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fderfler(at)gmail.com
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 Posted: Thu May 28, 2009 2:19 pm Post subject: Corrosion Around the Landing Light Window |
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My 601XL sits outside at Marathon airport in the Florida Keys. It's been flying for about 30 months. Even in this environment, the only corrosion (I can find) is filiform corrosion around the screws holding in the landing light window. Two photos attached. My screws are stainless and I suspect that a good portion of this corrosion is electrolytic. I'm scrubbing with ScotchBrite and going down to bare metal. Then, it will be aluma-prep, alodine, and then, Zinc chromate.
By the way, I'm removing a nice layer of yellow primer, so this corrosion is not a matter of improper priming.
I've only tackled stripping the area around two holes so far and already I'm sorry I started.
When it comes to the question of how to preclude this happening again, the local experts have as many opinions as eyeballs... maybe more. So, let's see what you think..
1. One group says the stainless steel screws are to blame and I should switch to plain painted steel screws.
2. Another group says "How about aluminum screws?" Since the screws do not really do much ..eight screws to hold the plastic piece in place.. this sounds like an idea.
3. Another group says.. use the stainless screws, but dip them in Teflon grease..
4. Another group says use nylon screws.
5. And another group says, "You have holes in the skin.. they go through the pure aluminum coating. there is nothing you can do except to treat it every two years or so."
And so, 601/650 builders and owners... what do you think? Does anyone else have corrosion around the sheet metal screws holding the landing light cover and, if so, what have you done about it? (and did it work?)
Frank Derfler
601XL flying with never a flutter
Islamorada, FL
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Thu May 28, 2009 2:53 pm Post subject: Corrosion Around the Landing Light Window |
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Stainless and aluminum don't play well together. Either switch to zinc
or cadmium plated screws or use zinc, cad or plastic washers under the
screw heads.
On May 28, 2009, at 6:18 PM, Frank Derfler wrote:
| Quote: | My 601XL sits outside at Marathon airport in the Florida Keys. It's
been flying for about 30 months. Even in this environment, the only
corrosion (I can find) is filiform corrosion around the screws
holding in the landing light window. Two photos attached. My screws
are stainless and I suspect that a good portion of this corrosion is
electrolytic. I'm scrubbing with ScotchBrite and going down to bare
metal. Then, it will be aluma-prep, alodine, and then, Zinc chromate.
|
--
Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
do not archive.
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_________________
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Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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jaybannist(at)cs.com
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| Posted: Thu May 28, 2009 2:53 pm Post subject: Corrosion Around the Landing Light Window |
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Frank,
Just my two cents worth:
Stainless steel and aluminum are far enough apart on the chart of galvanic activity that, in the presence of salty moisture, there is going to be some corrosion to the aluminum. The Idea that you have "gone through the layer of pure aluminum" is bunk. The XL is built with 6061-T6 which doesn't have a layer of pure aluminum. I would go with the coated steel screws or aluminum screws. I think that would have the best chance of eliminating corrosion in the future.
Jay Bannister
--
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fderfler(at)gmail.com
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| Posted: Thu May 28, 2009 4:41 pm Post subject: Corrosion Around the Landing Light Window |
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In researching my own question, I found this informative chart at http://www.estainlesssteel.com/corrosion.shtml
Looks like I should be using some Zinc plated sheet metal screws. -- FJD
Guideline for Selection of Fasteners based on Galvanic Action
Fastener Metal
Zinc &
Galvanized
Steel
Aluminum &
Aluminum
Alloys
Steel and
Cast Iron
Brass, Copper,
Bronze, Monel
Martensitic
Stainless
(Type 410)
Austentic
Stainless
(Types 302,
303, 304, 305)
Base Metal
Zinc & Galvanized
Steel
A
B
B
C
C
C
Aluminum &
Aluminum Alloys
A
A
B
C
Not
Recommended
B
Steel and Cast
Iron
AD
A
A
C
C
B
Lead-Tin Plated
Sheets
ADE
AE
AE
C
C
B
Brass, Copper,
Bronze, Monel
ADE
AE
AE
A
A
B
Ferritic Stainless
(Type 430)
ADE
AE
AE
A
A
A
Austentic Stainless
(Type 302/304)
ADE
AE
AE
AE
A
AA - The corrosion of the base metal is not increased by the fastener
B - The corrosion of the base metal is marginally increased by the fastener
C - The corrosion of the base metal may be markedly increased by the fastener material
D - The plating on the fastener is rapidly consumed, leaving the bare fastener metal
E - The corrosion of the fastener is increased by the base metal
Note - Surface treatment and environment can change activity
Source - "Stainless Steel Fasteners A Systematic Approach To Their Selection" AISI 502-476-18M-CP
[quote][b]
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Thruster87
Joined: 16 Apr 2008
Posts: 193
Location: Australia
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| Posted: Thu May 28, 2009 9:04 pm Post subject: Re: Corrosion Around the Landing Light Window |
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A product called Duralac is what we use in the airline and restoration game for dissimilar metal contact especially SS to Al.Cheers [best to avoid it in the first place by using the cad plated screws]
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