Machinery's Handbook, 31st Edition
1642 Plating Standards designed for limited life under dynamic loads. Class 2c will be used on parts below 40 RC and designed for unlimited life under dynamic loads. Class 2d parts have hardness of 40 RC or above, which are subject to static loads or designed for unlimited life under dynamic loads. Class 2e parts have hardness of 40 RC or above, which are designed for unlimited life under dynamic loads. All coated steel parts having a hardness of 36 RC and higher shall be baked at a minimum of 375 ± 25 ° F (190 ± 14 ° C) per the following conditions.With a tensile strength of 160–180 ksi (1103–1241 MPa), the time at temperature will be 3 hr.; at 181–220 ksi (1248–1517 MPa), the time will be 8 hr.; and at 221 ksi (1524 MPa) and above, the time will be 12 hr. Copper, MIL-C-14550B: Has good corrosion resistance when used as an undercoat. A number of copper processes are available, each designed for a specific purpose such as, to improve brightness (to eliminate the need for buffing), high speed (for electro-forming), and fine grain (to prevent case-hardening). All steel parts having a hardness of 35 RC and higher shall be baked at 375 ± 25 ° F (190 ± 14 ° C) for 24 hours, within 4 hours after plating to provide hydrogen embrittle ment relief. Plated springs and other parts subject to flexure shall not be flexed prior to baking operations. Class 0 will have a thickness 0.001 - 0.005 in. (25.4–127 μ m) and is used for heat- treatment stop-off; Class 1 is 0.001 in. (25.4 μ m) and is used to provide carburizing shield, also for plated through printed circuit boards. Class 2 is 0.0005 in. (12.7 μ m) thick and is used as an undercoat for nickel and other platings. Class 3 is 0.0002 in. (5.08 μ m) thick and is used to prevent basis metal migration into tin (prevents poisoning solderability). Class 4 is 0.0001 in. (2.54 μ m) thick. Tin Lead, MIL-P-81728A: It has excellent solderability. Either a matte or bright luster is acceptable. For electronics components, use only parts with a matte or flow brightened finish. For brightened electronic components, the maximum thickness will be 0.0003 in. (7.62 μ m) Tin 50 to 70% by weight and with a lead remainder, 0.0003-0.0005 in (7.62–12.7 μ m). Magnesium Process, MIL-M-3171C: Process #1-A chrome pickle treatment for magne sium. Color varies from matte gray to yellow-red. Has only fair corrosion resistance (< 24 hours, 20 percent salt spray resistance). #7-A dichromate treatment for magnesium. Color varies from light brown to gray depending on alloy. Only fair corrosion resistance (< 24 hours, 20 percent salt spray resistance). #9-A galvanic anodize treatment for magnesium. Produces a dark brown to black coat ing. Designed to give a protective film on alloys which do not react to Dow No. 7 treatment. Only fair corrosion resistance (< 24 hours, 20 percent salt spray resistance). Type/Class Thickness (inch) Comments
Removes metal. (approx. 0.0006 for wrought, less for die castings.) No dimensional change
Used for protecting magnesium during shipment, storage and machining. Can be used as a paint base. NOTE: Must remove Type I coating before applying Type III and Type IV treatments. Note: precleaning and pickling may result in dimensional changes due to metal loss. Can be used as a paint base, and is applicable to all magnesium alloys. Used where optical properties (black) are required on close tolerance parts. NOTE: Precleaning and pickling may result in dimensional changes due to metal loss.
Type 1
Type III
…
Type IV No dimensional change
Magnesium Anodic Treatment, MIL-M-45202C: The HAE anodic finish is probably the hardest coating currently available for magnesium. It exhibits stability at high tempera tures and has good dielectric strength. It serves as an excellent paint base. It requires resin seal or paint for maximum corrosion protection.
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