After my prior post on electrolytic rust removal, I got a few more suggestions
and a
couple of challenges as to how safe this technique is from various lists and so
did some
more checking with the following comments. The most important thing to note is
I'm just
a hobbyist like you guys exploring what my options are and reporting results;
I'm not a
professional in this field. Treat the info accordingly.
1--White Vinegar can also be used to clean some rust; I haven't tried this one
but
others have reported that it works. It shouldn't have any negative effects per
below.
2--A more thorough treatise on electrolytic de-rusting can be found at:
http://www.htpaa.org.au/article-electro.php
For some reason, I couldn't get the whole document to print though. If you
intend to
try this technique, read that whole article.
3--There is one major concern with electrolytic cleaning and that is hydrogen
embrittlement. ShopNotes (my experiment reference) didn't mention it at all
(but in all
fairness, their interest was in cleaning tools), but the site in item 2 does
even though
they treat it mundanely. After a comment from one email that I had ruined my
steering
arms, discussing this issue with a PhD metallurgist specializing in hydrogen
embrittlement and a little further study, I came up with the following:
* The issues are embrittlement of the metal due to hydrogen takeup and possible
stress
cracks from hydrogen buildup in the material around internal defects in the
object.
Hardened steel tends to be susceptible; softer material is not usually.
* Hydrogen embrittlement is temporary. it will go away on its own after a few
weeks or
can be removed by heating the treated object to about 160C for about 14 hours.
* Obviously the stress cracking that may occur during hydrogen embrittlement
would be
permanent and could lead to catastrophic failure of the object, hence the
reason for not
using this technique on safety-related items.
* Sodium bicarbonate electrolytic cleaning is mild and would not normally be a
problem
on any steel for an hour or so. However the effect is time, material, and
electrolyte
dependent; at the very least, hardened steels should not be treated for extended
periods.
* Final suggestion is don't use this technique on hardened steel such as
springs and
restrict use on any high strength steel components...such as steering arms
(oops!),
suspension components, etc. Stick to good old sandblasting for hardened steel.
The
electrolytic technique is fine for non structural items or anything that is not
high
strength steel. Of course, my interest in this technique was that I didn't
have a sand
blaster, and I have had parts damaged by over zealous commercial blasters that
I have
taken parts to.
* Since I had already treated my steering arms, one suggestion to determine
hardness
was to use a file on a safe portion of the object. If the file can readily
remove
material, then the object is relatively soft and was probably not affected.
The file
cut into the one I tried fairly easily...shouldn't these be pretty hard? I'll
probably
see if I can get them tested at the local university metallurgy lab to see if
they are
ok. The only way to be sure is not to electrolytically treat critical parts.
4--I tried another experiment, this time with the center mount tail light
assembly from
a 50s era Suburban tailgate; these are very rare and I have managed to collect
two
complete units plus most parts for a third. This particular unit had heavy rust
inside,
so much so that I couldn't even begin to work the nuts on the internal screw
studs to
take things apart to restore it. Sandblasting would have ruined it. I put it
in the
bath for about 12 hours and it reduced the rust about 80%, to the point where
I can
work with the internal parts. I'll disassemble it as much as possible and and
then dunk
the subassemblies that need it again. There are no structural issues with this
part so
the dunk time is not an issue. This is the kind of cleaning task for which the
electrolytic technique is perfect.
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