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Re: [TCML] DIY dent-proof Toroids

Keep also in mind that 2 comp. foam creates a substantial amount of heat
when it's curing.
If the ducting ends are (hot)glued together, the heat could re-activate the
glue and you might end up with a split seem.

There is a simple solution to prevent deformation caused by the expansion
and/or heat of the foam:  wrap the toroid in plaster cast

2013/5/27 David Dean <deano@xxxxxxxxxxxxxxxx>

> Hi
> (...)
> "Real" polyurethane foam is available as a 1:1 part A part B mix and pour
> product. This stuff WILL
> cure in an enclosed space. If I were going to try to fill a toroid I would
> use this stuff rather than
> the spray can kind. We used something similar to the 2 LB density foam
> described here:
> http://www.uscomposites.com/foam.html
> only from a local supplier to fill the aluminum pontoons on a pontoon boat
> last year.
> If I were going to fill a toroid (I haven't done that, just a mental
> exercise based on my experience
> with the pontoon boat) I would:
> Make a suitably large hole in the inner portion of the torus to pour the
> foam into. We used 4 inch
> holes as the stuff is pretty thick and goes off fast, so you have to pour
> it quick. Something like 20
> seconds after it is mixed until it starts to go off :-)
> Mount the toroid on a horizontal axle so it can be spun to distribute the
> foam
> Have plenty of suitable funnels and mixing containers available. Measure
> carefully. Always use the
> same measuring containers for the same parts (part A measured in part A
> bucket, part B measured in
> part B bucket). You need to have extra foam as some will be wasted on the
> mixing containers and
> funnels. This stuff sticks well to polyethylene and is quite hard to
> remove. The more you scratch the
> surface of the bucket or funnel removing cured foam, the better it sticks
> the next time:-)  We used
> a drywall/paint mixing attachment in an electric drill to mix with. Being
> steel, a bit easier to
> clean up with a power wire brush :-)
> I would pour in layers. Mix and pour in enough to fill to 20% capacity of
> the torus, then spin slowly
> to distribute the foam about the periphery of the torus until it is set.
> Repeat adding layers until
> torus is filled. Note that this stuff will develop considerable pressure
> if it is confined while
> expanding, so probably best to have plenty of vents around the inner
> periphery of the torus to let
> excess foam escape. The excess which extrudes from the vent/fill holes can
> be easily removed with a
> saw or knife and filled or sanded to shape.
> My 2 cents
> later
> deano
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