Sulphuric Acid for anodising

[AjohnwParticipant @ajohnw51620]

Posted by Chris Denton on 13/06/2016 16:16:38:

Caustic soda isn't used for anodising, sometimes etching prior to anodising.

Nitric acid solution is used as desmut.

Correct. The workshop practice series on it is pretty good BUT the current density mentioned can be way out so best try a bit first. I used lead flashing for the anode ?? cathode and cleaned it up with white vinegar – acetic acid etches it.

John

–

[KWILParticipant @kwil]

Dylon dyes work after anodising I believe and you have to subject the coloured part to a steam treatment to "fix" the dye.

Pure Ali works best, alloys will vary the colour so do not mix you metals for the best cosmetic effect. If you have a part "black hard anodised" the dimensions increase slightly.

[Clive HartlandParticipant @clivehartland94829]

Holding devices should be made of Titanium for anodising. Clip or hold where the marks cannot be seen.

All work is done hot and with clean rinse between baths. I have known coloured inks to be used for colour work.

maybe it's a matter of suck it and see as some colours are no good. Again due to type of Alu. HE30 and HE15 seem OK. Cast not so good as even black will not take up very well.

Clive

[Chris DentonParticipant @chrisdenton53037]

Posted by Ajohnw on 13/06/2016 16:29:46:

Posted by Chris Denton on 13/06/2016 16:16:38:

Caustic soda isn't used for anodising, sometimes etching prior to anodising.

Nitric acid solution is used as desmut.

Correct. The workshop practice series on it is pretty good BUT the current density mentioned can be way out so best try a bit first. I used lead flashing for the anode ?? cathode and cleaned it up with white vinegar – acetic acid etches it.

John

–

Have you you got a link to this?

[AjohnwParticipant @ajohnw51620]

**LINK**Posted by Chris Denton on 13/06/2016 17:51:14:

 

Posted by Ajohnw on 13/06/2016 16:29:46:

Posted by Chris Denton on 13/06/2016 16:16:38:

Caustic soda isn't used for anodising, sometimes etching prior to anodising.

Nitric acid solution is used as desmut.

 

Correct. The workshop practice series on it is pretty good BUT the current density mentioned can be way out so best try a bit first. I used lead flashing for the anode ?? cathode and cleaned it up with white vinegar – acetic acid etches it.

John

–

 

Have you you got a link to this?

 

**LINK**

I found the current levels suggested were too high but that could be down to size and the aluminium I used. I used quink for dying so any colour of that should be ok. Some dyes don't work so it's safer to buy the correct thing. They were listed on ebay.

I simply suspended the part on aluminium mig wire. Small part tube like over an inch bore, thin and 1 + long. It was something to finish off a fishing rod tidily.

To get the correct current levels I just used a scrap bit of 10mm dia aluminium rod that was lying about.

John

–

Edited By Ajohnw on 13/06/2016 18:13:11

[GeorgineerParticipant @georgineer]

Dave Smith the 16th –

Johnny was a nice young lad but now he is no more,

For what he thought was H2O was H2SO4.

As taught to me by my father!

George

[BazyleParticipant @bazyle]

I thought caustic soda had a violent reaction with aluminium or is that just Dural because of the copper content. I think some of the drain cleaners will be HCl like the patio cleaner even more diluted as that also gets sold as a loo cleaner. Check the label. Perhaps someone with the pink version for pickling could try a scrap and see if it does stain.

[Cyril BonnettParticipant @cyrilbonnett24790]

Amazon!

**LINK**

[Chris DentonParticipant @chrisdenton53037]

You can you either lead, low alloy aluminium (6061, 6063) or titanium for the cathode.

Dyes are so cheap you might as well use anodising dyes, the others are just hassle if they work at all.

The work piece is held with either titanium or aluminium.

6061 & 6063 anodise the easiest / brightest, followed closely by 6082. 7075 is a bit more difficult to get a very bright finish, although the way it anodises it tends to hide small scratches etc.

