Spray Rinsing

In the industry of metal finishing all of the process steps and control parameters are critical. Naturally most of all of the process steps are scrutinized, tracked, and analyzed, however often times those process steps that may not seem as critical should be not be taken lightly.  One of these often over looked areas is rinsing and what constitutes good and efficient rinsing.

The critical nature of rinsing can be measured in many ways such as component quality, process solution contamination or overall line process quality.  The metrics may vary from application to application. Naturally the more critical the component being finished the more critical the rinsing aspect becomes. The closer the rinsing is to important process steps the more those areas are deemed important, but what is more important than another if in fact the entire process is said to be important?

Conventional wisdom says simply use as much water as possible, but due to the high level of regulatory pressure and discharge restrictions concerning this is not allowed nor is it practical or economical.  So with that said it is important to optimize the process rinses and rinse flow while conserving water and reducing regulatory pressures.

There are many simple areas where even the smallest finishing facilities can utilize in an effort to improve process rinsing while controlling costs. The following outlines some simple suggestions to improve process rinsing while reducing water consumption.

Spray rinsing:  Spray rinsing combines the act of physical impingement on the work piece while reducing flow. Areas where spray rinsing is very effective and reduces chemical solution and solution losses are as follows.

  • Heated Cleaners:  Since most cleaners operate at elevated temperatures it is a practical application to actually spray rinse production parts as they exit the cleaning process. In this case the evaporation rate will usually exceed the amount of water necessary. In the case of a conventional ferrous substrate process line the water source for the spray rinse is the first process rinse following the cleaner. Here chemistry is returned to the tank by way of removal from the part surface as well as the chemistry that manages to be dragged out to the first rinse.
  • Re-use water(s):  In the above spray rinse scenario by simply counter flowing the rinses from the alkaline cleaning processes back through the line to the first alkaline cleaner rinses minimal fresh water is consumed while still providing for good quality rinsing. This can also be used successfully at the plating process by using the plating “drag out” tank to also function as the plating process pre-dip. Whether an automatic line or a manual process line this will allow the chemistry dragged out to return to the plating bath. In the use of re-use rinse water it is critical to make sure the processes being considered are compatible and to not compound issues in the next process.
  • Drip-Time:  Upon exiting a process it is important to allow for sufficient time for drainage but again this is a fine line depending on part configuration and the chemistry of the process.  This is a simple process step that is overlooked.
  • Submerged agitation:  Low pressure air blowers have been used for many years and supply reasonably good solution movement however excess air agitation can produce quality issues.  A reasonable solution to this is small filter pumps that supply high solution movement without bringing air into the equation. Conversely the implementation of filters with the pump provides additional rinse cleanliness and clarity

The above suggestions are effective and will not produce a large financial drain while improving your process rinse quality.  Consult your chemical supplier on the best way to employ these techniques and gain control over processes that may have once been ignored.