surface treatment of aluminium
The versatile use of aluminium is assured with its suitable surface protection as the raw aluminium oxidizes very quickly on air. We can essentially improve aluminium’s own protective ability to produce the natural oxide layer on the surface with the procedure of anodizing (eloxation). In this way treated surface of aluminium is resistant to weather, mechanical and some chemical influences.
The anodizing plant of Aluminium Kety Emmi is one of the most up-to-date lines of this kind in Europe. It is intended for anodizing of bulky components of the highest quality with the emphasis on special effects, like the colour of stainless steel and anodizing bright surfaces.
Work pieces of the following maximum dimensions can be anodised 3.500 x 650 x 1.550 mm.
The following groups or looks of anodised surfaces are available:
- natural anodised surface,
- electrochemical colours according to EURAS (C31 – C35) (UV resistant),
- stainless steel colour / look and
- chemical colours (not UV resistant).
The following possibilities of surface pre-treatments (according to DIN 17611 standards) are available:
E0 pickled,
E1 grinded,
E2 brushed,
E3 polished,
E4 brushed and grinded,
E5 grinded and polished,
E6 satinised (strongly pickled),
E7 electrochemically polished,
E8 mechanically polished + electrochemically polished,
E9 sanded.
Mechanical pre-treatments
The aluminium profiles gain a special look with the mechanical surface treatment, for instance with polishing and grinding. Smaller flaws on the surface are namely removed, a unified look is created and the surface is prepared for further treatment (decorative surface).
Polishing
It is carried out automatically or manually. With the insignificant loss of material we achieve a smooth, bright surface without scratches and with high shine.
Grinding/brushing
With the procedure of grinding and/or brushing we can remove bigger flaws on the surface and unify its look.
Chemical pre-treatments
Degreasing
It occurs in three levels: pre-degreasing, degreasing and rinsing. The procedure removes different impurities from the aluminium surface, like oil and dirt.
Etching – satinising and pickling
Etching is a chemical process, which happens in alkaline solutions. By implementing etching-satinising process the surface gets tarnishing look, which varies according to type of aluminium alloy, state of surface, temperature and handling time. The stated procedures are also used as a pre-treatment of anodizing.
Electrochemical polishing
Aluminium gains with it a shiny surface which is however very sensitive and therefore must proceed to the further treatment of anodizing as soon as possible.
Anodizing is an electrochemical process in which a thicker oxide layer is created which not only protects the surface, but by adding certain colour shades can gain different colour tones.
In the process of anodizing, the aluminium is plunged into a vat with electrolyte where it is connected to the positive pole of the regular electrical source and through it becomes an anode. With the regular voltage the oxide anions travel from the cathode to the anode where they give off the oxygen. This reacts with the aluminium and produces aluminium oxide. The thickness of the oxide layer depends on temperature, electrolyte – H2SO4, voltage used and anodizing duration. Formed oxide layer consists of numerous open pores, which need to be closed. We can do that by sealing process. The anodised layer can be coloured in different ways.
Additional service: Screen printing, tampo printing, engraving.
Table: Recommended layer thickness at anodizing
| Layer thickness in µm | Field of usage |
|---|---|
| 25 | External usage: surface is exposed to very strong influence because of corrosion or wearing out. |
| 20 | External usage: strong or normal influence, for instance building materials, vehicles and ships |
| 15 | External and internal usage: - relatively strong influence in the interior, for instance railing, - external decoration details. |
| 10 | External and internal usage: regular interior and exterior influence in dry and clean environment. Reflectors, borders, finishing car reels, sport requisites. |
| 5 | Internal usage: regular influences. |