Is alternating current the standard with TIG welding then ?
Anyway I'm in the camp of 'lost and not found yet' items. The spring to hood
rod attachment clip flew during installation one day. that was 2002. I
lamented to Norman Nock about it - not seeing which way it went - or hearing
it land or hit something - and not finding it with my light shining across the
floor. He was patient with my story and sent me a replacement clip - along
with a copy of his Tech book. So I've been watching for that clip ever since.
It might be in same place as the more recent missing brass nut. Or maybe it's
in the much talked about Healey frame black hole.
Dick Matson / Bj8
Cashmere, WA
----- Original Message -----
From: Bob Spidell<mailto:bspidell@comcast.net>
To: BJ8 Healeys<mailto:sbyers@ec.rr.com>
Cc: Healey forum<mailto:healeys@autox.team.net>
Sent: Sunday, October 17, 2010 8:10 AM
Subject: Re: [Healeys] Healeys] Boot pan to shroud
Agree on the galvanic scale stuff, so I was surprised--and delighted--that my
shroud Al was perfectly intact.
Another factor is that bare aluminium instantly forms an oxide layer when
exposed to oxygen (anodizing is a form of oxidation). The oxide layer is an
excellent metal protectant, so even though the Al should corrode faster than
the steel, the oxide layer protects it. I suspect the aluminium parts of a
Healey sat around before installation and had plenty of time to form an oxide
layer (and you can bet the assemblers wouldn't bother to clean it off before
attaching to the cars). Our BN2's Al flanges are in good shape as well, though
I have seen pictures of cars where they are all but gone.
This is also why Al is often welded with a TIG welder on alternating
current--half of the current cycle cleans the oxide layer off the surface and
the other half of the cycle does the actual welding.
bs
--------------------------------
Bob Spidell - San Jose, CA
Jaap, the word "weakest" in your response can be interpreted as meaning the
material that is structurally less strong. Comparing aluminium/aluminum to
steel, yes, it is structurally weaker. But what causes the
aluminium/aluminum to corrode rather than the steel is that it is higher on
the galvanic scale than steel and therefore more anodic. When two metals
are in contact with each other in the presence of an electrolyte (like
moisture), the more anodic will corrode first.
Lead is structurally weaker than aluminum, but in an aluminum/lead joint,
the aluminum is still more anodic and will corrode first.
And "rust" is just a special term for corrosion on iron and steel.
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
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