can go to just about any store these days and buy a tube of RTV (room
temperature vulcanizing) rubber caulk. That was not the case as recently
as the 1960s and 70s (assuming you're old enough to consider that recent).
Here is a short news item about how Dow Corning Corporation's breakthrough
new compound was set to revolutionize hermetic sealing of critical electronic
assemblies. It shows entire subassemblies of connectors, wires, and
discrete components (no ICs at the time) completely engulfed in the
stuff. I remember at Westinghouse Electric, where I worked as a technician
after a tour in the USAF, we used RTV for sealing bulkhead-mounted connectors
on torpedo heads and towed sonar arrays. We also used massive
quantities of it to seal off molds for ceramic transducer element arrays
prior to potting them with a polyurethane compound. That was cool work.
The heavy aluminum molds, about 6-feet long, were placed in a huge,
thick-walled aluminum tube and a vacuum was pulled while the compound
was curing in order to eliminate trapped bubbles. After about 6 hours
of non-stop, tedious labor, it was as close as a male can come to experiencing
the joy of birth when removing the arrays from the molds and seeing
the newborn sonar array. The equivalent birth-related pain came when
a potting job went bad.
U. S. Air Force Snark, a guided missile, roars from its launching
cradle with its rocket boosters flaming. The Snark couples intercontinental
range with the ability to carry a first-priority warhead.
New silicone rubber that cures at room temperature provides a protective
coating for vital circuits.
Using a new silicone rubber that
cures at room temperature, engineers at Northrop Aircraft, Inc., have
developed a quick, easy, and almost foolproof guarantee of top performance
for vital high impedance circuits in the
Snark guided missile, the F-89 interceptor, and other projects.
After electronic panels in the circuits are packed with resistors,
capacitors, transistors, and other gear designed to record or transmit
information during flight, the panels are coated with Silastic RTV,
the room temperature curing silicone rubber developed by Dow Corning
Corp. According to Northrop designers a single coating of the silicone
rubber cushions vibration, provides moisture resistance, improves surface
resistivity of the panels, and protects the assemblies from rough handling.
Individual components may be inspected after assembly by simply slitting
open the silicone rubber to expose the unit. Slit is then patched with
the same rubber.
Among the electronic components which Northrop Aircraft protects
with the new silicone rubber are these junction boxes, shown here before
and after the potting.
The silicone rubber material is applied with an air-pressure gun
to many electrical components of the Snark missile. Here is a filter
assembly during and after potting.
Posted July 19, 2013
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