There’s an old adage – “One Hand Washes the Other.” Although this adage is seldom applied to cleaning technology, it certainly could be. In fact, most successful cleaning consists of a combination of chemistry (soap, solvent or whatever) and some kind of added mechanical force to enhance or enable the cleaning process. If one could just dip parts to be cleaned into some magic liquid and have them come out clean things would be very easy. But, that is almost never the case. Hence we have a need for a “second hand.” In a previous blog, we briefly talked about the need for dissolving, emulsifying, diluting and/or moving dirt away from a surface. To accomplish this, most cleaning is performed using a liquid cleaning media. The chemical properties of the liquid are very important. Mechanical force is the second important component required for successful cleaning. Consider, for example, last night’s spaghetti plate. You finished dinner late, enjoyed a few glasses of wine and as a result the plate sat on the kitchen counter next to the sink overnight. In the morning, you dutifully filled the kitchen sink with water, added a little soap and put the plate in the sink to soak before going to work. Would you, in your wildest imagination, expect to return home that evening and find that the plate was totally clean from just sitting in soapy water all day? Of course not! To finish the job requires a little “elbow grease” using a sponge or dish rag. Manual cleaning utilizes rags, brushes and other means that physically contact the soils and the surface to be cleaned. Automated cleaning systems, however, supply mechanical force or “elbow grease” in ways that don’t rely on direct physical contact other than that which can be delivered through the cleaning liquid. Sprays, agitation of the part, turbulation of the liquid and ultrasonics are common ways to introduce mechanical force in automated cleaning systems. The selection of one or more of these means is as crucial as the selection of the cleaning liquid itself to the success of the process. The selection of the proper mechanical force is driven by the geometry of the part as well as the amount and nature of the contaminant to be removed. Major mechanical force for removing thick buildups of contaminant is best supplied by sprays, turbulation, or part agitation. All of these, however, are limited in their ability to access some areas of parts with complex geometries. Sprays, for example are “line of site.” If the spray nozzle can’t “see” the dirt, its success will be severely limited. Turbulation and part agitation rely primarily on a “flushing” action which is difficult to create in a closed cavity such as a blind hole. Ultrasonic energy is limited in its ability to remove thick layers of contaminant but excels at removing fine traces of contamination and reaching inside otherwise inaccessible areas of some complex part geometries. No one “recipe” meets every cleaning requirement. Fortunately, it is possible to design cleaning equipment that utilizes an optimum combination of the various forms of mechanical energy to clean almost any form of contamination from nearly any part geometry.