4 - Aluminium Extruders - South Africa

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Extrusions going through the anodizing process.

Aluminium and most of its alloys are highly resistant to most forms or corrosion. The metal’s natural coating  of aluminium oxide provides a highly effective barrier to the ravages of airs, temperature, moisture and chemical attack, making aluminium a useful construction material.  Unlike steel, aluminium does not rust.

We have been proud members of AFSA and the Aluminium Surface Finishing  Association since 1998. Our SABS certificate was issued in 1999. Aluminium can be surface finished in different ways. The most important types are mechanical, chemical, electrolytic oxide and organic finishes.


When aluminium is exposed to atmosphere, an oxide film forms naturally to protect the surface

against contamination, but it is not thick enough to protect the metal from corroding over time. The anodizing process  is used to strip this layer and to replace it with a hard protective film which protects the aluminium surface from corrosion.

Anodizing requires a bath containing an electrolyte capable of yielding oxygen. The most important electrolytes used are sulphuric and chromic acids. A direct current is passed through the  electrolyte and causes oxygen ions to migrate to the aluminium surface (the anode) to form an oxide film. Upon further electrolysis, the oxide film increases in thickness. The oxidation takes place at the oxide-metal interface and thickening takes place from the inside.

The penetration through the entire oxide film is possible because the film is porous throughout. After anodising and before drying, the pores can be sealed by placing the aluminium in hot water. Since the anodic film is porous, colours can be introduced  into the film during or after anodising, but before sealing. A thickness of 15 micron is recommended for use inland and 25 micron for use around the coastal areas according to the specifications of SANS999.

Anodizing process
The aluminium extrusions are clamped to a jig with enough space left in between to allow each length to be exposed to the chemicals. It is then submerged into the respective tanks holding the chemicals until the process is complete. In between every chemical dipping, the extrusions are rinsed.

After the sealing process is complete, the extrusions are placed in a ventilated area to dry. The anodized extrusions are then checked for any defects and transferred to the sorting and wrapping area.

The chemicals in the respective tanks are sampled and analysed by Chemserve Systems every week and a chemical analysis is provided by the laboratory giving recommendations on how much of which chemical needs to be added to maintain the levels required for quality finish in the Natural colour.

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