GRINDING ANODISED ALUMINIUM
A discussion started in 2005 & continuing through 2017(2005)
Q. We have some anodised parts which require rework. We were considering grinding back the required dimension but when we commenced grinding, the fumes caused some concerns. Can anyone advise if these fumes are dangerous or if grinding anodised aluminium is an acceptable practice?Bernard O'Neill
automation - Limerick, Ireland
Use a dust collector, respirator, or wet grind. This would be a good practice for just about any metal that you would grind.
Read the MSDS for aluminum and see if you want to breathe it's dust, and go from there.
- Colorado Springs, Colorado
A. What you are grinding off is aluminium Oxide, If the Anodizing you are taking off is "type 3" (or Hardcoating), first remember that anodizing is also penetration and your parts will show that dimensional difference. I would heavily recommend that you have it stripped off the surface before grinding, not because of environmental reasons, but because you tend to embed some of the aluminium into the surface and this will not recoat well.Chris Snyder
plater - Charlotte, North Carolina
A. Also, depending on the seal, there may be a smidgen of nickel, or cobalt, or chromium in the dust.
And, depending on whether dye is involved there may be a smidgen of dye in the dust. Heated dye turns into all sorts of asphaltic compounds.
Robert H Probert Technical Services
Garner, North Carolina
Q. I do a lot of engraving onto anodized (25 µm) aluminum plates, and have noticed that the dust that comes off the engraver irritates my nasal passage.
Does anyone believe this may be causing long term health effects?
A. Hi Dan. Glass is probably the least hazardous chemical in the world, but swallowing glass shards is one of the most deadly things you can do. Similarly, the main issue isn't whether aluminum dust is a "hazardous chemical" -- it's the issue that you should not be inhaling aluminum dust or wood dust or plaster dust or any kind of dust. None of that garbage belongs in your nasal passages, let alone those super sensitive gas exchange membranes that we call lungs.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Surface grinding a nickel acetate sealed surfaceJuly 6, 2017
Q. We plan to have an aluminum alloy 6063 vacuum chuck anodized by electrolytic 2-step anodization (Type II, Class II) followed by a nickel acetate seal. After the sealing, is it possible to perform surface grinding on these type of surfaces?
Thank you in advance for your time!
- Orange, California, USA
July 6, 2017
A. I had a customer that needed round hydraulic valves-pistons Type 3 anodized to 50-60 µm thickness (6061), which I did, and they later did some hand lapping using diamond paste to smooth out the sliding surface. Factory method of finishing was to turn the part, Type 3 anodize to oversize dimension (the tolerance was a couple microns), and then grind them to final size using diamond wheels on excenter grinder.
Also I had a customer that needed some 6082 parts anodized for his custom showroom HD bike, the parts were polished and anodized to around 25 µm thickness, dyed black and nickel acetate sealed, and since 6082 loses some of the shine during anodizing, he did some light buffing-polishing on them, worked out quite well.
This is to say that some machining on the anodizing layer is definitely doable, probably worth running a test piece to work out which stones or diamond wheels will work best and how much you can afford to take off in one pass before there are any major problems or damage to the anodizing layer.
Another note, sealing will cause the anodizing layer to crack, especially at max thickness, and you want max thickness, since you want as much available material to machine off as possible to be able to make the table flat again, and this micro cracking may lead to peeling later on, so if the service environment of the table is not particularly corrosive to aluminum, then you might want to leave the anodizing unsealed. There are room temperature seals though, I'm not familiar with them, so I cannot comment on their performance in this application.
And another note, if I remember correctly, there was a NASA paper on the adherence of sealed/unsealed/dyed/undyed anodizing in various service temperatures, and the conclusion was that undyed unsealed anodizing had the least problems holding on to the base material, just something to keep in mind.
- Riga, Latvia
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