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Formulation for Green Chromate on cyanide zinc plating
Hello!
I am a metallurgy engineer. I have a cyanide zinc electroplating industry. I use the green chromate coating that I buy from a company. My bath composition is: chromic acid (10% wt)-sulfuric acid (5%)-nitric acid (5%)-phosphoric acid (10%)-HCl (5%)
TEMPERATURE=80-90° C TIME=30-60 Sec.
MY COATING'S COLOR IS BLACK GREEN with iridescent shadow. why is the shadow created?
why is the color black green?
which material will build the green color in my composition?
- Tehran, Iran
2005
A. Hamed
Try working at temperature - 35-40 °C.
T.K. Mohan
plating process supplier - Mumbai, India
2005
A. Remove nitric acid from your formulation.
P. Gurumoorthi
electroplating process chemicals - Chennai, Tamilnadu, India
2005
Q. Hi. I am coating automotive parts with a cyanide zinc bath,
I want to make a green chromate solution for that.
Please give to me a recipe to make and use of this.
thanks.
electroplating manager - Tehran, Iran
April 19, 2011
A. Hi, Hasan.
We assume that you are speaking of Olive Drab chromate rather than the pastel green dye we would see on grounding screws? Please remember that hexavalent chromium conversion coatings are not used on automobiles anymore due to RoHS restrictions, and that you must purchase a proprietary trivalent formulation.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 19, 2011
Q. Hi, Ted you are understanding my meaning exactly!
But in my country hexavalent chromium conversion is useable and is Vogue! By this Explanation can you help me for
resolving this problem?
- Tehran, Iran
April 22, 2011
A. Hi, Hasan.
Although I do not know the formulation myself, we appended your inquiry to a thread that seems to offer a starting formulation plus two comments on how to improve it for a good green color. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April , 2011
Q. Hi,Ted.
I want to know how I can pursue this inquiry?
Thanks again.
- tehran-iran
April 28, 2011
ASM Metals Handbook Vol. 5: "Surface Engineering"
on
AbeBooks
or
Amazon
(affil links)
Hi, Hasan.
Hamed gave you his formulation and mentioned its imperfections, to which Mohan replied that he should lower the operating temperature and Gurumoorthi suggested omitting nitric acid from the formulation. You may want to see if a library has the ASM Metals Handbook vol. 5 which has an excellent "Chromate Conversion Coatings" chapter that explains that a coating weight of about 200-500 mg/ft2 is required for a deep green color, and that you probably won't be able to achieve this without fluorides in the formulation. You may also need ferricyanide. Although you won't find an exact formulation in that book, you will find the information you need to start your development effort.
What you may not quite realize is that the more advanced chromate conversion coating chemistry has been held as proprietary information for 60 years, so you probably will never find exactly what you are looking for, i.e., a detailed public-domain recipe for generic chromates that approach the effectiveness of proprietary formulations. Best of luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 28, 2011
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