Metal Finishing Guide Book

2013

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the soil. Soils that are allowed to age on the metal surface for an extended time become increasingly difficult to remove. A classic example is aged buffing compounds on zinc die castings. It is important, therefore, to clean parts soon after they arrive from their last operation. PROPRIETARY CLEANERS To begin with the concept of one cleaner for all soils and all metals does not exist, although chlorinated solvents have come close to achieving that honor. Proprietary cleaners fall into the following groups: alkaline (mild to strong); neutral (pH 7.0); acidic (mild to strong); emulsion; and solvent. The physical forms of cleaners on the market may be powder, liquid, or gel. In the development of a cleaner not only are the soils a consideration but also the base metal to be cleaned. As a rule the cleaner's function is to remove the soil and not have any detrimental effect on the metal's surface. For example, a product containing caustic soda would be satisfactory for cleaning ferrous metals but not for cleaning aluminum alloys, zinc die castings, galvanized stock, or yellow brass. Such a product would attack these nonferrous surfaces. The proper selection of a cleaner for the metal substrate to be cleaned is thus paramount. The bulk of the proprietary cleaners used in industry fall into the alkaline group. Many solvent cleaners are being phased out because of environmental considerations and other hazards. Acid cleaners generally are used for cleaning stainless steel alloys, wrought aluminum alloys, copper, and brass alloys. Proprietary alkaline soak and spray cleaners are generally formulated to clean a variety of metal-forming lubricants from a metal's surface, and may also find application for cleaning a variety of metals, i.e., ferrous metals, aluminum alloys, brass, and magnesium alloys. Within the last three years the development of a new cleaner formulation has become further complicated by environmental restrictions imposed by federal and local regulations and by corporations themselves. For example, a specific requirement given for a spray cleaner was that the product must be safe on most metals within the specific allowed cleaning time, but must also be free of phosphates, silicates, chelators, and nitrites; have a low COD/BOD; and have an operating pH between 8 and 9. If, for example, some of the restrictions encountered when formulating a cleaner were applied, it would have to have the following characteristics: Chromate free Phosphate free Silicate free Fluoride free Chelator free Nitrite free Amine free Low COD Borate free Noncyanide Noncaustic Solvent free No foam products High flash point solvents Powders or liquids Low BOD Emulsifier free pH of 7.0-9.0 Some of the reasons for these restrictions are self-evident such as cyanide free, solvent free, chelator free, and phosphate free. From the collection of restrictions given one may readily note that the products of the future must be not only safe to the environment, but also relatively safe to use in the work area, and provide a cleaner that will allow the separation of the soil from the cleaning solution. 55

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