Zenith Aircraft Builders and Flyers
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powder coat
Replies to This Discussion
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Permalink Reply by Tim Treat on
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Hmmm. I like this idea. I used to pcoat all of my racecar frames. Since it is baked on, I wonder if the heating process warps the skin. did you pcoat before riveting or after?
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It was light, durable, and resisted chemicals. The only downside was when it came time to repair. It's a chore to grind it off to weld the frame. Also, it hides stress cracks pretty well. I think it would be great on a plane. I built a Cobra kit car and I did all the aluminum sheet metal in gloss black and riveted it after powdercoating to give it a military type look with aluminum rivets on black coating.
Powdercoating is applied dry to the with an electrostatic charge. Then the baking melts the plastic coating. I have never seen a run. I love the stuff too.
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Permalink Reply by Bob Pustell on
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My concern (while not really knowing if it is a valid concern or not) would the heat used to melt/bond the powder onto the part. 6061 T6 is heat treated (the "T" in the code indicates heat treatment to condition 6) and I know that heat can reverse the tempering process. I do not know how much heat. You may want to research the effect, if any, of the temp and duration of time at that temp on your structure.
I know that Grove recommends against powder coating their landing gear assemblies because the heat of the powder coating can weaken the part by removing the heat treatment from the metal. Grove uses a different alloy of aluminum, but it is the heat treating we are worried about here, not the alloy.
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Permalink Reply by Louis W. Ott on
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I checked the heat treating and annealing of 6061 aluminum and came up with this information. It looks like 400 degrees F is above the temperature used to age the 6061 after heat treating, but less than the annealing temp. You may end up with aluminum that is harder than T6 and possibly more brittle. However, it is hard to estimate what would happen with the powder coat 2nd "aging" process so long after the original aging.
>>>>
HEAT TREATMENT
Solution heat treat at 990°F for adequate time to allow for thorough heating and then water quenched. Precipitation hardening is done at 320°F for 18 hours and air cool, followed by 350°F for 8 hours and air cooled.ANNEALING
Annealing should be done at 775°F for at 2 to 3 hours at temperature, followed by controlled cooling at 50°F per hour down to 500°F then air cooled.
AGING
The aging precipitation heat treatment is done at 350°F for 8 hours followed by air cooling. This produces the T6 temper.>>>
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Permalink Reply by Chris Aysen on
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Louis - Very good research. The problem here is material thickness. My personal experience is that a thin enough material such as .016 6061 T6 it can be annealed at a much lower temperature than 775 F. I annealed the nose partial of my flaperon nose ribs, horizontal, and elevator nose ribs before forming at about the 400 F mark.
Kenneth - Cut your self some 6 inch square pieces of .016 one before powdercoating and one after. Bend them completely (do not use any type of radius bending) in half and notice when they fracture. If they fracture at the same point your probably OK (make sure grain direction [across grain] is the same on both bends). If the powdercoat one bends more or substantially less you may want to reconsider. Just play it safe.
Safe Flying!
Chris
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Permalink Reply by Ken Ryan on
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I don't have access to the entire article, but I did find this:
The effects of curing temperature, based on new, low-temperature powder coating methods and traditional high-temperature powder coating methods, were studied. Heat-sensitive aluminum alloys (2024-T3, 6061-T6, and 7075-T6) were subjected to two different heat-treatment cycles, which were based on temperatures of 121 and 204 °C. Findings indicate that although both cure temperatures achieved powder coatings adhesion and thickness appropriate for industrial uses, the high-temperature cure treatment negatively affected the mechanical properties.
Journal of Materials Engineering and Performance, Volume 18, Issue 1, pp.70-78
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Permalink Reply by John Austin on
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FWIW, I read "somewhere" on the web that since powdercoat forms a plastic coating, if it is later penetrated - say with a screw or cutting a hole for a modification, etc., - moisture can "creep"under the plastic coating and cause concealed corrosion. I have NO personal experience, it's just something that was mentioned on a website. YMMV!
Regards,
John
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Permalink Reply by mike blemenschutz on
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Im not sure of the weight issue but for me i would concerned with the flexability of the powder coating. it my be more susseptable to cracking and peeling than aircraft coatings which stay highly flexable which is really important on our light skinned aircraft.
Good luck
mike
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Permalink Reply by Ben Haas on
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My gut feeling is the 400f heat will harm the heat treatment of the 6061T6. I cannot fathom the skins didn't warp / wrinkle any... And I would question whether the cortec was altered by the high temp.. As a disclaimer.. I LOVE Powder coating and all my steel parts on my 801 were done in a nice shade of blue.... Hope it all works out for you sir.
Ben
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Permalink Reply by Paul Bonasera on
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I believe all powder coating will leave an orange peel finish. For the WT. you could give them a one foot SQ. of alum. and have them coat that and take another and paint it as you would the plane, then you could compare the two. Paul
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Kenneth - If your happy with your decision then go with it. I doubt the plane will just fall apart on you. This is the experimental world and I'm kinda curious to see how it turns out.
Safe Flying.
Chris
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Permalink Reply by Craig Payne on
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The easiest way I have found to remove powder coat is carb cleaner. Spray it on, wait, wipe it off.
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