Anodising

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Anodising

This topic has 94 replies, 32 voices, and was last updated 23 December 2016 at 14:26 by KWIL.

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27 March 2010 at 23:22 #50213
Ramon Wilson
Participant
@ramonwilson3
Hi,

I am intending to try to anodise some of the parts for the ‘Racer’ engines currently being built.

I have two articles to turn to, one from the Stictly I/C magazine and one much older by Ian Bradley from ME plus there is some information on the MEN site.

I have no experience of this process other than having read about it so would welcome any thoughts or advice from anyone who has tackled this at home.

I can see that the need for thorough degreasing is paramount but the one thing I really would like to know is – are the parts are best anodised immediately after machining or can they be left until all parts are ready then the lot is done as a batch?

Many thanks – Ramon
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27 March 2010 at 23:22 #2265
Ramon Wilson
Participant
@ramonwilson3
28 March 2010 at 10:02 #50220
KWIL
Participant
@kwil
I have only home cleaned prior to anodising using a quick dip in caustic soda solution. Does not seem to matter when the cleaning is done, the anodising [commercial] seems to come out OK.

Just be aware that with hard anodise (black), material has to be pure aluminium, not alloy. Also different alloys colour to give different shades of the intended “colour”. Hard anodising “grows” the item, the dimensions do change, slightly.
28 March 2010 at 11:03 #50223
Frank Dolman
Participant
@frankdolman72357
     Caustic soda is nasty. Washing soda is much less so and for this reason

   to be preferred. Dissolve as much of the washing soda crystals as you can

   in warm water then add just a little extra water for luck. The resulting solution

   will etch the ali very effectively but more slowly than caustic. You can give it

   a bit of encouragement with an old toothbrush, to get into corners etc.,

   without endangering the flesh on your bones. This strong washing soda

   solution is not harmless but it is at least manageable. Caustic is nasty.

     As with caustic, rinse well under a running tap and then inspect. Dry with

   a hair drier and put in a polythene bag to keep grease off until needed.
28 March 2010 at 12:36 #50229
Ian S C
Participant
@iansc
To colour the metal when anodising Dylon fabric dies are idealfor colouring. Important, after the etching the aluminium MUST NOT be handled, surgical gloves may be OK, but wooden tongs are recomended. Can’t find all my info but Franks’ got it. Ian S C
28 March 2010 at 13:09 #50231
John Stevenson 1
Participant
@johnstevenson1
Just to correct some remarks by Kwil above.

Hard anodising is a different process to anodising, basically the same but the acid is kept at less than 5 degrees C for the whole of the process.

This means the acid has to run thru refrigeration pumps or heat exchangers making it not viable except for the most dedicated home shop.

Hard anodising is also clear in it base form but can be coloured just as well as normal anodising, a Taig bed is hard anodised but it’s alloy coloured. The colour won’t tell you what process has been used.

Also hard anodising will work with alloys and not just pure hence the Taig bed example.

John S.
28 March 2010 at 14:05 #50232
Ramon Wilson
Participant
@ramonwilson3
Hi,

Thank you all for the response so far.

I was assuming that KWIL’s mention of hard anodising was more to do with surface quality as opposed to basic colour but thanks for explaining it John. Thanks too for the safety tip Frank – I shall get some washing soda.

Basically I just want to anodise the cylinder fins, the prop driver and spinner. I was hoping to do these green though I have read that green is not always the easiest of colour to get to take. If I can avoid it I don’t particularly want to do red because that’s the original colour and I would like these to have a certain amount of ‘based on’ look about them rather than exact (but larger) copies.

I shall get all the parts made first and try to ensure that they all come from the same grade and certainly do some test pieces first.

Thanks again everyone – much appreciated – I will keep you posted on the results, good or not so!

Ramon
28 March 2010 at 15:32 #50233
Terryd
Participant
@terryd72465
Hi Ramon,

There are a couple of useful websites that I have found in the past that explain the anodising process for diy in some detail. you need to scroll down past the sales section of the first one and there is a lot of information below. The second is a true diy one. you may find them useful.

Terry

http://www.focuser.com/atm/anodize/anodize.html

http://astro.neutral.org/anodise2.shtml
28 March 2010 at 19:59 #50238
Alan Worland 1
Participant
@alanworland1
Interesting articles above, but I see that the process will alter dimensions to a small degree – not a problem in most places but worth noting for press fitted bearings perhaps?
29 March 2010 at 06:07 #50242
ZigFire
Participant
@zigfire
Hi

I do quite a bit of anodising at home mainly for astronomical eyepieces and telescope adaptors etc. It is a tricky process and results depend greatly on the grade of aluminium used.

The process is quite interesting in that it grows hollow tubes on the surface of the alloy. These tubes are basically the same chemical structure as sapphire, that is why anodised aluminium has such a hard surface. The tubes being hollow “suck in” the colour, once tubes are sealed by hot the colour is locked in.

