Another anodising query sorry

[BevelParticipant @bevel]

Hi All,

Bit long winded so kindly bear with me.

Bought anodising kit from reputable company and set-up to the letter. Only difference I made was I bought a proper power supply from Amazon.

Ok, piece part area calculated as 0.084 sq ft / 12.09 sq inchs and using 720 calculator I determined 0.5 amps/15v for 120minutes.

Part thoroughly de-greased and etched for 30 secs in Sodium Hydroxide solution, then rinsed in de-ionised water. Part suspended with 3mm aluminium wire and cooked as described, then again rinsed in de-io.

Black dye heated to 40°C and part immersed for 20mins but straight away I can tell the dye is not taking as I'd like. Here my friends lies the problem I just can't get the part as black as night. What am I doing wrong? This is the 5th attempt and I just can't get the parts any darker than a light grey? I also notice there are some lighter patches which I cant explain as I didnt handle this at all between procedures?

Can somebody please advise your help would be invaluable and greatly appreciated. Many thanks in advance

[BevelParticipant @bevel]

Dye not taking??

[Brian HParticipant @brianh50089]

Are you stripping the anodic layer before re-anodising?

Brian

[Barnaby WildeParticipant @barnabywilde70941]

There are many variables involved in succesful & repeatable anodising, as you are about to become aware.

Black is the easiest colour to get right & also the most unforgiving.

Firstly, I would say you need to ditch the idea of alu wire giving you a good connection. I have only ever had good & repeatable results using Ti.

Secondly, I am immediately thinking your 'blotchy' results is due to a lack of agitation in the tank.

Thirdly, I have only ever had 'purple' colour where the black has failed. Are you sure that you using a black dye?

Fourthly, It's like those folk who attempt to bleed their brakes their way, it will never work & the rest of us cannot possibly hope to diagnose the problem. Those folk that bleed their brakes & stick to the instructions, can be helped 'cos those of us who've been there & done that before can spot where they went wrong.

You are doing something wrong. You are not following the instructions.

[BevelParticipant @bevel]

Hi guys,

Firstly Brian, these are freshly machined parts so theres no 'stripping' required. I gave them a good scrub, then de-greased then slightly etched in sodium hydroxide before anodising. The anodising seems fine its a good hard coat its just the dye will not take up.

Barnaby, it's definately 100% black dye as my first attempt came out great. I believe your suspicion correct as I am convincing myself it's the connection thats doing it. My first attempt, the success, was attached with an aluminium rod thru the part and an aluminium end cap threaded on holding the part solid. What do you mean by agitation in the tank Barnaby?

Any tips or ideas on how to connect would be appreciated, cheers guys

[mark smith 20Participant @marksmith20]

I suspect your final rinse before colouring is the problem, usually the pH of the rinse should be below 2 which means acidic.

If the rinse is too clean (and pH wrong)as with  what you would have with `deionised water`, gelatanous aluminium oxide can form in the pores which doesn`t accept dye very well and the result will  be patchy.

To remedy you would add a little acid such as sulphuric to lower the pH of the deionised water youve been using.

Edited By mark smith 20 on 27/07/2019 19:35:28

Edited By mark smith 20 on 27/07/2019 19:37:28

[old martParticipant @oldmart]

The anodic layer is porous and the pores tend to close up during rinsing, especially in hot water. The dye is trapped in the pores in a heated dye tank.

You may have to run a series of test pieces to find the best method of rinsing before the dye tank, also the optimum time in the dye.

 Maybe your voltage is too low, anodising is a non conductor, and the voltage is normally increased as the coating gets thicker.

Edited By old mart on 27/07/2019 19:45:52

[BevelParticipant @bevel]

Ok thanks guys all good points and plenty for me to take a closer look at.

First part I ever tried came out great I was thrilled but it was a fleeting victory by looks of it lol.

regards,

NJ

[Nigel Graham 2Participant @nigelgraham2]

You do need to ensure good electrical contact throughout both anodising and plating, and anodising is trying to insulate the aluminium! Industrially, the work-holding jigs are commonly springy, which has production-handling advantages too, but keeps the contact with the work-piece.

Agitation: either user a simple stirrer, or, again borrowed from trade practice, bubble air through the fluid. I believe some people use an aquarium aerator for this.

Mark Smith advises on pH. It may be worth buying a pH meter and the better ones of those sold for testing home swimming-pool water might be accurate enough. They are colorimeters that examine a solution of a reagent in the water under test.

[old martParticipant @oldmart]

I forgot to ask what alloy you are using.

[Neil WyattModerator @neilwyatt]

30 seconds in the caustic soda before anodising doesn't seem long enough to me for anything other than a freshly turned surface, especially if you are trying to strip a previous attempt at anodising. I leave it long enough to see the surface start to turn matt.

