Metal Finishing Guide Book

2013

Issue link: https://metalfinishing.epubxp.com/i/218436

Contents of this Issue

Navigation

Page 551 of 843

solution of sodium chloride in 95 parts of ASTM D1193 Type IV water. The pH of the solution is adjusted with the addition of glacial acetic acid to be within the range of 3.1 to 3.3. This solution is then atomized into the exposure zone to create a fog that has a condensate collection rate of 1.0 to2.0 ml/hr per 80 m2 of horizontal collection area while the temperature of the exposure zone is being held at a constant 35° +/- 2°C (95° +/- 3°F). This variation is particularly useful in research when evaluating the effect of altering the parameters of an electroplating process or evaluating the quality of the process on decorative chromium plating. It is used primarily for steel and zinc die-casting substrates. It should be noted by users that even though this test is utilized as a more severe alternative to the ASTM B117 Salt Spray (Fog) test, the type of actual corrosion produced is not necessarily of a "like-kind" to that resulting from the B117 test on the same test specimen material. Annex 2—Cyclic Acidified Salt Fog Test For this variation the pH of the test solution is adjusted to a range of 2.8 to 3.0, the exposure zone temperature is raised to 49°C (120°F), and the humidifying tower temperature is raised to 57°C (135°F); however, the most significant change is the wet and dry cyclic nature of the test. This change in the test requires that the test chamber be equipped with apparatus to produce differing atmospheres for the various steps in the test cycle and timing apparatus that will cause the atmosphere within the chamber to vary as follows. Every 6 hours, the test pieces will be exposed to 3/4 of an hour spray of atomized salt solution, then a 2-hr dry period, during which the chamber is purged of humidity. The final cycle is 1 ¾ hours of high humidity as described by the temperature and collection rates specified. Adding the cycles to this test increases its effectiveness if evaluating how products perform in a continuously changing environment. Annex 3—Acidified Synthetic Sea Water (Fog) Test The addition of 42 g of synthetic sea salt and 10 ml of glacial acetic acid per liter of solution, in this variation, is to increase its usefulness for production control of exfoliation-resistant heat treatments used in producing 2000, 5000, and 7000 series aluminum alloys. The pH is adjusted into the range 2.8 to 3.0 and the test is performed at a temperature of 49°C (120°F). When using this variation to test organic coatings on metallic substrates the test is performed at a pre-selected temperature in the range 24 to 35°C (75–95°F). The collection rate specification for fog cycles of this test is unchanged from the B117 Standard at 1 to 2 ml/hr of operation; however, 2-hr cycles are used throughout the test period. Because of the cyclic nature of this test, prior to starting the test a separate 16-hour salt fog test is necessary to establish and verify proper condensate collection rates. The test chamber must be equipped with apparatus and controls that will cycle the exposure zone repeatedly through a ½ -hr spray step then 1 ½ hours of soak time at 98% relative humidity (see Fig. 5). Annex 4—Salt/SO2 Spray (Fog) Test In this test either a sodium chloride or synthetic sea salt solution can be used. The determination of which will be used is dependent on the product being tested and the requirements of the interested parties. A primary difference in this test procedure is the addition of sulfur dioxide (SO2) to the exposure zone using a predetermined cycle. The requirement of the ASTM G85, Annex 4 stan542

Articles in this issue

view archives of Metal Finishing Guide Book - 2013