Please note it doesn’t matter if you wait after any machining is done as basically aluminium oxidises immediatly in contact with air forming a layer of aluminium oxide that needs to be removed prior to anodising, as a matter of fact this layer is actually forming as you are machining. Also note items anodised generally have their sizes reduced slightly.

Here are a couple of good sites I used to get started.

http://www.warpig.com/paintball/technical/anodize.shtml

http://www.shadowguarddev.com/alex/anodizing/

http://www.bikepro.com/products/metals/alum.html

http://kraftkolour.com/index.php?categoryid=1

http://asuwlink.uwyo.edu/~metal/anodizing.html

Hope these help.

Cheers

Michael
29 March 2010 at 08:47 #50244
KWIL
Participant
@kwil
John, Thanks for the “corrections” I was merely repeating what I had been told by the Principal of my local anodising company, he is the specialist as far as I am concerned. Looked at the Taig site, yes their anodizing is “alloy coloured” not coloured alloy.

Dye coloured anodising needs to be set/sealed by using steam.

Do not agree Caustic Soda is “nasty”, nasty is something you cannot see like radiation.

Caustic soda, strong acids and indeed electricity could all be called nasty, but deal with them in the correct and safe manner, taking the proper precautions and they are safe to use. They are a good servant but a poor master.

You can of course buy caustic soda crystals/powder in a plastic tub from the local hardware shop so it is obviously not deemed nasty in today’s nanny society

Edited By KWIL on 29/03/2010 08:48:11
29 March 2010 at 10:09 #50247
jomac
Participant
@jomac
Ramon Hi .

Go to the modelenginenews site again. There is a couple of articles on anodising in there some where, aimed mainly at the IC engine builders.

I have not done any work on the Bol-aero 18, since my last posts, cause Iv’e been lopping/chopping down a few trees, I also have been making jigs for the sieg X2, so that I can hold accurately the bits that I machined, and then had to take them off the lathe and mill to do another job, Which was idiotic, cause now its hard to replace them in the exact position.

John Holloway.
29 March 2010 at 11:21 #50252
Ramon Wilson
Participant
@ramonwilson3
Hi all

I’d just like to say thank you again to all of you for responding so informatively.

Terry – the websites are very helpful particularly the first one. I have only just read your post Michael but will check your links out later.

Interesting to hear about ‘growth’ and/or slight reduction though this should not have any influence on the parts intended to be treated at this stage.

I recently bought some caustic soda crystals as you describe KWIL to use as an alkali should there be any spills using some another acid based product for cleaning the steel parts on the Nova engine. I don’t intend to carry this process out inside the workshop but outside on a warm day. I am very cautious of and shall be careful too in using the materials involved.

I was intending to purchase green writing ink for the dye as I have read somewhere that this was more successful for green than Dylon though I know that these (Dylon) dyes are used with good success rates on other colours.

Could someone tell me please — I have some neat sulphuric acid. What will the proportion to water be for this process using this – other than volume I currently have no method of measuring the strength.

John – I have found the articles on MEN but thanks for the thought. Hope you get back on the Boll Aero soon – your comments on jigs for the kind of situation you describe could be the making of a whole new thread?

I hope to machine the parts this week so shall be getting everything ready fairly soon.

Thanks again

Ramon
29 March 2010 at 11:36 #50253
Terryd
Participant
@terryd72465
Ramon,

The acid concentration should be 15 – 20% according to the experts. I believe that the industry standard for this type of anodising is closer to 15%.

That would be about 1 part acid to 4 or 5 parts water (I stand to be corrected!)

I’m sure that you already know that water should never be added to acid but it won’t hurt to repeat it here in case any newcomer is not sure. Always remember the 3As rule – Always Add Acid (slowly).

Let us know the results of your experiments and post some pictures if possible,

Best regards

Terry
29 March 2010 at 11:52 #50254
mgj
Participant
@mgj
Just to make a quick point about the caustic thing.

Gloves and eye protection and some care. On the other hand, it will munch you, and worse, it doesn’t hurt as it does so, so you don’t actually notice you are being eroded.

I have 2 rather large holes in my foot, acquired absolutely painlessly over about 2 hours to prove it . (CIP in the dairy industry where it is the standard detergent)

Personally I would use caustic, because it is so effective and I would use it hot at that – but I would be careful. (Its also a very good pickle for silver soldering flux)
29 March 2010 at 12:27 #50255
Circlip
Participant
@circlip
No one tried inkjet inks yet?? Should be able to mix a vast range of colours (colors).

Regards Ian.
29 March 2010 at 13:11 #50257
Frank Dolman
Participant
@frankdolman72357
     I worked for ten years in the lab as a wet-bench chemist. My advice to expert

   machinists is to avoid the use of caustic soda if you can. The same goes for

   strong acids.

