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Painting metal parts

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asarangan(at)yahoo.com
Guest

Posted: Mon May 07, 2007 7:56 pm Post subject: Painting metal parts

I know nothing about painting, except for routine touchups I have done

around the house. Now I have to decide how to paint Europa's external

metal parts such as flap arms. All my metal parts have been treated

with  alodine and sprayed with zinc chromate. I am assuming that no

further primer is needed before top coat. But what kind of top coat

should I use? Can I use the garden variety Krylon brand spray paint

from the hardware store? Any special considerations? 



Any insights would be greatly appreciated.

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hagargs(at)earthlink.net
Guest

Posted: Mon May 07, 2007 8:19 pm Post subject: Painting metal parts

Why not go with powder coating it is more durable than paint and looks good

too.

Everything metal part I could fit in my oven got powder coated.



Steve  Hagar

a143

Mesa AZ



Just finished mod 72

 	  Quote: 	
		   [Original Message]

 From: Andrew Sarangan <asarangan(at)yahoo.com>

 To: <europa-list(at)matronics.com>

 Date: 5/7/2007 8:59:38 PM

 Subject: Painting metal parts



 

 I know nothing about painting, except for routine touchups I have done

 around the house. Now I have to decide how to paint Europa's external

 metal parts such as flap arms. All my metal parts have been treated

 with  alodine and sprayed with zinc chromate. I am assuming that no

 further primer is needed before top coat. But what kind of top coat

 should I use? Can I use the garden variety Krylon brand spray paint

 from the hardware store? Any special considerations? 



 Any insights would be greatly appreciated.

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue May 08, 2007 4:48 am Post subject: Re: Painting metal parts

Andrew,



I did some of both in A224.  Risks and benefits to both methods, paint and 

powder. In very brief

spray paint scratches off very easily, 2 part epoxy is much tougher

powder coating will conceal cracks in critical areas like welds

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_________________
Ira N224XS

rparigor(at)suffolk.lib.n
Guest

Posted: Tue May 08, 2007 7:08 am Post subject: Painting metal parts

Hello Andrew



Watch the temperature used with powder coat, you can kill the temper on

aluminium parts. Some powders require temps too high for tempered

aluminium. Even if you have a lower temp powder, make sure oven does not

overheat part. I didn't powder coat anything as of this moment, but if I

do, will use Thermal color indicating telltales along side my parts to

make sure over temp did not occur.



I fooled with at least a dozen cans of spray primers, self etch, zinc

oxide and zinc chromate. Also fooled with Dupont self etch in gun.



Some cans work OK as far as adhesion and things went downhill from there.

The Dupont stuck OK, but either the DPLF or DCC did not adhere well to it.

Most companies do not advocate using other companies product. I think

scuff sanding was part of the problem with the self etch, it filled the

sanding scores and volatiles were probably trapped because it was on too

thick in those areas.



My choice of paint is PPG DELTRON  

http://www.pwpaints.com/ppg-p-sheets.html

DPLF as the Epoxy Primer can be used on metal and airframe. On airframe I

apply a very thin coat as an adhesion promoter, then wait for a full cure

(many days), then light scuff and K36 high build primer to fill, then DPLF

to seal and DCC Concept as top coat. The reason for DPLF on airframe first

is as a adhesion promoter, and an attempt to seal porous surface from

volatiles getting trapped if I were to use K36 first. Put paint in direct

sunlight and let it heat up, and pimples will appear if you have volatiles

hidden below your spectacular paint job.



On metal, trying DCC on top of all the primers I tried works from OK to

poor. Not great adhesion. I tried DPLF on top of the primers then topcoat,

and again OK to poor adhesion.



Scuffing metal and putting DPLF on it, WOW. It sticks incredable. On all

metal parts they get sanded or sand blasted with Aluminium Oxide media,

DPLF, and then top coated. If metal is permanent stuck to the airframe,

they just get painted along with the airframe. If needed you can use K36

high build primer over DPLF to fill imperfections on metal.



Make absolute sure that the volatiles have evaporated before putting on

next type of paint. That includes whatever you decide to clean surface

with. If you were to topcoat too soon over a not full cured primer,

adhesion would be not too good between paints. You sometimes can peel

layer off and actually smell volatiles years after paint.



Just a side note, JB Weld (JB KWIK) is a great pinhole (and scratch)

filler. It is very thick and stays put. If you use a 1+1/4" flexible putty

knife to apply and scrape, then a very sharp razor blade to squeegee, all

that is left is pinholes and sanding marks filled. Amazing. The regular JB

Weld long cure is not as thick and does not work anywhere near as well. JB

KWIK is harder to sand than Expancel, so not a great idea to fill anything

other than pinholes or scratches where you can squeegee off almost all

excess. 



Good Luck

Ron Parigoris

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Dave Miller

Joined: 10 Jan 2006
Posts: 51

Posted: Tue May 08, 2007 9:51 am Post subject: Painting metal parts

Ron, 

 

I'm pleased to see there is another JB Weld fan out there. 

I use it around the house, will stick just about anything to anything. 

Also good for little jobs on the plane, such as bonding the nut to the washer in the throttle friction set up. 

