Immersion or spray methods are used in most industrial cleaning processes. Both are effective but one may be better suited than the other in some applications and often for reasons that aren’t immediately obvious. Let’s take a minute to explore some of the benefits and limitations of each.
The most often recognized limitation of spray is the fact that surfaces must be accessible to be effectively reached by spray. It is often said that spray is a “line of sight” method. Although spray is most effective at the point of impingement, the flooding effect of high volume spray may be all that is needed in some cases. Spray should not be eliminated as an option just because there is no line of sight to all surfaces. This is especially true in the case of rinsing. Although the “line of sight” limitation hampers spray in many applications, there are some pretty powerful pluses in cases where spray can be used. Not the least of these is the fact that unlike immersion techniques, spray offers the opportunity to deliver fresh solution throughout the process cycle. For example, in a recirculating system, wash solution can be filtered immediately before being delivered to the spray nozzle. In an immersion system, filtration is an exponential process requiring considerable time and/or high flow rates to maintain even a relatively particle free solution as discussed in an earlier blog. In the case of rinsing, spraying with fresh water completely eliminates any concern for a buildup of contaminants in the rinse process.
Immersion processes provide access to all surfaces where liquids can reach and opens the door to the use of agitation, turbulation, and ultrasonics. Ultrasonics requires a sound-conducting liquid path from the transducer to the surface being processed though it need not be in a direct sight line. Ultrasonics, of course, can penetrate inside cavities and blind holes when correctly applied and is recognized as an extremely effective technology especially where the removal of very small particles an/or marginally soluble contaminants is required. On the negative side, immersion technology is difficult to apply in cases where there is high contaminant loading due to extremely dirty parts. Keeping the cleaning solution free of contaminants requires constant filtration and/or frequent bath replacement.
Immersion and spray used in combination may result in a more effective and efficient cleaning process than can be achieved using either technology exclusively.
For example, in the case of very dirty parts, a spray preclean stage prior to an immersion stage may significantly extend the useful life of the immersion stage chemistry by reducing the amount of contaminant introduced into the immersion stage. Spraying parts with freshly filtered solution or water after an immersion process may significantly reduce the dragout of contaminants built up in the immersion stage to a subsequent cleaning or rinse stage.
Process Improvement Opportunity –
It is not always necessary to dedicate a process stage to implement spray technology. Exit sprays can often be added over existing immersion tanks to improve a cleaning or rinsing process while still utilizing the existing hardware. The temporary use of a manual spray can quickly establish if the addition of spray will be beneficial in a given application.
– FJF –