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topic 48706

Two-color anodizing


May 5, 2008

Q. I am currently working on some custom aluminum link bracelets and would like to anodize the 6061 material. However, after anodizing I would like to pencil blast a pattern onto the surface, removing the anodized color. I would then like to re-anodize the parts so a different color can be added into the blasted pattern.

I have three questions:
1. What is the best media to use for blasting the aluminum so not to leave foreign material in the aluminum (aluminum Oxide, glass, etc.)?

2. Once blasted, can the part be dyed and sealed again or does the part need to be acid etched again and if so will this remove the original anodized color?

3. If the part can be re-anodized, will the sandblasted texture be too rough to accept the dye properly?

I would greatly appreciate any insight into this process.

Nate Hallee
artist - Minneapolis, Minnesota, USA


Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

May 6, 2008

A. Hi, Nate. What you want to do can be done. In fact, very exotic multicolor anodizing can be done -- visit the paint ball gun section of a store for examples. But sandblasting is not the way for most. Instead, maskants are usually used. Mask the area , and anodize and dye and seal the rest. Then remove the masking, do your pencil blasting, and anodize and dye and seal that area. It would be best to mask the original area when you anodize the blasted area, but it may not prove necessary.

Most people don't encourage sandblasting of aluminum because it's so soft, so you might consider chemical etching as an alternative way to get a matte area. Possibilities include caustic etch and ammonium bifluoride etch.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 7, 2008

thumbs up signTed, I appreciate the prompt reply and the information. I will explore masking techniques and pencil blasting further in order to achieve what I am looking for.

Thanks again for your thoughts.

Nate Hallee
- Minneapolis, Minnesota, USA



Anodizing aluminum, machining it, and re-anodizing it for multiple colors?

December 18, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello, everyone. We're designing the aesthetic of some machined aluminum products and our local metal finishing facilities have told us this is impossible: we want to machine an aluminum surface, anodize it, and then machine other features and re-anodize to accomplish the aesthetic of the following three examples:

48706-1a  48706-1b  48706-1c

from m.aliexpress.com/item/535828802.html,
www.goldsprintshop.com/bilder/produkte/gross/Sugino-MC130NC-double-anodized-Bahnkettenblatt-130BCD-1-8_b3.jpg,
and www.aliexpress.com/item//32338438490.html respectively

If anodizing/re-anodizing isn't the process, what is this process? How is it accomplished? What should we be asking for to accomplish this?

We have a facility capable of machining parts like this, but we have no experience with these kinds of metal finishes (we outsource this), and this is a baptism by fire situation. Our attempts at asking our local metal finishers (they're great, but very old school) have left everyone scratching their heads.

Thanks in advance.

Thomas Weider
- Lehi, Utah


December 20, 2015

A. Practically it is almost impossible; however, it is theoretically possible. First the first anodize must be completely sealed but most job shops never completely seal anything after the first day because their seal is contaminated or they use a so-called low temp seal which never works even the first day. If you get by the first seal, then the next problem is how to prepare the surface, after machining, for the second anodizing. Use a cutting fluid that is water soluble and find a way to get it off without harming the first anodizing, probably with solvent cleaning and water rinsing. Then, the same day you did the machining. before it sets a hard weathered oxide, dip it briefly in a ferric sulfate based deox, experiment with the max time you can use without leaching the previous dye, anodize and dye, good luck with that. It can be done. People who do splash gun dyeing, keep it secret, but many secret processes are out there.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como


December 2015

A. Hi Thomas. As the three examples show, people are doing two-color anodizing in production. I have no inside information on it, but my guess is they are doing it by anodizing the whole part, then selective masking and into the first dye tank and seal, then removing the masking and going into another dye tank and seal. A second masking step before the second dye might be required though.

If I ran an anodizing shop and had a regular customer who wanted two-color anodizing I would certainly take that opportunity to figure out how to do it rather than let my business seep away to bolder shops.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


December 22, 2015

A. Thomas

The Sugino chain ring appears to have been black anodized, machined, then red anodized where the machining was performed. Not too sure about the other two items.

Robert is correct that if the seal is less than perfect, you won't be pleased with the results. Typically, the lighter shade is applied after the darker, as lighter shade doesn't require the coating thickness of the darker, and the immersion time in the anodize bath is shortened.

Masking the first coat and re-anodizing is an option but in most cases not cost effective. I have seen Ted's suggestion used where the article is anodized completely then masked for dyeing, with mixed success.

Willie Alexander
- Colorado Springs, Colorado


December 23, 2015

thumbs up signI appreciate everyone's thoughts on this. Thank you for helping us figure this out. This is tremendously helpful.

