Annodising Aluminium

[Kram]

Hissing sound... The sound of failure

Eating straight through my wires due to poor contact and the full current acting on wire, no current with the wire raised out of acid.
Everyone else seems to have success wrapping wire loosely around a hole. This is crimped with pliers, still no good.
I know titanium wire can be used, but that wont stop the part anodising in contact with the wire and doing the same thing..

Any ideas? Cant be arsed to get the tig out..

 

[MattF]

Cherry red, & try scrubbing the oxide layer off by the wire.

 

[Kram]

I tried anyway.. since it had nearly an hour. electrical resistance read zero.. it would only take a light pink

Stripped it off and will use it just a matt NaOH etched finish.

That makes it two successful parts out of 5, in 7 attempts.

 

[Misterg]

Hissing sound... The sound of failure

Eating straight through my wires due to poor contact and the full current acting on wire, no current with the wire raised out of acid.
Everyone else seems to have success wrapping wire loosely around a hole. This is crimped with pliers, still no good.
I know titanium wire can be used, but that wont stop the part anodising in contact with the wire and doing the same thing..

I'm not sure what you mean...?

What is your wire made of? Aluminium should just get anodised and sit at a stable current unless your voltage is way high.

The wire needs to make good contact with the part. wedging / jamming it into a hole will work, but you need to make absolutely sure it doesn't move during the process: You don't get any anodising where the wire and the part are touching, so they stay in electrical contact unless or until something moves (you can often see a little bright spot on commercially anodised parts). Once something moves, you have anodising in the way and the contact is lost. It only takes a few minutes in the bath for this to become a problem. I've spoiled parts by giving them a gentlre swill round and causing the contact point with the wire to move. Titanum wire is easier to live with IMHO.

Are you using sulphuric acid or NaHSO4?

 

[Kram]

2.4mm 5356 tig filler wire, in a drilled 2.5mm hole, bent 180 and crimped flat with vice. This should be a million times better than what I see others doing on yt..
Perhaps 5356 is not a good choice.

How does titanium wire avoid the connection point on the part becoming insulated?

When connection is lost, the current will rapidly etch the exposed wire, makes the loud hissing sound. There are bubbles off the wire but hard to see.

My previous failed attempts, which were tig welded on, should have been a perfect connection, had the same hissing noise with the wire being rapidly etched away in places.

Still using NaHSO4.

 

[Misterg]

Perhaps 5356 is not a good choice.

When I used Al wires, all that happened if the wire loses contact with my stuff is that the current dropped right down (plain Al). Does your voltage go high when this happens?

How does titanium wire avoid the connection point on the part becoming insulated?

It doesn' t work any differently that an aluminium wire - there isn't any anodising where the wire and the part are physically in contact, so as long as it's undisturbed there is electrical contact - as soon as something moves, then the electrical contact will probably be lost. Where titanium scores is that it doesn't, get anodised itself, so is easier to re-use; and it's usualy a bit more springy than Al.

 

[Kram]

When I used Al wires, all that happened if the wire loses contact with my stuff is that the current dropped right down (plain Al). Does your voltage go high when this happens?

Using constant current, it stayed at 1A and 18-23v.

Previous failed parts were tig welded to wires, had the hissing noise and etch of the wires but much less, so Im not sure theres a bad conection, just seems to preferentially eat the wire.

Shopping list - titanium wire, titanium bolt and nut - to clamp wire to parts. Where to buy titanium...?

 

[Bki26]

Where to buy titanium

Good ol'ebay

 

[Hood]

Had a go at the rack I bought from Rugged Roads.

First I stripped off the previous anodising, not sure what dye they used but it left a horrible slimy black sludge on the rack but it cleaned off ok in water and then I anodised it. Seemed to go well so hauled it out after the 3hrs calculated time and dyed it, had to make up an aluminium tray 500 x 400 by 100 sides so I could heat the water up to seal it. All went well and colour was nice and even but couldn't get the water higher than 65 degrees but gave it an hour. Looked good until I pulled it out the water and it started to go really dark at one side, you could actually see it spreading. Not sure what was going on but looks like I will have to have another go, I might get a bigger tub seeing as the sodium bisulphate linked to earlier seems to work and I still have about 1/2kg left. Might also try with aluminium cathodes although I only have 5083 so not sure how that will work.

 

[Misterg]

couldn't get the water higher than 65 degrees but gave it an hour. Looked good until I pulled it out the water and it started to go really dark at one side, you could actually see it spreading.

I don't think you will have sealed it. I do black dye at 65°C and it soaks in well - I think that's the optimum temperature for dye penetration before you start to run into sealing. I think the water needs to be almost boiling in order to seal the anodising (>96°C ??). It's a chemistry thing, so you can't compensate for low temperatures with longer times.

I think (again!) that what you're seeing is water/dye seeping out of the un-sealed surface causing the dark colour.