 

Dave A061 

 

do not archive [quote][b]

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robh(at)hyperion-ef.com
Guest

Posted: Tue May 08, 2007 10:48 am Post subject: Painting metal parts

You are on the right track because Alodine and zinc chromate each provide a

good basis for making coatings stick to aluminum.  Do not try painting

aluminum without pre-treatment because the naturally formed oxide on the

surface will prevent any coating from sticking.  At first the coating will

seem OK but it won't take long for the coating to lift off the substrate.  



Here's a link that answers your question with a bit more detail:

http://www.ronjoseph.com/Q&A/B2001_painting_aluminum.htm

Best regards,



Rob Housman

Irvine, California

Europa XS Tri-Gear

S/N A070

Airframe complete



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rparigor(at)suffolk.lib.n
Guest

Posted: Tue May 08, 2007 1:39 pm Post subject: Painting metal parts

Hello Rob



There are more than 1 way to skin a cat or paint metal on a Europa. If you

read the link you posted:



http://www.ronjoseph.com/Q&A/B2001_painting_aluminum.htm 



bout half way down:



Q: What would a common procedure be to resurface a corrosion pitted marine

motor outdrive (mercury-aluminum outdrive).  I have heard that 2 part

paints and epoxies have incredible adhesive properties as well as

corrosion resistance, but what would be recommended in this application?



A: An epoxy primer followed by a polyurethane topcoat is still my number

one choice, but the real issue is cleaning up the pits in the motor

outdrive. Once the pits have been thoroughly cleaned, your friend will

need to immediately apply the epoxy primer. By immediate, I mean within a

few hours and not the following day. One method to clean the pits and

prepare the surface is by abrasive blasting with glass beads. But your

friend will probably need to take the drive to a ob shop to have this

done. In the industrial world the drive would probably be pretreated with

a chromate conversion coating, but in all likelihood your friend won't

have access to this process, unless he/she is willing to take the drive to

a job shop that has the capabilities of pretreating aluminum. (Many job

shops can blast clean the surface with glass beads and pretreat in a

conversion coating).



Glass beading is very bad advise though. Glass beading creates rounded

scratches that do not bode well for adhesion. Sharp media is needed.

Downside to 2 part Epoxy or powder coating is like stated you must paint

shortly after you sand. You can apply DPLF over Alodined parts though. If

acid creeps somewhere it is not supposed to be and you can't get it out

that will do no good for the long term.



I provided link for manual for paints, here is one for DPLF:

http://www.pwpaints.com/images/downloads/dplf-p-196.pdf



1 note on self etching zinc primers, they use acid to etch the surface,

half or more of the magic provided by zinc is used up to neutralize the

acid! I know many folk coat aluminium with zinc primer, but it is porous

and for best corrosion properties, sealer is needed.



PPG and Dupont have technicians you can talk to, whoever system you

choose, don't be bashful to call. Or if you are going to have your plane

painted by someone, now is a good time to perhaps talk to a few shops and

get their opinion on painting various materials and what to use.



No matter what you decide, try on something other than your aeroplane

parts first, and always have a sample you can do a scratch test then heat.

You will learn a lot, 3M 375 packaging tape is pretty aggressive, use it

to try and lift paint, use dental tools for adhesion testing.



Ron Parigoris

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robh(at)hyperion-ef.com
Guest

Posted: Tue May 08, 2007 4:01 pm Post subject: Painting metal parts

Agreed, Ron, there are several ways to do the job.  My main point was that

aluminum MUST be treated in some fashion in order to make any paint adhere.

In your link to dplf-p-196 the footnote for painting aluminum addresses this

point, "+ Film build of 1.2-1.5 mils of DPLF is required or the surface must

be treated with Metal Cleaner/Conditioner or coated with DX 1791/1792."



However, in my view, MIL-DTL-81706B makes a rather strong case for using a

conversion coating prior to painting. Links to this specificaiton and other

relevant stuff are available at

http://www.chemical-supermarket.com/Henkel_Alodine_1201_Chromate_Conversion_

Coating-p364.html



Alodine provides corrosion resistance and promotes adhesion of the

subsequent organic coating to aluminum, and its application is relatively

quick and painless.  True, we are playing with chemicals here so a certain

amount of caution is required but the chemistry is nowhere near as hazardous

to work with as oven cleaners or drain cleaners.  Henkel, incidentally, is

the owner of the Alodine trademark.

Best regards,



Rob Housman

Irvine, California

Europa XS Tri-Gear

S/N A070

Airframe complete

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asarangan(at)YAHOO.COM
Guest

Posted: Tue May 08, 2007 7:22 pm Post subject: Painting metal parts

If I may add, Alodine process is really quite simple and not as messy

as it is portrayed. The key is to have pre-mixed phosphoric etch (Metal

Prep 79), Alodine 1201 and water in separate plastic buckets with air

tight lids. When ready for the process, open the bucket, drop the

aluminum part, and close the bucket. Then use a plastic tong to

retrieve it. Usually I don't even spill a single drop, and is clean and

mess-free. If you minimize the time the bucket lids are open, you don't

even have to wear breathing apparatus. The chromic acid is nasty

smelling fume so you obviously don't want to inhale too much. I would

rate this process as significantly less messier and hazardous compared

to trimming fiberglass with a dremel.



Most of the messy problems with alodine happened when I tried to mix

the solutions for each use. I ended up with lots of spills, as well as

permament discoloration of shop floor.

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