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You 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
1970s. 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 encapsulated 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 machined
metal 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 miracle of birth when removing the arrays from the
molds and seeing the perfect newborn sonar array with an equivalent
Apgar score of 10.
Rubberized Circuits for Guided Missiles
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.
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.
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.
Posted March 5, 2021
(updated from original post on 7/19/2013)
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