Anodising is an electrochemical process which converts the metal surface into a decorative, durable, corrosion-resistant, wear-resistant oxide layer. This aluminium oxide is not applied to the surface like coating or plating, but is fully integrated with the underlying aluminium substrate. This means it cannot chip or peel. It has a highly ordered, porous structure which allows for secondary processes such as colouring. Our anodising layers meet all the quality standards for outdoor use, such as QUALANOD and BS.

principle of anodising

Following the discovery of how well a very thin oxidation film can protect the aluminium, it was an obvious decision to search for other methods to make the oxide layer thicker so that it offers even more protection. Initially, chemical methods were used. At a later stage, the electrochemical process of ‘anodic oxidation’ was developed. This is usually referred to as ‘anodising’, although this process is also referred to as eloxation, which is derived from the German word ‘Eloxalverfahren’. Sulphuric acid anodising is also referred to as the GS process, from the German ‘Gleichstrom Schwefelsäure’.

A rectifier has been set up next to the anodising bath, with the negative pole connected to the cathode plates and the positive pole connected to the workpiece. The flow of current causes oxygen formation at the anode and hydrogen gas formation at the cathode.

The oxygen (and hydrogen) are initially present in the form of free atoms, which are highly reactive and impact on the aluminium by formation of an oxide layer. Only the atomic oxygen, which causes further oxidation of the aluminium, is used here. In effect, the anodising bath provides a way of bringing pure oxygen – in the form of free atoms – in contact with the metal surface.

In theory, the type of liquid used in the bath is not important, as long as it is an electrolyte, meaning that it conducts the electrical current. The oxide layer that is formed has very different properties to the aluminium itself. This layer has mechanical properties that lie somewhere between glass and porcelain. The layer is hard and brittle and also acts as an electrical insulator.

Advantages of anodising

Attractive appearance whilst retaining metal character

Colour card

High solar reflectivity, Cool Buildings

Solar Reflectance

Durable, corrosion-resistant and colourfast

Research

LCA, expected lifespan of more than 80 years

Research

20 year guarantee on all colours Qualanod

Guarantee

40 year guarantee on all colours BS 3987

Garantie

Low maintenance

Cleaning instructions

Easy to recycle (Cradle to Cradle)

Easy to reuse (Circular Economy)

Cleaning products

Only products that do not damage the anodised surface should be used for cleaning. These are ‘pH neutral’, synthetic cleaning products. These synthetic cleaning products are strongly diluted in water when used for regular maintenance. Warm water can be used if necessary. A number of cleaning products can be ordered from Alumet. Contact info@alumet.nl for more information.

We must emphasise the warning that alkaline cleaning products, such as soda-containing products and strong detergents, must not be used. Acids such as hydrochloric acid (often used for the cleaning of stone-work façades) and phosphoric acid-containing products should not be used either, as this causes the anodising layer to disappear. Aluminium, including aluminium oxide, is ‘dissolved’ at low pH (acid) or high pH (salt/alkali). Abrasive or scouring materials – such as steel wool, steel wire brushes, sandpaper and hard polishing agents – will also damage the anodising layer.

Cleaning frequency

The cleaning of anodised aluminium in buildings and other structures must be performed according to a set schedule. This schedule is dependent on the atmosphere to which the aluminium is exposed or the extent of natural cleaning (rainfall). The following can be used as a guideline: Under normal circumstances and with natural cleaning through rainfall, it is enough to clean the aluminium once a year with a cloth or brush and plenty of water. A neutral synthetic detergent can be used if necessary and then left to dry. However, cleaning should be performed twice a year in the case of an industrial environment or in the absence of natural cleaning through rainfall.

SG / VEC anodising

Alumet has special printing equipment installed to print dates and production numbers on aluminium profiles in order to fulfil the requirements for “Structural Glazing” or “VEC anodise”. The ink form of this inkjet printer is a permanent mark, which is difficult to remove. This is necessary for facades with structural glazing. The product coding makes it easy to obtain al relevant information concerning anodizing, if something is wrong with the façade.