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Letter 1042
Inspecting for full anodizing
coverage
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I need an inspection procedure that can be used on Anodized
surfaces to ensure 100% coverage. The hardware is moderate in size
[2' x 2' x 4']. We would prefer some technique other than salt spray
as defined in some of the specs. The technique would be used
immediately after anodize and if practical on finished and assembled
hardware. Would a dye or some type of top coat, that would give a
visual indication of a break or damage to the anodize, be practical?
Kenn Clark
Derlan / D-Velco Facility
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Inspection for coverage of anodize would be an unnecessary
operation for most people. A dye will give a very quick visual
indication of coverage. No anodize, no color. A thin anodize will
give nearly the same color as a thick coating. What dye does not do,
is tell you how much anodize there is on every square millimeter of
surface. Random checks with a handheld gague for aluminum substrate
will give a decent idea of the uniformity of the thickness. You
probably will want to continue weight loss and salt spray testing for
quality control.
James Watts
- Navarre, Florida
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I have another question about quality.
How clean is clean? A TCE vapor degreaser is used as a precleaning
step prior to anodizing aluminum to remove waxes. I have been testing
some alternative cleaning technologies and have found a simple steam
cleaning to work farely well. The work piece fails a water break test
afterwards, but appears to anodize successfully.
Has anyone struggled with this? I am looking for ideas on how I
can insure that the anodic coating is high quality.
Will the anodic coating grow under a microscopic coating of
hydrophobic contaminant?
Does anyone else preclean with only steam or hot water to remove
waxes?
Thank you for your help with this, and excuss my naiveity. I am a
surface cleaning person, not an anodizer.
Andrew Bray
Toxics Use Reduction Institute
One of the chemical suppliers--I forget which one, but I could
find out--did something a few years ago that you might find
interesting. They put together a test kit that contained 5 solutions
of different surface tension that could be used in a laboratory water
break test, so that cleanliness could be given a relative rating
rather than just a go/no go.
Your proposal is interesting. It is possible that metal needn't be
as clean for anodizing as for plating.
The thing is, though...
Would you buy computer software where the computer engineer said
there were some bugs in it and s/he could do better but she wanted to
save electricity by not making the disk work so hard. Would you fly
on a plane controlled by such software? Surface finishers want
'robust' cleaning cycles, just like software engineers want
'bulletproof' algorithms.
So I think you would need to demonstrate that the cycle would work
even if the work was fingerprinted, or the parts got sprayed with a
little bit of oil or brushed them with a stick of
jeweler's rouge [link is to product info at Amazon], or if
somebody modified the wax a trifle. Steam cleaning is a nice concept,
but I'm not confident that it constitutes a robust cleaning cycle,
and I wouldn't want to fly on a plane where critical components were
steam-cleaned before anodizing without a lot of evidence that it was
adequate.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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Would a continuity check at various points plus some number of
random spots be enough? Or do you have some special application where
conductivity at any point would be a safety problem, i.e., are you
using the coating to prevent the flow of electricity?
How about a fixture which you could place on the part, with all
the points in parallel, so any ground would sound a buzzer?
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