Grant Erwin wrote:
I have some really old but strong casters which were once cleanly
galvanized but which have corroded through the zinc in many places.
They appear basically sound, though. I am contemplating heating a strong
solution of lye, then shutting off the heat (no open flame!) and putting
in the casters (sans wheel, of course) with the goal being to remove all
dirt, oil, grease, and, of course, zinc. Then I'd rinse in boiling water
after which they should self-dry quickly. Then I could brush off any rust
and prime the tops and then weld them to a plate, after which I'd paint
the plate and the casters all together, then reinstall the wheels.

OK, I took a 1-pound can of Red Devil lye, and a 10-quart stainless pot (I
have an old one I use for this kind of thing). I removed the wheels from
the casters and arranged them in the pot, then filled it with hot water from
the tap and poured in the whole can of lye. A day later, I reached into the
pan with long pliers and removed the casters and ran them under hot tap
water while scrubbing them lightly with a 3M pad. Then I dried them with a
paper towel and hit them with a water displacing spray to dry.

The heavy rust is completely gone. The areas that were rusted have a
different look, you might say they were stained black, but there isn't
any rust left. At first I thought the zinc remained, because most of the
metal was still so shiny. But after looking at it dry, in bright sunlight,
I now think the zinc plating is entirely gone as well. I'm going to weld
them onto a steel plate and I'll know for sure then if there's any zinc
left -- after spending a year doing nothing but cutting, fitting and
welding galvanized angle in the shipyards, I'll never forget that smell.

I had thought what would happen was that the lye would simply dissolve
the zinc. What I found out was that with the zinc ions in solution, they
reduced the rust back to iron, similar to electrolytic derusting, only
with no electricity. Very cool.

Grant