Annodising Aluminium

[Misterg]

approx 0.06mm, so 0.03 per side, not sure what it is meant to be.

You should get 0.2 microns per minute of anodising at 6A/sq foot (6mA / cm^2).

The process eats the original surface away slightly, so about half of the anodising thickness is proud of the original surface, and about half is below the original surface.

An hour at 6A/sq foot should give a layer thickness of ~12µm which would also increase the part dimensions by 12µm (2 surfaces affected, half thickness on each).

I aim for 12µm as a minimum, or 25µm if I want to dye it (black, especially).

In practice, the dimensions are also affected if you do a pre-anodising etch in sodium hydroxide - this isn't as predictable (heavily dependent on temperature and the thickness of the oxide film on the original parts), but can be of the same order as the dimensional growth during anodising, so you may see no net change.

 

[hotponyshoes]

Looking good so far, set for 24v and 4 amps, initial switch on and CC active and sitting at 4 amps, after about 15/20 seconds the current drops down and stops at maybe 1-1.5 amps then starts slowly climbing. After a while it creeps up to the 4 amps I have set and the CC kicks in again and it sits there with voltage dropping. We will see how the part turns out after the 1.1/2 hrs it is in for, so far it has been an hour.

View attachment 398368

Been a while since i did any (and i was hard ano) so I might have forgotten but, I thought you worked out the current density requirements and then set the psu to that in constant current mode.
Left the voltage free-floating.
The current might fluctuate slightly right at the start (as the hanging rods arc a contact etc) but should stabise quickly and stay there.

Fluctuations could be caused by nearing/exceeding the limits of the psu (lower the asf and increase bath run time)
Or you might be over doing it. Once you have built up a certain thickness of coating it starts to break down again, current rises, coating rebuilds etc ect..

 

[Hood]

The part I am doing the current should be 3.13A going by the 720 (think that's what it is called) rule, and would take 2hrs. I am setting to 4 amps and it is to take 1.1/2hrs. Voltage wise I am not sure what it should be, I have often seen 24v mentioned here so that is just what I am setting as the max although as the current gets to its 4amps and CC kicks in it is dropping and at last look was 21v as can be seen in the previous picture.

 

[hotponyshoes]

As above, the layer eats in as well as growing.
Soft anno is around 50/50 but can be varied.

You can use a mask on a test piece as a control area for measuring.
Use a multimeter to check resistance as you take away the coating to measure actual thickness (if you really need to know?)

 

[Hood]

As above, the layer eats in as well as growing.
Soft anno is around 50/50 but can be varied.

You can use a mask on a test piece as a control area for measuring.
Use a multimeter to check resistance as you take away the coating to measure actual thickness (if you really need to know?)

I don't really need to know although knowledge is always a good thing.
For me the parts I have done usually come out well, nice even colour and surface has that anodised feel and so far everything has been durable, unless I get distracted and the current goes too high and it doesn't dye so evenly and if it is crazy then I get the eating away at a corner like I had previously when I was trying to go too fast and using too much current.
This new PSU seems to be doing what it should and so far very happy and will make my life easy for small parts which require 0.4 amps or less as it is now easily set

 

[hotponyshoes]

The part I am doing the current should be 3.13A going by the 720 (think that's what it is called) rule, and would take 2hrs. I am setting to 4 amps and it is to take 1.1/2hrs. Voltage wise I am not sure what it should be, I have often seen 24v mentioned here so that is just what I am setting as the max although as the current gets to its 4amps and CC kicks in it is dropping and at last look was 21v as can be seen in the previous picture.

The voltage "shouldn't be" anything fixed.
You are putting in power using Watts.

So (fake numbers) you set the psu to 4a current. The psu puts out 10v to create 40w.
As the coating grows it starts to insulate the part from the circuit.
So the voltage then rises to maintain the same 4a.
So half way through you might see 4a @ 15v with 4a @ 25v at the end.

Keeping the amps constant is important for even pour growth.

If you wanted consistency in identical parts on multiple runs you can log the total Watts going in and use that rather than time.

The 720 rule is a good starting point but your setup will be unique so you'll have to work your own numbers..

 

[hotponyshoes]

I don't really need to know although knowledge is always a good thing.
For me the parts I have done usually come out well, nice even colour and surface has that anodised feel and so far everything has been durable, unless I get distracted and the current goes too high and it doesn't dye so evenly and if it is crazy then I get the eating away at a corner like I had previously when I was trying to go too fast and using too much current.
This new PSU seems to be doing what it should and so far very happy and will make my life easy for small parts which require 0.4 amps or less as it is now easily set

I had poor low range resolution on my psu, to do small parts I'd stick sheets of alloy in the bath at the same time to increase the overall surface area

 

[Hood]

Yes, basically I am setting a max of 24v and 4amps for this part and the PSU is doing what it is meant to.
I have just put another one in and this time it went onto CC but the voltage never got up to the 24v, maybe because the bath has warmed a bit, just lukewarm so far, will keep an eye on it.
I took a vid of switch on, will upload to youtube in a bit.

 

[hotponyshoes]

Yes, basically I am setting a max of 24v and 4amps for this part and the PSU is doing what it is meant to.
I have just put another one in and this time it went onto CC but the voltage never got up to the 24v, maybe because the bath has warmed a bit, just lukewarm so far, will keep an eye on it.
I took a vid of switch on, will upload to youtube in a bit.

Mine was just set to cc mode, voltage set to 48v (max)

The temp of the bath effects things (as well as the bath heating the alloy when you put it in)
That's why I started logging watts as the time would change for each run.
You can chill the parts first but that causes its own problems...

 

[Hood]

 

[Misterg]

I’ve noticed that the voltage depends on the bath temperature - colder = higher voltage. My normal peak voltage is ~21 V in winter and ~18V in summer, but that’s at the 6A / sq ft. You’re going for slightly more than that, so it’s reasonable that the peak voltage will be higher. I think I get nicer results when the bath is cold. I’ve had problems when the bath gets even luke warm - rough looking surface and a sort of brown film on the surface of the parts. I took to standing my anodising bath in a bucket of water to limit the temperature rise.

(The process is current driven, so you would need to integrate amps for a true guide - I just plug it in and it works! )

 

[hotponyshoes]

A colder bath (amongst other things) gives a denser pour growth.
Better for durability but harder to dye.

 

[Kram]

Oh and the bench supply I got is pretty small, it is no bigger than the current PSU and boards I have and much better as it is all in one rather than 3 separates. I measures 200mm front to back, 100mm wide and 150mm high and is 30v/10A.

Do you have a link to it?

Pics of your anodised parts are also required

 

[Hood]

Do you have a link to it?

Pics of your anodised parts are also required

https://www.amazon.co.uk/dp/B09C8LWV9W?psc=1&ref=ppx_yo2ov_dt_b_product_details

This one has just left for Englandshire.

Two that will be going to USA.

 

[Hood]

Bloody hell, just noticed they have dropped the price of that PSU by £11 since I bought two days ago

 

[daleyd]

Bloody hell, just noticed they have dropped the price of that PSU by £11 since I bought two days ago

Which one did you get?

 

[Hood]

30v 10 amp

 

[Kram]

How much!


Parts look good!

 

[Hood]

How much!


Parts look good!

LOL the problems it saves me is well worth it, should have got one ages ago.
Done another and also a couple of spacers and I don't have to worry about looking in every 10 minutes to check on the current

 

[Misterg]

Very tidy