring and sealing.
Anodising is accomplished by immersing the aluminium in an acid electrolyte bath and passing an electric current through the medium. A cathode is mounted to the inside of the anodising tank; the aluminium acts as an anode, so that oxygen ions are released from the electrolyte to combine with the aluminium atoms at the surface of the part being anodised. Anodising is, therefore, a matter of highly controlled oxidation: the enhancement of a naturally occurring phenomenon.

Pre-Treatment

The aluminium is clamped onto racks and chemically etched before anodising to remove minor surface imperfections and to create our smooth satin finish.

Colour

We have 24 exclusive colours, which are broken into two categories – Electro Colouring or Interference Colouring

To view the colours available – click here

Electro Colouring

After anodising, the metal is immersed in a bath containing inorganic metal salt. When current is applied metal salts are deposited into the base of the pores. This process offers colour versatility and the most technically advanced colour quality, from sandstone to dark bronze and black.

Optical refraction, diffraction and reflection

of white light causes an interference between the electromagnetic wavelengths of the light spectrum. This interference may result in the absorption of superimposition of wavelengths – and a colour being perceived.

Interference colouring

An additional colouring procedure involves modification of the pore structure. The colours are caused by optical interference rather than light scattering, as with the basic electro-colouring.
The colour perception is a result of an optical illusion. White light can be dispersed into its colour bands by a prism. The various spectral colours arise.

The modification can be either achieved by applying an additional electrochemical process with special additives in a separate tank or by using an advance power supply and controller system that does not require any additional process tank.

Various theories explaining what happens to the oxide layer during the modification step are readily available. In summary the term ‘interference colouring’ in fact describes the optical phenomena taking place in the oxide layer to create an interference effect.

Another theory is derived from TEM results produced by an electrical modification system. A ‘second barrier’ is formed at a certain distance to the initial barrier layer. In the next step a metal salt is deposited in the pore and the incoming light then passes a metal filter, generating an interference effect and thus creating a new colour perception.

Our interference colours include Azure, Reef and Steel Blue, Sage Green, Gum Tip, Stainless, Silver, Slate and Charcoal Grey. For more information on Interference colour, please contact us at Universal Anodisers.

Pre-Treatment

The aluminium is clamped onto racks and chemically etched before anodising to remove minor surface imperfections and to create our smooth satin finish.

Colour

We have 18 exclusive colours, which are broken into two categories – Electro Colouring or Interference Colouring
To view the colours available – click here

Electro Colouring

After anodising, the metal is immersed in a bath containing inorganic metal salt. When current is applied metal salts are deposited into the base of the pores. This process offers colour versatility and the most technically advanced colour quality, from sandstone to dark bronze and black.

Optical refraction, diffraction and reflection

of white light causes an interference between the electromagnetic wavelengths of the light spectrum. This interference may result in the absorption of superimposition of wavelengths – and a colour being perceived.

Interference colouring

An additional colouring procedure involves modification of the pore structure. The colours are caused by optical interference rather than light scattering, as with the basic electro-colouring.
The colour perception is a result of an optical illusion. White light can be dispersed into its colour bands by a prism. The various spectral colours arise.

The modification can be either achieved by applying an additional electrochemical process with special additives in a separate tank or by using an advance power supply and controller system that does not require any additional process tank.
Various theories explaining what happens to the oxide layer during the modification step are readily available.
In summary the term ‘interference colouring’ in fact describes the optical phenomena taking place in the oxide layer to create an interference effect.
Another theory is derived from TEM results produced by an electrical modification system. A ‘second barrier’ is formed at a certain distance to the initial barrier layer. In the next step a metal salt is deposited in the pore and the incoming light then passes a metal filter, generating an interference effect and thus creating a new colour perception.
Our interference colours include Azure, Reef and Steel Blue, Sage Green, Gum Tip, Stainless, Silver, Slate and Charcoal Grey.
For more information on Interference colour, please contact us at Universal Anodisers.

Reproduced with permission from SAI Global Ltd under Licence 1208-c126.
Purchase the Standard online at www.saiglobal.com

Colour Variation

Colour variation information as per the Australian Standards – AS 1231-2000 Appendix G

Anodic treatment may accentuate the effect of any lack of homogeneity or differences in metallurgical condition of the aluminium. As a result, some non-uniformity of appearance may be encountered on different areas of a component and/or between different batches of material of the same specification.
With colour anodising in particular, the metal composition, form and surface texture, as well as viewing angle, can have a profound effect on the subjective impression of colour.
It is also possible on close inspection or from certain viewing angles, to observe variations in brightness, banding and other visual effects on the significant surfaces. These variations seldom impair the performance of the anodised coating.
It is important that the viewing distance be agreed to: for example, a distance of not less than 3 meters is required when viewing external architectural applications.
The samples to be used as colour and texture standards should, if possible, be duplicates of production components, or otherwise be similarly shaped in order to facilitate comparison with production components.
Anodised finishes are preferably matched in daylight but not in direct sunlight.
Co-operation between metal supplier and ourselves in achieving high standards in both finish and colour is of the upmost importance.

Anodising Hardness

The aluminium oxide surface is the same material as sapphire or carborundum and provides a hard, wear-resistant and weather-resistant surface for architectural aluminium products.

The accompanying test sheets illustrate hardness comparisons – See test results below.

Corrosion Resistance

Thicknesses from 10 microns to 25 microns are available, giving the required degree of wear and corrosion resistance from internal to severe external applications. At 25 microns, the aluminium is impervious to salt. See test results below.

