RE: Hard coating for foam toroid

["David Dean" <deano-at-xxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Hi Gary,

The epoxy resin that is made for fiberglass (Bondo Brand marine fiberglass
resin) that I use to coat my secondary coils comes in a quart size (1 pint
hardener, 1 pint resin) at a cost of approx. $20.00. It pours well and
hardens slowly, takes at least an hour to set up hard enough not to run.
It seems to level itself very nicely. It also is safe to use on polystyrene.
The resulting finish is tough and durable. I don't know how well it will
work to prevent dents in your application however.

later
deano


> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, November 07, 2000 7:55 PM
> To: tesla-at-pupman-dot-com
> 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
>
>
>