Dying Anodised Aluminium

[Rod]

I have made a mistake! (Well, no surprise yet.) I just bought and fitted a threshold / weather bar at our front door. It is fine except for one minor detail. It is "gold" anodised aluminium and someone round here does NOT like the colour. (I would have got a plain aluminium one but had a hard enough job sourcing the one I did get!)

I believe that anodised aluminium is dyed to achieve the colour range we see. Is there any sensible DIY process of changing its colour? (I want to avoid a) paying for a new one; b) going through fitting a new one.) Not sure what colour would be acceptable - the range of possibilities might influence the choice.

I do have the offcuts so there is some scope for experiment. The old one was dirty, corroded plain aluminium - but apparently preferable to "gold".

[Alan]

In message , Rod wrote

[Dave Plowman (News)]

I've got dyes for use on electronics panels, etc. Red, blue, green, yellow and black. Dunno if they can be mixed to achieve an exact shade - I suspect not. The kit I have has no instructions for reversing the process

- indeed emphasises being careful when applying them. Once they're fixed they're pretty robust.

[Dave Baker]

The colour achieved by anodizing is an integral part of the process not a dyeing operation afterwards. Anodizing chemically changes the surface skin of the aluminium to leave it hard and corrosion resistant. Anodizing can be plain or coloured with a range of common colours primarily gold, red, blue and black. The only way to remove it is to remove that skin which would leave plain soft easily corroded aluminium underneath which will then need lacquering to keep it looking nice. You could achieve that with an ungodly number of hours of sanding or flapwheels or you could take two other routes.

1) Give her a good slap and in the best James Bond tradition tell her to not be such a silly goose and go and cook or clean something. 2) Buy a can of aluminium wheel silver spray paint from Halfrauds. It will look surprisingly good once you've coated it and only take a few minutes.

[EricP]

No not really. If you were an experiment freak like some hovering in here it might be worth a weekend playing with a tank and PSU.

You could try working it off with wet/dry but it would take a lot of work as it is part of the surface now.

Only practical way is to paint it IMHO. :)

(Sits back in asbestos suit and waits to die)

[nightjar]

Yes, but only as part of the anoidizing process. The dye needs to be absorbed into the oxide coat as it is formed.

No

Usually silver or gold. You would need to find an anodizer that does a lot of some other colour for them to have a bath of anything else. The next most probable choices are blue, red and black.

Colin Bignell

[Rod]

Well that was an impressive collection of replies. Thank you each and all.

I have tried a few inky things - they just wash off. Ho hum - maybe painting time... But I shall try a few other things before giving in.

[The Natural Philosopher]

Its an integral part of the operation achieved by dyeing as part of the process. Its a moot point as to whether that's 'afterwards' or not.

But uncoloured.

created by dippng the freshly anodized unit in a dye bath.

Re anodise it.

[The Natural Philosopher]

Black is very common. But all colours have a silvery metallic sheen.

Fortunately a bit of etch primer and some two pack epoxy paint will make a really tough finish to aluminium. and the anodising may indeed act as a primer, reducing the need for etch primer.

[Dave]

When I worked in the aerospace industry, the first layer used to be alocrom, which was dropped along with the etch primer stage that followed. These 2 processes were replaced with anodising. After this the usual path was indeed epoxy primer and then top coat.

Hysol is a step forward from araldite. It is used as an adhesive or a liquid shim, depending on the mix. Liquid shim has aluminium powder added, to make it a paste that has thixotropic characteristics. The epoxy primer adhered so well to the anodising that we used, that the hysol gave way before the primer. Some impressive bonding of the epoxy primer :-)

Dave

[The Natural Philosopher]

Gosh am I geeky, I found that interesting..

where can one get the relevant paints though?

[Dave]

I put into ggogle...

"Aircraft quality epoxy primer" without the quotes. Being aircraft quality, I would have a box of tissues by your side when you see the prices.

Google came up with the first page and within this I found paints that are, as far as I can tell, what I would expect to find at British Aerospace, where I used to work. One of them mentions the Eurofighter, so that might be a later type of epoxy primer

Look out for the following links as you look at the google page, after opening each find (hope you understand that.

Type I Lead and Chromate Free Epoxy Primer CC-M4

It looks like there are several colours available, just as we expect different colours of undercoat. The one I remember was a fairly light, dull yellow and the other was tending to green, but I am slightly red/green colour blind.

WE, the Germans and the Italians used the above, but I can imagine that civil aircraft that are predominantly white, use a lighter coat of epoxy.

Dave

[Rod]

Fascinating. Whenever I have seen pictures of aircraft assembly (whether Airbus, Boeing, Eurofighter, others) the airframes are a pleasant shade of green. (Sometimes little areas have been other colours.) I assume this is because they have been so treated?

On my google search page, I got an advert for Screwfix. Couldn't find it on their site. :-)

[Dave]

All aluminium parts are treated like that, before any assembly starts. The only addition is the interfay between parts that are put together using rivets and sometimes bolts, but the latter is unusual.

Wife googling for quiz questions earlier and I got a different screen to her by typing in an identical search question :-(

Dave

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