scope:

Introduction

This specification defines four grades of seals for noncryogenic use in the design of electrical components and their assemblies, containers, and equipment used in ground support equipment at the John F. Kennedy Space Center (KSC). The requirements specified herein are not applicable to the National Electrical Manufacturers Association (NEMA) electrical enclosures.

Classification

Seals shall be classified as described in the following subsections.

Grade A

A Grade A seal is (1) metal-to-metal (welded, brazed, or soldered joints), (2) metal-to-glass, or (3) ceramic (brazed or solder joints). A Grade A seal is accomplished by the bonding of metallic and ceramic materials or a combination of the two. This includes the bonding of metals by welding, brazing, or soldering; the fusion of ceramic materials under heat or pressure; and the fusion of ceramic materials into a metallic support.

Grade B

A Grade B seal is accomplished by fusion, vulcanization, or adhesion to the metallic case, using a chemical or mechanical process (or combination of the two), with any material such as thermosetting plastics or elastomers (e.g., polytetrafluoroethylene, polychlorotrifluoroethyene, and silicones). A Grade B seal can be accomplished by encapsulating, molding, or potting a component or assembly with a plastic or elastomer.

Grade C

A Grade C seal is a gasket-type seal. The seal is accomplished using gaskets, O-rings, or other similar items held in proper relation to the abutting surface by pressure exerted by screws, bolts, or other clamping devices.

CAUTION

Where Grade B or Grade C seals are specified, consult the responsible design organization for information about environmental conditions, such as sun rays, radioactivity, and hazardous liquids or vapors, that could cause the seals to deteriorate.

Grade D

A Grade D seal is a ground, lapped, or polished abutting-surface seal. The seal is accomplished by grinding, lapping, or polishing the abutting surface to produce a precise fit. The mating surfaces are held in intimate contact by bolts, screws, or other suitable clamping devices.