Lye as an aluminum cleaner?

You can say that again. I printed that text out for my keeper file.
Excellent information. Thank you.

Don...

On 14 Oct 2006 12:38:50 -0700, "
wrote:

So don't use lye. Unless you know how to, when to and why. Do use
phosphoric acid, then neutralize it good with copious amounts of
BOILING HOT water (and use an oven or a heat gun to make sure all the
cracks are water-free after).

But be careful here; 20xx and 60xx can handle 350F for a pretty long
time with few problems, but 7075 is less tolerant. A heat gun can
overdo what you want if you aren't careful. I don't know a good way
to know when you overheat; those optical thermometers are probably
pretty good, though.

Limit those temperatures to 250F for safe measure.

I wrote:


When the depth of the corrosion is 10% of the material's thickness,
you then estimate the AREA of the corrosion. If it covers more than
20% of the surface area, the part is usually tagged for replacement.

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Which caused someone to ask,

"Can you expand on that?"

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Mebbe. It's really the inspector's call, not a rigid rule.
Where the corrosion occurs is the clue. With Alclad you can expect to
see it on edges, that feathery looking discoloration that may not be
significant. But could be.

You also tend to see it around rivets, where it may brush away, giving
the impression it isn't a problem.

If it's fairly extensive, such as on every edge or around every rivet,
even if it looks to be only minor surface corrosion the inspector will
ask (or, SHOULD ask...) to see what's UNDER those edges, requiring you
to drill out a few rivets, separate the parts and take a peek at what's
underneath.

Sometimes there's no problem. Sometimes. But the edge-corrosion may
have etched a line in the lower part creating an unacceptable
stress-riser. Or the edge-corrosion my have bled back farther UNDER
the piece than on the exposed surface.

Drilling out a rivet, you sometimes find the edges of the hole has
turned into a powdery circle (lots of riveters store the rivets in
their MOUTH, treating each rivet and the hole it goes into to a free
dose of spit). A corroded rivet hole may clean-up by going up HALF a
size, in which case you may be required to dismantle the thing,
re-drill and re-assemble with new, plus-size rivets.

Lotsa stuff like that.

Corrosion begs the question: "How bad is it?"

If you treat only the VISIBLE corrosion you leave the question
unanswered. The inspector's job is to come up with a definitive answer,
which then dictates whether the part can be repaired or if it needs to
be replaced.

Okay, so it's a royal pain in the ass and the part is probably good for
another twenty years. Try looking at it this way: You're safe, feet
firmly on the ground, probably warm & dry over in the corner of some
hangar. So you take the time to find the answer; to leave nothing to
Chance. Do the job right, it's a life-time sort of thing. And yes,
there's several ways to interpret that :-)

-R.S.Hoover

And the problem with KOH is???

Jim


(NOT Drano, as it
contains potassium hydroxide, in addition to the sodium hydroxide)

In article ,
"RST Engineering" wrote:

And the problem with KOH is???

Jim


(NOT Drano, as it
contains potassium hydroxide, in addition to the sodium hydroxide)

Too reactive!

You are telling me that KOH is more reactive than NaOH? That's not what
they taught me.

Besides, this whole thread is remarkably void of solution concentration data
.... just that "lye" is really bad for aluminum. Hm. How about a gram of
solid NaOH in a hundred liters of water? Ten liters? One liter? A hundred
milliliters? What is the optimum cleaning-not-disintegrating concentration
and what time span do we use for soak?

Jim




"Orval Fairbairn" wrote in message
news
In article ,
"RST Engineering" wrote:

And the problem with KOH is???

Jim


(NOT Drano, as it
contains potassium hydroxide, in addition to the sodium hydroxide)

Too reactive!

Phosphoric acid. Diluted about 50% with distilled water. apply with
brush. Leave on 3 minutes Rinse the hell out of it with fresh water and
neutralize with baking soda. Taste the rinse water. If it tastes like
acid, rinse some more. Dry, prime.