Water rinsing is used between each process step and at the end of the cycle to remove all traces of chemical that remains on the surface. This avoids drag-in of solution into the next bath and provides a clean surface for maximum adhesion and plating quality. It is generally best to use DI water for rinsing as it is free of contaminant ions that would otherwise build up in the bath(s). The importance of proper rinsing can not be overstated. The secret is to achieve maximum rinse quality with minimum water usage.
Small lot processing generally uses a single Reclaim Rinse Tank. This is an empty tank where the part fixture and anode are spray rinsed as the final cleaning step to remove all traces of chrome. Using an empty tank avoids having a large quantity of chrome water to dispose of. The smaller quantity of water generated from spray rinsing is easily filtered and returned back into the plating bath for recovery and re-use as part of the Zero Discharge approch, generally at the end of each shift.
Production processing uses multiple immersion counter flow rinses which are proceeded by an empty drag-out spray rinse. The spray is fed by a pump from the most concentrated portion of the counter flow. Flow restriction is used to control the water input and avoid overflows. This can be a simple as a foot switch, a timer & solenoid or as complicated as a conductivity controller. The liquid from the drag-out spray rinse is then filtered into the plating bath for recovery to replenish evaporation. The immersion rinses should be warm if possible and must be air agitated for proper mixing.
Final Hot Rinse
A final hot rinse can be used to improve the operation and facilitate the rapid drying of part(s). This is typically operated at 140 - 150 deg. F. The use of Chrome Kill #318, at only 1 oz/gal. in this rinse will reduce any remaining chrome to trivalent and prevent both chrome and water stains on the part(s). Chrome Kill #318 can also be used to clean up any chrome spills that may occur.
Here’s a suggestion for making a good impression on the environmental inspectors when they come around for their routine visits. Chrome Kill # 318 is used for reducing chrome and eliminating stains in hot rinse tanks. It’s also used to “kill” any chrome spills that may occur on the shop floor from time to time. Some shops keep a drum or two on hand at all times just for this.
On a recent visit to a smaller hard chrome plater, the inspector noticed a drum of Chrome Kill #318 sitting in a corner of the shop and asked what it was for. The owner told him that some of it was used in final rinsing, but primarily it was for cleaning up any small spills that may happen. The inspector then commented that “Any company concerned enough to keep this product on hand must be doing other things right too.”
He then seemed to be much more relaxed and lenient during the rest of their time there. This shop now keeps the drum of Chrome Kill #318 out in the open where it can easily be seen as soon as you walk out into the plant. The large label on the drum just jumps out at you and says “This Guy Is In Compliance”.