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Corrosion protection
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Alf



Joined: 31 Jul 2008
Posts: 5
Location: Louisiana

PostPosted: Thu Jul 31, 2008 6:49 pm    Post subject: Corrosion protection Reply with quote

Hi,

I am new to this forum. After searching for info. about corrosion protection I have a question.

Cortec seems to be favored by ZAC but I noticed in one post that it was dissolved by fuel. Does anybody knows how would it react with Corrosion-X?

I ask this because that is the sequence of protection I have in mind, i.e.: use Cortec first (interior surfaces, spars, etc...), then apply Corrosion-X every year or two.

Does it makes sense?

Thanks for any help.

601-XL


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Thruster87



Joined: 16 Apr 2008
Posts: 193
Location: Australia

PostPosted: Fri Aug 01, 2008 2:06 am    Post subject: Re: Corrosion protection Reply with quote

VpCI™-373Description: VpCI™-373 is a water-based wash primer. VpCI™-373 is used for bonding other primers and coatings such as VpCI™-386 to a variety of metal substrates. Cortec VCI 373 to my understanding is NOT a corrosion prevention coating such as alodine is, but a surface adhesion coating so that other primers/coatings bond to it.Also remember NOT to use etch primers with alodine as it will damage the protective coating. That's why I decided to use the Aluprep,Alodine and Zinc Oxide coating system on the inside structure other then the skins where I use Ardrox spray [dimitrol].For the outside skins I'll use Pre-Kote then a two part primer then a two part top coat [automotive paint made by Valspar] Cheers

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chuck_maggart



Joined: 20 Mar 2007
Posts: 16
Location: St. Louis

PostPosted: Fri Aug 01, 2008 8:16 am    Post subject: Corrosion protection Reply with quote

Alf, I don't know about Corrosion X, but I used Cortec and it does a good job and easy to apply. However; I have one issue with it because it remains soft and sticky. Small metal shavings and filings and dirt are impossible to vacuum up and items, like seat cushions, will melt to it. If I did it again I would consider zinc oxide.

Chuck M.
601XL ready to fly
[quote][b]


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Alf



Joined: 31 Jul 2008
Posts: 5
Location: Louisiana

PostPosted: Fri Aug 01, 2008 9:15 am    Post subject: Re: Corrosion protection Reply with quote

Thanks. It clarifies a lot about Cortec 373 but also brings some more confusion. You mention NOT to use etch primers but it is my understanding that Aluprep is an etching solution. In your case you would be etching the aluminum before the Alodine.

Please correct me if I am wrong.

Thruster87 wrote:
VpCI™-373Description: VpCI™-373 is a water-based wash primer. VpCI™-373 is used for bonding other primers and coatings such as VpCI™-386 to a variety of metal substrates. Cortec VCI 373 to my understanding is NOT a corrosion prevention coating such as alodine is, but a surface adhesion coating so that other primers/coatings bond to it.Also remember NOT to use etch primers with alodine as it will damage the protective coating. That's why I decided to use the Aluprep,Alodine and Zinc Oxide coating system on the inside structure other then the skins where I use Ardrox spray [dimitrol].For the outside skins I'll use Pre-Kote then a two part primer then a two part top coat [automotive paint made by Valspar] Cheers


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Thruster87



Joined: 16 Apr 2008
Posts: 193
Location: Australia

PostPosted: Fri Aug 01, 2008 2:15 pm    Post subject: Re: Corrosion protection Reply with quote

Hi Alf The reason you use aluprep is to remove any oxide etc from the surface so that the alodine will work.You can tell if the surface is clean enough by pouring water on the surface and it will adhere /run nicely on it.Alodine produces a chemical reaction with the aluminum surface a bit like electro plating and this layer would be removed or damaged if you then use an etch primer. Cheers

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Alf



Joined: 31 Jul 2008
Posts: 5
Location: Louisiana

PostPosted: Mon Aug 04, 2008 9:18 pm    Post subject: Re: Corrosion protection Reply with quote

