MIL-DTL-16232G

Abstract

This specification covers two types of heavy phosphate coating for ferrous metals, applied by immersion. The coatings consist of a manganese phosphate or zinc phosphate base and, when specified, a supplementary treatment (see <a>6.1</a>). <b><u>Intended Use:</u></b> The "heavy" phosphate coating 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 such as TT-C-490. Heavy zinc phosphate coating may be used when paint and supplemental oil coatings are required on various parts or assemblies. Type M coatings are more resistant than type Z to alkaline environments. Type M coatings should not be exposed to temperature in excess of 121 C (250 F). Except for special purpose applications, phosphate coatings should be used with a suitable supplementary treatment. Each class for type M is described below: a. Class 1 allows the procuring activity to specify a suitable supplementary treatment depending upon the particular application. b. Class 2 covers coatings impregnated with MIL-PRF-3150 lubricating oil or MIL-PRF-16173, Grade 3 rust preventive. This class may be specified for general purpose applications in which a moderate degree of corrosion resistance is required during storage, to prevent wear, and assist in the "breaking-in" of bearing surfaces. Supplemental oil may be removed from phosphate coated items by contact with absorbing material. c. Class 3 covers coating without supplementary treatment. This class is intended for special purposes in which a supplementary treatment is not desired. d. Class 4 covers chemically converted coatings, chemically converted with supplementary treatments that are suitable for use where corrosion protection is required in addition to other properties (see <a>1.2</a>). This coating is recommended for use where a dyed or colored coating such as olive drab or black (non-reflective) coating is needed. The class 4 coating provides improved corrosion resistance; however, the supplementary coating provides most of the corrosion protection when used in conjunction with phosphate coatings. The class 4 coating provides an improved "break-in" coating and is recommended for reducing the sliding friction in preference to the class 2. The use of the class 4 coating reduces the variation in torque versus tension values usually found with threaded fasteners. Type Z coatings should not be used if contact with alkaline materials or exposure to temperatures above 93&#176;C (200&#176;F) is expected. Type Z coatings may be used to prevent galling in cold-extrusion and deep-drawing applications. Except for special-purpose application, Type Z coatings should be used with a suitable supplementary treatment (see <a>1.2</a>). Each class for Type Z is described below: a. Class 1 allows the procuring activity to specify a suitable supplementary treatment depending upon the particular application. b. Class 2 covers coatings impregnated with grade 3 of MIL-PRF-16173 or MIL-L-3150. This class may be specified for general purpose application in which corrosion protection is the primary consideration. MIL-PRF-16173, grade 3 compound is equivalent to P-3 of MIL-P-116. c. Class 3 covers coatings without supplementary treatment. This class is intended for special purposes in which a supplementary treatment is not desired. <br>