Metal finishing Q&As since 1989
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Processes for steel passivation
Q. Hello,
We are planning to set up a steel passivation line. They are two type of steel passivation process that were requested by our customer.
Type 1 uses two different solution i.e : Nitric Acid : 200 - 400 g/l Sodium dichromate : 15 - 25 g/l Temperature : 50 - 55°C Soak : 20 - 30 min after that proceed to Sodium dichromate : 40 - 60g/l Temperature : 60 - 70°C Soak : 30 - 40 min Meanwhile Type 2 only uses : Nitric Acid : 400 - 450 g/l ( 61%) Temperature : Room temp Soak : 20 - 30 min
What is the difference between these processes? Do these two process give the same results?
Thanks,
Zuraida MohamedPlating shop at aircraft manufacturing company - Sungai Buloh, Selangor, Malaysia
2004
A. Interesting question. In order for others in a position to help you, we need you to help us. Several questions:
What specification are you passivating to?
Is there an engineering requirement for this process?
Why is your nitric and sodium dichromate solutions separated?
How are your rinse tanks positioned in relationship to the acid tanks?
Regards,
Brad Huddleston- Haysville, Kansas, USA
2004
A. They are interchangeable for SOME alloys, but a precise "ONE" is normally specified in the manufacturing spec.
James Watts- Navarre, Florida
2004
A. First process was treated by chromating chemical that gives protection on the passivated metal. The second one is just etching the metal with no protecting agent thereafter. Process one is widely used even in our treatment line.
Marlon L. Cordez- Sta. Rosa, Laguna, Philippines
2004
A. See ASTM A967. This tells you which grades of steel you can passivate with which formula of nitric acid or citric acid.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2004
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