Technology

Our new workshop is fitted out with two automatic, computer-controlled, data-recording lines. The maximum usable dimensions of the tanks are 2m x 0.5m x 1.4m on the smaller line, and 2.7m x 0.5m x 2.2m on the larger line. Both lines use chemicals supplied by Alufinish to guarantee a high-quality finish. They process parts mainly for the automotive, aeronautical, electrical engineering, furniture, and construction industries, as well as parts for general engineering and sporting goods.

Aluminium Surface Treatment – Anodic Oxidation

Anodic oxidation, or anodizing, is a highly convenient surface treatment for aluminium and its alloys. This electrolytic passivation process is used to increase the thickness and density of the natural oxide layer on the surface of metal parts. A thin aluminium oxide layer (5 – 40µm) with a corundum-type micro-crystalline structure, which makes it very hard and wear-resistant, is added by passing a direct current through an electrolytic solution. During the anodizing process, parts can also be colored with organic dyes in a range of colors, to achieve the decorative look required. The final stage of the anodizing process is called “sealing” and can be done in either a hot or cold bath. The process makes it possible to achieve very high color fastness and corrosion resistance. 

Surface treatment aims at achieving a finish which performs to predefined functional specifications. Surfaces face demands that cannot be met by the material alone. Manufacturing processes can affect the properties of parts in ways that may or not be reversible. Anodized surfaces protect the parts and minimize maintenance costs. Anodizing is also environmentally friendly because it generates no heavy metals or other harmful or hazardous by-products.

 

Anodizing – Anodic Oxidation of Aluminium and Aluminium Alloys

Anodic oxidation – anodizing is an electrolytic process that aims at creating an aluminium oxide (Al203) layer on the surface of aluminium parts. This anodic film is transparent and very hard – its micro-crystalline structure is that of corundum. It is wear-resistant, and protects the surface of aluminium parts from corrosion. During the process, the parts to be treated are suspended in an anodizing bath and form the anode electrode of an electrical circuit – hence the term “anodic oxidation”.

Before the anodizing itself, the surface of the parts is pre-treated. To remove all greasy impurities left on the parts from upstream mechanical processes, the parts are first degreased in degreasing baths. These baths are slightly alkaline to minimize damage to the surface of Al parts.

Since aluminium exposed to air oxygen self-passivates by forming a surface layer of non-conductive oxide, an etching step is usually carried out. Etching also aims at making the surface uniform so as to obtain homogenous anodized parts. Moreover, an “E6” etching in high-aluminium-content baths may be performed to achieve a decorative satin (matte) finish.

After etching, certain alloying elements such as Cu, Si, etc., often form a dark layer on the surface. This is why the parts are brightened in diluted nitric acid or sulfuric acid with special chemicals (such as ALFIDEOX). This step also removes – by neutralizing – any residues from the etching or cleaning baths.

Anodizing – anodic oxidation – is an electrolytic process performed in a bath where the main component is sulfuric acid at 180 g/l. The anodizing current ranges from 1.5 to 1.7 A/dm2, and the bath temperature from 18 to 20°C. Layers of up to 25μm can be achieved in this bath within 60 minutes. Once the anodic layer has been created, it can be colored either with organic dyes or by means of an electrolytic process in special baths; a whole range of shades can be achieved. Our company offers coloring in organic dye baths only.

Since the anodic layer created in this way is porous, a sealing process is needed to achieve the required corrosion resistance and color fastness of the surface. This is done through extended immersion in boiling-hot distilled or deionized water, or through a cold sealing process, i. e., by impregnating fluorides and nickel salts in special baths.

High-gloss anodizing

Our high-gloss anodizing technique has been developed in cooperation with Alufinish; it is mainly targeted at our customers from the automotive, furniture, and plumbing industries. This process generates an outstanding look and high surface resistance for the parts.

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