[time-nuts] Thermal insulation choice?

[Rick Karlquist]

Neville Michie wrote:

> I wonder if TVB knows what the brown foam in 10811 is? Does it have a
> radiation absorbing powder in it?
>
> cheers, Neville Michie
>

Various foams were tried and or used in the 10811.  The main
concerns with foams had nothing to do with insulating qualities
and certainly no one worried about radiation absorbing powder.
They wanted a foam that would not fatigue or disintegrate
mechanically.  It had to have good castability in the mold,
as the dimensions are fairly critical and the shape is intricate.
It could not outgas hazardous substances under normal oven
temperatures.  There was also an issue about what it would
do if the oven ran away.  It could not catch on fire, etc.
There are the usual manufacturability issues like cost, availability,
whether the vendor was "approved", etc.

In the E1938A, with a demonstrated thermal gain of over 1 million,
it was still the case that any foam or no foam worked fine thermally.
The most the foam could do is possibly change the ratio of heat
between the main surfaces and the rim.

There are minor differences in the amount of oven power for various
types of foams.  In general, it is fairly difficult to screw up
an oven oscillator by choosing the wrong foam.

Rick Karlquist
N6RK