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Another Anodising query - sorry

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torxx

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Hi All,
Bit long winded so kindly bear with me.

Bought anodising kit from reputable company and set-up to the letter. Only difference I made was I bought a proper power supply from Amazon.
Ok, piece part area calculated as 0.084 sq ft / 12.09 sq inchs and using 720 calculator I determined 0.5 amps/15v for 120minutes.
Part thoroughly de-greased and etched for 30 secs in Sodium Hydroxide solution, then rinsed in de-ionised water. Part suspended with 3mm aluminium wire and cooked as described, then again rinsed in de-io.

Black dye heated to 40°C and part immersed for 20mins but straight away I can tell the dye is not taking as I'd like. Here my friends lies the problem I just can't get the part as black as night. What am I doing wrong? This is the 5th attempt and I just can't get the parts any darker than a light grey? I also notice there are some lighter patches which I cant explain as I didnt handle this at all between procedures?
2019-07-27 12.34.35.jpg

2019-07-27 12.34.50.jpg

Can somebody please advise your help would be invaluable and greatly appreciated. Many thanks in advance
 

RJSakowski

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I'm not an expert on dyed anodizing as my attempt ended up much like yours. I believe where I went wrong was heating the dye solution. The heat closes the pores in the anodize before the dye has a chance to penetrate thoroughly. After my failed attempt, I didn't pursue it any further.

As to the splotches, aluminum can be very tricky that way. I found that mechanical scrubbing in the prewash and desmutting steps was effective. In my case, I had a matte finish so I used a fine bristled stainless steel brush. I did quite a bit of clear anodizing as a protective coating with success.

FWIW, we had sent parts out to an anodizing shop for a deep black anodize. Thge coating was photosensitive and where exposed to sunlight, the coating faded to a rose color so even the professionals get it wrong sometimes. Their explanation was a bad dye batch.

Another thing that we discovered was in our laboratory environment, the chemicals used would eat the coating. We sprayed with a urethane clear coat. I got several of these scrapped plates which I use for stock. Before cutting or machining, I like the strip the anodize coating and I have found no chemicals to date that will remove the urethane. I have the scrape it off with a razor blade so I can dissolve the anodizing beneath it.

I will be interested in the results of your efforts. Please keep us posted.
 

torxx

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Hi RJ,

Very interesting thank you. I have another part anodising as we speak, this time I will indeed try without heating the dye.

Results to follow.......
 

rgray

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Your aluminum wire it is suspended from may be taking the anodizing and once it does the electrical connection is lost or reduced. At that point it doesn't matter much how long you leave it in there nothing is happening.
Also I started wrapping the suspension wire around the aluminum rod I was suspending from and also adding an alligator clip to help it make connection there.

You should be able to see the bubbling action of the anodizing happening, if not it's not working.
You can always increase the voltage if it appears the connection is failing and the process is stopping.

Definitely heat the dye, and watch the anodizing acid temp it should be cool.
 

torxx

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Hi rgray,

I'm convinced it's the connection thats the problem here tbh. I noticed at first the bubbles are clearly visible but as time goes by they get less and less.
Any good tips on attaching the part would be greatly appreciated.
 

rgray

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Some of the parts I do have a threaded hole. I build threaded aluminum rods to tighten into them. Then I stainless lockwire that rod to the overhead aluminum rod and then add the alligator clip.

Aluminum wire sucks, but is necessary if it's going in the acid.

Often times there are areas you don't want or need colored. Like your bushing if the inside was not colored would it matter? If not shove it on an aluminum rod that is long enough to wire and clip to your overhead rod.

Size of the center hole will change slightly smaller with anodizing. Also anodized aluminum is aluminum oxide (think grinding wheel) so you may not want the inside of a spacer/bushing that aggressive.
 

Flyinfool

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It could be a number of things.
What alloy of aluminum are you using, there are some that do not take anodizing well.

Are you doing a desmuting step?

where your suspension wire is making contact with the part you have to have a very good contact, Anodize is an electrical insulator. As the part starts to anodize it will insulate its self from the wire. If the part has a through hole put some S bends in the wire so that it is making contact in as many places as possible. it also helps if the part can not move on the wire. If the part is moving on the wire then it is easier for the anodize to get between the wire and the part to break the connection.

Heat is used to seal the pores of the anodize after they are filled with dye, You want the dye warm but not hot, you have to keep the pores open to allow the dye to fill them before you do the sealing step.

There are many dyes that will fade in direct sunlight, it is not an issue with your process, it is just an issue with the dye itself.

Remember that anodize will make your part bigger. Anodize converts some of the aluminum to the coating. If you anodize to .002 thick the part will measure .001 bigger as the process will have converted .001 of aluminum into anodize. This is all per surface. If you later strip the anodize to try again the part will be .001 smaller that where it started from. Something to keep in mind if the part has precision fits.
 

rgray

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I noticed at first the bubbles are clearly visible but as time goes by they get less and less.
This is normal as anodized aluminum is non-conductive.
Problem is if it loses connection early then anodizing stops.
 

torxx

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Thanks guys all good points and I've learned a lot from this first post as I'd hoped.

