INTERN MPAPS G-4518 PDF

This specification covers the general coating process, coating performance and fastener torque-tension requirements, quality, KCC, source approval and quality control, packing, shipping, and identification requirements, and designation on drawings.

Restricted Chemical Substances

All product supplied to the requirements of this specification must comply with the requirements of the MPAPS B-50 specification.

APPLICATION

This specification covers the requirements for a silvery colored, corrosion protective coating consisting of a zinc phosphate conversion coating, covered by a zinc-rich basecoat, and an integrally lubricated aluminum-rich topcoat. This coating system is free of both hexavalent and trivalent chromium. These finishes are intended for use on ferrous fasteners and clips where high levels of corrosion protection and freedom from hydrogen embrittlement are required (such as high hardness parts). This coating should not be used on parts which will come in contact with uncoated copper, magnesium, or stainless steel, but will provide good bi-metallic corrosion resistance when in contact with aluminum. Coating should not be used on materials which might be adversely affected by the cure temperature range of 200-255°C (392-491°F). The maximum continuous service temperature is 260°C (500°F).

Two types of coatings are included:

Type I – silver color; for use on externally or internally threaded fasteners M6 and larger and other small parts such as spring clips, brackets, etc.; 840 hours minimum salt spray to red rust.

Type II – silver color; for use on internally threaded parts M6 and larger (e.g., nuts); 480 hour minimum salt spray to red rust.