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Zinc Chromate Paint Replacement
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I have a serious galvanic corrosion problem where aluminum panels are riveted to steel plate. Previously, the steel plate was painted with a zinc chromate primer which worked OK. The current unsatisfactory system has an alkyd primer only on the steel. This application is truck trailers operating on salt laden roads in the upper Midwest.
What would be a paint replacement for the zinc chromate with comparable performance.
I am also curious about usage of zinc chromate paints. Is there much use today. If not, when did the use start to decline.
Thank you for any responses.
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Larry Hanke |
--Larry,
The use of zinc chromate virtually disappeared from use because of the word chromate. Since hexavalent chrome is a known carcinogen, the world has gone the same way that it did when it found that if you gave a lab rat the equivalent of 500 cokes with saccharin,he would have a higher rate of cancer. Zinc chromate is still available to commercial users but not over the counter. Most painters do not want the hassle of chrome bearing waste disposal so went to substitutes.
If it were me, I would talk to at least three painting giants like Sherwin-Williams engineering departments. There are many better products than what you are using, but will cost more. Then, will your painter apply it?
James Watts
- Navarre, Florida
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I would like to know a safe (an approved) alternative to zinc chromate primer TT-P-1757 [link is to spec at TechStreet]. Can you point me in the correct direction?
Dave Gubics
--It is my understanding that it is the chromate content of the paint that provides the corrosion protection for the aluminum.
Zinc or Aluminium rich paints protect steel wonderfully from corrosion by sacrificial means but do nothing for Aluminium alloys as the alloy corrodes to protect the paint. The chromate ions react with the Aluminium forming a tough skin over the surface.
As I am building a light aircraft I would like to see a safer system with equal performance to protect the all alloy structure
The alloys used are 2024 sheet riveted with 2017 rivets.
Any other comments?
Allan Gibson
--I hope that it gives someone pleasure to know, that while I was barreling down some salt laden interstate in the upper Midwest, drinking my saccharin free soft drink, and some rivets pop off of the oncoming truck, that I will never get cancer from the chromate it didn't use. (Don't he look natural?)
Tom Pullizzi
Falls Township, Pennsylvania
--Phosphating treatment may be a promising alternative to zinc chromate primer.
Ling Hao
- Grand Rapids, Michigan
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I have a big problem. I need to put the color blue zinc chromate on mild steel c12l14. The problem is that the chromate blue doesn't stick to the steel. Does anyone have a miracle solution for me?
Christian F [last name deleted for privacy by Editor]
--Christian:
Zinc plated parts are virtually always chromate conversion coated. To answer your question, if I am understanding the situation: a blue chromate works on a zinc plated surface, not on a steel surface. There is a chemical reaction between the zinc and the chromate, and it is the reaction products that "stick" to the surface of the zinc, not the chromate solution per se. So, in brief, the only way you will ever get it to stick is to zinc plate the parts.
Also, note that a "blue" chromate will only be very faintly blue.
But how did you get this carcinogenic, EPA-regulated chemical without the tech data sheet and the MSDS? You may be stuck with a bill to legally dispose of it. Good luck.
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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Colleagues:
Zinc chromate containing coatings are still readily available. However, with the drive to eliminate Cr+6 you may want to look for an alternative. General Motors specification GM7111M is a chrome-free product that performs exceptionally well against aluminum. Opel has another similar process as GME00255-B.
Edward Koneczny- Birmingham, Michigan
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I understand that there is a micaeceous iron oxide based paint that has been used on road chassis on trucks for many years. Is this true?
Why does it work and where can I get some?
Thanks in advance.
Hans Waltl- Durham, North Carolina
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I'm trying to find a Zinc Chromate Primer that I can apply to bare copper wire. I have installed copper wiring inside a dollhouse, and I need to seal it so when I apply a water base paint or wallpaper to the walls, the copper will not turn green. Currently the only size available to me is in one gallon size. Is there any other product available to do the same thing as the zinc chromate. Any help with this problem will be greatly appreciated. Thanks, David Roth- Carrollton, Texas April 2008 Hi, David. brass lacquer [linked by editor to product info at Amazon] would probably be the thing to use on copper to preserve its appearance. G.J. Nikolas specializes in this, but it sounds like you just need one little can. Good luck. Regards,
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FYI
Quote: "P&W -UTC concluded that
TT-P-664 [link is to spec at TechStreet]D High Solids (Zinc Phosphate) Primer and
TT-P-645 [link is to spec at TechStreet]B Zinc-Molybdate Primer are both acceptable alternatives to zinc chromate primer, with TT-P-664D being preferred, for providing galvanic corrosion protection for inserts and fasteners used in aircraft engines manufactured at P&W -UTC."
- Holly Springs, North Carolina
April 15, 2008
I want to know various options to protect Mild Steel surfaces, aluminium surfaces, and stainless Steel surfaces exposed to
1) high moisture conditions
2) saline moisture conditions
The options should be weighed over constraints like eco friendly, cost, and availability in this part of world.
- Mumbai, Maharastra, India
April 17, 2008Hi, Neeraj. That sounds like an appropriate subject for a 5-credit course if not a 4-year degree program :-)
For steel your choices include organic coatings such as paint and thermoset or thermoplastic powder coating on top of phosphatizing or electrocoating; and galvanized or electroplated inorganic coatings. For aluminum, eliminate the galvanizing but add chromating as an alternative to phosphating; and add anodizing in the inorganic category. For stainless, all of the alternatives for mild steel, plus passivation, electropolishing, or anodizing.
All of these are valid alternatives and are widely used, and none can be eliminated in an abstract discussion. But if you describe a particular piece part of a particular size and particular production volume, and add all of the additional constraints on the finish, the list may be shortened sufficiently that you can compare a few specific finishes. Good luck!
Regards,
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
April 3, 2010
I am preparing some 2024 aluminum parts for painting and carpet adhesion in an aircraft. The yellow zinc chromate primer spray can I had bought for this project turned out to have a defective nozzle and wouldn't spray. Not wanting to leave the aluminum unprotected after stripping, cleaning and Scotchbriting, I used a zinc rich primer that I had left over from another project for undercoating galvanized steel. Only after I had used it did I realize that it specified galvanized steel and not aluminum. Will I need to restrip this zinc-rich paint, and re-apply one formulated for aluminum? Have I done any damage to the aluminum by using this primer instead of a zinc chromate application for aluminum?
Coleman Weidenbusch- Plattsmouth, Nebraska, USA
November 15, 2011
A plethora of information is available on alternate primers.
Since there are so many experts all over the USA in the coatings field. I propose that we should have an annual get together at different sites, where we all can get together and exchange ideas, verbally in an informal setting, much like the Gordon Conferences in Chemistry.
Let me know what you all think.
Regards
- Novi, Michigan, USA