Got it. Thanks for the info.
.
Thruster87 wrote:
Hi Alf The reason you use aluprep is to remove any oxide etc from the surface so that the alodine will work.You can tell if the surface is clean enough by pouring water on the surface and it will adhere /run nicely on it.Alodine produces a chemical reaction with the aluminum surface a bit like electro plating and this layer would be removed or damaged if you then use an etch primer. Cheers


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Alf



Joined: 31 Jul 2008
Posts: 5
Location: Louisiana

PostPosted: Tue Aug 05, 2008 1:47 pm    Post subject: Re: Corrosion protection Reply with quote

Alf wrote:
Got it. Thanks for the info. again, but when I went to order it I found TWO types of Aluprep, the BP Cleaner and the BP Zincate II. Logic tells me it is the Cleaner the one I need. Am I right?

Thanks again for your help.
.
Thruster87 wrote:
Hi Alf The reason you use aluprep is to remove any oxide etc from the surface so that the alodine will work.You can tell if the surface is clean enough by pouring water on the surface and it will adhere /run nicely on it.Alodine produces a chemical reaction with the aluminum surface a bit like electro plating and this layer would be removed or damaged if you then use an etch primer. Cheers


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jimandmandy(at)yahoo.com
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PostPosted: Tue Aug 05, 2008 2:16 pm    Post subject: Corrosion protection Reply with quote

Metal Prep #79 or Alumiprep #33 (for corroded aluminum) are the recommended clean and
etch agents to use before Alodine. I tried Alodine without using a prep, just a solvent wipe, and it didnt "take".

--- On Tue, 8/5/08, Alf <alebron(at)bellsouth.net> wrote:
[quote]From: Alf <alebron(at)bellsouth.net>
Subject: Re: Corrosion protection
To: zenith601-list(at)matronics.com
Date: Tuesday, August 5, 2008, 2:47 PM

[quote]--> Zenith601-List message posted by: "Alf"
<alebron(at)bellsouth.net>
Alf wrote:
Quote:
Got it. Thanks for the info. again, but when I went to order it I found
TWO types of Aluprep, the BP Cleaner and the BP Zincate II. Logic tells me it is

the Cleaner the one I need. Am I [quote][b]


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Thruster87



Joined: 16 Apr 2008
Posts: 193
Location: Australia

PostPosted: Wed Aug 06, 2008 3:12 am    Post subject: Re: Corrosion protection Reply with quote

Howdy, As mentioned earlier Alumiprep 33 is the go, it's my choice.It works like a charm using it with the green Scotch bright pads. Cheers

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dalemed



Joined: 25 Dec 2007
Posts: 46

PostPosted: Wed Aug 13, 2008 6:11 pm    Post subject: Re: Corrosion protection Reply with quote

Why are people using primer on 6061T6? Do they live near the ocean?

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Alf



Joined: 31 Jul 2008
Posts: 5
Location: Louisiana

PostPosted: Wed Aug 13, 2008 6:27 pm    Post subject: Re: Corrosion protection Reply with quote

dalemed wrote:
Why are people using primer on 6061T6? Do they live near the ocean?


I live about 30 miles from the Gulf Coast and any flying would be much less than that distance from salt water should I decide to go to East or West.

Only a few drops of sweat were enough to start some corrosion on the surface of my stabilator. That was enough for me to start considering protection.


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carlossa52(at)gmail.com
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PostPosted: Wed Aug 13, 2008 6:31 pm    Post subject: Corrosion protection Reply with quote

Not necessarily - people have seen corrosion on stored sheets in many different occasions, see archives.
Look at it this way: you will not regret having your plane primed, while not having it primed may cause regret.


Cheers
Carlos
CH601-HD, plans
Montreal, Canada

2008/8/13 dalemed <dalemed(at)gmail.com (dalemed(at)gmail.com)>
[quote] --> Zenith601-List message posted by: "dalemed" <dalemed(at)gmail.com (dalemed(at)gmail.com)>

Why are people using primer on 6061T6? Do they live near the ocean?

--------
Dale
Flying Cessna 170B
Building Zenith 601XL


[b]


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PostPosted: Wed Aug 13, 2008 7:11 pm    Post subject: Corrosion protection Reply with quote

[quote][b]

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dalemed



Joined: 25 Dec 2007
Posts: 46

PostPosted: Thu Aug 14, 2008 7:33 am    Post subject: Re: Corrosion protection Reply with quote

carlossa52(at)gmail.com wrote:
...
Look at it this way: you will not regret having your plane primed, while not having it primed may cause regret.


