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topic 59468

Clear anodized aluminium part turned yellow from contact with rubber belt

November 21, 2013

Q. My aluminium (6061) part with Clear anodize coating turned into GOLDEN COLOUR after contact with flat belt for some time.

anodized aluminum turned yellow-1 anodized aluminum turned yellow-2

The surface of the flat belt which makes contact with the part is made of NBR (Special abrasion-resistant synthetic rubber), P/N: Nitta SG-250

-I'm wondering how can a rubber material cause the clear anodized aluminium part to change colour?
-Is there any solution other than changing belt or part material (Aluminium)?

- Malaysia

November 25, 2013

A. Hi K.C. Perhaps it can be better sealed to resist such staining? I'd suggest that you do a seal test such as ASTM B136-84 [affil. link to spec at Techstreet] on the aluminum. Or see letter 14462, "Spot type seal check for anodized aluminum" for more info on seal tests. Good luck.


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

July 15, 2016

I have seen this before with rubber and aluminium. I don't know the cause or the chemistry, but I suspect it could be sulfides leaching from the rubber and reacting with the Aluminium.
I have also seen a test for this which concluded (rightly or wrongly - I don't know) that sunlight accelerated the yellowing, maybe due to UV or heat.
The type of rubber and the type of Aluminium Alloy could be a factor.
I'd be interested to find the real cause. I hope this helps.

Ian Worswick
Sartorius - Cambridgeshire, UK

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