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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Color anodize stainless steel, is it possible?

Q. I am a tooling supervisor at an automotive weather strip manufacturing plant. One of our processes (plastic extrusion) utilizes stainless steel calibrators and sizing plates which the extruded section runs through submersed in water.

I am looking to color code the stainless calibrators and sizing plates by job/section #.

Can you anodize stainless steel and if so can you color anodize and "mask" off areas so as not to anodize the working surfaces if necessary?

Thanks

Michael Laskey
automotive - Gaylord, Michigan
2004

A. Yes, you can anodize SS and you can mask off some areas.

SS colour anodizing (only for 18/8 SS):
1 lit sulfuric acid
7,5 gm sodium bichromate object=anode, cathode=lead
70-95 °C temp., 0,06 A/dm2, 1,3V

Colour sequence: brown - blue - yellow - reddish brown - purple - green.

Good luck!

Goran Budija
- Cerovski vrh Croatia

Q. Goran,

What is the strength of the sulfuric acid?

Is color time or voltage sensitive?

James Watts
- Navarre, Florida
2004

A. Dear James!

Colour is time sensitive. You must use 1,24 gm/cm3 sulfuric acid, chrome can be up to 50 gm (shorter time)! according to Dettner /Elze: Handbuch der Galvanotechnik/electroplating handbook, four books. [occasionally avail. from eBay, AbeBooks, or Amazon affil links]

Goran Budija
- Cerovski vrh Croatia
2004

Q. Is this is a safe process?

Lukasz Ancypo
- Sokolka, Poland
August 11, 2011

A. Hi, Lukasz

It is certainly not a safe process for a school science project, and it involves hexavalent chrome. But what do you mean by safe? What is the context?

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 11, 2011

Q. Hello.
I have few question about this project. I have sulfuric acid 98.08%, and I dilute it with distillate water to have 28%. Then I take this acid (100 ml) and add to it 4gm Na2Cr2O7 x 2H20 (298 g/mol). Then I take a small piece of stainless steel (AISI 304) and connected it to anode, cathode was a graphite. I worm it up (90 °C), and put a 1.3V. After this stainless steel colourized at golden-brown, but surface was unstable and easy to remove. What I do wrong. Can somebody help me?

Lukasz Ancypo [returning]
Stainless steel - Sokolka, Poland
August 29, 2011

adv.

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