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Castings - black anodise, not grey

I am Value Engineer for a large camera mounting company.
Currently we are having trouble producing castings a dark black colour. So much so that we have to paint to achieve the required colour. This is very costly.

Can it be done ? Is there a pre process that may be carried out first.

It is purely cosmetic so there is not a issue with physical growth.
My goal is to produce a good cosmetic black finish on the casting as cheap as possible.

Regards.

Nick Boyle
Value Engineer - Suffolk, England, UK
2007

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It isn't clear if you are dyeing or not, Nick. If you are not dyeing, you need to dye them. If you are dyeing them and they are grey, the anodizing is probably not thick enough for a saturated color.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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You anodize aluminum. You do not anodize all that silicon on the surface of a casting. To reduce the area of silicon, and to increase the area of aluminum on the surface, in order to get a blacker dye, then skip the alkali etch, dip the parts in 100% nitric acid plus 2 pounds per gallon ammonium bifluoride until the part turns "frothy white" all over, about 20-30 seconds, double rinse quickly, do not stop to look, anodize. The parts will be blacker.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

The castings are dyed twice but still appear "off black" in colour. I am assuming this is to do with the silicon content on LM24. Is there a pre process that can reduce this "skin" ?. Is there another aluminium alloy material that would colour better, but have similar properties to LM24.

Nick Boyle
- Suffolk, England
2007