Sealing and Silicon Resistance

An essential factor in corrosion resistance and colour durability is sealing. This process closes the pores in the anodic film, giving a surface that is resistant to scratching, abrasion, crazing, and colour degradation. The sealing products used by Universal Anodisers are highly effective, medium temperature, low foam liquid sealing compounds for use on a wide variety of aluminium alloys, which have been clear or colour anodised.
The product works by penetrating into the void spaces of the anodised film for added corrosion resistance. Sealing quality on the aluminium production sample is tested externally on a weekly basis. UA’s continuous results are <1.9mg/dm2; the International Anodising Standards recognise <30mg/dm2 as a pass.
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Cleaning Recommendations & Care

To maintain the decorative and protective properties of anodising against atmospheric pollutants and grime, a regular cleaning schedule should be specified and adhered to.

The preferred method of cleaning the anodised aluminium is warm soapy water, gently rubbing with a damp cloth or sponge until any grime is to be removed. It is important to rinse thoroughly with fresh water to remove any traces of detergent.
  • Severe or very severe interior conditions could result from moisture condensation, e.g., in indoor pools or steam.
  • Severe or very severe exterior conditions could result from a coastal site exposed to saltwater vapour.
  • There are excellent barrier products available for this type of salt protection.
Anodising Thickness & Cleaning Frequency
Interior Applications Exterior Applications
Conditions Thickness Frequency Conditions Thickness Frequency
Mild 10 microns 12 months Mild 15 microns 12 months
Moderate 15-20 microns 12 months Moderate 15-20 microns 9 months
Severe 25 microns 6 months Severe 25 microns 9 months
Very Severe 25 microns 3 months Very Severe 25 microns 1-3 months

Cleaning Recommendations & Care

To maintain the decorative and protective properties of anodising against atmospheric pollutants and grime, a regular cleaning schedule should be specified and adhered to.

The preferred method of cleaning the anodised aluminium is warm soapy water, gently rubbing with a damp cloth or sponge until any grime is to be removed. It is important to rinse thoroughly with fresh water to remove any traces of detergent.
  • Severe or very severe interior conditions could result from moisture condensation, e.g., in indoor pools or steam.
  • Severe or very severe exterior conditions could result from a coastal site exposed to saltwater vapour.
  • There are excellent barrier products available for this type of salt protection.
Anodising Thickness & Cleaning Frequency
Interior Applications Exterior Applications
Conditions Thickness Frequency Conditions Thickness Frequency
Mild 10 microns 12 months Mild 15 microns 12 months
Moderate 15-20 microns 12 months Moderate 15-20 microns 9 months
Severe 25 microns 6 months Severe 25 microns 9 months
Very Severe 25 microns 3 months Very Severe 25 microns 1-3 months
Interior Applications
Conditions Thickness Frequency
Mild 10 microns 12 months
Moderate 15-20 microns 12 months
Severe 25 microns 6 months
Very Severe 25 microns 3 months
Exterior Applications
Conditions Thickness Frequency
Mild 15 microns 12 months
Moderate 15-20 microns 9 months
Severe 25 microns 9 months
Very Severe 25 microns 1-3 months
The following must not be used:
  • Any item that may scratch the surface, eg. abrasive materials (sandpaper) or sharp items.
  • Acid or alkaline cleaning compounds should be avoided as they may attack the anodic surface. Nor should abrasive cleaners be used.
  • Strong solvents must be avoided.
  • All detergents must be washed thoroughly with water to remove all detergent residue.
Avoid the following on the anodised surface:
  • Cement mortar, grout or plaster. Traces of these products must be totally removed from the anodic surface immediately to prevent blemishing.
  • It is important to mask the aluminium prior to installation.
  • Avoid continuous moisture against the anodic surface.

Independent Testing

Hardness Tests
Metallurgical testing has confirmed that Universal Hardcoat is up to twice as hard as stainless steel, which is important wherever abrasion is a consideration. To view a report summary, click here.
Test Results

Examination of Universal Hardcoat samples indicated sealing of the highest quality. To view a report summary, click here.

Test Results

Accelerated UV irradiation testing has confirmed Universal Hardcoat is virtually unaffected by the equivalent of 50 years of Sydney (Australia) UV exposure. To view a report summary, click here.

Test Results

Salt spray testing has confirmed that the 25 micron Universal Hardcoat is virtually unaffected by exposure to salt spray corrosion. To view a report summary, click here.

Test Results

Warranty

Warranties are available upon application for the integrity of the anodising process.

Quality Control

Throughout the anodising process, UA monitors the process and quality of the product. The application of electrical power and colour is pre-programmed and verified on all batches. This quality control ensures uniformity of the end product specification for film thickness, density, abrasion resistance, corrosion resistance, reflectivity, image clarity, insulative properties, adhesion and sealing.

UNIVERSAL

ANODISERS

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Metal Quality

Anodising is integral to the aluminium, therefore it is of the utmost importance that only the highest quality metal is supplied for anodising.
Aluminium containing remelt will result in the finish showing what we refer to as ‘zebra’ or ‘tiger’ stripping. This effect is caused by the metal composition. It is imperative that metal supplied for anodising is from virgin billet and from the same batch or coil to help alleviate colour variation.
As explained under our ‘Colour’ heading, there are varying processes required to achieve our colour range.
  • Interference Colour - to achieve interference colours, the pore of the aluminium is modified, therefore requiring the highest quality sheet. There are aluminium sheet suppliers that will provide guarantees as to the anodising quality. Supplying us the correct metal will provide a paramount finish that is uniform in colour consistency and metallic lustre. (Please contact us for supplier details).
  • Electro Colouring - is created via a two-step process - metal is still of the utmost importance. Contact us for further details regarding the preferred supplies of the sheet.
In some sheet light and dark lines appear, these lines are caused by rollers during the sheet production process.

Thin dark lines may appear on quoting information. These lines are referred to as dye lines.

Since the anodising process is a reinforcement of a naturally occurring oxide process, it is non-hazardous and produces no harmful or dangerous by-products.