ASTM B816:00(R2021) pdf free download – Standard Specification for Coatings of Cadmium-Zinc Mechanically Deposited.
7.2.2 Supplementary Treatments—Type II coatings shall be produced by treatment with addle solutions that contain hexavalent chromium compoundS and anions that act as catalysts or lilni-forming compounds.
7.3 Appearance:
7.3.1 General—The coaling on all readily visible surfaces shall he uniform in appearance. well compacted. and complete in coverage. SuperfIcial staining from rinsing and drying and mild variations in color and luster arc acceptable.
7.3.2 Surfiwe l)efrct.s—Defects and variations in appearance in the coating that arise from surface conditions of the substrate (scratches, pores. roll marks, inclusions. etc.) and that persist in the coating despite the observance of good metal finishing practices shall not he cause for rejection.
mt I—Coatings generally perform better in service when the suhs*rate oser which they are applied is smooth and free of torn metal. inclusions. pores. and other defects. The specifications covering the untinished products should provide limits for these defects. A metal linisher can often remose defects through special treatments, such as grinding, polishing. abrasive blasting, chemical etches, and electropolishing. Hossevcr. these are not normal in the treatment steps preceding the application of the coating. When they are desired, they are the subject of special agreement between the purchaser and the seller.
7.4 Thickness:
7,4.1 Conformance to Specified Class—The thickness of the coating everywhere on the significant surfaces shall conform to the requirements of the specified class as defined in 4.1.
7.4.2 Significant Surfaces—Significant surfaces are usually defined as those normally visible (directly or by reflection) that are essential to the appearance and serviceability of the article when assembled in normal position; or that can be the source of corrosion products that deface visible surfaces on the assembled article. Significant surfaces are further defined at those surfaces that are identified as such by the purchaser, for example, by indicating them on an engineering drawing of the product or by marking a sample item of product.
7.4.3 !siinimuin Thickness Requirement—The coating requirement of this specification is a minimum requirement: that is. the coating thickness is required to equal or exceed the specified thickness everywhere on the significant surfaces. Variation in the thickness from point to point on an article and froni article to article in a production lot is inherent in mechanically deposited coatings. Therefore, if all of the articles in a production lot are to meet the thickness requirement. the average coating thickness for the production lot as a whole will be greater than the specified minimum.
Soft 2— The thickness of mechanically deposited coatings varies from point to point on the surface of a product, characteristically tending to he thicker an flat surfaces, and thinner at exposed edges, sharp projections. shielded or recessed areas, and interior corners and holes, depending on the dimensions, with such thinner areas olten being exempted from thickness retluirements.
Now 3— Processes used to produce Type II tinishcs remove some nt the coating. Because thickness requirements apply to the finished article. additional thicknesses may have to he applied to compensate for the metal removed in the Type II process.
7.5 Adhesion—The coating shall be adherent, as defined or tcsted in accordance with 9,6.