Machinery's Handbook, 31st Edition
Plating Standards 1647 relief steel parts at a minimum 375 ± 25 ° F (190 ± 14 ° C) or more prior to cleaning and plating if they contain or are suspected of having damaging residual tensile stresses. All types and grades will have a minimum thickness of 0.0005 in.(12.7 μ m) unless otherwise specified. Type I is matte, Type II is semi-bright, and Type III is bright. Grade A has a chromate post-treatment to improve tarnish resistance. In contrast Grade B has no supplementary treatment. Tin, MIL-T-10727C: There are two different types of coating methods used, electrode posited (based on Use ASTM B545 standard specification for electrodeposited coatings of tin) and hot dipped. Thickness as specified on drawing (thickness is not part of the specification) is 0.0001- 0.0025 inch (2.5–63.5 μ m), flash for soldering; 0.0002–0.0004 inch (5.08–10.16 μ m), to prevent galling and seizing; 0.0003 inch (7.62 μ m) minimum, where corrosion resistance is important; and 0.0002–0.0006 inch (5.08–15.24 μ m) to prevent formation of case during nitriding. Color is a gray-white color in plated condition. Tin is soft, but very ductile. It has good corrosion resistance, and has excellent solderability. Tin is not good for low temperature applications. If a bright finish is desired to be used in lieu of fused tin, specify Bright Tin plate. Thick ness can exceed that of fused tin and deposit shows excellent corrosion resistance and solderability. Vacuum Cadmium, MIL-C-8837B: Is used primarily to provide corrosion resistance to ferrous parts free from hydrogen contamination and possible embrittlement. Recom mended on steels with a strength of 2.2 × 10 5 psi (1517 MPa) or above. Coating is applied after all machining, brazing, welding, and forming has been com pleted. Prior to coating, all steel parts shall be stress relieved by baking at 375 ± 25 ° F (190 ± 14 ° C) for 3 hours if suspected of having residual tensile stresses. Immediately prior to coating, lightly dry abrasive blast areas are to be coated. Type I shall be as plated; and Types II and III require supplementary chromate and phos phate treatments respectively. Classes 1, 2, and 3 have thicknesses of 0.0005, 0.0003, and 0.0002 inch (12.7, 7.62, and 5.08 μ m) respectively. Cadmium coating shall not be used, if in service, temperature reaches 450 ° F (232 ° C). A salt spray test is required for type II and is 96 hours. Zinc, ASTM B633: This specification covers requirements for electrodeposited zinc coatings applied to iron or steel articles to protect them from corrosion. It does not cover zinc-coated wire or sheets. Type I will be as plated; Type II will have colored chromate conversion coatings; Type III will have colorless chromate conversion coatings; and Type IV will have phosphate conversion coatings. High strength steels (tensile strength over 1700 MPa or 246,500 psi) shall not be electroplated. Stress relief: All parts with ultimate tensile strength 1000 MPa (145, 000 psi) and above at minimum 190°C (374°F) for 3 hours or more before cleaning and plating. Hydrogen embrittlement relief: All electroplated parts 1200 MPa (174,000 psi) or higher shall be baked at 190°C (374°F) for 3 hours or more within 4 hours after electroplating. Corrosion Resistance Requirements Types Test Period Hr. II 96 III 12
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online