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White spots on anodised surfaces

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We are making H2SO4 anodising in our plant. Although we are able to keep constant temperature of 21 °C, we are facing problems after anodising.

1-) Sometimes we see tiny white spots on the profiles which are permanent.
2-) What is the necessity of air agitation in the tank. We don't have agitation at the moment.
3-) What happens if we don't reach the necessary temperature at hot sealing.

Serdar Yolcu
- Balikesir, Turkey

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I think the white spots are atmospheric corrosion developed on the aluminium between extrusion and anodizing processes.

Air agitation is very important not to have hot areas during anodizing which results in softer anodic film and variations in film thickness.

If you do not reach the sealing temperature, the anodic film is not sealed properly. The anodic film is prone to chemical and physical attack during service. It holds dirt and loses decorative appearance with time.

QUALANOD specifications tell you what the conditions of anodizing process must be to have a good quality in anodizing.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey