Chemistry question regarding anodising Aluminium

[justvisiting]

Madmat, I agree about carryover for most parts. In our situation, aluminum built up in the bath rapidly, and caused dull patches due to the precipitation of aluminum phosphate on the parts. Our plant was run by the seat of the pants and wishful thinking methods, and it was my job to make these methods work. Our aluminum built up due to infrequent cleaning of the tank, poor racking, rushing parts through, etc... My best efforts to improve those things failed. Dragout was the best way to keep the aluminum content of the bath down. We were running heavy extrusions, and the heat would bake the bright dip on if the Aluminum content was too high. I had to decant a quarter of the bath sometimes. We used a proprietary phosphoric acid blend from Albright and Wilson, the phosphorus and chlorate people The copper was already in it. Our S.G was 1.720-1.730, temp was 205-215F, nitric was 4%. Whenever a load was pulled from the bright dip, a HUGE cloud of nitrogen dioxide was released, which was 'dealt with' by our scrubber system. More than a few cars in the parking lot got damaged over the years. I can't believe the insults to the environment that we got away with.

 

An interesting story: We probably lost over a million dollars due to hazy parts, which I consulted the best experts in North America about. We tried everything, and did outside comprehensive testing of our dip. Everything checked out OK. I had a PHOTOCOPY of an anodizing manual in the 'lab' as a resource. That's what led me to think about the aluminum content, which was always within range. But the range didn't change when we went from thin automotive trim to heavy appliance trim. A poor, grainy photo was my clue. The only solution was to decant the bath, which was a sin. Besides, we were sitting on thousands of gallons of spent acid because it was contaminated with chromium, and A and W wouldn't buy it back. The contamination resulted from frick and frack in the maintenance department using cheap stainless steel fittings for the agitation line, which kept dissolving in the hot acid. I had to jump through flaming hoops just to keep the line running. I needed to prove my theory, and North America's experts didn't buy into it. I contacted the publisher of my photocopied manual, and it was out of print. They gave me the printer's number, and they said a newer edition was coming out soon. It was a rare book. The printer said the author lived just down the road, and gave me his number. Well damn, he was home! He listened to my tale of woe, and totally agreed with my theory. We decanted the tank, topped it up with fresh, and fixed the problem. A couple of weeks later, I was called into the office to answer for my very expensive phone call to England during prime time. Trial by fire it was, working there!

[Arthur]

I used to have a manual from Canning Ltd (a plating and metal finishing company) it had descriptions if almost every wet process used for metals. Maybe it can be found on Abe books or scanned into Google.

[MadMat]

Justvisiting, yeah, I remember hearing the name Albright and Wilson. The big plating specialty companies we dealt with the most was Enthone and M&T Chemicals. The Reps from Enthone were great. Every time they paid us a visit, it meant us lab guys were going out to lunch on the Reps expense account and lunch with those guys was always a "three martini" lunch. Yeah, I couldn't believe the environmental crap we got away with either. I won't go into any details... you have probably seen it all yourself, but it was pretty bad.

Edited July 1, 2021 by MadMat

[stix]

Thanks all for the good info everyone. Interesting that some of you have done this professionally. It sounds like a real nightmare though .

 

This is the Red (Caswell Deep Red L) that I anodized the other night:

It think it has worked out just great!! .

 

One other thing that I didn't mention was that I'm using Aluminium (instead of Lead) for the Cathodes. This may be an issue over a longer period of time, but it doesn't seem to have affected anodizing the Red piece - which I'll be stripping back, and trying black again. I'm also using Aluminium for the Anode and connections - a square block onto a round hole.

 

The reason I decided to go with the RIT clothing dye for the black (actually called Graphite) was because Caswell only sell black in larger qty at more than double the price of most colours. Also, I only wanted to do a few small pieces.

 

This whole experiment started as a "proof of concept" but has gotten way out of control . At this stage, I'm going to blame the RIT dye degrading over time for the poor colour takeup. Anyway, I've got some more black RIT dye and will try it again shortly. If the colour turns out as good as it was 5 weeks ago, then I guess that will prove that the dye went bad.

 

As far as my process goes, this is pretty much the same as I do. From another Aussie:

https://youtu.be/Z1zT8p7d9Z0

 

Cheers.

 

[Additional Question]:

At the moment I'm adodizing at 0.5 amps for 2hrs. Would there be an issue if I anodized at 1 amp for 1hr - or is it best to do it slowly?

Edited July 2, 2021 by stix

[Arthur]

Canning Handbook On Electroplating

https://icare.eng.chula.ac.th › RAP3EKU_canning...

PDF

Plating and Metal Finishing Books. Can you change the colour of anodized aluminium in. the canning handbook Download eBook pdf epub tuebl mobi.

from google search. It may be history but so is chemistry.

[MadMat]

You can anodize at as high a 1 amp/ square inch of part surface area without any problems, as long as your anodizing bath doesn't heat up. If you find a way to cool your bath down, give it hell! You will know if you go too high on the current though as the corners and edges of your parts will get rough. Way too high and the edges will get black and crispy looking . Sorry for the American measurements I know you're probably more comfortable with metric units. Current density is a very important measurement in electroplating of any type. In fact, you can determine how thick your coating will be in a given time period by current density. Try googling anodizing, the 720 rule (or something like that) and you will be able to calculate the coating thickness. I don't remember the specifics for anodizing, I do, however, remember for hard chrome plating @2.4amps/square inch you will get chrome deposits of .001" per hour. Well for a typical bath

[MadMat]

BTW, why would you want to strip that red part? I think it looks great!

[stix]

BTW, why would you want to strip that red part? I think it looks great!

.

Thanks Mat. Yeah the red does look rather pretty but it's purely an aesthetic choice.

The attached image below shows the piece (now black/graphite) in the middle of the image attached to a load cell.

Black matches the rest of the design, whereas red just looked too weird.

 

.

That piece is no longer required in version 2 of my test stand design. So the only pieces needing to be black are 2 x "spacers" which is the piece shown to the left of the red version above. (post #29).

 

In conclusion:

The proper Caswell dyes work exactly as they should. The RIT dye seems a bit finicky. To get the black colour I wanted, I had to leave it in the dye bath overnight (8hrs or so). It's also likely that I should have anodized the piece for longer. I say this because the original "spacer" pieces that I was tying to match were done 2 at a time, and the total surface area was around 1/4 less than the load cell attachment piece. I should have taken more notice using the 720 rule calculator.

 

Therefore it's possible, even probable, that the original black dye that I discarded was fine.

 

In any case, it seems that RIT dyes require longer anodizing than the Caswell dyes.

 

Cheers.

 

[Additional Info:]

 

The purpose of doing the Caswell Red was to prove that the electrolyte solution was not at fault. Which it seems it's not. I also did the Caswell Blue (as shown above) using the same electrolyte mix. So in the end, it's only been the RIT dye that has been problematic.

 

So at the moment, just for the hell of it, I'm doing another test piece using the RIT dye. However, this time I've woofed up the amps to 1 and will also add 50% to the anodizing time. I'm hoping that this will help the take-up of the RIT dye. If not, whatever . . . . I don't care too much because those pieces are few, and not that important.

 

I should know the result in the next hour or so.

Edited July 4, 2021 by stix

[justvisiting]

Wow, that's quite a project you made of it! What will stabilize the motor during testing?

[stix]

Wow, that's quite a project you made of it! What will stabilize the motor during testing?

.

A few winds of cloth or glass tape does the trick:

 

 

------

 

Btw. I screwed up on my last black anodizing test and "over-cooked" it - lots of tiny pits everywhere .

My fault. There is an old adage: measure twice, cut once. In my case it's measure twice, anodize once!.

I blame "inches". When working out square inches, I entered the thickness of the part as 0.8 of an inch, but it should have been 0.08".

Made a big difference to the anodizing time calculation. Whoops!!

 

Anyway, back to the drawing board.

 

Cheers.

[stix]

[justvisiting]

Very informative, thanks! The anodizing on the blue parts even sounds good When I was a kid, I loved making nitrogen tri-iodide, but I had to make the iodine first. The book said I needed sulfuric acid, manganese dioxide, and sodium iodide. The iodide was easy enough to get at the hobby store. The manganese dioxide was isolated from dry cell batteries. I read that sodium bisulfate solution could act as sulfuric acid does, but where to get it? As I sat on the john one day, I read the label of Vanish toilet bowl cleaner- sodium bisulfate, 75%. I reacted it with hot water until all the fizzing stopped, and evaporated the solution most of the way. Sodium bisulfate crystals! I rinsed the crystals briefly to wash away the other crud, and got a product pure enough to use. What snappy fun we had, until my mom 'found' a coffee filter covered with dried out triodide that we had forgotten about. She called me down to the basement to admonish me for taking the coffee filters (again). When she pointed to the filter, she accidentally touched it. That action precipitated a very disagreeable chain of events that involved a trip to the dump with all my chemicals.

[stix]

Hey Justy. Take some time to make paragraphs. Damm hard to read.

[stix]

Very informative, thanks! The anodizing on the blue parts even sounds good When I was a kid, I loved making nitrogen tri-iodide, but I had to make the iodine first. The book said I needed sulfuric acid, manganese dioxide, and sodium iodide. The iodide was easy enough to get at the hobby store. The manganese dioxide was isolated from dry cell batteries. I read that sodium bisulfate solution could act as sulfuric acid does, but where to get it? As I sat on the john one day, I read the label of Vanish toilet bowl cleaner- sodium bisulfate, 75%. I reacted it with hot water until all the fizzing stopped, and evaporated the solution most of the way. Sodium bisulfate crystals! I rinsed the crystals briefly to wash away the other crud, and got a product pure enough to use. What snappy fun we had, until my mom 'found' a coffee filter covered with dried out triodide that we had forgotten about. She called me down to the basement to admonish me for taking the coffee filters (again). When she pointed to the filter, she accidentally touched it. That action precipitated a very disagreeable chain of events that involved a trip to the dump with all my chemicals.

Arrrggghhhhhh....

[stix]

Very informative, thanks! The anodizing on the blue parts even sounds good .

 

When I was a kid, I loved making nitrogen tri-iodide, but I had to make the iodine first. The book said I needed sulfuric acid, manganese dioxide, and sodium iodide. The iodide was easy enough to get at the hobby store. The manganese dioxide was isolated from dry cell batteries. I read that sodium bisulfate solution could act as sulfuric acid does, but where to get it?

 

As I sat on the john one day, I read the label of Vanish toilet bowl cleaner- sodium bisulfate, 75%. I reacted it with hot water until all the fizzing stopped, and evaporated the solution most of the way. Sodium bisulfate crystals.

 

I rinsed the crystals briefly to wash away the other crud, and got a product pure enough to use. What snappy fun we had!!.

 

Until my mom 'found' a coffee filter covered with dried out triodide that we had forgotten about.!! She called me down to the basement to admonish me for taking the coffee filters (again). When she pointed to the filter, she accidentally touched it.

 

That action.... precipitated a very disagreeable chain of events that involved a trip to the dump with all my chemicals....

 

Edited July 6, 2021 by stix

[stix]

Thanks for saying so.

[stix]

ooop.

[stix]

The aluminum colour did not work out quite right.

https://soundcloud.com/user-566434468/chicky-pie-vst-mix

[stix]

You ARE a Spleener.

https://soundcloud.com/user-566434468/i-am-a-spleena-final

[stix]

https://soundcloud.com/user-566434468/pulp-mixdown-may2019

[Mumbles]

For what it's worth, sodium bisulfate is also often sold as solid pH decreaser for pools and hot tubs. No boiling of toilet cleaner required.

[stix]

For what it's worth, sodium bisulfate is also often sold as solid pH decreaser for pools and hot tubs. No boiling of toilet cleaner required.

.

Yes, thanks Mumbles. This is what I have been using from my local hardware store:

 

It seems like it's a very reasonable alternative to using Sulphuric Acid.

 

------

 

After further testing, this is the result:

 

 

The blue block in the middle is the same piece using (Caswell) dye from about 6 weeks ago (post #1). On the right, is the same Caswell dye, and the same 6 week old chemicals which I used about 2 days ago. The reason the blue is darker was because I left the pieces in the dye for longer on purpose - to check, as a test.

The grey (2nd from the left) is lighter than the original almost black (shown left most). This is the RIT dye.

 

I wish I could explain why the difference in colour. The only conclusion that makes sense is that the RIT dye is very particular to the chemistry, whereas the Caswell dye, the "proper" Aluminium dye has more leeway when used with Sodium Bisulphate.???

 

---

 

I'm sure that there are some forum members that would ask "why bother posting your anodizing issues on APC?".... "Why not ask these questions on the "Caswell Anodizing Forum?" (which there actually is). Well, for one, I think people on this forum are pretty smart and would have no "vested interest", whereas on the Caswell Forum, I likely would have been slammed down straight away for not using the correct dyes.

 

In the end, those people are probably correct. Why bother with "pretend" dyes when you can use the real thing? I suppose I'm a bit of a tight-arse. There are lots of aspects, various ways, that you can make things yourself. In the pyrotechnic world you have to be more careful, but with anodizing aluminium, the ramifications of a mistake are small in comparison.

 

I can't remember who mentioned this (paraphrased):

 

The 1st difficulty when anodizing aluminium, is getting the piece absolutey squeeky clean, then the harder part is how to attach the piece, for a good connection to the buss bar.

 

It is not easy.

 

I love blue in pyrotechnics, but I can't get a nice blue with the pyrotechnic chemicals I have access to. But I sure can get a nice blue with anodizing aluminium... Oooohhh... Shiny!!

 

---

 

After testing for the last 10 days or so, my final conclusion (ver 2.0) is that using Sodium Bisulphate for anodizing aluminium works just fine when using the correct dyes.

[stix]

BLACK IS BACK.!!!

 

I got the black back. The piece of aluminium is nicely dyed black.

 

The RIT dye works better when the Sodium Bisulphate solution is slightly heated. What do you call it, supersaturation?

[stix]

Ooop. I almost shat myself because it's pissing down with rain here, and I thought the noise was coming from... my stove.

[stix]

I'll post the image if anyone has an interest.