Anodising at home.

[th62]

[original post, restored by moderator]
I bought 5 litres of acid and cobbled this anodising bath together, easy as.

10litre plastic bucket filled with diluted acid, two aluminium cathodes, wired together, a Projecta battery charger/power supply and a bit of aluminium wire. I'll be updating the settup with titanium wire , lead cathodes and an ammeter as soon as they arrive. But it does a good job as it is.

First shot is the first piece I anodisied. This piece was mirror finished before being anodised. As you can see, it dulled the shine, but did give a nice finish. Second and third shots are of my second test piece, half the strip was polished, other half was brush finished, came out much the same both ends.

Final piece was the cable splitter I made. I assembled the the splitter with O rings on both end caps and inserted rubber bungs in the three holes before dunking it in the bath. This was necessary as the threads are a very neat fit, if anodised they wouldn't fit together. Also, I didn't want the bore anodised as this would effect the fit of the brass slide. Came out with a nice grey finish.

Happy with the results. Another tool to add to my collection.

 

[graham-xrf]

Nice finishes. That comes from meticulous cleaning!

Foe me, the sulfuric acid supply has become awkward, apparently because of people who would attack others with it. It makes no sense. I don'y thing any sales restriction measure would do anything to make a difference except inconvenience users. Now, in UK, you can't even buy battery acid! It only moves in bulk to licenced registered manufacturers, I think with every drop recorded. You can buy reagent acid in small quantities at crazy prices.

I scored some on eBay about 2 years ago, and I have it stored, and I use it sparingly.

 

[RJSakowski]

Fifteen years ago, I did some anodizing of parts for a project that I was working on. I built a 25 amp constant current power supply with a digital volt/ammeter. I used aluminum grounding wire from a tv antenna for my electrical connections and threaded some aluminum rod for use where I had threaded holes in the workpiece. My cathode was a sheet of aluminum from a distribution transformer. My results were satisfactory for clear anodizing but I was unsuccessful when I tried dyed anodizing.

 

[RJSakowski]

In the states, we can still buy battery acid at auto supply stores. $10 for a quart. If I recall correctly, battery acid is 25% sulfuric acid and is diluted to around 10 - 15% for anodizing.

 

[addertooth]

... and don't forget the high temperature steam for sealing it afterwards... that is part of the process too, for a lasting anodized coating.

 

[th62]

Nothing to see here.

 

[th62]

Ditto.

 

[addertooth]

Actually it's boiling and that's for sealing in the dye. Not required unless you are dying the anodising.

Closing the pores makes even a clear anodized coating less susceptible to chemical attack. It is vital for sealing in dyes, but it also has use for clear. They "big boys" use steam, as it allows them to perform this function on larger batches with greater ease, but yes, boiling water works too.

 

[RJSakowski]

Battery acid is 35% sulphuric acid. For anodising it's further diluted down to around 19%. Both battery acid and sulphuric acid are difficult to find in Oz too. Motor accessory outlets and battery outlets are not permitted to sell it, the only place you can buy it are from chemical outlets.

You have to state whether the concentration is weight/weight or volume to volume. When I worked in an analytical chem lab back in the seventies, we used a dilution of 1 part sulfuric acid to three parts water which is a 25% v/v. solution. Sulfuric acid has a sp.gr. of 1.83 so this would be a 38% w/w solution. I noted at the time that this was very close to the concentration of battery acid. Thinking about it, maybe we used that concentration because I worked for a battery company?

A 19% w/w concentration would be an 11.4% v/v concentration. It is simpler and safer to dilute acid by volume rather than weight. I dilute battery acid 1 part acid to 1 part water by volume for anodizing.

 

[hman]

I recall hearing/reading about using sodium bisulfate instead of sulfuric acid for anodizing. Here are a few links I found with a quick Google search:

Anodizing aluminum - Synth DIY Wiki

sdiy.info

Anodizing and dyeing aluminum without battery acid...

There is now an updated video on YouTube here . I did not show the dyeing step and it should be mentioned that after being in the dye, the anodized piece should be placed in boiling water to seal in...

www.observationsblog.com