The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Zn contamination in chromating bath

I am doing a research regarding passivation process using hexavalent chromium and trivalent chromium. During the in-line process, some of the Zn will dissolve into the bath. it is about 1000 ppm. As I know, Zn contamination in the bath will highly effect the performance. But I have no idea on how to control the Zn content in the bath. As what we currently do is just top up the bath whenever the hexavalent chromium reduce below control limit. Is it the correct way? Any advice?

Quah Ban Kheng
Tube Mill Industry - Bukit Mertajam, Penang, Malaysia
2004

---

The buildup of zinc in an acidic chromate is unavoidable and expected. That is one of the reasons that chromates have to be dumped and replenished on a fairly frequent basis. The only method to reduce the amount of zinc in the chromate is to either have a less acid pH or leave the parts in the chromate for a shorter period of time. While that may reduce zinc buildup it will probably lead to problems with the chromate finish quality. Run the chromate by the manufacturer's recommendations and don't try to reinvent the wheel.

Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
2004