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1. 06:35 AM - Re: Insulator in durable gas tight compression (Robert L. Nuckolls, III)
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| Subject: | Re: Insulator in durable gas tight compression |
At 11:48 AM 3/4/2019, you wrote:
>Tasker <dick@thetaskerfamily.com>
>
>I believe you are asking is it okay to use some
>sort of laminate in the stack-up of layers
>wherein the goal is to have something to mount
>the connection to and insulate it from your
>airplane sheet metal and that will not affect
>the "gas-tightness" of the connection.
>
>If that is the question, I believe that the
>answer would be that there are very few
>materials that would allow that.=C2 Ceramic would
>work, but that is hared to work with.=C2 Any
>plastic type material probably is too soft to
>not allow some relaxation over time of the joint.
Great catch Dick . . . I had a totally
different image for his question!
Yes, the way to achieve the ultimate
gas-tight connection between two
conductors is to mash them together
with enough force that the two metals
deform to conform with each other.
Obviously, limits to force that can be
applied are influenced by the relative
hardness of materials involved in the
force column. Too hard won't mash; too soft
(like an intermediate layer of non-conductor)
and the important materials (conductors) don't
mash and retain their intimate contact over
time.
One or more OBAM aircraft feature composite
firewall structures. To install a high
integrity firewall ground . . .
https://tinyurl.com/y4x3k24g
. . . we included a stack of washers(4)
from which the installer might craft a
HARD spacer between the forward and
aft bus bars. This feature prevented
crushing the firewall composite matrix
such that gas-tight integrity of the
electrical connections was compromised.
Having said that, one might appropriately
question the design of Carling switches
(and others) that place insulating
materials in the force-column that joins
electrical conductors of their products.
https://tinyurl.com/8cm52v
This is one (of no doubt many) instances
where the designers have selected their
non-conducting housing materials carefully
to minimize effects on manufactured
joints in the conductor pathways.
Ideal? Perhaps not. Failure proof? We
seen some failures . . . precipitated
by heating events OUTSIDE the force
column that degraded the plastic
and destroyed integrity of the
otherwise dependable joints.
Hundreds of thousands of these
switches have met design goals in
tens of thousands of TC aircraft
for decades.
So the short answer is, yeah you can
do it . . . others have done it . . .
but with well considered properties
of materials.
Bob . . .
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