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Hard Anodizing Question
We are seeking lighter weight alternatives to stainless steel for a product in development. Think of it as a mid-range watch case. The requirements for the article are that it have similar or greater impact and abrasion resistance as 316L stainless, and that it be able to be finished attractively (brushed or mirror polish finish).
We have begun to look at aluminum. It seems that Type 1 and 2 anodizing does not give us the required abrasion resistance, but that hard anodizing might.
Questions:
1. Can hard anodized materials achieve a fine, jewelry quality finish? All our research seems to indicate that is can't. Can you get a clear, white finish with any type of aluminum, or does the process always give a color?
2. Ballpark, and in bulk (10,000 pieces), with a few square inches of surface area, and being racked, how much does hard anodizing cost?
Design Engineer - Culver City, California, USA
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Hello Mark. Forget Type I. My gut feel is that no anodized aluminum finish will give you quite the look you seek, but Type 2 is certainly best. It can be left uncolored (aluminum color, not white) or it can be dyed (almost any color except white). If you look around you can find examples to work with to get a feel for what it's like (aluminum clothes hangers, knitting needles, crochet hooks, archery arrows, paintball guns, flashlights). Type 3 hard coat will not be reflective; it will be matte in appearance and probably light gray to not quite black. Sorry, I can't offer pricing estimates except to say that anodizing is not a particularly expensive process.
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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You can achieve and almost white appearance on a type 2 anodized surface with the correct surface preperation is key. I can get my type II to an off white color but it still does have a shade to it. feel free to contact me if you have any other questions.
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Ryan Cook Toccoa, Georgia |
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Ryan - I've always been under the impression that a white was impossible in a type II bath... any chance you'd describe your methods?
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Jim Gorsich Accurate Anodizing Inc.  Compton, California, USA |
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I will be happy to.. I have achieved an "Off-White" coating coloration on type 2 anodizing by preparing the surface with Glass bead blasting. and then with my type 2 bath at 175-180g/l and at a temp of 70 degrees. I can plate to a thickness of 2.5 - 3.5 tenths this results in an off white appearance of the aluminum. If you plate over 3.5 tenths the coating becomes more greyish off-white. Now keep in mind that I use a caustic etch and I etch commonly 2-3.5 minutes @ 120 degrees after a 10 minute soak clean at 140 degrees. as well as a Ni-acetate seal to end it all up. I can send photos if you would like.
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Ryan Cook Toccoa, Georgia |
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Interesting... very similar to my standard process for clear anodize with the exception of the bead blast and the fact that I run my etch hotter and my acid a little stronger. I'll have to expirement sometime. Thanks for the tip Ryan, I much appreciate it! I know that certain acid combinations and alloys can be used to get a white (at least, according to the books I have), but this is the first time I've heard it mentioned for a standard type II.
Out of curiosity - what current density do you use? Do you drop it down to allow larger pore size and more light scattering, or am I on the wrong path?
Thanks again! - Jim
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Jim Gorsich Accurate Anodizing Inc. Compton, California, USA |
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I use roughly 14.5 to 15 amps per square foot.
It is a lower asf than normal and yes it allows the pore size to be larger. That is my guess.. But it comes out an off white color..
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Ryan Cook Toccoa, Georgia |
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Ed. note: other letters which talk about white anodizing include
11600,
20562,
41596 and
47306.