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 MIL-HDBK-419A
m. Mount gaskets in permanent seams as shown in Figure 3-20. The features to be observed in this
figure are:
(1) Gasket is bonded to one metallic surface of the seam with conductive adhesive; surfaces are
cleansed of nonconductive material before applications.
(2)
Metallic surface is machined to smooth finish and all nonconductive materials are removed.
(3) Appropriate mechanical fasteners (i.e., clamps, bolts, etc.) are used to provide a high pressure
on the rf gasket. The pressure should be reasonably uniform along the entire length of the seam.
Ensure that all rf gaskets are adequately compressed.
n.
On hinged side of doors or panels, mount gasket as shown in Figure 3-21(a). if the gasket is mounted
o.
in this manner, it receives little or no sliding motion as the door compresses it. Whereas, if the gasket is
mounted as shown in Figure 3-21(b), it will be more likely to wear out quickly because of the sliding motion of
the door.
p.
Ensure that the metal surfaces which mate with gaskets are free of oily film, corrosion, moisture,
and paint.
q.
Handle finger stock with extreme care and install it in a recessed or inner lip to minimize the
possibility of mechanical damage.
Carefully maintain the pressure exerted by the spring fingers because this pressure is highly
r.
important to the shielding effectiveness of the seam.
3.4.3.2 Penetrations and Apertures. Mechanical and electrical interfaces require that openings exist in the
equipment enclosure. Since each interface degrades the shielding effectiveness of the enclosure, the selection
and implementation of techniques to provide continuity at these interfaces are important. Figure 3-22
illustrates both good and bad practices.
Mount filters for power and control cables inside the shield and extend the filter input terminals
a.
through the shield.
Metal control shafts extending through an enclosure should be grounded with metallic fingers, a
b.
grounding nut, or an rf gasket. An alternative to the grounded metal shaft is a nylon, teflon, or other dielectric
shaft inserted in a waveguide-below-cutoff cylinder as illustrated in Figure 3-23.
Keep holes for ventilation or drainage of moisture small in effective electrical area to avoid
c.
decreasing the shielding efficiency. A "small" hole is one which is small in dimension compared to the operating
wavelength. Larger holes should be covered by a fine mesh copper screen, or alternately, a series of small holes
may be used.
3-28
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