Standard Specification for Coatings of Cadmium Vacuum-Deposited on Iron and Steel
This specification covers the standard requirements for cadmium coatings vacuum deposited with or without supplementary chromate treatment on iron and steel basis metals. The cadmium metal for the production of the coating and the resultant coating shall conform to the chemical composition requirements as shall be determined by chemical, electrochemical, spectrochemical, or X-ray fluorescence analysis. Steel parts that have been machined, ground, cold-formed, or cold-straightened shall be heat treated for stress relief before cleaning and coating. The basis metal shall undergo surface cleaning, abrasive dry blasting, and outgassing by electron bombardment with high-energy positive ions to ensure satisfactory adhesion, abrasion resistance, and corrosion resistance performance. Chromate treatment shall be done in or with special aqueous acid solutions composed of hexavalent chromium along with certain anions that act as a catalyst or film forming compound to produce continuous, smooth, protective film. Coating adhesion shall be determined either by scraping or shearing with a sharp edge, knife, or razor blade through the coating down to the basis metal; plastically deforming by clamping and bending; or any suitable procedure such as burnishing, draw, or scribe tests. Salt spray corrosion test and visual examination shall also be performed on the coatings.
1.1 This specification covers the requirements for a cadmium coating vacuum-deposited on iron and steel basis metals. The coating is especially beneficial to those ferrous metals, heat treated to 46HRC and higher or having an ultimate tensile strength greater than 1500 MPa, wherein protection against corrosion and appearance are important (see Appendix X1).
1.2 Vacuum-deposited production items are normally free of hydrogen embrittlement, a danger when using electroplating processes for deposition. Vacuum deposition can handle large high-strength parts that cannot be conveniently mechanically plated in the rotating barrels.
1.3 The coating is provided in various thicknesses up to and including 12 μm (3.1) either in the as-deposited condition or with a supplementary finish (3.2).
1.4 The following precautionary caveat pertains only to the test methods portion, Section 9, of this specification: This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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