Subject: Anodizing?

From: [email-masked] (Stan Huyge)
Date: 8 Nov 93 18:56:27 GMT

I searched for the FAQ but couldn't find it.  Therefore I will ask anyways.
I checked my news.answers and rtfm.mit.edu to no avail.

Could someone enlighten me about anodizing.  I am completely clueless about
this (and metalworking in general).  About the only thing I know is that the
end result looks nice.

Could someone please elaborate on the following points:

1) Exactly what is anodizing?

2) How is it done?

3) What equipment is required?

4) Can it be removed?

5) What metals can it be done with? (is it restricted to aluminum?)

Thanks in advance for your time.

Stan

-- 
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Opinions are mine not theirs.  What did *you* think?
[email-masked]
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From: [email-masked] (Dion Hollenbeck)
Date: Tue, 9 Nov 1993 16:34:04 GMT

>>>>> On 8 Nov 93 18:56:27 GMT, [email-masked] (Stan Huyge) said:

Stan> Could someone enlighten me about anodizing.  I am completely
Stan> clueless about this (and metalworking in general).  About the
Stan> only thing I know is that the end result looks nice.

Please understand that my knowledge of anodizing is from being an
electroplater 20 years ago, working in a commercial facility.  There
may be new methods around, or ways of doing this in a home shop, but
for the most part, I would not recommend trying this at home because
of the nature of the process.  There may be home methods which cause
the end product to look like anodizing, but true anodizing, IMHO,
ain't something to do yourself.

Stan> Could someone please elaborate on the following points:

Stan> 1) Exactly what is anodizing?

The process of creating an artificially induced aluminum oxide coating
on aluminum.

Stan> 2) How is it done?

The surface is lightly etched in a caustic bath and then rinsed with
water.  The piece is suspended in sulfuric acid and a current is
passed through it with the piece to anodize being the "anode".  After
a suitable length of time, the piece is removed and optionally dipped
in a colored dye (anodizing is colorless by itself).  The dye takes
because when the aluminum comes out of the sulfuric tank, the pores of
the oxide film are very open.  After the optional dye coat, the piece
is immersed in very hot water to close the pores.

Stan> 3) What equipment is required?

Source of current (high amperage, low voltage), lead lined tank (the
lining is the cathode), sulfuric acid, anodizing dyes and plenty of
ventilation.  Cooling system to cool the sulfuric acid, usually
consisting of near freezing water piped through lead pipes immersed in
the sulfuric tank.  Tanks to heat water in.  A large pool of water
under the area you are doing this in because spills are inevitable.

Stan> 4) Can it be removed?

Mechanically, or with caustic, but the caustic can ruin the underlying
metal if you are not careful.

Stan> 5) What metals can it be done with? (is it restricted to aluminum?)

Nothing other than aluminum that I know of.  Some people may mention
getting a rainbowish coating on titanium, but unless this is done with
an anodic process in acid, it is not anodizing, although the end
product may look similar.

-- 
Dion Hollenbeck (619)455-5590x2814     Email: [email-masked]
Senior Software Engineer                      [email-masked]
Megatek Corporation, San Diego, California    ucsd!megatek!hollen