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1-3 Meg-Ohm-cm water needed for plating line?


My name is Gina Wagner and I work at a lock manufacturer in Security, Colorado. We manufacture locks and architectural hardware. Currently, we have a DI water system-mixed bed that is over 17 years old and is rusting apart because it is in a corrosive atmosphere. I want to replace the existing system with an RO water system for chrome and nickel plating baths and rinses.
How important is it to use RO or DI water, at the purity of 1-3 Meg-Ohm-cm water for plating large parts like locks and doorknobs, etc.?
I am interested in knowing if cleaner water, rather than city water makes a difference in the plating quality or increases plating bath life?

Gina Michelle Wagner
plating shop for locks and hardware - Security, Colorado, USA

First of two simultaneous responses --

Hi Gina,

Don't compromise on the quality of your water. You will eventually start to see various "problems" come up that you won't be used to seeing with your current water. Could be an enormous amount of things that poor water might affect, tank contamination, rinsing stains, etc...

I put a RO system in at my old plant and many, many recurring problems went away plus we could go awhile longer before we had to do any tank maintenance. The major component in any plating line is the water.

Good Luck

Trent Kaufman
Trent Kaufman
electroplater - Galva, Illinois

Second of two simultaneous responses --

Water in a plating shop serves three purposes. The first is to rinse the components as they proceed down the line, so that there is no cross contamination from tank-to-tank. The second purpose is to rinse off any chemicals from the final plating stage to ensure there is no unwanted material left on the surface that can cause unsightly and unwanted staining. The third use is to top up the process tanks. The first and third uses of water require the water to be as pure as possible in the sense it doesn't contain any unwanted ions or particles. The simplest way of checking for the presence of ions is by conductance - pure water is a pretty good insulator, so it will not conduct electricity very easily. Consequently, the higher the resistivity, the better the water should be - all other things being equal. High resistivity does not always mean the water is pure, as it can contain suspended solids that are not electrically conducting, but as a rule of thumb, it is a good guidance. The second use of water, that of rinsing the final articles, requires clean water; this need not be high resistivity as it is sometimes advantageous to use slightly dosed water (i.e., slightly acid or alkaline) to remove the final remnants of surface contamination. Hot water is also very useful as a final rinse. What rinse waters must not contain is anything that will result in leaving unwanted debris on the surface. It is generally accepted that a resistivity of 1-3meg-ohm is a pretty good quality water.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


For your cleaners, your city water should be fine.

For your plating solutions and post-plate treatment solutions, I recommend DI or RO water- we use DI >2 mega-ohm.

Final rinse should be clean as well. For all other rinses, city water should be fine.

The best way to extend your plating bath life is to minimize contaminate drag-in. I presume you are filtering, and retrieving lost parts on a regular basis.

Willie Alexander
- Colorado Springs, Colorado

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