Annodising Aluminium

[Kram]

Started with the small test piece. Based on 37cm² and 6A/foot² Im running at 240mA, aluminium cathode and sulphuric acid. As this sulphuric was generated using a lead annode theres a fair bit of dissolved lead which is plating out on the cathode. I'll clean it off before I do the proper parts.

 

[Hood]

Is there a reason you are sticking to the low current?, me being impatient I would be using 2 amps

 

[Kram]

Its a tiny test piece. I want to be successful at this for once!

Was I...? I went out yesterday as weather was toogood, picked up another bag of Dylon dye, black this time. Rubbish. Dylon dyes do not work, did not take at all, 15 minutes at 50c. I rinsed the dye off and warmed up the red.

10 minutes got a nice colour, not as dark as last time, it took instantly and well. Knowing the little hob doesnt have the power to boil, I got the big hob out, forgetting it boils a bit too violently! Boiled all the dye out. I should have used a steel plate under saucepan to reduce the heat a bit.

Result compared with the first part I did:

The epoxy wire coating worked perfectly. I need to get a fast setting type.

About to do one of the proper peices, I will try the bottle of Rit Indigo dye.

 

[Kram]

The test peice was running about 100 mins.

Im calling it 210cm², 0.226foot². Running at 1.35A. The test peice was running around 19v but this is just under 13v. I'll give this one 2 hours.

 

[Kram]

The next bit is in. Btw I found the chinese boost regulators do still give constant current control below the input voltage! Something I didnt expect.

It took the indigo dye instantly, too well.

I left it in a few minutes, too long.

I did try the hob on full power to try and boil some of the dye out. It will do. Darker than I wanted.

 

[Kram]

Ive put the test peice back in, to try the Dylon orange. I dont expect it will be any good.

I like the red.

Needed the big pan for this one.

Compared with the first bits, Id say its a shade lighter. Theres a small defect which I think is where I pulled out of the dye and let it dry, before I had the water warmed up. Possibly I should have rinsed in the clean tub.

I may order some more Rit branded bottle dyes.

Test piece wouldnt take the warmed Dylon orange. Rinsed it off. Tried the red (cold.. 20c) wouldnt take either thats annoying as I cant rule out the orange, I may have cocked it up.

 

[MattF]

Not normally a fan of red, but I like that colour.

 

[Kram]

From yesterday - I used the previously epoxied wire, bent in a U, filed flat faces and bolted with m3 stainless, with some fresh epoxy. Worked perfectly, about 90 mins to fully cure two coatsat 60-100c. Half of the tapped threads I painted to protect them, to be honest the anodised threads feel better. I was expecting them to be tight and need retapping, which the epoxy ones did need tap to clear them, anodised did not.

Used clamps to lower the volume of container, and had to dilute the acid a little. I'll have to get some more - I think I prefer sulphuric, lower voltage also means less heat. I used the large alu saucepan as a heat sink.
553cm², 0.595foot². 3.57A for 105 minutes.

Container was a problen again.. I'll get another bottle of this dye so I can have twice as much at the same dilution.

Die ground off the connection wires - prefer bolted!

 

[Kram]

Test peice for the Rit black, a bit of a failure. Previously anodised part of a computer case.

I may have allowed the croc clip to dip in once or twice, the tip did get eaten, and the acid did get mildly warm, about 40c.

Result was a bit yellowed. Yellow in chemistry is always bad..

Didnt take much dye.
0.2in², 1.24A for just under 2 hours.
Edit: rinsed off.. tried the blue, wgich I know works perfectly.

Nope. I have cocked something up.

 

[Misterg]

Previously anodised part of a computer case.

Did you strip it first? Were there masses of very fine bubbles all over the surface after stripping?

 

[Hood]

Any idea what this problem might be?
Making, or attempting to make a small bracket but always getting the alu eaten away at one of the lugs on the 4mm, not so bad on the 5mm but still sort of burnt as can be seen with the dye takeup compared to the rest of the part.

 

[Hood]

Meant to say that the middle one (worst) was only suspended at one end, the good end, the left and right ones were suspended both ends.

 

[Misterg]

What current density are you using?
Anything odd about the aluminium grade?

 

[Hood]

The first one (middle) was 4 amps the other two were 6 amps.
All 5083 alu.

 

[Misterg]

The first one (middle) was 4 amps the other two were 6 amps.
All 5083 alu.

What sort of size are they? (Guessing about 100mm x 50mm - ish)

 

[Hood]

Yes, more or less.
4mm one is about 13,400mm2 area, the 5mm 13,800 or so.

 

[Hood]

BTW the discolouration/burning starts within the first few minutes and doesn't seem to get any worse.

 

[Misterg]

The first one (middle) was 4 amps the other two were 6 amps.

4mm one is about 13,400mm2 area, the 5mm 13,800 or so.

If my maths is correct, that means you've got somewhere around 27 and 41 amps / square foot (30 - 45 mA / cm^2)

I believe commercial anodising is typically done at ~14A / sq foot (~15mA / cm^2) so I think your current is pretty high for the parts - I use 6A / sq foot which is ~6mA / cm^2.

I'm not sure if you're using constant current or constant voltage. If the latter, you may have to reduce the voltage (a lot - down to 6 volts, or so) to reduce the high initial current that will 'burn' the metal (which is I think what's happening) and build it up over a few minutes.

The problem may go away if you reduce the current. FWIW, I would do those at 1 amp each.

The 3 larger larger parts on the left are 5080

 

[Hood]

This is my calcs.

I am using constant current, it starts off fairly low, 0.8Amps maybe but builds up to the set current in maybe 30 seconds.

Will give one a go at a low current and see.

 

[hotponyshoes]

Agitation of the bath solved my burning issues at higher currents