Removing Solder Flux from Brass and Steel Assembly

Q: We currently use a 5% Citranox solution to clean our Brass and Steel Assemblies that have solder flux. The bath is at 55-80C for 15 minutes. Is the temperature ok? Any concern with the parts sitting overnight in this mixture?

A: First, as we always ask, is this process working? Is the flux being removed? Is there darkening or oxidation occurring on the parts? Critical cleaning is of course a science. There is also an “art” component to it in that every application, setup, running conditions and instruments are different. Getting the job done in a critical cleaning activity is priority one. Optimization comes after.

Generally, with a reactive metal like brass, we want to keep temperatures on the luke warm side, and minimize contact cleaning times as much as possible.

We should try, as discussed here: Ultrasonic Cleaner for Mixed Metal Baths, to avoid cleaning mixed metals in an electrolytic solution – which any detergent solution is. We don’t want galvanic reactions occurring whenever it can be avoided. A part that is both brass and stainless cannot be avoided. The good news is that Citranox detergent is excellent at removing this oxidation, and with minimal contact times, you shouldn’t see any galvanic plating occurring. (Minimal can of course be subjective, but we would recommend avoid leaving overnight and focus minimizing contact time to the amount to get the cleaning job done.).

We also recommend thorough rinsing and complete drying to avoid rusting.

We are always happy to review results and discuss further!

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