Bill,
Actually, using acid etch and then alodyne is recommended before
priming with epoxy primer. The acid etch is used to clean up the
surface corrosion, and then washed off with water and then blown dry
with a blow gun on an air hose. The alodyne is brushed onto the
surface continually for about 10 minutes until a nice golden color is
achieved, and then the excess is washed away and also blown dry with a
blow gun. These solutions should not be in contact with the metal
long enough for their intrusion into the extruded metal piece to act
as an electrolyte if instructions are followed carefully.
Syd
On Aug 3, 2009, at 9:54 AM, Bill BIGGS wrote:
Syd,
Is it recommended that the aluminum be etched first with alodyne or
is this asking for the posibility of it seeping into cracks and act
as an electolyte if not properly rinsed and dried?
Thanks,
Bill
CC: [email protected]
From: [email protected]
Date: Mon, 3 Aug 2009 09:38:49 -0500
Subject: Re: [ercoupe-tech] corrosion
Hi Darick,
Good to see you again at Oshkosh.
The only way to delay intergranular corrosion is to completely seal
the surface of the part from moisture. Impurities introduced into
the metal during the extrusion process become tiny anodes and
cathodes, and all that is needed is an electrolyte to start the
corrosion process. This electrolyte is moisture that works it's way
in through any pores in the metal. Sealing the metal surface with
epoxy primer works well. Zinc chromate DOES NOT seal the surface,
so do not rely on it.
I showed pictures of fuel tank rivet corrosion during the Ercoupe
Maintenance Seminar, which were hard to see due to the light coming
in from the sides of the building. I'll post those pictures soon
for all to see.
Syd
On Aug 3, 2009, at 8:03 AM, [email protected] wrote:
Syd did an excellant job of explaining intergranular corrosion at
the Oshkosh table, plus alot of other topics I'm sure. It's great
to have that talent in our group.
One question I forgot to ask...how can intergranular corrosion be
delayed? Is there statistical evidence that it is happening more
frequently? Is there a "useful life" we can expect to see in the
spars? Are we soon approaching this time?
I'm thinking this will be more of gut feel answer than anything
else, but I'd still be interested in everyone's opinion.
Darick
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