We offer a wide range of treatments from traditional Chromic acid anodising (using hexavalent chrome) and Sulphuric acid anodising (either natural, or died, with a range of seals including hot water, Nickel acetate & dichromate), to REACH compliant options such as Airbuses Tartaric acid anodising and Thin film sulphuric acid anodising, the later of which can be combined with a TCS/PACS seal in order to be totally REACH compliant. Combined with our experience and expertise in masking this can provide a great option to our customers.

Anodising Overview

Anodising transforms aluminium surfaces into hard, uniform, and wear-resistant layers through controlled oxidation, creating a metallurgically bonded aluminium oxide layer. This dense layer, though porous, requires sealing to prevent further corrosion, achieved through immersion in hot demineralised water supplemented with chemicals for added protection. Prior to sealing, dye immersion can enhance aesthetics, particularly in sulphuric acid anodising. Anodising’s electrical resistance ensures even film distribution, facilitating uniform growth and providing an excellent bonding surface for subsequent paint finishes when applied without sealing, offering durability and customisation options for aluminium components.

Chromic Acid Anodising

This method produces comparatively thin but dense oxide films, usually dark grey in colour. It imparts very good corrosion resistance but, is not suited to subsequent dyeing as it is only 2-5microns thick. However, as it’s thin it does not affect close tolerances so is used extensively in the aerospace and defence industries. If left unsealed chromic acid anodising is an excellent base for subsequent painting operations. But, it does have the one major disadvantage of using hexavalent chrome which can only be employed on Aerospace and Defence articles under current REACH authorisations for it’s use.

The thin film thickness, however, does reduce the possibility of fatigue fracture on the component, furthermore unlike Sulphuric acid, Chromic acid protects rather than attacks aluminium so any residual solution that may have been trapped in cracks, pores or folds will not corrode the component, these two attributes make Chromic acid anodising ideal for critical components in the aerospace and defence sectors.

A further benefit of the chromic process is that the chromic solution is extremely searching and will seep in to even the smallest of flaws and as it is also a brownie/orange colour there will be a stain apparent around the flaw thus, allowing the process to act as a non destructive flaw detection method used extensively on defence related products.

Sulphuric acid anodising

This produces much thicker films than the chromic process, and is generally used for corrosion resistance, or decorative applications. As part of the pre-treatment aluminium can be mechanically polished, satin etched or even left in its natural state prior to anodising. Thus, combined with the ability to accept dye, sulphuric anodised films offer a wide variety of visual finishes.
Sulphuric anodising can be found in almost every walk of life wherever aluminium is used and examples of this process can be seen on domestic cookware, hand tools, facias for computers and phones, automotive trim etc.

Tartaric sulphuric acid anodising

Like Thin film Sulphuric acid anodising this is considered a more “environmentally friendly” option to chromic acid anodising and is now the preferred option for Airbus, and offered by Ashton and Moore Ltd. This is despite the fact that it currently still requires a hexavalent chromic seal, unless the surface is subsequently painted.

Thin Film Sulphuric Anodising

Probably the best “environmentally friendly” process considered as a viable option to chromic acid anodising, this process offered by Ashton & Moore Ltd., can mimic the thin anodised layer of the chromic process whilst using Sulphuric acid instead. It can even be combined with the Socomore TCS/PACS, as a non-hexavalent chrome seal to produce a very REACH compliant coating with many advantages to other options. This process is already accepted as an alternative to chromic acid anodising in some areas of the aerospace sector (eg. by Claverham) and is seriously being considered by other Primes.