Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 298 of 331

perature, which is held at 38°C (100°F) and the elimination of the corrosive salt (electrolyte). ASTM D 1193 Type III water is used. This test method is used to test the life expectancy of coating systems by measuring their resistance to water penetration. ASTM D 2247—Testing Water Resistance of Coatings in 100% Relative Humidity The ASTM D 2247 Standard is used to investigate how a coating resists water, which can help predict its useful life. This is generally a pass/fail test; however, the time to failure and degree of failure can be measured. A coating system passes if there is either no sign of water-related failure after the specified test period or less than an established specified amount of failure. For the ASTM B 2247 Standard the ASTM D 1193 Type IV water is placed in the bottom of the exposure zone to a depth of 6 to 8 in. and heated.The area of the exposure zone above the wa- ter is not heated directly in or- der to cause condensation on the test pieces. The water is intro- duced into the chamber before the test pieces and maintained at a temperature approximately 5 to 10°C (10–20°F) higher than the temperature of the vapor above it. The major variation in the chamber is the elimination of the fogging tower. The 100% humidity results from the va- porization of the heated water in the bottom of the chamber Fig. 4. Humidity test chamber schematic drawing. and/or having heated humidified air pumped through the water. The humidi- fying tower is used when the option of having air pumped through the heated water is chosen. The exposure zone is maintained at 38° ± 1°C (100° ±2°F) and 100% relative humidity. This test method is performed in water-jacketed chambers (see Fig.2) with 6 to 8 in. of water in the bottom of the exposure zone and the water jacket filled to 12 in. above the bottom to ensure that the immersion heaters are sub- merged. It can also be run in larger chambers, such as walk-in or drive-in size units (see Fig. 3), equipped with heated water tanks in the exposure zone to gen- erate the required humidity. A primary concern when conducting the ASTM D 2247 test is that the chamber be sufficiently insulated. Figure 4 is a schemat- ic of a typical humidity test chamber. To ensure that the ASTM D 2247 test is being performed consistently, it is rec- ommended that a control test piece with known durability be included in each test run. ASTM B 368—The Copper Accelerated Acetic Acid-Salt Spray (Fog)Test (or CASS Test) The ASTM B 368 Standard, originally developed by the American Electroplaters and Surface Finishers Society (AESF), is used primarily in the development of coat- ed metal products, including decorative coatings, which will be exposed to severe 297

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