Anodising Basics

Anodising of aluminium is an electrolytic surface treatment process where the work is made anodic in a acid solution. This is normally sulphuric acid, but this can be replaced with other acids for specialised coatings. The process is unlike other finishing methods. Where most processes coat the surface with an organic or inorganic deposit, anodising is a conversion of the base material itself to form a protective oxide coating.

This aluminium oxide film is formed on the surface of the part under a narrow range of temperatures, current densities, agitations and acid strengths. The processing time ranges from 20 minutes to about one hour, depending on end use requirements.

The work is processed on specially constructed racks that are required to conduct the electric current used in the processing. These racks are made from either aluminium or titanium, as other rack materials can interfere with the anodising process. Although we have many standard racks in stock, it may be necessary to construct special racks for some jobs, which may incur extra charges.

Before the anodising process commences, the part must be chemically cleaned. This most often involves a mixture of alkaline cleaners to remove oils and surface contamination. This is generally followed by an acid or caustic etching process.

Although racking marks are kept to a minimum, there always will be some evidence on the part of contact marks where it has been held for processing. With this said, it is usually possible to work with the customer to ensure that the marks occur in cosmetically appropriate places on all components.

Once deposited, anodic coatings can be coloured with a wide range of subtle or vivid dyes, or even electrolytically coloured with metallic compounds when an application requires light-fastness against UV fading.

The final operation in the anodising process is known as sealing. This is where the anodised part is treated in special chemical baths to seal the microscopic pores that the process creates.

It should be noted that components to be anodised must be free from any inserts, screws, bolts and the like. Assuming that they aren’t made from aluminium, they will most likely be attacked by the acids used in the anodising process.

Why Choose Us?

  • Anodising experience dating back to the 1960s.
  • Access to a world-wide anodising knowledge base.
  • In-house quality and testing team.
  • In-house corrosion testing facilities.
  • One to one million component capabilities, with the ability to do custom work.
  • A true ‘one-stop-shop’ for all your coating needs.

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Standard Anodising

Without dyes or electrolytic colouring, the anodised component takes on that characteristic ‘frosted silver’ appearance seen on many modern consumer products.

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Coloured Anodising

Anodising can also be coloured in a wide variety of shades. Where resistance to UV is required, such as in architectural applications, electrolytic colourings can be used. Please note that available colours are dependant on order size.

Bright coloured anodising

Bright Anodising

Bright Anodising is a process used to brighten up the aluminium prior to anodising. The aluminium is dipped in chemicals that polish it to a mirror finish.

More on Anodising

Thickness: 5-25 microns (specified according to end use).

Uniformity:  High.

Hardness: Varies depending on Alloy and Temperature of Electrolyte Bath; for example:  Alloy 6061 Anodised  at 25oC;  Knoop 350 gf·mm−2.

Wear resistance: High (subject to thickness).

Gloss: From mirror to matt films (subject to alloy used and post processing).

Colours: Limited (check with us on stock colours).

Flexibility: Anodic coatings are very hard and glass-like. With that said, they can crack when bent and thicker coatings can also craze when heated above approximately 80°C, which may effect their corrosion resistance.

Toxicity: Anodic coatings are nontoxic and can be used for food contact applications.

Corrosion resistance: Excellent, subject to thickness and sealing process.

Chemical resistance: Anodised coatings have good resistance to mild acids, but are attacked by alkali materials. This includes cement and lime mortars. Contact us to learn more about our special sealing processes that can greatly increase the resistance to alkali attack.

Recommended alloys: Purer grades of aluminium will anodise best. Other grades may result in discoloured anodic coatings due to the alloy components or restrict the formation of the film on the metal’s surface.

Standards: Due to the age of the anodising process, there are now long-established standards for anodic coatings both in Australia and internationally.

Conductivity: Anodic coatings are non-conductors. If used as part of an electrical circuit, provisions must be made for masking the component to prevent coating or removal of the coating post-processing.

Cost: Our charges will be subject to a number of factors such as volumes processing conditions rack requirements. Like many of our processes, the labour for racking, un-racking, inspection and packing play a very significant part in our overall charges. Please contact us to find out more.

Size limitations: Impreglon can anodise components up to 2800mm long, 1000mm deep, and 400mm wide in our general line. Our second line is a clear-only set-up that can fit work 3000mm long, 1200mm deep, and 600mm wide.

Recommended Uses

Anodising is a long-established and well-accepted finish that has many useful applications both for interior and exterior use. Before we process any work, we always provide a specification or a service requirement for the anodising so we can ensure our anodising meets all your needs, no matter how great or small.

Download our Anodising Fact Sheet

Want more information, or prefer to download something to read later? No problem at all.
Here’s a downloadable .pdf document that covers off all of our service details so that you can read more or share it with a colleague.

IMPREGLON ANODISING FACT SHEET.PDF

Anodising Case Study: Qantas Food Trays

As with all work for the aviation industry, the finishes required were highly specified and only the best quality coatings were to be expected.

READ MORE

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