Neil

P.S. I use a Ti rod as a connector and ALWAYS clean up the contact points with wet and dry before each run.

Edited By Neil Wyatt on 28/07/2019 10:16:08

[BevelParticipant @bevel]

Hey Neil,

All the parts I'm attempting are all freshly machined. I don't use any old material at all. Good point about the Ti rod though but isn't it very expensive?

Old Mart, I'm using 6000 series Ali but not sure exactly what.

[Barnaby WildeParticipant @barnabywilde70941]

If the dye isn't taking then the anodise pores aren't forming properly, assuming you are using proper anodise dye & not ink or clothes dye ???

Like I said, I have never experienced black dye coming out grey, I have only ever seen dark shades of purple down to deep blue depending on the size of the pores. Is it possible that the part or the bath is contaminated???

I have only ever had repeatable results using Ti connections. My favourite method is to utilise a Ti fastener into a screw hole. Ti fasteners & welding wire can be had quite cheaply.

It is vitally important that you agitate the anodise bath & keep the temp ambient & the bigger the bath the better. You aren't using a jam jar are you???

If you're using a 720 calculator then you need to follow the 720 methods rules, it only works if you follow the rules & stick to the rules.

[BevelParticipant @bevel]

Hi Barnaby,

Thx for suggestions, the Ti rod seems to be well appreciated method of connection so I'll be sure to try that now I know it's not way too expensive to procure.

I'm using proper dye from a well known company and lol no I'm not using a jam jar I assure you haha. The parts are def not contaminated and the bath has only been used less than a dozen times. Are we talking about the dye bath or the anodising bath?

I haven't used an agitator tbh as I only found out thru advice on this forum that that was a recommendation but I'm currently looking for a small air pump to use.

Cheers

[Barnaby WildeParticipant @barnabywilde70941]

Posted by Bevel on 28/07/2019 12:06:58:

Hi Barnaby,

I haven't used an agitator tbh as I only found out thru advice on this forum that that was a recommendation but I'm currently looking for a small air pump to use.

Cheers

If you don't agitate the tank then you can/will get air bubbles & localised hot spots on the part, it is highly likely that this is what's causing the blotches. I no longer home anodise but I used to have a semi-pro setup using 25l tanks and there's lots of info & build diaries on t'interwebs of how to go about it.

I found that the Caswell Plating forum was the place, some very knowledgeable folk on there.

[old martParticipant @oldmart]

I checked up on suitable alloys and any of the 6000 series are ok, 6063 being the best for colour anodising. It was also mentioned, that for consistent colour, make all your parts out of the same alloy.

[BevelParticipant @bevel]

Just ordered and received a stock bar of 6063 funny enough so good to go there.

If I use a fish tank aerator as somebody has advised won't I be introducing more air bubbles and stand a great chance of patches?

[Neil WyattModerator @neilwyatt]

I don't do any aeration.

Current wise, I have a 50W 12V transformer and let the size of the work, cathode to anode distance and internal resistance limit the current, except for really small parts where I put a resistor in series.

I use a 5A moving iron meter to monitor current, it usually swings across to the stop then drops rapidly to about 3-4A.

May sound hit and miss but it's the prep, clinical cleanliness and getting excellent electrical contact (the meter will tell you if its OK) that matter, and the results are passable:

[mark smith 20Participant @marksmith20]

Regardless of what hes doing hes still using a final rinse of de-ionised water which is as far as i was taught is wrong. It has to be below pH of 2. I worked for a while at an aluminium extrusion plant which eventually was took over by Alco and we used to do alsorts of anodising for the MOD etc.. like missile and aircraft parts.

But this was 30 years ago so maybe things have changed.

We used to seal the coloured layer with lithium salts or sodium tetrofluoroborate solution if i remember right.

Edited By mark smith 20 on 28/07/2019 18:59:27

[BevelParticipant @bevel]

looks pretty darn good to me Neil

[BevelParticipant @bevel]

Mark smith 20,

I have some pool chems here, could adding a teaspoon of PH minus into a spray bottle of de-io be what we are looking for?

[mark smith 20Participant @marksmith20]

Im not sure i suppose your talking of so called dry acid pH reducer . Ive used it before for other things. It may work but cant be sure ,we always used sulphuric acid.

[BevelParticipant @bevel]

Sulphuric acid is pretty difficult to get your hands on these days, presumably becuase of all these bl**dy idiots we have here using it as a weapon.

I know of one product that uses 91% acid in its make-up and thats readily available so maybe a splash of that would be the answer eh

[mark smith 20Participant @marksmith20]

i would stick with the pool chem if it is dry acid (sodium bisulphate) . You never know what else is in things like drain cleaners etc… containing sulphuric acid.

[Author]

Posts