NAVAIR 01-1A-509-3
01 March 2005
TM 1-1500-344-23-3
TO 1-1-689-3
Figure 7-2. Classification of EMI Problems
a. Conductivity: Good conductivity is taken as a
g. Wear resistance: Important when the gasket is
rough, indirect measure of EMI shielding. In addition,
repeatedly compressed and depressed.
a contact resistance of 2.5 milliohms is specified
across joints for grounding and lightning strike
h. Conformability: Accommodate joint unevenness.
protection.
7-5. EFFECTS OF CORROSION.
b. Corrosion resistance of gasket material:
Properties should not change with service (e.g.
7-5.1. GENERAL. Corrosion can degrade the electrical
corrosion which produces an insulting layer of material).
and mechanical properties of a joint. The exposure of
EMI gaskets to various environmental conditions can
c. C o m p a t i b i l i t y with the mating surface:
significantly reduce its shielding effectiveness and
Electrochemical compatibility to prevent galvanic
service life. Under field service conditions, military
corrosion.
d. Good adhesive qualities: Required for electrical
Table 7-3. Materials Used in EMI Joints
contact and environmental scaling.
Enclosure
Coatings
Fillers Used in EMI
e. Chemical resistance to solvents: Properties
Gaskets
should not change with exposure to operational
Carbon
Silver
Steel
chemicals (e.g. fuel, paint stripper, hydraulic fluid).
Silver
Copper
Aluminum
Copper
Nickel
Magnesium
f. Resilience: Resistance to compression required
Beryllium/Copper
Tin
Composites
Phosphor Bronze
Cadmium
Plastic
for electrical contact and environmental scaling. Long
Monel
Aluminum (IVD)
term pressure should not cause permanent deformation
Stainless Steel
Zinc
(compression set). Normal deflection for solid
Steel
Chromate
rectangular elastomer seals range from 5 to 15%.
Nickel
Phosphate
Tin
Aluminum