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Anodised Aluminium: Need Dying and Sealing help

Hi guys,

I'm a Year 11 student doing an IGCSE product that will ultimately be made out of aluminium.
I've tested on small scale with small pieces of aluminium with a 10% concentration of H2SO4 on around 7 V for 12 hours. I've managed to dye some really nice pieces with Dylon fabric dye (ebony black).

However, I'm really concerned with how many times I could use the dye (1 small tin= 1 L of dye; I need around 8-10 L of a dye solution to fit into my large trays). I need to dye at least 7 large pieces and following the guide to anodising that I found on the internet; the dylon dye I can only really use for 4-5 times max before the colour becomes too faded. I'm currently looking at anodising dyes from a hobby plating supplier, does anybody know how many times I could effectively use it before it becomes too faded?

Also; would I need to purchase the hobby plating suppliers anodising sealant to effectively seal my anodised pieces? I'm currently steam sealing my small sample pieces, how long should I really steam seal my piece for? I'm currently sealing them for around 5-10 mins.

Thanks

Brian L
Student - Hong Kong
September 23, 2011

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September 26, 2011

Words like large and small are totally relative and are not finite terms.

You could always add a 10% dye makeup after every 2 parts and probably be very safe.

7 V is far too low a voltage. 12 is an absolute minimum. A normal battery charger works on about 13 volts and a marine battery charger works on about 14 volts. Start it on the 6 V setting for a couple of minutes to prevent a serious overload and then shift to the higher settings. A variable power supply is far better if you can find one or rig a variac in line.

After an hour, the acid is eating the anodize off as fast as it is being formed, so extra hours should not be doing you any good.

James Watts
- Navarre, Florida

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Thanks for those suggestions

I'm going to try and follow the 720 rule for anodising:

formula is
720=size (ft^2)/mils (1 mil= approx. 25.4 microns)

Do you know anywhere where I can get relatively cheap anodising dye that can make around 10 liters? or where I can get some small samples of dye to refine my process before I start my final project pieces?

Brian L.
- Hong Kong
September 27, 2011

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Hi, Brian.

The 720 rule is just a limited case of Faraday's Law, with the specific factors for aluminum plugged in. But it doesn't change what James has told you: if you are operating in the proper anodizing range, it holds; if you're not, it doesn't. If fabric dye is not up to the demands of your project, you might be able to get real anodizing dyes from U.S. Specialty Color Corp. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 28, 2011

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Do you know what kind of amounts that they sell in? Would I need one of those commercial anodise sealers if I use the commercial dyes?

Thanks! I'll go and check them out now.

Brian L.
- Hong Kong
September 29, 2011