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topic 2337

Analytical procedures for cyanide bronze plating solution


(1998)

Q. I was recently charged with the responsibility of our plating shop. We perform cyanide bronze plating on aerospace components. We currently do not perform in-house analysis of the plating baths. I need assistance in developing analytical procedures for bath control.

Any help in developing these procedures or locating resources would be greatly appreciated.

Terry Van Dien
- aerospace - Beaufort, South Carolina


(1998)

A. Hi Terry. The vendors of the solutions, unless you are using homebrews, have procedures that are proven.

The Metal Finishing Guidebook has a nice section on analysis.

Commercial books such as Chemical analysis of plating solutions (Irvine) are good.

The Electroplating Engineering Handbook edited by Durney has a analysis section.

Do not forget to analyze your prep cleaners and acids also.

James Watts
- Navarre, Florida


(1999)

A. Don't blindly accept any published analysis procedure, even Metal Finishing's. Always prepare a bench top (laboratory) test solution and perform the analysis procedure on it. Then muck up the test solutions; i.e. add carbonates to your alkaline cleaners and cyanide solutions, add copper to your acid activators. Analyze these test solutions with the same procedure you initially tried. If you get the same results and the results agree with what you actually put in, then you got a reliable procedure. We found that the normal analysis procedure for alkaline solutions was useful for only newly make baths. As the baths aged they got stronger when using a phenophthalein titration endpoint. We now use methyl orange and phenophthalein endpoints (to calculate carbonate increse and hydroxide decrease). This method has given us some measure of reliability for determining concentration of active ingredients in alkaline cleaners.

Marjorie K. Turton
- Winnipeg, Manitoba, Canada



Cyanide bronze bath with strange titration readings after chemical additions

October 16, 2015

Q. Good morning all...

I have an anomaly in my cyanide bronze bath titration readings and I don't know where to start looking for issues. This is completely out of the ordinary for this process.
We do a very consistent production load through the line. We make regular adds and the bath is normally VERY stable.

Our method is we do a titration first thing in the morning every day, make our add per the reading and then test the next morning (after the chemical has had time to circulate through the bath). Our bath size is approx. 12K gallons.

Recently, we did an add of both sodium and copper cyanide per our normal methods and have seen the numbers drop significantly during the next titration; however, it's not as if we have a ramped up production load. There is no obvious cause for losing the chemical.

What would I look for in the raw chemical or in our process than may cause the number to drop significantly after an add rather than stay stable? The only process change that we've done within the last month is upgrade our bath's carbon filter with some new replacement parts.

Any help in a starting point where to look would be GREATLY appreciated!!

Thank you,
Dawn

Dawn Baeckeroot
Process Engineer - Alden, Michigan


October 19, 2015

A. Do you add copper cyanide directly? Is there now a different person doing the additions?

The only thing I can think of is that the CuCN being added is not properly dissolving. I have never run one of these baths, but the way I would do this is to suspend the CuCN in warm DI water, then add sufficient NaCN such that a transparent, light yellow solution is obtained.

Needless to say, this should all be done with a proper fume removal system by a trained individual wearing the prescribed PPE.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


October 20, 2015

Q. Thanks Dave,

Nope, nothing has changed. We thought the same thing about not being dissolved properly. We checked the props on our mixers and the circulating pump and all are functioning normally.

The operator is the same one who has been doing adds now for months.

What just came to light this morning is that we have a small metal tank in this system. All our others had been converted to poly years ago. We know that there's stray current and that the metal tank started plating, but it was very slight. Well, now we suspect that it wasn't as "slight" as we thought.

We're looking back in our records to see if that tank was operational when we were having these dips. That would explain where the copper is going!

Thanks for the help!
Dawn

Dawn Baeckeroot [returning]
- Alden, Michigan USA



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