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letter 702
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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
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
I 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
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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?)
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Tom Pullizzi |
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
--Christian:
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 a tech data sheet and the MSDS? You may be stuck with a very large bill to legally dispose of it.
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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
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 , 2008Hi, David. Brass Lacquer would probably be the thing to use on copper to preserve its appearance. Our supporting advertiser G.J. Nikolas specializes in this, but it sounds like you just need one little can. Good luck.
Regards,
Ted Mooney
finishing.com
Brick, New Jersey
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."
Everett Tsosie
- Holly Springs, NC
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April 15, 2008 I want to know various options to protect Mild Steel
surfaces, aluminium surfaces, and stainless Steel surfaces
exposed to NEERAJ SHARMA
April 17, 2008 Hi, Neeraj. That sounds like an appropriate subject for a full 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,
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