     If you can’t avoid them, OK but watch out. As Mgj says, use protection and not

   just for the very vulnerable eyes and hands, but for all of you.
29 March 2010 at 13:43 #50258
Terryd
Participant
@terryd72465
I would wholeheartedly concur with Frank. Washing soda is perfectly good for home use. I even use it hot and concentrated to remove enamel paint from small metal items (mostly Meccano) instead of using caustic strippers. It is also used in the automotive trade to clean oil caked road dirt from components very effectively. It is slower than caustic soda but much safer and who’s in that much of a hurry in our hobby?

Circlip, regarding Inkjet inks, I’m not sure how stable these are, the colours in prints tend to fade quite quickly in sunlight, might this not be a problem. Worth a test though perhaps.

Regards

Terry
29 March 2010 at 13:59 #50259
Ramon Wilson
Participant
@ramonwilson3
Thanks Terry – I’ll begin with 15% by volume and see how the test pieces go. BTW do I have to use distilled water for this?

Your caution is duly noted Meyrick as well as Franks. Whatever I use I shall be very careful – other than pickling I have no experience in handling acids or caustic soda.

Your thoughts on Inkjet inks Ian is another possibilty but possibly rather expensive? Can this be bought in ‘bulk’ as opposed to cartridges?

I hadn’t given much thought to light fastness of colours – I believe ‘green’ is well known for poor qualities in this direction but would this happen to an anodised part over time?

Now, off to that lathe!

Regards – Ramon
29 March 2010 at 14:34 #50260
Terryd
Participant
@terryd72465
Hi Ramon,

I have used distilled water as a matter of course in my limited experiments with some success but haven’t tried normal tap water so I can’t really comment on it’s effectiveness or otherwise.

Just be careful with that caustic soda, it can do very nasty things to flesh. At least with acid you can feel it and respond accordingly, but not necessarily with Caustic soda. When my wife worked for an international chemical import / distribution company all the guys handling this material (and other – I will say nasty – substances) they wore rubber suits, gloves and full head protection. Obviously you wouldn’t go to those lengths at home with small quantities but it’s better to be aware of the dangers.

Regards

Terry
29 March 2010 at 15:56 #50261
mgj
Participant
@mgj
And even washing soda (hot or cold) defats the skin so again, gloves as a minimum, and I would use eye glasses as well.

A lot depends on the proximity of fresh water – however, a .5% solution of hot caustic will be very effective without being deadly. (Yes – that is 1/2%) You don’t need full IPE for that, and that is plenty strong enough, and it gives you plenty of time to get to fresh water before personal erosion sets in.

Yes, start getting into the 35% caustic liquor and sure you want the full monty so don’t mix too strong. its not necessary.

As well to be aware of the dangers without going OTT. (Paint stripper is a lot worse than what is being suggested, and you can buy that over the counter. )

With apologies – back to the anodising process.
29 March 2010 at 16:02 #50262
Terryd
Participant
@terryd72465
Of course mgj, I should also have pointed out that when using washing soda basic protection is needed. Thanks for rectifying my omission.

Best regards

Terry
30 March 2010 at 08:29 #50274
Allen Paddock
Participant
@allenpaddock42703
All this talk on anodising reminds me when i worked at at factory called SONA or NC Josephs at Stratford on Avon before it closed down,(( They made tea pots coffee percolators saucepans sugar bowls etc etc all anodising )) I was a maintenance fitter there, The anodising vats were about 40 feet long filed with very hot acid and every Friday we had to drain out the acid put wooden props in the center of the vats on to hold up the agitating mechanism and clean off old lubrication and reapply with new oil ,,It was a really hot smelly job working over the acid tanks as there was always about a foot of acid still in the bottom i hated doing that job. NO safety equipment..Ah memories !!!
30 March 2010 at 08:53 #50276
mgj
Participant
@mgj
Have I been a bit dim – not knowing a great deal about anodising, or how they degrease ali comercially.?

Be warned, both caustic and soda pit ali very aggressively.

Soda I know from cleaning flesh off bones boiling up in an ali saucepan, which started to disappear slowly.

Caustic from work where we use a .5-1% solution for cleaning pipes. A welder made a stand with ali treads, and the once daily overflow from one wash disappeared a complete 1/4″ ali tread plate in less than a week.

So you might just get your etch and degrease all in one!!

Might be wise not to dawdle while degreasing!
30 March 2010 at 09:47 #50280
Les Jones 1
Participant
@lesjones1
In the process of aluminium dissolving caustic soda (Sodium hydroxide) hydrogen is given off which would be a fire / explosion risk. I would think a brief dip in the caustic soda would be OK.

Les.
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