Metal Finishing Guide Book

2012-2013

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substrate, the purpose of the test must be kept in mind. This gas introduction may be acceptable when testing materials used in an environment that may include similar acids, such as roofing materials, that could be exposed to acid rain. EQUIPMENT With continued developments in accelerated corrosion testing, basic changes and improvements have been made to the equipment. The basic requirements for accelerated corrosion testing equipment are listed on Table II under the ASTM B117 Standard. The adjustments required for each variation on the accelerated corrosion-testing model are then listed next to the appropriate ASTM standard. Typical applications are listed in Table III. Along with the basic operating requirements, improvements have been made in the materials used in the construction of the chambers, the hardware and software controls, and data recording capabilities. Programmable logic controller (PLC) systems provide for increasingly sophisticated data acquisition, manipulation, and display (see Fig. 6). As a result, both test chambers with manually entered settings for automatic operation, and test chambers with increasingly sophisticated programmable controls for automatic temperature changes; varying levels of controlled humidity; automatic changes for different environmental atmosphere cycles; and automatic data logging/accumulation, record keeping, and output with graphic data display, are available through a variety of suppliers. These comprehensive capabilities allow each laboratory to find accelerated corrosion testing equipment that meets their specific needs. TEST PIECE PREPARATION/CLEANING In order for any of the above accelerated corrosion tests to obtain comparable results, all test pieces must start the test in a similar condition without contaminants present on the surface of interest. The ASTM test standards discussed above indicate reference standards to be used for the preparation and cleaning of test pieces. Particular attention must be paid to the wide variety of materials being cleaned and recognition of differing specialized material and coating operations. ASTM test standards state that the cleaning method is to be dependent on the product being cleaned and then refer to ASTM D609 Standard Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint, Varnish, Conversion Coatings and Related Coating Products where required. This standard describes five cleaning and preparation methods. The preparation methods described are: Procedure A���Conversion Coating; Procedure B���Vapor Degreasing; Procedure C���Solvent Brushing; Procedure D���Solvent Wiping; and Procedure E���Alkaline Cleaning. Procedure A (Conversion Coating) addresses the issue of ensuring that the test piece be protected from rusting between the manufacturing process and the corrosion test. Procedure B (Vapor Degreasing) exposes the test pieces to solvent vapors within controlled conditions to remove contaminants. This procedure is currently discouraged for environmental reasons. Procedures C (Solvent Brushing) and D (Solvent Wiping) both use Mineral Spirits as the cleaning agent. Procedure E (Alkaline Cleaning) describes methods for cleaning with an alkaline cleaning agent that is appropriate for the product. The cleaning method and cleaning agent chosen for any test run should be as agreed upon between the purchaser and seller. ASTM D609 refers to the water break test as a method of checking test pieces for contaminants. The procedure is simply to 600

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