Metal Finishing Guide Book


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Table II. Coating Weight Classifications Specification ASTM B 499 Class 1 Class 2 Class 3 MIL-C-5541 Class 1A Class 3 AAMA 605.2 AAMA 603.8 Color Coating Weight, Application mg/ft2 Yellow to brown Iridescent to yellow Yellow to colorless 30���100 10���35 Less than 1 or 2 Maximum protection General purpose Decorative, contract resistance Unspecified Greater than 40 Unspecified Greater than 40 Yellow to brown 30���100 (Unspecified coating properties Maximum protection Corrosion and contact resistance Maximum corrosion resistance 3. Remove from the salt bath and carefully rinse in cold water. 4. Dip for 30 seconds in equal parts by volume of concentrated nitric acid and water at room temperature. 5. Rinse thoroughly in cold water and blow dry. 6. Reweigh. 7. Repeat steps 2 through 6 until the weight loss is less than 0.6mg. 8. Calculate the costing weight as follows: Coating weight = total weight loss/total area Verify that the observed coating weight meets the required specifications. Manufacturing specifications for coating weights differ for various applications. Guidelines for quality manufacturing practices are covered by specifications from agencies such as American Society for Testing and Materials (ASTM), American Architectural Manufacturers Association (AAMA), military specifications (MIL), and AeroSpace Material Specifications (AMS). See Table II for typical examples. Other Test Requirements Salt spray resistance tests are also required as standard quality-control practices. Comprehensive testing procedures listed in the following standards and specifications evaluate the performances of the composite film consisting of the conversion coating and paint topcoat. ASTM D 1730: Standard practices for preparation of aluminum and aluminum-alloy surfaces for painting. ASTM B 449: Standard practice for chromate treatments on aluminum. MIL-C-81706: Chemical conversion materials for coating aluminum and aluminum alloys. MIL-C-5541: Chemical conversion coatings on aluminum and aluminum alloys. AAMA 603.8: Voluntary performance requirements and test proce dures for pigmented organic coatings on extruded aluminum. AAMA 605.2: Voluntary specification for high-performance organic coatings on architectural extrusions and panels. 140

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