Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

Issue link:

Contents of this Issue


Page 300 of 331

that altering the parameters of an electroplating process or evaluating the qual- ity of the process on decorative chromium plating.It is used primarily for steel and zinc die-casting substrates. Annex 2—Cyclic Acidified Salt Fog Test For this variation the pH of the 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 tow- er 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 a timing apparatus that will cause the at- mosphere 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 pe- riod, during which the chamber is purged of humidity. The final cycle is 1 3/4 hours of high humidity as described by the temperatures and collection rates spec- ified. Adding the cycles to this test increases its effectiveness if evaluating how prod- ucts 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 varia- tion to test organic coatings on metallic substrates the test is performed at a preselected 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 B 117 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, periodical- ly a separate 16-hour salt fog test is necessary to establish and verify proper con- densate collection rates. The test chamber must be equipped with apparatus and controls that will cycle the exposure zone through a 1/2-hr spray then 1 1/2 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 pro- cedure is the addition of sulfur dioxide (SO2 into the exposure zone on a periodic basis requires ad- ) to the exposure zone using a pre- determined cycle. This cycle is also dependent on the product being tested and agreement between the purchaser and the seller. The requirement of the ASTM G 85, Annex 4 standard is that all the cycles during the test period be equal in length. Introducing SO2 ditional apparatus. The chamber can be equipped with a device that will dis- burse the SO2 test pieces. The SO2 with any set cycle. It is imperative to address all safety issues: equipment, personnel, apparatus, and procedures prior to testing with SO2 tor, flow meter, and timer to allow for accurate introduction of SO2 . Note that the primary changes to the chamber are to allow for the correct in- troduction of the SO2 . All parts of the chamber that come into contact with the 299 evenly throughout the chamber without directly impinging on any supply source attached to the chamber must have a regula- in accordance

Articles in this issue

view archives of Metal Finishing Guide Book - 2012 Organic Finishing Guidebook Issue