Cleaning Chromate Finished Zinc Plated Bolts

Q. I need to specify a cleaning protocol for chromate finished zinc plated bolts. The plater commented that any cleaning (except for a very mild one) can damage the chromate finish. The customer is concered about residual oils. My guess at a cleaning protocol would be: clean in ultrasonic bath, 2 min with 1% Alconox solution, rinse with de-ionized water. All we are doing is cleaning fasteners to be installed in a clean room. The level of cleanliness for these fasteners is a bit fuzzy. Does this sound reasonable?

A. A 1% Alconox solution (1.25 oz/gal or 10 g/L) ultrasonic clean for 2 minutes followed by a thorough deionized water rinse is a perfectly reasonable cleaning process for zinc plated bolts that will be installed in a clean room. A 2 minute clean is a suitable cleaning time if you are cleaning at a hot enough temperature. At 65 deg C, a 2 minute clean is fine. At 55 deg C, a 4 minute clean would be better, at 45 deg C an 8-10 minute cleaning cycle would be typical. Whatever temperature you clean at, it is desirable to have the first rinse be at the same temperature if possible so as to avoid breaking any emulsions and redepositing residues.