On Dec 9, 2012, at 8:34 AM, "Joe Preston" wrote:
Great comparison Russell. Did you compare weight between the two? I would love to see that as well.
Joe
Sent from my iPad Mini
On Dec 9, 2012, at 1:45, "Russell Williams" wrote:
> Both Tom and Jack are correct, you can get corrosion under either powder or paint. I think a lot of the argument boils down to religion and isn't based on fact. Here's the limited set of data I've been able to gather. Just for the record I prefer paint on my aircraft restorations, and use powder all the time on shop tooling & lawn furniture.
> My paint comparison point is an epoxy primer that includes strontium chromate for corrosion protection. I use Deft 44GN11 (BMS 10-11 spec) water soluble primer, and if the part is exposed I follow with an Imron urethane topcoat.
> I don't typically specify powder coat chemistry, and I think that if you care about corrosion protection, as opposed to shininess, you should specify a particular chemistry and type with your powder coater.
> Powder and primer + paint - ends up roughly same thickness *if applied correctly*, somewhere around 2 to 3 mil. I have noticed that many powder coaters tend to "lay it on thick". My belief is that thicker often leads to a higher chance of surface failure (cracks) which then leads to corrosion. I don't think there's any appreciable difference on coating on noticing an underlying crack in steel tubing but I have no data on which to back this up. My belief is that your likelihood of noticing a crack in tubing is more about color of the coating, white is going to be a lot easier to inspect than black because you'll see a hairline and likely some fretting residue or discoloration. My view: net equal.
> Discounting abrasion, which I think is the biggest compromise point on coatings and where corrosion most often starts - both coating technologies have some degree of porosity. With strontium chromate primer you get the benefit of the strontium chromate's chemical inhibition of corrosion in addition to the toughness of the epoxy film. Urethane paint is also highly corrosion resistant on top of the primer. With powder the corrosion resistance of the film depends on what powder chemistry gets used. Polyester base powders has so-so resistance, epoxy formulas are good but don't look as good. So you need to consult with your powder coater. If you don't ask you probably get the cheapest stuff that looks shiny. My view: advantage anti-corrosion epoxy primer + paint.
> Chemical resistance: epoxy powder is good - it cures to a cross-linked epoxy surface. Aircraft-grade urethane paint and epoxy primer is excellent. In fact the aircraft grade primers are designed to withstand regular exposure to skydrol and fuels which will often soften regular industrial paints and powder coats. That said, do you likely see skydrol on a GA aircraft? No. Do you get fuel exposure and hefty MEK solvent exposure when fabric covering? Yes. 44GN11 in particular laughs off prolonged MEK exposure. The powder coat datasheets I've seen hedge on resistance to MEK and other solvents warning of softening and surface failure with prolonged exposure (1 hr or more). My view: advantage epoxy primer + paint, but you may not care depending on application for example an engine mount.
> My belief is that corrosion resistance and surface quality & appearance often boil down to surface prep. If you use a powder coater usually you'll get an abrasive blast followed by some sort of chemical wash. To do a prime + paint job right you need to do something similar, I always blast followed by two solvent wipedowns to remove oils and residual dust. Net equal.
> Material cost - powder (at least the run of the mill stuff) is cheaper. Quality anti-corrosion epoxy primer and urethane paints are both very expensive. Advantage powder.
> You can get applicators for run of the mill powder quite easily, the labor is simpler and closer to unskilled. Harder to get labor for primer + urethane, you'll probably be doing it yourself or paying much more for the more intensive and skilled labor involved: the person painting has to be a decent painter, you apply two coats (really 4 once you count tack + cover spray passes) and painting tubular frame structures is a huge pain in the butt to get inside facing sides of tubes. Advantage powder.
> DIY ability: If you're doing small parts you can use or buy a small oven with powder. Unless you have infinite $$ and space it won't be economical to buy a powder oven big enough for an entire airframe, you'll need to use somebody else's. So you'll be having the vendor do the powder coating. I personally don't like giving up control on my restorations to laborers I don't know, so I prefer paint even thought it is a lot more work for me. Paint - with a paint gun, compressor, and forced air respirator (very important) you can safely paint pretty much anything of any size, but it will be a lot more work.
> Conclusion: I have an anti-corrosion fetish so I prefer using aircraft grade primer for the ultimate in corrosion protection. If BMS 10-11 primer is specified by Boeing and the air force I think it will work for me. The long-term anti-corrosion properties of strontium-chromate based epoxy primer have also been extensively studied. Not so much for powder beyond certification tests that I'm aware of, but maybe there is some data on this that somebody could contribute or point out.
