Machinery's Handbook, 31st Edition
1644 Plating Standards Electropolishing, ASTM B912-02 (2018): This process electrolytically removes or di- minishes scratches, burrs, and unwanted sharp edges from most metals. Electropolishing can be expected to reduce roughness average (Ra) by approximately 10 to 35 percent, with 50 percent improvement possible in some cases. By eliminating microscopic defects and impurities, electropolishing can improve both corrosion resistance and fatigue life of parts. In addition, this process passivates exposed surfaces, with results superior to chemical passivation methods. Finishes from satin to mirror-bright are produced by controlling time, temperature, or both. Stainless steels are the most commonly electropolished mate- rials, but many metals are good candidates for the process. Material thickness loss during electropolishing typically is 0.0002–0.0007 in. (5–18 μ m) but may be as much as 0.003 inch (76 μ m). The amount removed depends on desired surface improvement and usually can be controlled to within 0.0001 in. (2.5 μ m). Parts with tight tolerances can be electropolished if process parameters are well planned and controlled. Parts to be electropolished must be placed on racks. Features such as deep bores may require additional cathodes, and complex parts may need custom process tooling. Gold, MIL-G-45204C: Has a yellow to orange color depending on the proprietary pro cess used. Will range from matte to bright finish depending on basis metal. It has good corrosive resistance and a high tarnish resistance. It provides a low contact resistance, is a good conductor of electricity, and has excellent solderability. If the hardness grade for the gold coating is not specified, Type I shall be furnished at a hardness of Grade A, and Type II furnished at a hardness of Grade C. For soldering, a thin pure soft gold coating is preferred. A minimum and maximum thickness 0.00005 and 0.00010 inch (1.27 and 2.54 μ m), respectively, shall be plated. Unless otherwise specified, gold over silver underplate combinations shall be excluded from electronics hardware. Silver or copper plus silver may not be used as an underplate unless required by the item specification. When gold is applied to brass bronze or beryllium copper, or a copper plate or strike, an antidiffusion underplate such as nickel shall be applied. Type I is 99.7% gold minimum (Grades A, B, or C); Type II is 99.0% (Grades B, C, or D); and Type III is 99.9% (Grade A only). Grade A is 90 Knoop maximum; Grade B is 91-129 Knoop; Grade C is 130–200 Knoop; and Grade D is 201 Knoop and over. Class 00 has a thickness of 0.00002 inch (0.5 μ m) minimum; Class 0, 0.00003 inch (0.76 μ m); Class 1, 0.00005 inch (1.3 μ m); Class 2, 0.0001 inch (2.5 μ m); Class 3, 0.0002 inch (5 μ m); Class 4, 0.0003 inch (7.6 μ m); Class 5, 0.0005 inch (12.7 μ m); and Class 6, 0.0015 inch (38.1 μ m). Hard Anodize, MIL-A-8625F: The color will vary from light tan to black depending on alloy and thickness. Can be dyed in darker colors depending on the thickness. Coating penetrates base metal as much as builds up on the surface. The term thickness includes both the buildup and penetration. It provides a very hard ceramic type coating. Abrasion resistance will vary with alloy and thickness of coating. Has good dielectric properties. Do not seal coatings where the main function is to obtain maximum abrasion or wear resistance. When used for exterior applications requiring corrosion resistance but permit ting reduced abrasion, the coating shall be sealed (boiling deionized water or hot 5% sodium dichromate solution, or other suitable chemical solutions). Type III will have a thickness specified on the contract or applicable drawing. If not specified use a nominal thickness of 0.002 inch (50.8 μ m). Hard coatings may vary in thickness by 0.0005–0.0045 inch (12.7–114.3 μ m). Class 1 shall not be dyed or pigmented. Class 2 shall be dyed and the color specified on the contract. The process can be controlled to very close thickness tolerances. Where maximum serviceability or special properties are required, consult metal finisher for best alloy choice. Thick coatings, those over 0.004 inch (101 μ m), will tend to break down sharp edges. Can be used as an electrical insulation coating. “Flash” hard anodize may be used instead of conventional anodize for corrosion resistance and may be more economical in conjunction with other hard anodized areas. Lubrication, Solid Film MIL-L-46010D: The Military Plating Specification establishes the requirements for three types of heat cured solid film lubricants that are intended to
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