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 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.
Rubberized Circuits for Guided Missiles
New silicone rubber that cures at room temperature provides a protective coating for vital circuits.
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.
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