It is no secret that good cleaning followed by poor rinsing can be worse than not rinsing (or cleaning) at all. A single-use rinse using a fresh water spray or a high flow rate or single use immersion rinse are often thought to provide the ultimate rinse. These options, however, are often extremely expensive because they consume a lot of costly water which is also costly to dispose of properly. Surprisingly, there are other rinse options that provide far better rinsing than any of the above using far less water.
Various implementations of multiple rinse stages offer better rinsing at less cost than any single rinse option I can think of. Two rinse stages can even be incorporated in a single tank!
Spray Over Immersion –
Consider an immersion rinse with a spray rinse on exit. Immersion of the part in the rinse tank removes the majority of contaminants. A low-consumption fresh water spray above the liquid surface provides a second, fresh water rinse while adding very little to the size or complexity of the tank. The immersion rinse tank is replenished (it has to be replenished anyway) by the run-off of the fresh water spray with the contaminated overflow from the immersion tank going to drain or collected for recycling or reclamation. In an extension of this concept, water from the immersion rinse can, in some cases, be pumped to an exit spray over the cleaning tank. This “pre-rinse” considerably reduces the load on the rinse tank by removing some of the carry-over of chemistry and other contaminants by returning them to the cleaning tank, not the rinse.
As the above example suggests, there are lots of ways to combine immersion tanks and sprays to provide excellent rinsing at relatively low cost. Sprays are not always an option but, as the cases above, they can be both useful and effective.
Hint – It is almost always possible to re-utilize spent rinse water in making up the cleaning tank. Doing this can save on the cost of water used to re-charge the cleaning tank, and, in some cases, on the cost of chemistry (since the rinse water already contains some chemistry) and on the cost of heating a fresh tank of water in the cleaning tank.
“Counterflow” Immersion Rinsing –
The ultimate utilization of water is provided by a multi-tank counerflow rinse. Several immersion rinse tanks are arranged so that rinse water flows from one tank to the next in the direction opposite to the flow of work. This concept and it’s benefits are thoroughly revealed in the article Ten Minutes to Better Rinsing. Although this article is “growing whiskers” it is still the best treatise I have found on counterflow rinsing.
Closed Loop ??? –
Disposing of dirty water can be both complicated and expensive. After reading the above article on counterflow rinsing, the reader may realize that with enough counterflow rinses in series, the reduction in water use for rinsing may ultimately become substantial enough that, considering evaporation, there may be no need for any water at all to go to drain. The overflow from the first rinse is totally consumed as makeup in the cleaning tank. Although many have tried, many have failed at capitalizing on this concept by making a “closed loop” process. There are complications, especially when the remnants of spent cleaning chemistry and contaminants removed from parts concentrate beyond a tolerable level in the cleaning tank. Totally “closed-loop” processes are, in fact, a reality but using other technology which is a topic for upcoming blogs on re-cycling and re-using water used for both cleaning and rinsing.
– FJF –