Metal Finishing Guide Book


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Page 97 of 843

FACTORS THAT AFFECT AQUEOUS CLEANING The success of a cleaner relies on more than just the functional chemistry that comprises it. Effective cleaner-to-surface contact must be made. A number of factors must be considered, understood, and properly implemented and maintained for effective results. Failure to utilize a workable combination of these factors will often produce marginal results and render the cleaning system less effective. There are several factors that directly impact aqueous cleaning. Because of their significance, each should be addressed: (1) application methods and equipment, (2) history and configuration of part, (3) soil, (4) type(s) of substrate(s), and (5) cleaner selection and operation parameters. APPLICATION METHODS AND EQUIPMENT Several questions must be answered in conjunction with the equipment and the application of the cleaner. The method of and amount of agitation must be determined. Chemicals must be selected in either the high-, medium-, controlled-, or low-foam category. More severe agitation or pressure at the nozzle, for example, would place your chemical choice in the least foaming category to prevent excessive foaming. The temperature range of the process equipment should be known. Cleaners tend to be formulated with surfactants and detergents that offer optimal cleaning within a given temperature range. Typically, low temperature ranges from 90¡F to 120¡F, medium temperature ranges from 120¡F to 140¡F, and high temperature ranges from 140¡F to 160¡F. The trade-off becomes this. If you are using a cleaner designed for high temperatures, but the equipment can only maintain process heat at 120¡F, the chances for poor cleaning and foaming are present. On the other hand if your chemistry is designed for low temperature and the process heat cannot be lowered to that range, you may experience stratification of the solution, and in severe cases oiling out of the cleaner's detergent package. The length of time that the solution is in contact with the part must also be decided. Pretesting the parts with the cleaner for the allotted time is always advised. The process equipment, based on the length of each stage and the speed of travel, will yield a total contact time. Typically these times for cleaners range from 60 to 120 seconds; however, many coil lines operate in a range from 3–15 seconds. The chemical choice for cleaning should be made only when the process contact time is known. History and configuration of the part play a key factor in not only cleaner choice, but also the application. Multiconfigured parts, for example, may be best suited for immersion cleaning rather than spray. Usually, machined castings, or parts with ports, threads, extensions, blind holes, etc., are very difficult to clean because the part positioning is typically fixed. In these cases, immersion, or immersion spray combinations, or rotating fixtures may be required. In addition to the configuration of the part, what is the history of the part? Is it a component, finished product, or subassembly? Will it be cleaned once, twice, or more before leaving the factory as a finished product? Finally, how long may the part be staged, or stored? Will the surface corrode or tarnish, and will the in-process soil or rust inhibitor adequately protect without becoming more difficult to remove if the part is not in a just-in-time, or on a first-in, first-out inventory schedule? 94

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