Hi Lee,
I just wanted to point out that the above points that I made were
intended for your specific application. Actually, there are many useful
applications for pickling/acid baths of various types, including rust
removal, prepping for plating, creating a conversion coating for
short-term corrosion protection (or longer on aluminum) and as I
mentioned, etching the surface for better paint adhesion.
Also, the suggestion for pressure washing and solvent (like DuPont
Prep-Sol) rinsing was intended as a practical approach to cleaning loose
scale and oil from the inside of your axle housing. The type of
preparation work that I would do for "general" parts cleanup would vary
considerably, depending on the part and how it was going to be painted,
plated, or otherwise finished.
For general small steel parts, I like to bead blast with glass beads,
apply a metal prep solution (phosphoric acid) for a few minutes, rinse
and dry, followed by primer-sealer and paint. In lieu of the metal prep
solution, I may use a self-etching primer, followed by primer-sealer,
then paint.
For plating, I bead blast, then take the parts in and let the plating
shop do the cleaning/pickling/plating. I've found that it's quite
reasonable in terms of price, and they have to take care of the nasty
chemicals.
If I'm having parts zinc plated that will be painted, I have the shop
apply a chromate conversion coating to improve paint adhesion.
If you wanted to get every speck of rust out of the inside of your axle
housing, you'd probably have to take it to a shop that could dip it in
an acid bath, unless you found someone with a sand blaster attachment
that could reach down into the tubes. I'd recommend the sand blasting
over the acid dip for this application (if you can find someone who can
do it). One thing about acid dipping is that the acid will attack the
steel, although more slowly than the rust. If you have any heavy scale
and magnetite (harder "rust" which I think is a more stable oxidation
state of iron), it will take a while for the acid to eat out all of the
rust. Meanwhile, it's attacking the good steel. Of course, if you have
real deep rust or heavy scale deposits inside your axle housing, I'd
strongly recommend getting a new/used replacement housing, since its
strength may be compromised.
Hope that additional information helps.
Regards,
Alan
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