a. Where temperatures do not exceed 1,000°F and other coating would not be adequate or suitable.
b. To minimize the effect of dissimilar metal contacts, such as mild steel with unplated corrosion resisting steel.
c. As an undercoat for other functional coatings.
d. To restore dimensions.
2-289. Chromium Plating (QQ-C-320). This coating is of two classes; Class I, intended for use as a decorative coating; and Class
II, for wear resistance and corrosion protection. Heavy chromium electro deposits (0-1-10 MILS) are often used to salvage under
machine parts. Unless otherwise specified, the plating shall be applied after all basic metal heat treatments and mechanical
operations such as machining, brazing, welding, forming and perforating have been completed. Hydrogen embrittlement relief shall
be in accordance with blue prints and /or applicable specifications. All plated parts which are designed for unlimited life under
dynamic loads shall be shotpeened in accordance with military Specification MIL-S-13165 prior to plating. All parts with a hardness
of Rockwell C40(180, 000 PSI),after shot peening and plating, shall be baked at 375° 25°F for 3 hours for hydrogen embrittlement
relief. It is extensively used as an undercoating for nickel and chromium plating.
2-290. Tin Plating (QQ-T-425). Tin plating is used where a neat appearance, protective coating and easy solderability are of prime
importance. The base metal for tinplate shall be low carbon cold steel.
2-291, Phosphate Coating (IL-P-16232). The description of phosphate coatings herein is specified as "heavy" coatings. Light
phosphate coatings used as a paint base are covered by specification TT-C-490. Type "'M" ,Oanganese) coatings are resistant to
alkaline environments and should not be exposed to temperatures in excess of 250°F. Except for special purpose applications,
phosphate coatings should be used with a suitable supplementary treatment. Type "Z" (Zinc) coatings should not be used in contact
with alkaline materials or temperature in excess of 200°F. For the different classes of coatings and required supplemental
treatments, refer to MIL-P16232. This coating should be applied after all machining, forming, welding and heat treatment have been
completed. Parts having a hardness of Rockwell C40 or higher shall be given a suitable heat treat stress relief prior to plating and
shall be baked subsequent to coating as follows:
a. Type "hM" shall be baked at 210°-225°F for 1 hour.
b. Type "Z" shall be baked at 200°-210°F for 15 minutes (embrittlement relief).
2-292. Silver Plating (QQ-S-635). Silver plating (electro deposits) has high chemical and oxidation resistance, high electrical
conductivity and good bearing properties. Silver is often used as an anti-seize and for preventing fretting corrosion at elevated
temperatures. Silver plating shall be of the following types and grades:
a. Type I, Matte. Deposits without luster, normally obtained from silver-cyanide plating solutions operated without the use
b. Type II, Semi-Bright. Semi-lustrous deposits normally obtained from silver-cyanide plating solutions operated with
c. Type m, Bright. Sometimes obtained by polishing or by use of "brighteners".
d. Grade A. With supplementary tarnish resistant treatment (chromate treated).
e. Grade B. Without supplementary tarnish resistant treatment.
2-293. Intended Use. The following applications of thickness are for information purposes only:
a. 0.0005 for corrosion protection of nonferrous base metal.
b. 0.0003 for articles such as terminals which are to be soldered.
c. 0.0005 to 0.010 for electrical contacts, depending on pressure, friction and electrical load.
d. 0.0005 for increasing the electrical conductivity of base metals.
e. On ferrous surfaces, the total plated thickness shall not be less than 0.001 inch. After all base metal heat treatments and
mechanical operations such as machining, brazing, welding, forming and perforating of the article have been completed, if the type is
not specified, any type is acceptable. All steel parts subject to constant flexure or impact having a Rockwell hardness of RC40 or
greater shall be heated at 375° 25°F for 3 hours for stress relief prior to cleaning and plating.
2-294. Hardened parts which have been heat treated at less than 375°F shall not be heated as noted above, but shall be treated by
any method approved by the contracting agency.
2-295. For complete information pertaining to silver plating, refer to Federal Specification QQ-S-365.