To Willie's point, "Masking the first coat and re-anodizing is an option but in most cases not cost effective."

This was our thought, as we can build silicone molding to form fit, but it seems to be overthinking it; even perfectly built silicone molding for masking doesn't create a perfect seal, and the examples we're seeing quite literally have the color transition immediately at the tooling line -- that's incredibly precise for any hopes that an injection molded mask could ever deliver.

This leads us to believe these specific processes aren't being masked; it seems unlikely that a mask could so accurately begin the color transition at precisely the tooling line where the chamfers begin.

That being the case, we've deduced from what we've observed on the parts, and with the helpful responses so far, that the anodized part must be perfectly sealed and then remachined and reanodized for this effect to be manufactured so consistently and precisely.

We'll begin testing with a few metal finishers soon and call out some processes; any ideas on what to call out specifically to ensure the parts are completely sealed and ready for a second phase of machining?

A tremendous thank-you to Robert, Ted, and Willie for all of your thoughts on this so far.

Thomas Weider [returning]
- Lehi, Utah


December 2015

A. Hi again. I'm not looking at actual parts, only photos (and with the large number of postings to deal with, not even looking closely at the photos). So if you can see machining transitions precisely at the color change lines, my revised theory is that they were anodized, dyed, and sealed all over, then masked completely all over with a dipped, brushed, or sprayed masking material rather than using a reusable mask. Then the masked component is machined (it may be necessary to remove the masking at a few points for accurate jigging). If any masking was removed for the jigging, those points could be easily repaired with a brushable maskant without any need for precision, then the part (with the existing masking everywhere but on the newly machined areas) goes to anodizing, dyeing in the second color and sealing.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


December 28, 2015

Q. Hi again, Ted!

"... my revised theory is that they were anodized, dyed, and sealed all over, then masked completely all over with a dipped, brushed, or sprayed masking material rather than using a reusable mask."

This is an interesting thought! What masking materials are we talking about in this scenario? Would a first anodization that's properly sealed not work well for masking; meaning we should definitely be seeking out this spray-on/brush-on masking material?

We're very interested in finding this masking material to test, but we'll need to know what it is to call it out for the manufacturing process (four local metal guys are unaware of this stuff, so it's fascinating to learn that it exists!).

Thanks again for your very helpful responses.

Thomas Weider [returning]
- Lehi, Utah


January 2016

A. Hi again. Sorry for the delay in posting your question and my response. Yes, well sealed anodizing can be used as a maskant to prevent further dyeing, but there might be limits to its total effectiveness. The masking I was speaking of is simple elastomer dips and brushable stop-off solutions made for the purpose. Even dipped wax may be useable if you are not doing heated cleaning or sealing, and only warm dyes. Where it suits, plater's tape can be used; it's similar to black electricians's tape except usually heavier and in colors like green (whether the adhesive is actually different, I don't know).

In the meanwhile, the below response came in from Geoff Smith, who is relating some actual experience in a similar process, rather than just book knowledge :-)

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


adv.   maskcoat banner 


January 2, 2016

A. Hi Thomas

I don't know if this helps but it could be worth passing on to your anodiser

Back in the 1970s at Kodak we developed multi colour anodising.

Standard sulphuric anodise but do NOT seal
Dip in methyl cellulose solution (common wallpaper glue)
Dry. This fills the pores in the oxide layer but prevents it sealing.
Print an image in resist - we used photoresist but you could screen print or paint an image. Dye the first colour. We probably cold sealed at this stage. Remove the resist with suitable solvent. Dry. Repeat the process with resist now coating the dyed area and producing another image on the undyed part, etc. We were able to produce a full colour image, yellow, cyan and magenta with a black overprinter of near photographic quality. The main application of the process was for the label industry.
All our work was on flat sheet but possibly it could be adapted.
If you would like to go the machining route, I must disagree with Robert Probert. There is no need to use cutting fluid for the light cut needed. Use modern carbide or ceramic tools dry and with a slow feed rate.

geoff smith
Geoff Smith
Hampshire,
       England



January 5, 2016

thumbs up signTed,

Thanks for the update on the masking; this will help as we experiment.

Geoff,

Wow! This was a really great response. I think this gives us enough with which to experiment. Thank you.

I want to give out a tremendous thank-you to everyone who has contributed in the thread. The responses have given us a good place from which to begin testing with some local finishers.

Thomas Weider [returning]
- Lehi, Utah


March 16, 2016

A. I would attack this differently. I would apply the darker anodize coating first. Then clear coat the entire unit with a good polyurethane. Machine the surfaces requiring the lighter anodize and then apply another coat of the clear coat as the final finish.

Ed Peters
- Frederick, Maryland USA



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