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FAQS: Pre-anodising of aluminium

What is pre-anodising of aluminium?

Anodising of aluminium is the electrolytic process of creating an oxide coating around 5 to 30µm in thickness on the surface of finished aluminium products to protect it against corrosion and increase surface resistance to wear and tear. When anodising is done as a pre-treatment, it can offer increased durability and heightened corrosion protection. This pre-treatment of aluminium is known as pre-anodising of aluminium. 

The concept of pre-anodising has been widely used in Europe by the ‘seaside class’ of powder coating to the Qualicoat Standard. This concept is relatively new in the UK but is gaining popularity. 

Why is pre-anodising so important?

Currently, hexavalent chromates are widely used to pre-treat aluminium prior to powder coating. But the European Commission (EC) has proposed to ban the use of hexavalent chromates due to its harmful effects. Initially, the cut-off date for applying hexavalent chromates was September 2017, but it has been moved to 2021 due to opposition from various sectors involved in the finishing industry. 

Is pre-anodising and chromate-free better?

Pre-anodising and chromate-free aluminium have various benefits aside from the obvious environmental benefits of this method. These include:

- Increase in longevity and durability resulting from improved quality.

- Avoids the use of chromate or other hazardous materials.

- Exceptionally resistant to corrosion.

- Better adhesion of the polyester powder.

- Uniform paint finish across the entire extrusion.

Is pre-anodising of aluminium a new technology?

Pre-anodising is not a new technology and has been used all over Europe and the UK by more professional powder coaters who add this process to their overall service. Most European architectural finishers operate a pre-anodising or other non-hexavalent chromate or pre-anodising system.

How is pre-anodising carried out?

The process of pre-anodising applies the same principles as that of regular anodisation, just before the application of the polyester powder. Under controlled conditions, an oxide layer is produced and, unlike the anodising for external finishes, this layer is not sealed. The process of anodising, however, does use up more electricity compared with other methods of pre-treatment. 

What paint guarantees come with pre-anodised extrusions?

The same extended paint warranties are applicable to pre-anodised aluminium that has been available with polyester powder-coated finishes. Guarantees specific to the use, application and location are also available for pre-anodised aluminium products. The process can be applied to the whole range of current polyester powder colours and powder manufacturers.

Pre-anodising of aluminium makes products more environmentally friendly, while increasing durability, attractiveness and resistance to corrosion.