I'm not so sure of that. I've used primer on my tail surfaces - zinc oxide brushed on some and a self etching spray on some others. I have some regrets because I'm not sure I've done it properly. Have I properly prepared the surface? Have I put on the proper thickness? These are nagging questions that I wouldn't have if I hadn't primed.

I've heard that airplane manufacturers used to be (back in the 40s and 50s at least) prohibited from priming surfaces before they were mated. Surfaces were primed after assembly or not at all. These days, we seem to be encouraged to prime before assembly.

I guess this is all part of the educational aspects of homebuilding!

Cheers,


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Thruster87



Joined: 16 Apr 2008
Posts: 193
Location: Australia

PostPosted: Thu Aug 14, 2008 1:18 pm    Post subject: Re: Corrosion protection Reply with quote

I've heard that airplane manufacturers used to be (back in the 40s and 50s at least) prohibited from priming surfaces before they were mated. Surfaces were primed after assembly or not at all. These days, we seem to be encouraged to prime before assembly. I 'm part of an old farts club that restores vintage a/c like the C47 and most of the parts were primed prior to assembly.In the next hangar they are restoring warbirds like the P47 and they were primed.One interesting thing was the way they de-burred the parts by just using a sanding disc as you can still see the scratches [looks like 80-100 grit].Seems like they were in a hurry and it appears [they havn't come across any]they didn't develop any stress fractures due to this method of de-burring.

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planecrazydld(at)yahoo.co
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PostPosted: Thu Aug 14, 2008 2:11 pm    Post subject: Corrosion protection Reply with quote

just remember that they did not understand fatigue well until after the war in the beginning of the jet era. Also, the old transports and fighters were "throwaway" hardware with very short specification lives. I don't think I would allow a bad practice then to define/over ride todays understanding and evidence.

David L. Downey
Harleysville (SE) PA, USA


--- On Thu, 8/14/08, Thruster87 <alania(at)optusnet.com.au> wrote:
[quote]From: Thruster87 <alania(at)optusnet.com.au>
Subject: Re: Corrosion protection
To: zenith601-list(at)matronics.com
Date: Thursday, August 14, 2008, 5:18 PM

[quote]--> Zenith601-List message posted by: "Thruster87"
<alania(at)optusnet.com.au>

I've heard that airplane manufacturers used to be (back in the 40s and 50s
at least) prohibited from priming surfaces before they were mated. Surfaces were
primed after assembly or not at all. These days, we seem to be encouraged to
prime before assembly.

I 'm part of
an old farts club that restores vintage a/c like the C47 and most of the parts
were primed prior to assembly.In the next hangar they are restoring warbirds
like the P47 and they were primed.One interesting thing was the way they
de-burred the parts by just using a sanding disc as you can still see the
scratches [looks like 80-100 grit].Seems like they were in a hurry and it
appears [they havn't come across [quote][b]


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Thruster87



Joined: 16 Apr 2008
Posts: 193
Location: Australia

PostPosted: Thu Aug 14, 2008 9:20 pm    Post subject: Re: Corrosion protection Reply with quote

Early 50's models of the de Havilland Comet suffered from catastrophic metal fatigue, causing a string of well-publicised accidents. As they found out how stress risers are a lot more critical on pressurized aircraft but do not under estimate there importance.

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z601(at)anemicaardvark.co
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PostPosted: Fri Aug 15, 2008 12:14 pm    Post subject: Corrosion protection Reply with quote

On Friday 15 August 2008 00:20, Thruster87 wrote:
Quote:


Early 50's models of the de Havilland Comet suffered from catastrophic
metal fatigue, causing a string of well-publicised accidents. As they found
out how stress risers are a lot more critical on pressurized aircraft but
do not under estimate there importance.

