Machinery's Handbook, 31st Edition
1646
Plating Standards
Methods / Types
Typical Thickness (in.)
Comments
Pretreatment Coatings
Type I
… Zinc phosphate. Class 1-spray application: Class 2A and 2B-Immersion or Dip application
Type II Type III Type IV Type V
… Aqueous Iron Phosphate 0.0003 – 0.0005 Organic pretreatment coating … Non-aqueous iron phosphate
… Zinc phosphate Type I is intended as a general all-purpose pretreatment prior to painting. Type II and IV are intended primarily for use where metal parts are to be formed after painting. Type III is intended for use where size and shape preclude using Type I, II, or IV and where items containing mixed metal components are assembled prior to treatment. Phosphate Coating: Heavy, DOD-P-16232-F: The primary differences are that Type M is used as a heavy manganese phosphate coating for corrosion and wear resistance and Type Z is used as a zinc phosphate coating. Type M has a thickness from 0.0002-0.0004 in. (5–10 μ m) and Type Z, 0.0002-0.0006 in. (5–15 μ m) Class 1, for both types has a supplementary preservative treatment or coating as specified; Class 2, has a supplementary treatment with lubricating oil; and Class 3, no supplementary treatment is required. For Type M, Class 4 is chemically converted (may be dyed to color as specified) with no supplementary coating or supplementary coating as specified. For Type Z, Class 4 is the same as Class 3. This coating is for medium and low alloy steels. The coatings range from gray to black in color. The “heavy” phosphate coatings covered by this specification are intended as a base for holding/retaining supplemental coatings which provide the major portion of the corrosion resistance. “Light” phosphate coatings used for a paint base are covered by other specifications. Heavy zinc phosphate coatings may be used when paint and supplemental oil coatings are required on various parts or assemblies. Rhodium, MIL-R-46085B: Rhodium is metallic and similar to stainless steel in color, has excellent corrosion and abrasion resistance, is almost as hard as chromium, and has a high reflectivity. Thicker coatings of Rhodium are very brittle. Class/Types Thickness (in.) Comments Type I … Over nickel, silver, gold, or platinum. Type II … Over other metals, requires nickel undercoat. Class 1 0.000002 Used on silver for tarnish resistance. Class 2 0.00001 Applications range from electronic to nose cones — wherever wear, corrosion resist solderability and reflectivity are important. Class 3 0.00002 Class 4 0.00010 Class 5 0.00025 Parts having a hardness of 33 RC or above shall be baked at 375 ° F (191 ° C) for 3 hours prior to cleaning. Parts having hardness of 40 RC and above shall be baked within 4 hours after plating at 375 ° F (191 ° C) for 3 hours. Silver, QQ-S-365D: Silver has an increasing use in both decorative and engineering fields, including electrical and electronic fields. Silver is white matte to very bright in appearance. Has good corrosion resistance, depending on base metal and will tarnish easily. Its hardness varies from about 90–135 BHN (Brinell Hardness Number) depending on process and plating conditions. Solderability is excellent, but decreases with age. Silver is the best conductor of electricity. Has excellent lubricity and smear characteristics for antigalling uses on static seals, bushing, etc. Stress
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