RE: Inner tubes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

Close.  I tried filling a corrugated aluminum duct toroid with the
"Great Stuff" polyurethane foam in a can, from Home Depot.  The stuff
cures by reacting to water or water vapor, so I added a few spoonfuls of
water inside the toroid.  The greatest problem is that you're guessing
with no feedback whatsoever as to when to stop adding the foam.  It
expands very slowly, so even if one had X-ray vision, it would be
difficult to know when to stop.  With the duct toroid, the consequence
to over-filling is that it burst the seam where the two ends of the duct
were joined (several HOURS after filling).  Perhaps with an inner tube
it would just keep on expanding, symmetrically.  Or perhaps there's no
way to prevent gasses separating from the foam and causing unpredictable
voids?

The machined toroid came out beautifully, but filling an inner tube
would have been much cheaper.  Who wants to be a hero and find out?

Gary Lau
MA, USA


Original poster: "Brian" <ka1bbg-at-webryders-dot-net>

Hi, I think both Gary Lau and i both tried the foam in a tube.. i could
get
it to harden but never a nice round donut. the foam just is not made to
do
what we want. maybe if the form was hard and strong it might work. Gary
had
one machined from foam. cul brian f.


  > Original poster: "Chris" <ct451-at-yahoo-dot-com>
  >
  > I've been trying to fill a 400x8 inner tube, the perfect size for my
mini
  > coil, with construction foam without any success for a wile now and I
was
  > wondering if anyone experimented with this idea.
  > The first time i tried just spraying some foam inside the tube and
letting
  > it dry. This didn't work. The foam did solidify but when I removed
the can
  > air trapped inside came out and the tube shrank.
  > Then i decided to puncture a bunch of holes all around another tube
and
  > then fill it with the foam. This failed as well but got some pretty
  > sculptures from where the foam came out of the holes. Again the tube
shrank
  > non-uniformly even though a lot of foam came out.
  > The foam does not set uniformly under pressure and the gasses
separate and
  > escape.
  > For my next attempt I'm thinking of either keep shaking the tube so
that
  > the gas is mixed with the foam until it solidifies or put the tube in
an
  > airtight box and suck the air on the outside so that there's less
pressure
  > inside the tube when the foam expands.
  > But perhaps there's a better approach or a different material I can
fill
  > the tubes with.
  > The coil works fine for more than 45 mins on a run with an aluminium
tray
  > as the top load but it would look so much better with a toroid.
  > These tubes cost about $1.50 each and the foam about  $4 for each
attempt
  > so any help welcome,
  >
  > Chris
  >