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Chromate bath life expectancy
Q. My company uses a dip tank process for brass parts, one of which is a dilute chromate solution. We are using a rather arbitrarily set conductivity reading to determine when the tank needs to be changed out. In my opinion we are changing it far too frequently. I'm looking for advice on how to measure contamination and expected bath life in a moderate volume dip tank operation.
Thanks in advance to all responders.
Kevin McHugh- Orland Park, Illinois, USA
2002
A. Hi Kevin, you're probably right that an arbitrary conductivity reading might not be the only or best indication that the tank needs to be dumped, but measuring 'contamination' probably won't work. If you were chocolate dipping cherries, you might be highly concerned with contamination of the chocolate by cherry juice because too much cherry juice would interfere with the properties of the chocolate. But chromating of brass is not an equivalent situation because, although dissolved brass might hamper the reaction, you are not coating the brass with chromate, you are reacting the chromate with the brass ... so you are exhausting the chromate more than contaminating it.
I think you need to determine the essential initial reactants like chromates, nitric acid, etc., and decide what level they can drop to before the reaction is unreliable. The supplier's technical data sheet may offer good hints for what to monitor to best predict the solution becoming too exhausted.
Sorry that I don't have an answer for you, just a theory about what you should be looking for in general :-(
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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