Zero discharge spray rinse system for electroplating operations

The zero discharge spray system comprises a tank for collecting and storing inse water, a set of spray nozzles aligned within the tank, and a pump for both pumping used rinse water through the spray nozzles and/or to the plating bath as makeup for evaporation. A timer level control system maintains the plating bath level and the rinse tank level, and limits the nozzles spray time. The system also includes a fresh water spray for final rinse of plated parts. By using a controlled spray rinse system which reduces the amount of water added to the system so as not to exceed that lost by evaporation, no contaminated rinse water is discharged as waste.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to electroplating processes and more 
particularly to the elimination or reduction of discharge of the rinses 
from electroplating operations which are normally discharged to industrial 
waste for treatment. 
2. Description of the Prior Art 
Prior methods use a dip-rinse technology for plated part cleaning by 
diffusion and some form of effluent clean-up. The prior methods use 
conventional dilution type rinses, either free flow or countercurrent, 
which use the principle of immersing the electroplated part in water to 
allow the "drag out" to be diluted from the part. The normal free flow 
rinses are then discharged to industrial waste for treatment. Hard chrome 
plating operations, for example, have a major problem with water usage. 
Large volumes of water with low concentrations of chrome are not 
economically recoverable by standard recovery processes. Frequently the 
problem is compounded by mixing the rinse waters from a variety of metal 
finishing operations. The elimination or reduction of the need to 
discharge the rinses to industrial waste and the elimination of high 
treatment costs provide significant savings, as well as provide a 
reduction in environmental pollution. 
SUMMARY OF THE INVENTION 
The present invention helps to solve the problems of prior art methods by 
eliminating the need to discharge rinse waters from the electroplating 
process to industrial waste. A spray system is used which results in water 
reduction and in waste discharge elimination. 
The improved system uses spray rinsing which operates on the impact 
principles, where drops of contaminators from the plating operation are 
"knocked" off the plated parts being rinsed by the impact of the rinse 
water being sprayed. This process uses only approximately 15% of the water 
that is normally required for a dilution rinse. First, a recirculation 
initial spray rinsing of plated parts using contaminated (i.e. used) rinse 
water is done, followed by a final fresh water spray rinse, and all spray 
water falls back into the rinse tank. From the rinse tank the returned 
spray water is recirculated for initial spraying purposes and/or pumped to 
the plating tank to help make up for water lost by evaporation in the 
plating bath. In sensitive electroplating baths, use of distilled water 
may be desired if return of the rinse water to the plating bath tank is 
contemplated. Otherwise, all water from the rinse operation is reused in 
the initial rinsing operations and in the plating bath. In a rinse system 
where drag-out may be returned to the source (e.g. a chrome plating 
operation where evaporation losses out of the plating bath can be made up 
from rinse water), this system eliminates discharge to sewer as well as 
reduces water usage. 
Other objects, advantages and novel features of the invention will become 
apparent from the following detailed description of the invention when 
considered in conjunction with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The apparatus, as shown in the figure of drawing, comprises a plating tank 
10 containing a plating bath solution 11 which can be replenished with 
water via pump 12 and inlet 14. A level control 16 in the plating tank is 
activated by the level of the plating bath 11. A rinse tank 18 includes: a 
freshwater inlet 20, a level control 22, water outlet 24 to the pump 12, 
and a plurality of spray nozzles 28 positioned about the upper portion of 
the tank in an area where plated items are rinsed off, above an overflow 
drain 28. Freshwater enters rinse tank 18 through inlet 20 near the tank 
bottom. Inlet 20 includes a screen, not shown, to keep out large solids 
and to prevent them from subsequently entering the pump piping at 24. A 
freshwater spray 30 is positioned above the area for plated items to be 
rinsed and preferably is a hand held spray unit although a movably mounted 
or other suitable freshwater spray unit can be used. 
Water is maintained in rinse tank 18 at a level above that of outlet 24, 
the intake to pump 12. A solenoid valve 32 in line 33 between pump 12 and 
the spray nozzles 26 is normally in the open position. Solenoid valve 32 
is electrically connected to and is activated to the closed position by 
level control 16 in the plating tank when the level in the plating tank 
drops below a predetermined level. Solenoid valve 34 in line 35 to inlet 
14 is normally in the closed position; this valve is simultaneously 
activated to its open position, along with the closing of valve 32 and 
actuation of pump 12, by level control 16 when the level in plating tank 
10 drops below the present level. 
The contaminated rinse water, which contains plating solution, etc., is 
pumped out of rinse tank 18 by pump 12 through a sediment filter 36. While 
in the normal mode, with solenoid valve 32 open and solenoid valve 34 
closed, water is pumped from tank 18 via line 33 and through spray nozzles 
26 of the spray system where it eventually falls back into the rinse tank. 
Sediment filter 36 located between intake 24 and pump 12 is one which is 
resistant to corrosion by the material being pumped. This filter needs to 
be one that is capable of removing all solids that would interfere with 
plating operations if returned to the plating tank. The sediment filter 
should be changed regularly so as not to interfere with flow rates. 
