Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 11 of 331

flectance, the cleaner the surface is. THE IMPORTANCE OF CLEANING Cleaning of metals and other finishing-related substrates is the single most im- portant consideration to successful coating application. Achieving clean sur- faces has applications throughout a manufacturing facility: for corrosion pro- tection, for welding operations, for part handling, for part inspection, and for metal finishing. All of these cleaning applications can and should have a quan- titative degree of cleanliness required. The degree can vary from gross soil re- moval to a high degree of cleanliness, which surpasses the standard water- break-free test of cleanliness. The ultimate requirement is dictated by the re- quirements of the part, the process, the chemical type, and control of process parameters. With today's new coatings, a greater emphasis is placed on achiev- ing a totally clean surface. 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 main- tained 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 equip- ment, (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 de- termined. 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 with- in 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 clean- er 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 oth- er hand if your chemistry is designed for low temperature and the process heat can- not 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 ad- vised. 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 10

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