Metal Finishing Guide Book


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hydrophobic contaminants. The water break test does not confirm the presence or absence of hydrophilic particulate contaminants or oxides. White Glove Test The white glove test is used to show the presence of particulate and, to a certain extent, organic contaminants on a surface after cleaning. The part may be tested while still wet from rinsing or after drying. The surface of the part to be tested is wiped with a white glove, cotton swab, or lens tissue. The material used to wipe the surface is then examined for the presence of black, gray, or off-white residue or oil staining. If contaminants are found to be present, microscopic examination or advanced chemical or surface analysis can be performed on the part surface or the item used to wipe the surface to determine the nature of the contaminants. Other Methods Sophisticated physical and chemical analytical methods can be applied to test for residual contaminants on surfaces that have been cleaned. Samples of parts that have been cleaned and dried can be immersed in a turbulent solution of a solvent. The solvent can then be analyzed for organic contaminants and insoluble particulate matter. The amount of contaminant found in the solvent is indicative of the degree of ceaning. Surfaces of parts that have been cleaned can be subjected to special analysis to determine the presence of oxides, organics, and particulate contaminants. Specifications can be written for the allowable presence and concentrations of contaminants in critical cleaning operations. Analytical techniques such as infrared microprofiling (developed by Sandia National Laboratories), X-ray photoelectron spectroscopy (Oak Ridge National Laboratory), and light reflective technology (Dow Chemical Inc.) have been used to analyze for residual contaminants in critical cleaning operations. If soils are doped with compounds that exhibit fluorescence exposure of cleaned parts to ultraviolet light will confirm the presence or absence of residual soils. Tests based on surface tension have been used to determine the cleanliness of surfaces. Care must be taken to ensure the use of test solutions specific to the substrate surface. SAFETY Unfortunately, one of the most overlooked aspects of industrial cleaning is safety. The use of chemicals for industrial cleaning exposes the user to potential injury if proper safeguards are not employed. The potential problems are well documented in Material Safety Data Sheets, books, and articles that have been written over the years. The warnings are of little value unless they are read, understood, and acted upon by those handling, using, or working in areas in which the chemicals are used. A summary of the safety aspects of chemical cleaning are as follows. Acids The use of acidic cleaners containing appreciable amounts of sulfuric acid can expose the worker to potential splashing due to exothermic reactions that can result in localized boiling. Additions should be made in a slow, controlled manner to prevent splashing and localized boiling. Acids should be added to water. Water should not be added to concentrated acids. Addition of acid cleaner concentrates to replenish working solutions should always be made to cool solutions (<100oF). Without exception, acid-resistant 60

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