[Chris DentonParticipant @chrisdenton53037]

Posted by Ajohnw on 13/06/2016 18:12:16:

**LINK**Posted by Chris Denton on 13/06/2016 17:51:14:

Posted by Ajohnw on 13/06/2016 16:29:46:

Posted by Chris Denton on 13/06/2016 16:16:38:

Caustic soda isn't used for anodising, sometimes etching prior to anodising.

Nitric acid solution is used as desmut.

Correct. The workshop practice series on it is pretty good BUT the current density mentioned can be way out so best try a bit first. I used lead flashing for the anode ?? cathode and cleaned it up with white vinegar – acetic acid etches it.

John

–

Have you you got a link to this?

**LINK**

I found the current levels suggested were too high but that could be down to size and the aluminium I used. I used quink for dying so any colour of that should be ok. Some dyes don't work so it's safer to buy the correct thing. They were listed on ebay.

I simply suspended the part on aluminium mig wire. Small part tube like over an inch bore, thin and 1 + long. It was something to finish off a fishing rod tidily.

To get the correct current levels I just used a scrap bit of 10mm dia aluminium rod that was lying about.

John

–

Edited By Ajohnw on 13/06/2016 18:13:11

Just seen this, thanks.

Yes, you can work out current density from anodising a piece of aluminium with a known surface area!

[Chris DentonParticipant @chrisdenton53037]

Posted by Bazyle on 13/06/2016 19:18:05:

I thought caustic soda had a violent reaction with aluminium or is that just Dural because of the copper content. I think some of the drain cleaners will be HCl like the patio cleaner even more diluted as that also gets sold as a loo cleaner. Check the label. Perhaps someone with the pink version for pickling could try a scrap and see if it does stain.

Yes, it dissolves it. It's used for stripping anodising from aluminium and for etching it prior to anodising.

[Chris DentonParticipant @chrisdenton53037]

Stainless steel will dissolve in sulphuric acid whether it has electricity flowing through it or not, it gives of some very nasty fumes.

Steel / magnesium will also dissolve.

[VersabossParticipant @versaboss]

I think I wrote this in another -earlier – thread about anodising, so I keep it short.

Here, Sulfuric acid (concentrated) is available in shops called Drogerie; according to my translator this might be chemist or drugstore. Similar to a pharmacy, but without prescription medication.

In shops of the do-it-yourself type, department for swimming pools, there are products for lowering the pH of the water, Here again, pH- liquid is sufluric acid of around 12 +/- 2 %.There is also a cristalline pH-, Sodium hydrogene sulfate (NaHSO4), which is also suitable for anodising. The Na ions don't do any harm…

As an aside, inkjet printer ink is suitable for colouring. Be prudent with the Dylon dyes, there is only one type suitable. Don't ask how I know, what I bought was totally crap for that purpose.

Regards, HansR.

[Dave Smith the 16thParticipant @davesmiththe16th]

In the UK anything stronger than vinegar and its like ordering stuff to make nuclear weapons. If it was not an essential ingredient in batteries it would probably be banned.

Shocked to find drain cleaner with it in a strong solution. I only found that out after reading someone complain that it was on the bottom shelves next to the till with sweets on the next shelf.

It was a what if the bottle leaked and the bag its inside also leaked and …… The sort of person that would ban all your home workshop stuff instantly and would faint if they knew i tought the kids to shoot air rifles in the back garden.

[Chris DentonParticipant @chrisdenton53037]

Some of the more dangerous chemicals are now only allowed to be sold to limited companies. Even attempting to purchase them is an offence!

I don't like sulphuric being used in drain cleaner as people also use bleach in sinks etc, it's a very bad combination! Having said that I've never heard of any incidents.

My wife followed instructions to make some 'slime' for the kids from the Internet, having looked at what she was using, the chemical "causes skin burns and serious damage to eyes" nice.

[JonParticipant @jon]

Tried anything and everything what could get my mittens on, still got the Quink and fabric dyes no substitute for the real thing which went off 11 years ago sold by a place over Leicester.