You've probably not got much to lose by keeping it wet until you can try to seal it again in boiling water (it might stain, but if you're planning on stripping it off anyway...)

It's a fair bit bigger than my latest effort!

 

[Hood]

Etched the plate again to get rid of the previous anodising, re-anodised and dyed then boiled but I got the same effect although this time it was evident as soon as I put it in the boiling water.

I think I know what the problem is, the tub is not deep enough so the part is touching the bottom of the tub. I will have to try and get a bigger tub, maybe a black dustbin or similar. Not so much of an issue now with the large capacity as the sodium bisulphate I got via the earlier link was cheap enough and I know it works fine.

 

[m_c]

I would have thought touching the bottom of the tub would only cause poor anodising where it touched.

Are you sure it was originally anodised, and not coated?
It could be made from a grade of aluminium that doesn't anodise well.

 

[Misterg]

I think I know what the problem is...

Another thought I had was whether you had enough cathode area for such a big piece - something like no more than 3:1 anode to cathode area is a rule of thumb that I have seen.

 

[Hood]

I would have thought touching the bottom of the tub would only cause poor anodising where it touched.

Are you sure it was originally anodised, and not coated?
It could be made from a grade of aluminium that doesn't anodise well.

It definitely was anodised and definitely has re-anodised both times as it is non-conductive and takes dye easily.
I the bottom of the tub likely has crystals of sodium bisulphate there as I never stirred.
We will see how it goes with a bigger tub so it can be fully suspended.

Another thought I had was whether you had enough cathode area for such a big piece - something like no more than 3:1 anode to cathode area is a rule of thumb that I have seen.

That could be the case, not sure what size the lead is in comparison. When I try it with the bigger tub I will likely also try it with aluminium anodes.

 

[Hood]

Today I gave it another go, well actually I decided to just do the one I made rather than another test on the bought one.

Got a berry barrel and chopped it in half, mixed up the solution and used aluminium cathodes.

Couldn't get as much current as I would have liked, possibly I made the cathodes too small. I had worked out the surface area of the anode and then cut the cathodes to 1/6 the size so both equalled 1/3. I think however I maybe should have just calculated for one side of the cathode instead of the complete surface area. Anywy it took twice as long as it should have but seemed fine so a bit of dye and then a hot bath.

The rack after 1/2hr in the water.

 

[Kram]

This time Im working out surface area. My dad suggested the weight, divided by density, to get volume, divided by thickness should give an accurate enough idea of surface area, but getting some odd results. I have subtracted the weight of my wires so they dont mess it up. Any ideas?

4.2x3.9x0.25cm = 37cm².
11.36g ÷ 2.7 ÷ .25 = 16.8cm²

16.8 x 16 x 2 = 281.6cm²
138.8g ÷ 2.7 ÷ 0.2 = 257cm²

These two are flat sheet with no features.

 

[Hood]

Why not just work out the area if they are flat sheets? Or are you trying to get a method for future parts that are not easy to calculate?

 

[Kram]

Yes, for future and it just seems like a good way to do it. The bigger peices with features are giving better results they seem to be within 10% of the measured value.

 

[Misterg]

This time Im working out surface area. My dad suggested the weight, divided by density, to get volume, divided by thickness should give an accurate enough idea of surface area, but getting some odd results.

I think your maths is off:

The first piece is 42mm x 39mm x 2.5mm ? And the second is 168mm x 160mm x 2mm? (or 20mm?)

If so, the area of one face of the first piece calculates as 16.4 cm^2 from the measurements and ~16.9 cm^2 working back from the weight, 2.7g/cm^3 density and 2.5mm thickness.

One face of the second is 269 cm^2 from the measurements and 257 cm^2 working back from the weight (assuming 2mm thickness).

For anodising, you would need to double these areas (the parts have two sides). If you were being pedantic, you would add in the area of the edges, but for thin sheets it's not much difference (If you were anodising something with lots of holes, then the edge area might matter).

As an example, the actual surface area of the first part (assuming rectangular) would be 36.8 cm^2 vs the 32.8 cm^2 (16.4 x 2) of the two main faces.

I've got am Excel sheet set up where I put in details of rectangular blocks, cylinders & discs and it spits out the surface area and anodising current - I've tried to attach it, but not sure if it'll work.

For anything very complex, I just get the area of the part from Fusion 360.

I don't worry about getting things super accurate - ±10% is fine (for me).

 

[hotponyshoes]

This time Im working out surface area. My dad suggested the weight, divided by density, to get volume, divided by thickness should give an accurate enough idea of surface area, but getting some odd results. I have subtracted the weight of my wires so they dont mess it up. Any ideas?

4.2x3.9x0.25cm = 37cm².
11.36g ÷ 2.7 ÷ .25 = 16.8cm²

16.8 x 16 x 2 = 281.6cm²
138.8g ÷ 2.7 ÷ 0.2 = 257cm²

These two are flat sheet with no features.

You can't use that formula as volume and surface area do not have a linear relationship.