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----- Original Message -----
From: JonWilcox <jonwilcox@bigpond.com>
To: Marvin Kaye <lancair.list@olusa.com>
Sent: Tuesday, January 30, 2001 11:39 AM
Subject: Galvanic series
> Greig Huggins.
> I have been reading on the list a lot about corrosion where two dissimilar
> metals are in contact with each other. Being in the metal finishing
> industry, thought I would add a few cents worth. Down here in OZ we are on
> the second of two IVP's. When constructing the first, we heated the hangar
> with an industrial propane gas heater where the combusted gas was vented
to
> the hangar. The combusted gas produced heat, moisture, and acidic
> bi-products. The moisture and acidic fumes resulted in accelerated
corrosion
> on the gear legs and other zinc coated components. We stopped heating
with
> gas and fixed the coatings, but the lesson was learnt. Many of the metal
> components of the lancair are coated with electroless nickel, such as the
> gear legs, and the plates that fix the undercarriage frame to the
fuselage.
> The coating looks a bit like stainless steel, but according to lancair it
is
> electroless nickel. A good choice in that it produces a uniform coating
all
> over the part and does not introduce hydrogen embrittlement. The corrosion
> resistance of electroless nickel is fairly good, given about a 25 micron
> build. The big problem is where it contacts other metals like aluminium or
> zinc. The aluminium is up one end of the galvanic series, and nickel
like
> stainless steel ) is up the other end. This will produce corrosion at the
> interface, especially in hot humid conditions. We removed all the
> electroless nickel coated parts and applied an electrocoat finish over the
> top. Electrocoat is an electroplated epoxy paint used on auto parts and
> marine outboard motors. This effectively insulated the two metallic
> surfaces. Another option is to apply an anti corrosive paste between the
> faces. This is always done on yacht masts where stainless fittings
contacts
> the aluminium. The paste contains barium chromate and prevents the
> inter-face corrosion. Ask your local yacht supplies about it or Aircraft
> Spruce may stock it for putting under stainless screws. Lancair has gone
to
> a lot of trouble to produce an aircraft that does not corrode like all the
> old ones, but if a few of the metalic bits are fine tuned as far as
coatings
> go, then you will have a fizz free aeroplane. Hope this helps. Jon Wilcox.
>
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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