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Chromate after Bake

We cyanide cad plate steel parts which require baking at 375 F for 4 to 24 hrs for hydrogen embrittlement relief. After bake we must yellow chromate the parts. We have problems getting the chromate to take on the parts.

Cycle after bake is alkaline soak clean ( 5 min ), rinse, yellow chromate ( 1 min ), rinse, and dry. Parts are spotty and must be hand rubbed with scotch-brite pads and re-chromated before we get a good yellow finish.

Is there some method to activate the cad coating after bake so that the yellow chromate will take the first time?

Appreciate any help.

Lee Blanton
- Denton, Texas
2002

Try doing less time in the cleaner after the bake. 1 minute should be sufficient. Also, go back through the cyanide bath after the cleaner and rinse to remove bake stains and activate the surface of the cad. Rinse well to remove any cyanide. The parts should look 100% better. Let me know how it works.

Greg Ginsbach
- Seattle, Washington, USA
2002

Why are you going through a soak cleaner? We used to let the parts cool to room temperature, then process them through 1 % nitric acid for about 30 seconds, rinse, go into the chromate. I have had to activate with 1/2-1 % sulfuric before applying olive drab.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan
2002

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We also CAD plate in a cyanide solution and also use a chromate coating after bake. You are correct in going into the soap first, but you must re-dip your parts in the CAD plating bath without current, in order to re-activate your Cadmium, causing the conversion coating to stick and be clear and uniform. Anymore questions, don't hesitate to ask.

Good Luck,

Tony Schmaltz
- Kent, Washington
2002