Re: Hard coating for foam toroid

["acmnovak" <acmnovak-at-xxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Gary-
I've been planning on doing the very same thing. However, on an aluminum
duct torroid. I have dented every single torroid I've ever made and this
time I'm going to try and protect it. I plan on using 2-3 coats of
"EnviroTex Lite" which is a "pour-on" finish with an epoxy base. (it runs
about $7 per cup (8oz) or $40 per gallon (128oz)) At room temperature it
takes ~8-10 hours to harden and 36 hours to cure. After the coats of epoxy
and a vigorous sanding, I'll cover the whole thing with aluminum tape
several times and rub it down with a spoon. The only problem I come accross
is the big open space in the interior which may be an accident waiting to
happen. By coating the torroid with epoxy I may inadvertantly make it more
brittle. To remedy this, I have a few different tricks up my sleeve but it's
still kinda up in the air. One idea I threw around was to put some sort of
lightweight filler material in the torroid followed by a fill of epoxy to
make it rigid. The filler material can be any of several different things;
styrofoam (as you pointed out), LDPE, cardboard, wood, or even cotton.
Cotton, when tightly packed, may make a suitable filler alone... I'll let
ya'll know how it turns out and what not to do after I complete my project.
Exactly how much did you pay for that styrofoam torroid?  By the sound of it
I'd say you paid about $100? That's judging by the 3-5lb adding $100-200
onto the cost... Why not just buy a commercially spun torrus or something?
My two cents....
Safe coiling Gary,

        -Michael






----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 07, 2000 7:55 PM
Subject: Hard coating for foam toroid


> Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
>
> I recently placed an order for a custom 7" x 30" Styrofoam toroid from a
> place that makes custom plastic shapes, largely for theatrical props.
They
> have a completely computer-controlled milling operation and can make any
> complex shape.  They normally work with 2 lb Styrofoam, similar to what
> coffee cups are made of.  They could also order 3lb and 5lb foam.  The 5lb
> foam is similar to the stuff they make bicycle helmets out of - very tough
> stuff.  But the 3 and 5lb options added roughly $100-$200 to the total
cost.
> I was concerned with the possibility of denting and wanted to make the
> toroid as dent-proof as possible, but at a reasonable cost.
>
> Initially I was told that they would be able to apply a very thick (1/8")
> coating of polyurethane.  I felt that such a coating on top of the 2lb
foam
> ought to make it pretty dent resistant, so I choose that option.  After
the
> foam was cut I learned that they would not be able to apply it as the cost
> would actually be very high.  So now I'm left with a foam toroid with
little
> protection against dents.
>
> What materials are there that I could coat it with to improve upon its
> dent-resistance?  I don't want to mess with fiberglass or anything that I
> would have to sand down.  I'm thinking self-leveling like epoxy.  Is this
> available at reasonable cost in bulk (quart)?  Is it thin enough that it
> could be poured on while the toroid is slowly rotated?  Is the cure time
> long enough that I can get the whole big thing coated before it starts
> curing?  Or are there other things?  Someone suggested the boating repair
> industry may have something I could use?
>
> I will post pictures and details of cost, contacts, etc, to my web site
> after I receive and evaluate the toroid in the next couple of days.
>
> Regards, Gary Lau
> Waltham, MA USA
>
>
>
>