Metal Finishing Guide Book


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Page 508 of 843

DROP TESTS The drop test for measuring plating thickness is based on the rate of attack of specially prepared corrosive solutions on a metal coating. For consistent results, the drop size, drop rate, temperature, time, and solution composition must be controlled. The test is performed by allowing the solution to drop on a particular spot at a rate of 100 drops per minute. The operator then observes the time at which the coating is penetrated. For the most common thicknesses, the elapsed time is less than one minute. Reproducibility of the test is dependent on the skill of the operator. The operator must detect the point at which the base metal is exposed and record the time. An experienced operator can reproduce his readings within ±5%. For best accuracy, the operator should standardize his technique with a standard of known thickness. The accuracy of the system is generally considered to be ±15%, because the operator cannot control some of the factors that affect the test. These factors include drainage of the solution, alloying at the coating/substrate interface, and composition of the coating. Low cost and the ability to measure thickness quickly on irregular shapes are the chief advantages of the drop test. The greatest disadvantages are destruction of the coating and objections to the use of corrosive solutions in some areas. The largest application is in the fastener industry. Standard guidelines for the use of this test are contained in ASTM B 555. Solutions for Coating and Plating Thickness Measurement MicrodermCMS Handheld beta backscatter systems. New probes, standards and services for all brands. Standards New and Recalibration of thickness standards for all brands Accredited for standards and instruments XRF 2000 X-ray systems for coating thickness measurement and analysis #1588.01 Dermitron Eddy-current and magnetic for measuring plating, paint and anodizing 499

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