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geekhack Projects => Making Stuff Together! => Topic started by: intelli78 on Wed, 11 June 2014, 18:52:06
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I just picked up calavera's red LZ MX Mini from the classifieds, but I want a black or gunmetal case instead of red. I will first try to find a trade, but failing that, I am planning to get the case powder coated. I have some questions for anyone with experience, though.
- My understanding is that powder coating is cheaper than anodizing, available in more colors, and offers more protection to the metal because it actually adds a layer. Anyone disagree or want to make an argument for re-anodizing instead?
(And on that note, I understand that anodizing actually chemically removes some material, and can theoretically make screw holes in the case too loose. Is that a practical concern or would that require many, many re-anodizings?)
- I understand that screw holes must be covered when powder coating, as adding a layer can also interfere with screw fit. Are there any other warnings to heed?
- Would you trust a local powder coating shop to do the work correctly without damaging anything, or should I mail it to that place in Iowa that has proven experience working on keyboard parts?
- Is there anything else I should know that I haven't discussed? I want to measure twice, cut once, so to speak.
Many thanks in advance.
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Melvang is an expert on powdercoating. Photoelectric is an expert on anodizing.
From what I've heard, anodizing may be better, because its chemically imbedded in the case. You'll need to sandblast it first, which removes a tiny layer, but depending on the shop, it won't do much to the screws
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Thanks for the info. Hopefully they will weigh in. You bring up a good point, re:sandblasting. Must the case be sandblasted first before powder coating, or only before a re-anodizing?
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You generally can powdercoat over anodized aluminum without issue.
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so, from a material standpoint, anodyzing is pretty cool.
It basically "rusts" the aluminium, forming a thicker layer of aluminium oxide. This layer naturally forms in air, as oxygen atoms diffuse through the aluminium and thicken it over time.
The reason why it works (and why "hard anodyzing" is theoretically a thing) is because aluminum oxide, or alumina is a very hard ceramic. A thicker layer will protect more. You can only have aluminum without this layer in an oxygen-free atmosphere (or vacuum). This outer layer will protect the aluminum metal underneath somewhat.
Titanium does the same thing with a titanium dioxide layer.
The issue you run into is the issue with all ceramics. This is why a powder-coating can be better in some ways.
The reason you get colours is usually because a dye is added to the bath, which diffuses into the aluminium. Pretty neat! There are other ways of getting colour, mostly with very precise layers and diffraction, but it's usually seen on titanium.
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I have a beamspring with some siginficant oxidation on the plate (through the zinc and/or nickel coating(s) and into the steel) that I plan ot sandblast and then either powder coat or spraypaint depending on costs. If anyone knows good shops in the New England area, please set me know.
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Either choice is perfectly acceptable for a case. Now she notes on both. Fair warning I am not an expert nor favor one side of the fence or the other.
Anodizing. Any good shop will media blast the part before dipping regardless of any prep work you do before sending. The reason is like with paint, but to a greater effect, any imperfections like scratches, dings, or even oils from you fingers will affect the quality of the finish. The difference between "hard" and "soft" anodizing is the amount of time in the tank. Hard sits in the solution longer. Though I have no idea where that cut off between the two is. As stated annodizing essentially forms a layer of corrosion that protects the base material. The longer it sits in the tank the deeper it penetrates. To my knowledge you don't need to worry about screw hole with it.
Powder. This is essentially a paint without all the solvents that harm the atmosphere hence the powder form. I am not sure if powder can be applied directly to an anodized part or not. Yes screw holes need to be protected unless you want to chase all the threads with a tap after. Powder is a very flexible bond compared to traditional paint as well. Powder is available in many more colors and finish options than anodizing as well. If you have any further questions about powder you can look up Rainbow Paint and Blasting in Cedar Rapids, IA. Tammi over there is very knowledgeable with this. They are also supposed to be getting a no bake ceramic coating process soon. From what she was telling me this can be applied to plastic.