The phosphate coatings covered by this specification are intended for use where "heavy" coatings are required. Light phosphate coatings used as a paint base are covered by other specifications, such as TT-C-490. However, "heavy" phosphate coatings may be used as a paint base where required on some Naval Gun Systems and 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-L-3150 lubicating oil. This class may be specified for general purpose applications in which a moderate degree of corrosion resistance is required and to prevent wear and assist in the "breaking-in" of bearing surfaces. MIL-L-3150 oil may be removed from phosphate coated items by contact with absorbing material.
c. Class 3 covers coatings 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 1.2). This coating is recommended for use where a dyed or colored coating such as olive drab or a 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°C (200°F) is expected. Type Z coatings may be used to prevent galling in cold-extrusion and deep-drawing applications. Except for special-purpose applications. Type Z coatings should be used with a suitable supplementary treatment (see 1.2). Each class for type Z is described below:
a. Class 1 allows the procuring activity to specify a suitable treatment depending upon the particular application.
b. Class 2 covers coatings impregnated with grade 1 of MIL-C-16173. This class may be specified for general purpose application in Which corrosion protection is the primary consideration and where a "dry-to touch" film is required, indoor or outdoor, for domestic and overseas shipment, with or without cover. MIL-C-16173, grade 1 compound is equivalent to P-1 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.
d. Class 4 covers chemically converted coatings with supplementary treatments that are suitable for use where petroleum base or wax supplementary treatments cannot be used but where extended corrosion protection is necessary. The color of the chemically converted coatings will be grey (see 1.2). Class 4 chemically converted coatings, treated with a high melting wax or a preservative oil, provide excellent corrosion protection where the wax or oil is not objectionable. This coating is recommended for use where a dyed or colored coating such as olive drab or a 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.
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