anodising and dye

I know nothing about this subject but did read about using foo

colouring, could try that

-- milg

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I know nothing of the particular brand of dye that you are using, but

have used clothing dye. While it is not as effective as the commercia anodizing dyes it does work quite well in most cases. The most commo problem of dye not taking is the anodizing temperature being too high If the bath and part are allowed to rise above 70 degrees F during th anodizing the pores that accept the dye close up and will not accep dye. A plastic bag full of ice cubes in the bath is a common way t keep the temperatue down on small tanks. Also make sure that you rins off the part with cold water between anodizing and the dye bath an that the dye bath is also cold

-- GailInN

First R/C 1956

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In article , James writes

You're anodising your wee?

That's... Odd.

In message , Nigel Eaton writes

You taking the piss? :)

LOL - thanks guys - I thought this being a UK group that I could get away with some Scottish slang - but I guess not ;)

so....the temp of the anodising bath was too high you think?

hmmm....I'll try again with ice and a thermometer and see what happens.

Cheers!

Also - does anyone know if you can get a 'bead blasted' finish with etching for a long time? I need to achieve a matt/blasted type finish on these parts - any thoughts?

Leave the part soaking in NaOH (25-50% solution) for a few minutes, that will give you a matt finish. Be careful if you have any sharp mahined edges as these will erode rather quickly.

ChrisH

Thats a pretty wide range - does it need to be that strong? I had it in 5% for 20 min and that just softened it a bit.

Also - with this strength how often does the solution become saturated? Surely taking that much off the surface would really hit it no?

Thanks for your help though :)

Cheers,

J

That's the strength I use now - I don't have all day to wait around for it to work :-)) 2 or 3 minutes is all it needs, you are just trading solution strength for a longer exposure time - your choice. You can also warm your weak solution up for faster effect.. When the solution is saturated I simply dump it and use new.

Also, I use the same bath for stripping old anodising off, and that does take a bit more effort. Again, I don't want to wait around, and I did say to be careful if you have fine machined edges, this procedure will quickly erode the corners no matter what the strength of solution.

A note on your dye selection - anodising dyes are small-molecule dyes which offer good penetration into the oxidised layer. Further, they are resistant to UV bleaching. Most any dye will add some colour, but you may well find the colour fades over time if you don't use the correct dye. It's also difficult to get a consistant colour saturation with general dyes.

ChrisH

What do you mean by "didn't take"?

Either part wasn't anodised properly, dye was too weak or you didn't fix it by boiling.

Dylon works, not as good as commercial stuff, but it does work. Mix twice as strong as recommended and put part in hot dye (60 deg C), once its a bit darker than you need, remove it and place in boiling water for half an hour.

Chris,

Thanks for your guidance - its really appreciated!

Can you tell me where in the UK you get your dye's from?

Thanks,

James

Other than 'playing around' with colours, I only use black dye. This I order from Sigma-Aldridge, but you might have better luck from specialist anodising materials suppliers. Now I had an email address somewhere but I'll have to dig deep to find it... There's not many that will supply small amounts, what you are after is 'sample' quantities.

ChrisH

James,

In the US, Caswell supplies small quanities of dyes. They have a U distributor also. It is: Speed Demon Motorcycles Unit 8 Southlands Industrial Park Latchford Lane Bordon Hampshire, GU35 9JD UK

Phone: +44 (0) 1420 474961 Fax: +44 (0) 870 136 5288 snipped-for-privacy@caswellplating.com

Also good to read some of thier tutorials. I dont know if they are o the UK site, but they are on the US site

-- GailInN

First R/C 1956

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Google for "anodising dyes" came up with this, could be useful.

I have done a small amount of anodizing - I had two similar failures - one I put down to the wrong type of aluminum and the 2nd I put down to not anodizing long enough.

I use used ink jet cartridges as a source of dye (cyan, magenta, yellow) - works pretty well. I have had some samples outside facing south since the winter - and only now are they showing signs of UV bleaching.

Steve

You get a good idea of how the reaction between aluminium and NaOH works if you throw a bit of screwed up aluminium foil in and wach. For a warm strong solution, almost nothing appears to happen for a minute or two, but then a VERY vigorous reaction starts to occur, releasing hydrogen and a lot of heat. The heat increases the reaction rate and the whole thing runs away, possibly even causing the solution to boil. It seems pretty clear that what happens is the oxide layer is slowly etched away for the first couple of minutes and then the bare metal is exposed, and this reacts at a quite startling pace as the temperature increases. For a large freshly machined item the oxide layer would be thinner and the rise in temperature would be slower, but presumably the same process would occur. Reducing the NaOH solution strength would slow the process down, but I think it would still involve a slow initial removal of the oxide followed by a more rapid reaction with the metal. Hope this is of some help.

Scrim

The scenario you describe is more true when using small volumes, my bath contains several gallons of NaOH so the heat of the reaction isn't able to warm the contents very quickly (certainly, not with the small number of items I have to deal with anyway).

When stripping an existing [hardened] anodised layer I find it's quite resistant to the NaOH at first and it does take time to eat through this layer. Some areas will be stripped before others as it's never a completely even layer. Sometimes it's difficult to remove all the anodising before significant erosion of sharp corners or pitting occurs, but this is true whatever solution strength you use - the whole process just takes longer in a weak solution. I don't know of a way to chemically remove an anodised layer and have no effect on the underlying metal, so there is a definitely a chance of damaging the metal during the stripping process. It's not something I do lightly, I weigh up the amount of time gone into machining it and decide whether it's worth trying. Sometimes the part can be re-finished with emery and a polishing mop, sometimes it just has to be junked.

ChrisH