Wash, Rinse and Dry

Today’s industrial parts cleaning processes commonly employ at least three distinct steps. The basic steps are Washing, Rinsing, and Drying. Each step is custom tailored to the overall requirement with the range of options for each much broader than one not intimately involved with the technology might imagine. In some processes, in fact, it is very hard to distinguish the steps with one overlapping another. The following will clarify the general definition of each step as we will address them in this forum.

Washing – Washing is the dissolution or displacement of contamination from the surface being cleaned. As mentioned earlier, this is usually accomplished using water mixed with a specialized chemistry or a solvent. Depending on the contaminant, washing may comprise one or more process steps. For example, if the contaminant load is heavy a “preclean” may be used to remove the bulk of the contaminant with a second “final clean” completing the job. Another case requiring two steps would be a contaminant made up of two or more distinct constituents. In any event, at the end of washing, contaminants, solid or liquid, should be fully displaced from the surface being cleaned and, to as great an extent as possible, segregated so as to be left behind when the part being cleaned leaves the washing stage.

Rinsing – Rinsing in fact, is a secondary cleaning step but should not be expected to further remove the original contaminant from the part being cleaned. Its primary purpose is to remove the residual liquid or loosened solids remaining from the washing step. Rinsing usually employs plain water or, in the case of a solvent system, pure solvent or the distillate of solvent vapors. The more stringent the cleanliness requirement, the more pristine the rinse must be. Water ranges from tap water (on the “dirty” end) to distilled water on the other end of the spectrum. Various methods may employed to maintain the purity of the rinse as contaminants accumulate over time.

Drying – Since the part being cleaned is commonly “wet” with one liquid or another after washing and rinsing, the final step in cleaning is usually drying unless “wet” is OK. Drying technologies either evaporate or mechanically remove residual liquid from the part. Drying in air or drying in an oven are two means used to evaporate residual liquids. Air blow-offs and spin drying are examples of mechanical means of removal. In most cleaning processes, drying is the “bottle-neck” of the process usually requiring more time than either washing or rinsing. Drying is also the process step that is most frequently overlooked or under-addressed in process development and, as a result, causes the most headaches in the equipment run-off.

So, there you have it in a nutshell – – Washing, Rinsing and Drying. What could be more simple . .        ???

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