Looking for non-sticky expanding foam

I want to make a mould for a clear headlamp cover on a sports car. The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape after it hardens then I could get a positive, and then vacuum-mould a bit of acrylic or polycarb to match. The fellow doing the body-work and painting would like it very much if this did not ruin his nice work. If there is not a non-sticky foam then what should I use as a release agent - could be something as simple as parchment papaer I suppose...
Is there a foam that would suit?
Any other suggestions welcome.
No, these covers are not otherwise available.
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Assuming this is not a tight void that would suffer from the foam's expansion, then line it with the thinnest polyethylene sheeting you can find -- 1/2-mil "painter's tarp" material comes to mind. It's like dry cleaners' garment bags.
Even where there are folds to take up the shape, the foam will expand to compress the film tight against the cavity, and three or four thicknesses will still take up only a few thousanths.
This is the same method they use to make custom-fit shipping boxes for delicate instruments. One lines the box with film, applies foam, covers the foam with another sheet, then "immerses" the object in the ersatz "water bed" of rising foam. The poly-sheet keeps everything from sticking to the foam quite effectively, so long as there are no sharp corners that might poke holes in it.
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

Oh... and, I would use the highest-expansion foam available in order that fine details will be reproduced. Cap off the whole affair with a final sheet of poly in order to force the expansion back into the cavity.
Regular "great stuff" will work just fine, so long as you lightly spray the inside of the (lined) cavity with water just before applying the film. Great Stuff, being a one-part mix, requires moisture to cure.
LLoyd
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On Mon, 22 Mar 2010 06:43:51 -0500, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:>

I bought some parts on eBay last month. The seller tried to use this method of packing.
Short story, the Great Stuff melted the bag. A week of cutting and scraping with a serrated knife finally freed my parts.
Test your bag.
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snipped-for-privacy@aol.com fired this volley in

Then it wasn't polyethylene, or he used a hot-mix dispenser.
Polyurethane neither deteriorates nor sticks to polyethylene.
LLoyd
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I have two points. Generally, your plan will work. As a separation, mold release agent, you can use Saran Wrap (Cling Wrap), but test it first. My first point is to be certain the foam can be removed mechanically. You will not be able to use just the foam as a polycarbonate mold, as the temperatures to vacuum form will destroy the foam. ( I think). Second, there are 3 grades of polycarbonate (lexan), natural, hardfaced on one side and hardfaced on both sides. Be sure you use the latter, or it will scratch very readily. Steve

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On Mon, 22 Mar 2010 04:29:13 -0700 (PDT), the infamous jmsiat

We used to foam parts in place in boxes by 1) spray foam in the bottom 2) put a sheet of poly on top 3) put the manpack radio on that 4) put down another layer of poly 5)spray foam on that 6)close the box. It filled the spaces and left few voids.
Couldn't you put poly in the socket, add foam, cover, remove it from the socket, fill voids, and cast from the result?
-- If we attend continually and promptly to the little that we can do, we shall ere long be surprised to find how little remains that we cannot do. -- Samuel Butler
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Larry Jaques wrote:

Actually, a little more clearance is needed.
So, make a plug, slightly larger than the manpack radio...
Because this stuff has NO sense of humor.
--

Richard Lamb
http://www.home.earthlink.net/~cavelamb /
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wrote:

Go to a hobby shop and look for "Mountains in Minutes". http://www.hobbymasters.com/islemountainsinminuteslandscapekit.aspx
Model railroad buffs use it. It's a two-part foam that is a lot less sticky than one-parts like Great Stuff, and it expands more. I'd use PAM as a release agent on the car if you'll want to paint later, because silicone release agents can be diffult to remove completely and they do play hell with paint. PAM is basically lecithin, easily removed with detergent.
Once the foam cures, it's non-sticky and easily shaped with sandpaper or hot element (hot wire or soldering iron) though hot seriously stinks so have good ventilation.
This stuff is also pretty good insulation. I measured the thermal conductivity once, don't recall now but it was quite low.
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Don Foreman wrote:

HIGHLY recommended for Ice Box insulation on sail boats.
--

Richard Lamb
http://www.home.earthlink.net/~cavelamb /
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