Fresh water is used as a final rinse through the freshwater spray unit 30; 
this water following use also falls back into the rinse tank. Level 
control 22 maintains the level in the rinse tank 18 on a system basis 
where evaporation in the system accounts for more water than freshwater 
spray 30 adds to tank 18. Level control 22 operates to open solenoid valve 
40 in freshwater line 42 when the water level in the rinse tank drops 
close to the top of the freshwater inlet 20. Solenoid valve 40, which is 
normally in the closed position, then allows fresh water through intake 20 
until the preset high water level is reached. The freshwater intake 20 to 
the rinse tank should be located as far from overflow drain 28 as 
possible. 
The spraying system is preferably controlled by a foot switch 44, for 
example, although any suitable switch control can be used. Switch 44 
operates to activate a timer 45. A waterproof foot switch 44 can 
conveniently be placed on the floor for activating timer 45 into its cycle 
for turning on pump 12. Timer 45 is an electrical timer and can be set for 
a desired time period (e.g. 0 to 3 minutes) to allow power to pump 12 for 
a preset time (usually 30 seconds) to activate the spray system nozzles 
26. 
Plating tank evaporation losses are made up from the rinse system. Level 
control 16 in plating tank 10 is adjusted so that the level in the plating 
tank can drop to accommodate the entire volume of the rinse tank (from the 
rinse tank full level near the top of control 22 to a point just slightly 
above outlet 24 to pump 12). When level control 16 activates, an 
electrical signal via line 47 causes valve 32 to close (taken out of its 
normal mode) and causes valve 34 to open to allow water to be pumped from 
rinse tank 18 into the plating tank. Level control 16 simultaneously 
activates pump 12 via line 48, along with valves 32 and 34. If the pump is 
activated for pumping water from tank 18 to tank 10 while the plater 
desires to rinse a part, then the plater would use all fresh water from 
spray unit 30, without using the nozzles 26 during the time while plating 
tank 10 is being filled. 
The type of pump used depends upon the number of spray nozzles (gal/min), 
pipe losses, material pumped (corrosive or not, etc.), pressure desired, 
and its position relative to the rinse tank. In general, the pump 12 
should be able to maintain 20 psi, for example, throughout the system. The 
pump can be either self priming or positioned to operate without priming, 
and should be resistant to corrosive materials, etc. being pumped. 
Generally, a centrifugal pump appears to be best for maintaining a 
constant pressure. 
Several types of spray nozzles can be used in the spray system 
simultaneously. Best results appear to be from nozzles that provide a full 
cone spray pattern, such as a 50 degree cone pattern that provides 1.3 
gallons of rinse at 20 psi, for example. 
The placement of the spray nozzles 26, the number of nozzles used, and the 
most efficient cone pattern for efficient rinsing will depend on the size 
of the rinse tank being used. Generally, the nozzles should be placed so 
that the cone pattern of the sprays overlap in the center of the rinse 
tank, and take up most of the area within the tank. Nozzles 26 should be 
located sufficiently below the top of the tank to prevent misting above 
the tank. Line pressure is basically limited by the conditions which cause 
misting. 
Freshwater feed 20 can be located higher than overflow drain 28; however, 
when feed 20 is below the liquid level of tank 18, line 42 should include 
a one-way valve to prevent backflow in the event of a pressure loss in the 
supply line. Freshwater sprayer unit 30 is preferably a hand held spray 
gun, although a movably mounted spray nozzle unit can be used. Any 
convenient spray pattern can be provided by sprayer unit 30, although a 
full cone spray appears to work best. For example, a spray gun nozzle 
using 3.1 gal/min of water at 40 psi with a 50 degree cone pattern 
operates very satisfactorily for the final rinsing of most plated items. 
The plating tank level control 16 operates valves 32 and 34 and is also 
used to start pump 12 to discharge its flow for making up the plating 
tank. Level control 16 is adjusted to activate the valves 32 and 34, and 
pump 12, when the level in the plating tank to be made-up is equal to the 
amount of water normally contained in the rinse tank above the level of 
intake 24 to the pump. This allows for the most concentrate to be 
replaced. 
The rinse tank overflow drain 28 is placed at about the upper limit of the 
liquid level desired in the rinse tank. A slight increase in elevation of 
drain 28 at the outside of tank 18 is preferred to prevent accidental loss 
of liquids due to splash or spray. 
This spray system is particularly useful for hard chrome plating 
operations. It is a zero discharge system, where all rinse water is 
returned to the plating bath to make up for evaporation losses. The spray 
system works well on all plating baths where the temperature is high 
enough to provide evaporation losses sufficient to allow use of all the 
rinse water as plating bath replacement water, such as with a nickel 
plating bath. 
Variations to the system are possible. On plating baths where there is 
little evaporation, the spray rinse system can be used to dramatically 
reduce water usage. In this type of situation the level control 22 in the 
rinse tank is changed to a conductivity probe, and drain 28 is located at 
the highest level desired. When the rinse water has been contaminated 
sufficiently, the conductivity probe will then activate solenoid valve 40 
and allow fresh water to enter at the freshwater intake 20 and highly 
contaminated water to exit through drain 28. Solenoid valves 32 and 34 
along with the return inlet 14 to the plating tank will not be used or 
needed if no flow of the used rinse water to the plating is desired, and 
could be inactivated or eliminated. 
Other variations to the rinse system can include a chill system if the 
rinse is to contain volatile liquids. The chill system can be used to 
minimize losses on the spray cycle. In addition, a heating system can be 
used, if desired, for providing a hot rinse. In this case a heat exchanger 
50 can be included within the rinse tank for providing either cooling or 
heating of the liquid in the rinse tank. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described.