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Pollution Prevention and Control Technologies for Plating Operations
Section 2 - General Waste Reduction Practices
2.5 RINSEWATER REDUCTION
2.5.1 Optimal Rinse Tank Design
The key objectives with regard to optimal rinse tank design are to attain fast removal of drag-out from the part and complete dispersion of the drag-out throughout the rinse tank. When these objectives are achieved, the time necessary for rinsing is reduced and the concentration of contaminants on the part when it leaves the rinse tank are minimized for a given rinse water flow rate. The following are rinse tank design elements that help to achieve fast drag-out removal and complete mixing. These methods can be combined to develop an optimal rinse tank design for a given workload. The optimal rinse tank design for different shaped parts, racks and barrels will usually result in the selection of a different combination of design elements. When parts with various configurations are rinsed in the same tanks, it may be necessary to compromise the design to provide adequate rinsing for all parts.
- Select the minimum size rinse tank in which the parts can be rinsed and use the same size for the entire plating line.
- Locate the water inlet and discharge points of the tank at opposite positions in the tank to avoid short-circuiting.
- Use a flow distributor/sprayer to feed the rinse water evenly.
- Use air agitation, mechanical mixing or other means of turbulence.
- Use spray rinsing for flat surfaced parts.
- Use ultrasonics, where applicable.
Air agitation was a relatively common element of rinse tank designs used by survey respondents. A total of 185 (or 58.2%) of the respondents reported its use. The average success rating was 3.71 (see Exhibit 2-16).
Spray rinsing is used by 124 (or 39.0%) of the survey respondents. The success rating for this method was 3.82.