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Re: Foam-core Toroids

Just keep in mind that the foam keeps expanding after the first "cure
period". I've seen  this stuff used under a window sill and after a few
weeks, the foam pushed the frame up at the bottom, thus bowing the frame in
the middle rendering it useless. The foam hardens from the outside inward,
likewise, it expands in the same manner. I think you could fill it 3/4 full
in different spots, then wait a while for it to fully expand, then add more
as needed.
Good luck,

If all else fails, bring out the "hunan topload" as Greg suggested ;)

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, September 10, 2000 12:43 PM
Subject: Foam-core Toroids

> Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
> While there is nothing that looks as nice as a professionally spun toroid,
> consider the agony you would feel if and when it fell off the top of your
> coil and became permanently dented.  I think most of us that have made
> toroids out of corrugated aluminum duct have eventually had them dented
> these sorts of mishaps.
> I recently tried an experiment to improve upon the durability of home-made
> toroids.  I attempted to fill my 6" x 22" Al duct toroid with a
> foam.  This stuff cures to a fairly rigid high density material.  The
> I used is called "Great Stuff", at Home Depot, for $3.97 a 12 oz can (not
> be confused with a latex-based product also sold there).
> I drained two cans of the stuff and it appears that another 1-2 cans are
> still needed to completely fill it.  I would recommend that anyone
> attempting this have more cans than necessary on hand so that it can be
> filled in one operation, rather than on successive days, with a portion of
> the filling hardened, then filling more.  I was initially concerned that
> foam wouldn't cure being in an air-tight container.  The can said that to
> ensure curing in enclosed spaces, to sprinkle some water, so I squirted a
> couple oz. of water into the toroid prior to foam injection.  It turns out
> that there is no problem with the foam curing, it hardened just fine.
> The resulting foam core toroid is now more dent-resistant than a
> one, but the density of the Great Stuff foam is still less than what I
> like it to be to render the toroid totally dent-proof.
> What I would REALLY like to find is a vendor who can supply a nice smooth
> styrofoam toroid, ready for me to cover with aluminum tape.  I think the
> density and light weight of this construction would make it very resistant
> to denting, and hopefully such a foam toroid could be bought for far less
> than a spun metal toroid.
> I'm interested only in sizes larger than my 6" x 22" so life preserver
> don't help.  Any thoughts on whether such a styrofoam core could be
> custom-made for a nominal fee?
> Regards, Gary Lau
> Waltham, MA USA