Non-Chrome primers

S

Shadowcruzr

Active member
exMember
Joined
Jan 1, 2000
RO Number
1702
Messages
1,621
Does anyone know of a good non-chrome based primer? Looking at painting aluminum but need to prime with a non-hexavalient Chromium coating.
 
I take it the aluminum won't be seeing high temps. What is the aluminum used for and is it out of the weather or water? Do you want the aluminum to be shiny ala chrome?
 
We (USCG) are investigating using non-chrome etch chemicals, primers and paints for aircraft. We have several brands in use but the corrosion prevention is lacking. Knowing I was in the marine industry before, I was asked about what the marine industry uses. So I came here because of the large knowledge base.
So far everything points to chromates still being used. Alodine and Zinc chromates being most prevelant as listed in the sticky Sandy pointed out.
 
Paul- I'm just curious why chrome/chromates are prohibitive for your aircraft aluminum primer use. Toxicity, or reflectivity, or non-compatibility with special topcoats or alu alloys.....?
 
Nice to know the purpose.

Aluminum has a great affinity for oxygen and quickly starts to surface oxidize after cleaning with alumaprep. If you leave it exposed to air a little longer to allow the pores to surface oxidize before painting with the converter(alodine), you'll get a thicker and more evenly deposited oxidized surface.

I've used the same idea when preping and painting my exhaust manifolds. Sand blasting to remove all paint and oils. Dipping in muriatic/hydrochloric acid get the surface and pores clean. Then rinsing several times with water to develop an iron oxide haze(rusty surface) The thicker the rusty haze, the thicker the iron phosphate conversion will be after painting with phosphoric acid.

Alodine is likely phosphoric acid.

Oh yeah, Greg sent me the aluma prep and alodine before he even put up his aluminum treatment. My BII outdrive is still free from any corrosion. How many years has it been???
 
Sandy, The chromates, when inhaled are considered cancer causing agents.

I agree that the prep that Greg recommends works great on outdrives, but repeated working with it be it the painting and the driling and sanding later, are the reasons we are investigating alternatives.

WHen a painted surface with chromates is scracthed the chromates "fill in' the edge of the scratch and prohibit corrosion expansion. Without the chrome, the corrosion works its way under the paint at a rate twice as fast.

Michael, I will forward that link to our materials engineer. I'll let you know his comments.
 
Paul, My company used to sell a chromate primer - not for the industries being discussed here, but for packaging applications. We got out of the business partly because we did not want our workers exposed to airborne hexavalent chromium.

That said, you might find that in your application what is applied as hexavalent chromiumis actually reduced to trivalent chromium as it, and the paint, are applied then dried and cured. In its trivalent form chromium is not the same bad actor which is how it ends up on the inside of soda cans and in flexible packaging made with aluminum foil.

I fully understand the need to protect workers from the wet primer as its being applied, but its possible that the same problem does not exist after the primer is dry. I AM NOT A CHEMIST, but I do have a team of them who work for me. You should do an anaylis to see if you have the reduction to Cr III that I'm describing.

Jeff
 
Ask United how that non alodine prep worked for them. They ended up repainting the entire fleet years before they needed to and so will the CG if they do the same thing. Low VOC and water based aircraft paints ditto. Sometimes you just have to realize that aluminum is a bitch and you suit up for the using the good stuff on it and do it right once rather than doing it over and over again using twice as much stripper and chemicals than if you used the good stuff in the first place.
 
Thank you Jeff. I will mention your comments to the materials engineers.
GEEBEE: We repaint ours every 4 years. We found that non-chrome only lasts about 2 years.

Has anyone tried the Tri-Valent chrome Alodine 5900?
 
You must log in or register to reply here.
Back
Top