I found this site while researching anodising specs: CLICK

Looks great, now i need several more old baths by the look of it. unlike the dealing with rust this job looks like it needs more than one container.

I removed the anodizing part from the address. the site doesn't look like the place I would to find DIY anodizing.

I mean telescopes, not exactly locost material is it.

[Edited on 20/2/05 by clbarclay]

It's quite a hazardous process and not to be undertaken lightly.

Strong Acid is involved and all precautions must be taken.

I'm not a namby pamby H&S type but this is dodgy for the uninitiated.

I've done some anodising, please remember that if you have machined fit parts, then the process causes shrinkage, despite the reading to the contrary.

quote:

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Originally posted by Rob Lane
...if you have machined fit parts, then the process causes shrinkage, despite the reading to the contrary.

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How do manufactures get the right size then? in particular parts like anodized bolts.
Do they make parts over sized or do they have some way of limiting the shrinkage.

I'm surprised that the dimesions of the base material change - not doubting you Rob - honest! Just surprised.

I could imagine that holes would get smaller though, due to the layer of oxide formed inside them.

David

Just experience Rorty.

We did some anodising on various parts with mixed results.

Plates shrunk, holes widened.

Two plates 400x300 drilled all around for mounting. Overall size decreased by 1mm and the holes were slightly increased from good fit to sloppy. This was worst case.

One very solid lump about 100mm overall machined all over with a second part to fit in a smaller thickness area. Both parts were anodised and when done they were no longer interference fit to each other but just fit.

All parts we did were finished off with a coat of Lanolin to seal the oxide.

All the above were done under guidance from one of my suppliers who does very large parts and tube lengths up to 9m.

It would seem that the first part of the process etches and converts the surface of the ali and then 'grows' the oxide. I believe it was the first etching part that removed a larger amount of material than oxide put back.

My suppliers gave me the relevant chemicals and lanolin. They usually do items at quick time for commercial reasons. They told me to watch out for plates in particular but shrinkage occurs at other times, suppose it depends on oxide coating.

Just did a quick search on Google and most sites did not mention shrinkage but in fact growth.

One or two though mentioned in passing that the article was etched down in size first then the resultant oxide growth was half the etched thickness unless allowed to grow longer.

One other mentioned grade of aluminium. When soft ali was concerned care had to be taken, maybe that was my problem!!

I was unable to find my original site that described model car part anodising and was a good site.

[Edited on 21/2/05 by Rob Lane]

Was thinking about this afterwards - there has to be a certain amount of material converted into oxide, so a change in dimensions is inevitable. I haven't a clue whether the increase in oxide compensates for the loss of base material!

David

Here's a couple of links

http://w3.uwyo.edu/~metal/anodizing.html

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


With Hard-anodising, Ice-Cold acid temps are needed. This puts it out of reach of the average home-anodiser.

Standard anodising can creat a 20 micron thickness of oxide, half of which etches into the original workpiece and half of which adds to the surface. So... you shouldn't have to encounter anything greater than a 0.01mm gain in dimmensions. (or tighteing of bores)

IF you loose material, your acid is far too strong.

http://www.locostbuilders.co.uk/upload/Img_3204b.jpg

Above is the kind of thing I design .. if there's aluminium on it, It's anodised. I spec both hard and standard anodising, and never have I heard of material being lost... then again, we pay through the A*se for it... So I expect it to be a good job!!!

I am going to give it a try at home when I have time... seems perfectly well within reach!!

quote:

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Originally posted by nick baker

http://www.locostbuilders.co.uk/upload/Img_3204b.jpg

Above is the kind of thing I design .. if there's aluminium on it, It's anodised. I spec both hard and standard anodising, and never have I heard of material being lost... then again, we pay through the A*se for it... So I expect it to be a good job!!!

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It's this... but a few thousand Euros later..

http://www.locostbuilders.co.uk/upload/tophandling_NJB.jpg

spose I Could tell you.. but then I'd have to launch it at you

Seems like every site suggests material gain but a couple mention shrinkage in passing.

I only posted what I knew to be true in my case. Remember I was an amateur when trying this, maybe I did it wrong!

check the concentaration of your Acid Rob... That's the only thing that I can imagine would cause the problem.

And remeber... add acid to water... not water to acid..

Did you try colouring it? and if so, what dye did you use and how did it go??

cheers,

N

Nick,

It's some time ago now that I did the anodising. Although I'm reconsidering doing my new inlet manifold.

I used 'Dylon' fabric dye, worked a treat.

It may be that I used too strong an acid, I was given it in bottled form at 25%.

I did ruin one piece when I was called away to phone and left it in pre-etch caustic soda bath! Came back to find the original small 8mm lugs on part had completely dissolved.

quote:

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Originally posted by nick baker

Standard anodising can creat a 20 micron thickness of oxide, half of which etches into the original workpiece and half of which adds to the surface......

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