I could be mistaken, but I believe the metal fatigue in the case of the Comet
was due to a structural aerodynamic problem. That is, there was structural
resonance within the airframe. The additional energy imparted by the (then)
much higher airspeeds caused the resonance to surface, which in turn flexed
the metal, causing the fatigue, and ultimate failure.
--
=================================================
Jim B. Belcher
BS, MS Physics, math, Computer Science
A&P/IA
Instrument Rated Pilot
General Radio Telephone Certificate
=================================================


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PostPosted: Fri Aug 15, 2008 12:36 pm    Post subject: Corrosion protection Reply with quote

http://en.wikipedia.org/wiki/De_Havilland_Comet

"Engineers subjected an identical airframe, G-ALYU ("Yoke Uncle"), to
repeated re-pressurisation and over-pressurisation and after 3,057 flight
cycles (1,221 actual and 1,836 simulated), Yoke Uncle failed due to metal
fatigue near the front port-side escape hatch.[13] Investigators began
considering fatigue as the most likely cause of both accidents and initiated
further research into measurable strain on the skin. Stress around the
window corners was found to be much higher than expected, "probably over
40,000 psi," and stresses on the skin were generally more than previously
expected or tested. This was due to stress concentration, a consequence of
the window's square shape.

The problem was exacerbated by the punch rivet construction technique
employed. The windows had been engineered to be glued and riveted, but had
been punch riveted only. Unlike drill riveting, the imperfect nature of the
hole created by punch riveting may cause the start of fatigue cracks around
the rivet.

The principal investigator concluded, "In the light of known properties of
the aluminium alloy D.T.D. 546 or 746 of which the skin was made and in
accordance with the advice I received from my Assessors, I accept the
conclusion of RAE that this is a sufficient explanation of the failure of
the cabin skin of Yoke Uncle by fatigue after a small number, namely, 3,060
cycles of pressurisation."[14]

Before the Elba accident, G-ALYP had made 1,290 pressurised flights and at
the time of the Naples accident, and G-ALYY had made 900 pressurised
flights. Walker said he was not surprised by this, noting that the
difference was about 3 to 1 and previous experience with metal fatigue
suggested a total range of 9 to 1 between experiment and outcome in the
field could result in failure. Thus, if the tank test result was "typical,"
aircraft failures could be expected at anywhere from 1000 to 9000 cycles. By
then, the RAE had reconstructed about two-thirds of G-ALYP at Farnborough
and found fatigue crack growth from a rivet hole at the low-drag fiberglass
forward "window" around the Automatic Direction Finder, which had caused a
catastrophic breakup of the aircraft in high altitude flight."

-- Craig

Do not archive

--


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PostPosted: Fri Aug 15, 2008 12:40 pm    Post subject: Corrosion protection Reply with quote

All of the data published since the mid 60s points to very specific fatigue critical geometry around the windows. Speed was not even involved, pressurization cycles were the specific cause identified in the failure of the fuselage surrounding the windows and escape hatches.

David L. Downey
Harleysville (SE) PA, USA


--- On Fri, 8/15/08, Jim Belcher <z601(at)anemicaardvark.com> wrote:
[quote]From: Jim Belcher <z601(at)anemicaardvark.com>
Subject: Re: Re: Corrosion protection
To: zenith601-list(at)matronics.com
Date: Friday, August 15, 2008, 4:16 PM

[quote]--> Zenith601-List message posted by: Jim Belcher
<z601(at)anemicaardvark.com>

On Friday 15 August 2008 00:20, Thruster87 wrote:
Quote:
--> Zenith601-List message posted by: "Thruster87"
<alania(at)optusnet.com.au>

Quote:

Early 50's models of the de Havilland Comet suffered from catastrophic
metal fatigue, causing a string of well-publicised accidents. As they
found

Quote:
out how stress risers are a lot more critical on pressurized aircraft but
do not under estimate there importance.

I could be mistaken, but I believe the metal fatigue in the case of the Comet
was due to a structural aerodynamic problem. That is, there was structural
resonance within the airframe. The additional energy imparted by the (then)
much higher airspeeds caused the resonance to surface, which in turn flexed
the metal, causing the fatigue, and ultimate failure.
--
=================================================
Jim B. Belcher
BS, MS Physics, math, Computer [quote][b]


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