Must have been lucky just drove up to a local chemical suppliers asked what needed then went back following week after they got to know me, no names and walked out with 25ltrs Sulphuric, 50ltrs distilled water, 10 ltrs hydrochloric acid £30.

Very true sulphuric at 17% will rot thin steels away within two weeks, don't ask had a leak from a 4ft tank but still got the little 12".

Back 15/16 yrs not much info available only three sources in the world and what was told was porkies or something blatant omitted.
Used to run anodising at 21% initially then dropped to 19% then 17% both at 13.6V. Even done hard anodising. Just a slight tingle retrieving parts that's dropped off at 21%, rinse off with water.
Sooner pay for it to be done since eventually found an anodisers that cares, can match up with existing even different aluminiums and finishes sent in. Usually send in two colours a month last 10yrs after 6 years diy then prior 6 yrs pro again. Only reason started diy anodising was of poor service, lost hand made one off parts, not ready when said would be, scrap parts quite often certainly the ones in Brum borderline scrapped three jobs £11k.

Just law to themselves anodisers, caused me serious grief over the years, excluding above when it don't come out right precision parts stripped once, twice, three times? who knows so when put threaded parts together nothing lines up. One job last year at a Brummy place 1mm pitch thread ended up 290 degrees further round than acceptable = scrap £400, nearly all like that from experience. If job done right first time with no or little cleaning anodising adds to any surface, more so hard anodise and forget the depth and surface build up off hand.

One of the pros use does stuff for a prestige major car producers, they do use titanium for jigging the parts usually spring clips of some sort o individual racks dunked in to the sulphuric black with use.

Never ever had any success using aluminium wire, fine at first then just lose electrical contact often within 3 mins. Used to use 6082 filed up tapers and wedge in a part or titanium wedge in to a hole.

[Howard LewisParticipant @howardlewis46836]

Anodising is an electrolytic process to produce an inert film of oxide, but if you just want to protect the Aluminium, concentrated Nitric acid will produce an oxide film. (It is very potent oxidising agent)

BUT, if the material is an alloy of Aluminium, the other elements may not be oxidised, and just dissolve.

Above all, IF you can get hold of conc Nitric, BE VERY CAREFUL, it is vicious stuff, and the fumes are bad for you.

Howard

[Chris DentonParticipant @chrisdenton53037]

Nitric acid is used to de-oxidise aluminium prior to anodising.

[mark smith 20Participant @marksmith20]

Nitric acid is used to remove the black muck after dipping in sodium hydroxide it is not de-oxidising

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Chris Denton on 16/06/2016 22:39:39:

Some of the more dangerous chemicals are now only allowed to be sold to limited companies. Even attempting to purchase them is an offence!

Well, here in France I can purchase strong acids and various solvents from any DIY shop and even many supermarkets. So I guess it's the British nanny state to blame. Better integration into Europe might be an advantage

Russell.

[KWILParticipant @kwil]

Russell

Just like the removal of cadmium?

[JasonBModerator @jasonb]

Neil, if you want some inspiration on anodising model engines have a look at this guys 1/3rd scale V10.

Details of his setup here and some photos of the engine to date part way down this page.

The thread is also a fine example of making blocks of metal look like castings and should answer the question as to why people want to do that.

J

PS it's all manual machining no CNC!

[Michael Cox 1Participant @michaelcox1]

Posted by Russell Eberhardt on 18/06/2016 11:25:36:

Posted by Chris Denton on 16/06/2016 22:39:39:

Some of the more dangerous chemicals are now only allowed to be sold to limited companies. Even attempting to purchase them is an offence!

Well, here in France I can purchase strong acids and various solvents from any DIY shop and even many supermarkets. So I guess it's the British nanny state to blame. Better integration into Europe might be an advantage

Russell.

Its much more likely that some safety zealot in Brussels will ban the sale of strong acids to private consumers throughout Europe.

Its already happened to cadmium, borax, creosote, to name a few and glyphosphate weedkiller is next on the list.

Mike

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