Great to reach out to people with experience and hopefully answers to my problems. Very frustrating as I'm so close I can taste it and as I said my first piece came out amazing! I will persevere and I will succeed and I will keep you up to date on my progress.

RJSakowski - I tried dyeing at room temp and it made no difference so we move on to next trial lol

Regards,

Torxx
 

mattthemuppet2

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titanium wire is better to hang the parts with - you can reuse it over and over with no need to strip it in sodium hydroxide before use.

did you base your SA value on the ID as well as OD? The speed/ current density with which you annodise a part affects the pore size - I think it's higher current = larger pores and vice versa. May be worth double checking your sums and playing around with the values.

I don't bother with a sodium hydroxide dip generally, unless I want a matt finish or the piece already had an oxide layer.

did your part pass the water break test?

did it turn slightly golden/ yellow coloured in the annodising bath? That's a good visual sign that the annodising went properly.

did you use distilled water for all steps and dilutions? Did you rinse the part off with distilled water between the ano bath and the dye bath?

dye should be heated to 160F

what type of aluminium is it? 6061 I'm guessing, but if it's one of the more copper rich alloys (2000 series?) you'll have problems with smut.
 

torxx

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Hi Matt,

Yes the SA was based solely on the OD only so you have a good point there for sure.

The part didn't turn gold/yellow but it did have some kind of residue that I noticed washed off in the de-io rinse before dyeing.

Someone else advised that if you heat the dye to anything above 50°C it would in fact start the sealing process?

Lastly I'm think the aluminium is 6000 series but not 100%. Could the residue actually be smut? If so is there a way to overcome this?
Thanks again
 

mattthemuppet2

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Sounds like it didn't get a complete oxide layer or that the pores were too small for the dye to take. Here's what I'd try for troubleshooting:

1. redo the SA calcs and run it again. If it's not gold/ yellow tinged (not so much a colour but a tint - doesn't look plain silver anymore), then
2. get some Ti wire and use that to hang the part

alongside both, do the waterbreak test (there's a video on Caswell Plating website about it) to make sure the surface is COMPLETELY clean. Can't be too thorough about that. Dawn dish soap, scrub, rinse with distilled water, rub down with acetone, rinse with distilled water at a minimum. On the last rinse, the water has to form an even film with no breaks or beading. If it beads/ breaks, clean it again. Wear nitrile gloves while you're doing this.

Are you cooling and agitating your anodising tank? Both are really important to get a good oxide layer.

To seal the part I hold it in the steam above a boiling pan of water for 10min then hold it in the boiling water for another 10min. I heat my dye to 140F (sorry about the 160F earlier, that's for the NaOH) and it's fine.

Smut is dark blemishes - I don't think that's your problem. I think it simply didn't anodise properly.
 

torxx

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Great thx Matt, I have in fact got some Ti wire that came in the kit I bought. I'll also have to get one of those fish tank aerators and try it all again.
 

mattthemuppet2

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no problem! Send me a PM with your email addy and I'll send you pdf of the guide I use.

I used a fish tank aerator hooked up to a loop of tubing that has a few small holes drilled in it, weighted down with a piece of alu plate, plus some old ice packs that I keep in a bag labelled "garage use only" in the freezer. Stick the ice packs in some time before you start, then some fresh ones when you start the run. That'll keep the solution down to a reasonable temp even when anodising somewhat large parts.
 

Karl_T

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many good points above. Titanium wire, looks to be one big one. Try Ti rod threaded into the part. I have a build thread over on weapons guild you might read if you are a member there. http://www.weaponsguild.com/forum/index.php?topic=64679.msg866354#msg866354

I did find big differences with back dye source. tried three with the Caswill dye giving the blackest part.

Also found cold bath (mid 60s F) and lower amps for longer time gave a deeper black color.
 

torxx

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Thanks Carl I'll be sure to check out that forum. Think perhaps Ti rod might be little out of my league for hobby purposes but I'll look into it anyways. As expressed definitely think contact is my biggest worry along with few other minor niggles pointed out by your good selves here on forum. Thank you
 

Karl_T

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eBay was my friend for the Ti rod. It worked EXTREMELY well, much better than Ti wire.

here's one offer for $15

another larger rod for $7
 

mattthemuppet2

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you can also get Ti screws in different sizes/ pitches from McMaster. I've used those occasionally when a threaded hole was in the right place. Definitely with Karl about the temperature though. Can't remember the precise details but heat is not your friend with the anodising step and you're dumping a fair amount of heat in there with the anodising current. From what I can gather, lower voltage (ie. longer anodising times) = smaller pores but more of them. So you don't want to go too low or the pore diameter will be too small for the dye to enter, plus different dyes have different sizes.

I just stick to the 720 guide on Caswell's site, though sometimes I go for 90min anodising time just because I'm impatient :)
 

torxx

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Haha yes I understand that for sure, I been waiting 2 hours with my fingers crossed every part I've tried so far.

Need to have to look around cos I'm in UK guys and things don't seem as readily available here as they do out in the US.

Yes I follow the 720 calculator I seen posted on this site actually
 
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