Author Topic: Anodizing tutorial (NaHSO4 version)  (Read 3291 times)

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Offline Remulos

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Anodizing tutorial (NaHSO4 version)
« on: November 11, 2015, 07:42:28 AM »
Hi Guys, here's a quick tutorial for anodizing which I wrote for my hackspace and I couldn't find anything on here so I thought it might be a good contribution. Anodizing can be really good if done properly and there are ways of doing it really cheaply with mostly household items. I'm going to be using this on my first build to put some gold aurebesh script on the shroud (a bit like a LOTR sword) but the colours are pretty much endless. Well, white... they actually end at white... you can't anodize white which is really annoying. Anyway, here it is:

P.S. All measurements are in Metric (including Celsius not Fahrenheit)

Preliminary notes:
Wear gloves throughout the process. Vinyl gloves will offer some protection against the chemicals and also stop the cleaned piece getting covered in fingerprints.
Goggles and necessary PPE are a must, NaOH will dissolve organic matter and while a drop of the 2% (dilute) solution on your skin wont kill you it will burn.
Consider how you are going to hang your piece. Only aluminium or, preferably, titanium can go in the anodizing bath. Any part of your piece touching the wire will not be anodized.
For large pieces with an amperage requirement of 8A+ (see Step 3), an agitation system will be needed but could be simply constructed.
Different aluminium alloys will behave slightly differently throughout the process so it's a good idea to test on scrap pieces of the same alloy before doing your final piece.

Step 1:
Clean the piece in either a NaOH + Water solution for a more matte finish or simply water + degreaser/ soapy water for a satin finish. This is possibly the most important step, any marks on the piece will not be removable once it has been anodized. Depending on the finish you want you may need to use a fine grit sand paper/ a polishing wheel/ whatever you want to get the finish you want.

Step 2:
Rinse in deionised water. It's also good practice to keep it in the water until you put it in the NaHSO4+H2O solution to avoid oxidation on the surface. You can even rinse it under the tap to make sure there is no NaOH on the piece when you put it in the tank.

Step 3:
The anodizing bath should be 20% Sodium Bisulphate to 80% deionised water with a pH of 1-2. This can be increased to 30:70 if needed (though I'm not sure why it would be)
2 Lead or Aluminium cathodes should be used and it's a good idea to make sure the cathodes (combined) are twice the size of the piece or at least as big but this is not make-or-break. Voltage is not super important but can be found using the same calculator as the current. The constant current is the important part and can be calculated using the 720 rule. (Easy to find a calculator on google for this)
REMEMBER the surface area includes the internal surface area as well unless you're using a plug of some sort!
The piece should stay in the bath for close to an hour, you can take it out, rearrange the wire/hanger and put it back in if needed. A good indication that it is done is a slight yellow hue but this is not always visible.
Obviously, negative wire to the cathodes, positive wire to the piece.
The colder the bath, the quicker it will anodize.

Step 4:
Once the piece is finished, take it out and rinse it in deionised water.

Step 5: Place the piece in the chosen dye. The dye you have should have the instructions written on it but generally speaking for liquid material dye you want 5 ml of dye to 250 ml of water at 30 degrees. Keep it in the dye until you get the colour density that you want. Special anodizing dye will look better and last longer but is less readily available.

Step 6:
Rinse again in water and even run it under the tap. (very important if you are going to do Step 7)

Step 7: (Optional)(also can be done before step 5 for a 'natural' and coloured finish)
Place your mask on the piece (several methods available such as vinyl stickers for detail work or super glue for 'splash masking') and then dip in bleach. The bleach will act really quickly, 30(ish) seconds in some cases, so don't leave it in there. Rinse off the bleach in deionised water and then repeat Step 5 with your second colour. Then remove the mask (Acetone will remove the glue and leave the dye) and repeat as desired.

Step 8:
Place the piece in a pan of boiling water for 20-30 mins to seal the piece. Alternative methods such as steam sealing and nickel acetate sealing also work. (5 g/l nickel acetate, 1 g/l cobalt acetate, 8 g/l boric acid (in distilled water) for 15-20 min at 70-90 C and pH 5-6)

And your done!

DISCLAIMER: This is done at your own risk! Anodizing involves dangerous chemicals, I have used this process rather than the sulphuric acid technique to try and reduce the risks and make it safer. 'Safer', not completely 'Safe'. Care should be taken throughout all steps.
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Offline erv

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Re: Anodizing tutorial (NaHSO4 version)
« Reply #1 on: November 11, 2015, 09:57:26 PM »
Nice. Adding pictures for a visual tutorial would be a plus here but it's great to have a tutorial made with no dangerous acid involved.

to be added : Sodium bisulphate is particularly known as Ph balancer (Ph-). That's a great source to know, as you can purchase this at the supermarket from spring to september, or all year long at the HW store.

You can also use it to etch aluminum combined with copper sulphate (IIRC), it acts as a "mordant" (biting).

Offline Spitfire

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Re: Anodizing tutorial (NaHSO4 version)
« Reply #2 on: November 11, 2015, 11:42:07 PM »
Cool you took the time to do this,
Do what you like, say what you like, be what you like. just be cool at it.