DIY Al anodizing - cause of this trouble

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
My finish is different to the original anodized finish, that I had to sand off (to remove the nicks and scratches).

The freshly sanded surface (done wet with emery paper) looks PERFECT. I was hoping it wouldn't change when anodized.

Maybe I should just reduce the time, and hence the oxide thickness, although the original oxide was thick - it took a lot of effort to remove with emery paper.
 
I suggest 15-20% H2SO4, a current of about 1A/1dm2, or something more, and a voltage of about 15V.
And your parts is probably silver painted after anodization.

There is also another type of anodization (hard anodization) with the acid solution at about 7%, kept at very low temperature, and a lot higher current and voltage. In this case, surface is as hard as stainless steel, and oxidation is a lot thickier (1/10 mm or more). Hard anodization is very difficult to do at home.
 
DIY AL Anodising

I had lots of similar troubles using various brands of automotive water papers like Norton or other generic, origin unknown brands.

My troubles ended when I changed the abrasives to 3M. Expensive but worth it. After sanding, you need to degrease it. I use proprietary stuff from Metalquip but I think Handy Andy (the real genuine type), will do the job.

After that, you can 'chemically polish' with phosphoric acid at 100degrees C for no longer than say, two immersions of 20secs and the final preparation with 5mins in a nitric acid bath to de-smut. Wear rubber gloves if you can and only aluminium or titanium should be used to attach the job in the bath.

I of course do not accept any responsibility or claims of whatever kind for the consequences of the information supplied in this post.

Apologies for the rider:D

bulgin
 
DIY anodized Aluminium will always be 'matt' as that is how aluminium oxide builds up (porous crystalls). The best you can do is after closing the pores (boiling), polish the surface using normal car polishing techniques (e.g. cutting and buffing wax). The slight discoloration can't really be avoided, as oxide has yellowish-gray tinge (that will depend a lot in the alloy used). Make sure you build up a decent layer of oxide, it is possible to cut through it with some more aggressive waxes. Go easy and slow!
 
Given all that bother, I'd just give the piece (with a few others, to make it worthwhile) to a professional anodizer and let him do his thing. I wouldn't rest too easy with all that methy-ethyl badstuff lurking around the house. I'ts expensive and nasty and attracts attention from the wrong sorts of people (the cops may get the notion that you're doing something you're not)... One thing to note is that the final finish in anodizing (unless its clear anodize) involves dying the aluminum oxide layer - that's how you get black, blue, gold, red, army green anodize. Another attractive finish is iridite/chromate, but it's expensive and hard to find, as hexavalent chromium is very bad juju these days.
 
- I checked my emery paper - it IS 3M
- The anodized surface I'm trying to copy is clear - no dye involved.
- There's no way any company is going to match my 2cmx10cm strip of aluminium to an exact finish for any reasonable amount of money
- I have plenty of chemicals in my storeroom, many of which are probably prohibited/banned substances in the US/EU. Luckily, here no-one cares.

I think polishing AFTER anodizing might be a good way to go! I was concerned that it might remove too much of the oxide though.
 
DIY AL Anodising

Hi Steerpike

I found anodising to be one of the most frustrating things to do, and this after building my own micro setup with current regulation, temperature control with lcd target readout, agitation of the electrolyte by air pump and even rotation of the item by motor-driven cable - a sight to behold and I may post a pic of what I made all these years ago. This equipment was for electroplating gold and nickel and I may just be ahead with poisonous stuff - anyone for cyanide?

Anyway, to polishing anodised aluminium. I guess you may want to 'even out' the anodised appearance? I have tried many abrasive compounds. The best I found was a little 'cake' of metal polish I got with a Proxxon motor for my workbench, which they also sell loose. Another polish which may deliver the goods is "Edel-Chromglanz" made by Autosol, available from auto accessory stores.

I found however that these polishes improve the job, it is still best to get all anodising parameters 'just right'. My own self-imposed apprenticeship lasted almost 2 years...

Most of the fiascos were because of insufficient, unstable current and ignorance of temperature increases and how this affect the result. On hot days, I always pre-chill the electrolyte, again depending on the size of the item being anodised and the current needed. If the temperature goes much over 25degrees C, you can expect problems with uneveness or discolouration. You should also try to find literature to read up on the various types of aluminium which can be anodised - not all works well.

bulgin
 
There is at least one excellent DIY site for anodizing on the web, I don't have it linked on this machine. The fellow does small parts but has a very good rundown on how to set it up and do it yourself. Probably not too hard to find it. He gets very shiny results, fwiw. USA site, fwiw.

Emery paper seems wrong for aluminum finishing.

Blems in the surface tend to come out when anodizing, beware!

Find "auplater" somewhere here and drag him into this conversation, he is a top pro in the field. He will have all the answers. :D

_-_-bear
 
DIY AL Anodising

Hi

How else would you get this finish without emery paper? Aluminium parts come off a manual mill or lathe, then worked on abrasive papers from 600 to 2000grit, prepped for anodising of which the second last process is chemical polishing, then de-smutted and anodised. The last processes are colouring if required and then sealed by boiling.

Chemical polish in boiling phosphoric acid will chew threads and change dimensions if not used sparingly for only seconds. I refer here to the mounting plate only, but the rest of it was also finished on abrasive papers of the brand stated earlier.

bulgin
 

Attachments

  • img_0005.jpg
    img_0005.jpg
    22 KB · Views: 119
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.