Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 498 of 707

After receipt, it is important to have a system to ensure the standard's reliability after use. One system makes use of primary, secondary, and working standards. The working standards are used for calibrating the thickness gauge daily. Once a week, the working standards are calibrated against the secondary standards. The secondary standards are then calibrated against the primary standard once a month. The time between calibrations can be varied based on experience with the expected life of the standard. When a new standard is pur- chased, it becomes the primary standard, and the remaining standards are low- ered in rank. SUMMARY To measure the thickness of a coating, many properties have been utilized. Measurements have been described that use the atomic configuration, electro- chemical equivalent, corrosion rate, electrical conductivity, magnetic proper- ties, density, and actual linear measure of the coating. In addition to these methods, tests have been successfully performed by using the electrical resistance and transparency of the coating. Each of these methods has its proper application. It is obvious that one system is not capable of satisfying the needs of every plater. Certainly, a plater coating 10,000 fasteners per barrel load at a rate of 50 barrel loads per shift has a problem that is substantially different from a plater that hard chromium plates printing rolls. Experience and judgment are required, and the responsibility for choosing the most economical thickness- measuring system adequate for a particular problem is not a simple task. 497

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