Thursday, March 30, 2023

Re: Vacuum forming flexible thermoplastics over foam carving

mark sethi

Thanks all for all the great advice on process. I have not had a chance to
try them all yet but Keep em comin’. I will post my results once I perfect:)

Below are the responses from today. If you get to test before I do, repost
your results.
Thanks again:

-Two layers of vacuum forming hose like you’d use to pull afos or feather
strech then pull a closed end pva bag that you let dry after applying over
the foam mold….after pva drys poke holes with a needle to allow vacuum to
work…. you can speed the pva drying with a heat gun or spin it in oven
for 2-3 mins to dry pva bag… good luck it’s the best way I’ve been
successful with a smooth finish over foam

-Pull two nylons over the mold and then soak it in water right before you
pull and it should be smooth. You can also spray it down real good with
water but I like to dip it. Good luck!

-We used light putty we mixed at the facility. Solkafloc mixed with quick
set resin to a porridge paste constancy. Then we’d fill a coffee can with
it and keep for use. When you need to putty something, we’d scoop
suitable volume, add promoter, mix and use. It’s won’t go bad for long time
without promoter added. Of course, you can buy same thing in cans from OB
for $$.
Anyway. We’ll seal foam carving with that putty, let it dry and shave bumps
away with sanding screen. Then gloss it with Ambroid.

-Have you tried putting sealing resin over the foam model?

-Pull the plastic over applied Endolite Latex cone (very very slowly) with
no silicone applied. Otherwise, I’m not sure what is happening. Hope it

-I don’t know if this would work or not but maybe using a plaster slurry
over your model. It may be a bit time consuming but just a thought.

-Here is what I do, and been the only thing that has worked for me. You
may have to account for an additional 1ply when you carve the foam if your
looking for that perfect fit. Take a long enough nylon hose and sew
across the middle so you can double it over. Pull hose onto foam and press
the seam into the foam in the distal end. Then add your plaster wash coat.
Plaster mix is important here. Not to thick and not to wet. Smooth but
try to not expose the hose a lot. Then let dry. then coat with Factor C
Silicone liquid before pulling. Add your valve dummy on top of plaster
and no more hose. Pull right over plaster. Just punch a through hole
under dummy to the proximal end so that good vacuum gets to dummy. Also
I prefer Thermolyn x-soft or excel for this with plastic no hitter then
340. Good luck!

-I tried 2 layers of flex a stretch sprayed with soapy water and that
worked fairly well but still texture.

-PDI has a silicone fluid that you can paint onto the foam and will
separate the plastic from the foam. It is kinda messy but you have to cool
it down fast after formed.
I have used a vacuum nylon painted with the pdi silicone and that has
worked. Good luck.

-Try wetting your carving with a stockinet over it. Like douse it. Works
for me. I think the steam keeps it from getting textured.

-Smooth-on has an epoxy resin to cover stuff. i just used it to cover the
rigid foam on a BKA exo. It work great. I will send you the name of it.

-Try joint compound with added water to thin and smooth it. Should be very
silky and easy to spread. Then coat foam by hand and smooth with sand
screen 150 grit and final buff with fine nylon

On Tue, Apr 5, 2016 at 8:36 PM, mark sethi wrote:

> Hello all,
> I have a fabrication question about how to smoothly pull flexible inner
> thermoplastics such as Northvane, Duraflex, Pro-Flex with Silicone, &
> Striefyflex over digitally carved foam models. I am using the basic
> Fillauer foam blanks.
> I have tried many technics pulling over a foam model and the inside of
> the cup has come out extremely textured. I would like the inside of the cup
> to be smooth and would appreciate advice on how to make it happen.
> Thus far into my trials I have tried the following:
> •Variable temperatures from 350 – 400 F on the variations below
> •Silicone mold release sprayed directly on the foam
> •Two layers of nylon stockinette coated in silicone mold release
> •One layer of nylon stockinette followed by a latex casting balloon
> •Latex casting balloon coated in silicone mold release
> -Vorums pulling instructions on co-poly, polypro
> Any nylon/cotton stockinette method just won’t work so far.
> Additionally, I have tried to float plaster with and without vermiculite
> over the foam and had limited success with that as well. It is possible for
> the plaster to stick to the foam, but for the most part the plaster slurry
> beads up and does not spread over it smoothly.
> I am stuck where I have to duplicate the foam model in plaster and smooth
> it to get the finish I want.
> Any advice or direction on how to get a smooth finish on the inside of the
> cup on par with direct plaster pulls would be greatly appreciated!
> Thanks all!
> Mark Sethi CP,CPA,CTP
> 818-825-3439


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