> I also have quality control issues so I like to control all aspects of the process myself, and I'm very concerned with corrosion prevention, so I go with epoxy primer + urethane that I spray myself. However if you are more willing to delegate than I, or are working with easily replaceable parts, e.g. a kitplane part, then powder makes a lot of sense from a cost & labor/effort perspective if you are clear on the particular powder chemistry you're using (I'd recommend epoxy).
> That's my religion with a limited set of facts..
> To:
fairchildclub@yahoogroups.com
> From:
nc19143@comcast.net
> Date: Sun, 9 Dec 2012 05:02:26 +0000
> Subject: [fairchildclub] Re: advise
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> Metal can corrode under paint and it cannot be seen.
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> When the metal is preped as required by the powder coating it has less chance of corroding than if preped for paint.
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> Powder coating is a better protection than paint and has a much less chance of being broken and allowing corrosive material to get to the metal surface.
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> "Jack Threadgill" wrote:
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>> Metal can corrode under power coating and it cannot be seen. As stated the
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>> integrity of the metal is more difficult to inspect when power coated.
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>> Jack M. Threadgill
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>> 1602 Brook Hollow Dr
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>> Bryan, Texas 77802
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>> 979-779-7155
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>> threadgl@...
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>> From:
fairchildclub@yahoogroups.com [mailto:
fairchildclub@yahoogroups.com]
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>> On Behalf Of Tom_Downey
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>> Sent: Saturday, December 08, 2012 7:31 PM
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>> To:
fairchildclub@yahoogroups.com
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>> Subject: [fairchildclub] Re: advise
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>> So does paint, at about the same rate. After all, powder coating is only
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>> powdered paint applied by heat.
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>> --- In
fairchildclub@yahoogroups.com
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>> , Jim wrote:
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>>> Powder coating prevents proper inspections in the future. It hides cracks
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>>> Jim Higham
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>>> N81207
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>>> F24R46-108
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>>> On Dec 7, 2012, at 8:52 AM, Jeffrey Whitesell wrote:
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>>>> Thanks, gentlemen. what your feeling on powdercoating?
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>>>> Jeff
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>>>> On Dec 7, 2012, at 8:09 AM, Cy Galley wrote:
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>>>>> Funny, The military used Yellow Zinc chromate for most anything on
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>> aircraft.
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>>>>> Today, Epoxy primers are a must as the paint solvents and fabric
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>> liquids
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>>>>> will dissolve most anything leaving the substrate unprotected. Use
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>> whatever
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>>>>> color you think you want or need.
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>>>>> From:
fairchildclub@yahoogroups.com
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>> [mailto:
fairchildclub@yahoogroups.com
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>>>>> On Behalf Of Tom_Downey
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>>>>> Sent: Friday, December 07, 2012 9:20 AM
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>>>>> To:
fairchildclub@yahoogroups.com
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>>>>> Subject: [fairchildclub] Re: advise
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>>>>> Actually the fuselage frame is 4130 steel, Zink Chromate is for
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>> aluminum and
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>>>>> Iron oxide primers are for steel.
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>>>>> --- In
fairchildclub@yahoogroups.com
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>>>>> , james chybicki
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>>>>> wrote:
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>>>>>> I've seen black, red, green, blue, Zinc Yellow....
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>>>>>> I guess it all depends on your need
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>>>>>> My frame was zinc-green primer and then Polurathane Green over that
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>> to
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>>>>> match our WOrld War 2 color scheme on our UC-61K
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>>>>>> Jim Â
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>>>>>> From: Jeffrey Whitesell
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>>>>>> To:
fairchildclub@yahoogroups.com
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>>>>>> Sent: Friday, December 7, 2012 12:40 AM
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>>>>>> Subject: [fairchildclub] advise
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>>>>>> Â
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>>>>>> If a fellow is restoring a F24 46R, what color should the frame be
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>>>>> painted?
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>>>>>> Jeff
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>>>>>> ---
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>>>>>> Jeff Whitesell
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>>>>>> mailto:topfun%40fivetogether.com
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>>>>>> [Non-text portions of this message have been removed]
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>>>>> [Non-text portions of this message have been removed]
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>>>> ---
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>>>> Jeff Whitesell
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>>>> topfun@
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