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Old 04-05-2007, 06:06 AM   #11
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Originally Posted by trebuchet03 View Post
I think that foam will melt if you expose it directly to polyester resins
I think that this urethane form is impervious to polyester resins. It is impervious to everything else, for sure.

Wear gloves, cause it won't wash off, like everyone has already told you.

This should be a lot of fun for you.
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Old 04-05-2007, 06:34 AM   #12
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Yeah - I'm looking forward to trying this. Now I just have to wait until winter goes away again. (Snow on the ground this morning.)

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would it be possible to use this kind of foam in a mold?
Should be - you can get foams with different expansion rates (so you don't bust your mold).

Or - just leave an opening so the foam can expand out if it needs to.
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Old 04-05-2007, 07:52 AM   #13
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would it be possible to use this kind of foam in a mold?
Not effectively. While it depends on the size of the mould, these types of foams require contact with air to cure. If it's a large piece (and by large, I mean larger than intended application) the outside will crust over but the interior will remain gooey. It can be cured by cutting through the exterior skin, but then the uncured foam will spew out as it expands and cures, often collapsing the shape of the object as it does so.

If you want to use foam in moulds, use the proper products. Check taxidermy catalogues, SFX suppliers, and marine (as in boat) outfitters for urethane or polyester casting foams. They're available in both rigid and flexible types, of varying densities.

http://www.tapplastics.com/shop/product.php?pid=79&
http://www.smoothonsecure.com/store/...7d82dc70d7c203
http://www.vandykestaxidermy.com/product/01352499/
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Old 04-05-2007, 10:23 AM   #14
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Quote:
Originally Posted by lunarhighway View Post
would it be possible to use this kind of foam in a mold?
This stuff probably isn't the best (as mentioned). And if you're casting - it would probably be beneficial to get a foam that skins

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Or - just leave an opening so the foam can expand out if it needs to.
Yep, that's the best way when you don't know exactly what volume the stuff will expand too It's much easier to sand off a nub than to add on a chunk :P

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I think that this urethane form is impervious to polyester resins. It is impervious to everything else, for sure.
Good to know Of course, it's always recommended to test :P
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Old 04-05-2007, 10:45 AM   #15
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would it be possible to use this kind of foam in a mold?

it would be easy enough to create a negative mold that can be filled with foam. one could set up a littele production line in case something like a front wheel fairing is damaged by the curb.
You could use an open-topped mold to mold "blanks" that you could then shape. For example, to make a deflector for in front of the tire, you could mold a triangular prism shape, let it cure, and then file/sand it to final shape. Like others have said, if you really want to mold parts, you can buy foam especially for that purpose and get better results.
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Old 04-05-2007, 11:20 AM   #16
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Bill -

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You could use an open-topped mold to mold "blanks" that you could then shape. For example, to make a deflector for in front of the tire, you could mold a triangular prism shape, let it cure, and then file/sand it to final shape. Like others have said, if you really want to mold parts, you can buy foam especially for that purpose and get better results.
Would a "paint roller tray" make a good triangular mold? I ask because I have been looking at them as being good wheel-well deflectors, but I could never find a good one to work with.

Question : From all of the examples posted in this thread, which one is the "foam especially for that purpose" that you are talking about?

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Old 04-05-2007, 11:42 AM   #17
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Would a "paint roller tray" make a good triangular mold? I ask because I have been looking at them as being good wheel-well deflectors, but I could never find a good one to work with.

Question : From all of the examples posted in this thread, which one is the "foam especially for that purpose" that you are talking about?
Sure, a paint roller tray could be a good mold. For large voids, the directions may give you specific guidance to help avoid some of the problems others have mentioned, like spraying with water. See http://greatstuff.dow.com/index.htm
Whatever you use for a mold, make sure that you line it with something like foil or plastic wrap.

Maillemann suggested some foams that might be more appropriate for molding a couple of posts up... I do not have experience with them. I have only used Great Stuff and Gorilla Glue.
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Old 04-05-2007, 02:23 PM   #18
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perhaps using an open mold and building up the shape with layers could solve certain curing problems?... something like that paint roller tray will not be all that deep to fill ... and perhaps drilling a few holes in the bottom might allow the foam at the bottom to dry. more appropriate foams would be preferable but they'd have to be available...

firmly attaching the foam to metal or plastic could be another problem...

i supose it won't support screws directly but perhaps plastic wall plugs or even a full armature can be molded in.

i really want to do some serious aeromods but i'm having a hard time finding any usable material this thread sparks new hope....
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Old 04-05-2007, 02:58 PM   #19
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perhaps using an open mold and building up the shape with layers could solve certain curing problems?... something like that paint roller tray will not be all that deep to fill ... and perhaps drilling a few holes in the bottom might allow the foam at the bottom to dry. more appropriate foams would be preferable but they'd have to be available...

firmly attaching the foam to metal or plastic could be another problem...

i supose it won't support screws directly but perhaps plastic wall plugs or even a full armature can be molded in.

i really want to do some serious aeromods but i'm having a hard time finding any usable material this thread sparks new hope....
The paint roller tray could be lined with damp paper towels or damp brown paper bags, or something like that. A layer of foam could be put in, spritzed with water and another layer put in. Maybe? Jangeo said something about steam...

As far as attaching, something like the expanding anchors for sheetrock might work. Or a simple armature. Or T-nuts inserted through expanded metal, and then foamed in place. Of course, you put something like shortening on the screw threads and thread them into the nuts or anchors before you put the foam in, and then unscrew them once the foam sets.
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Old 04-05-2007, 03:20 PM   #20
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firmly attaching the foam to metal or plastic could be another problem...
If you know where your attachment points are... You can include a sheet of steel or aluminum (pre-drilled and pre-tapped) into your mold before adding foam The same goes for composites - you can add a metal core if you know there's going to be a support attachment in that area Just make sure to make the plate big enough to get a good surface area to bond with the foam.

Compound curves make it a little more difficult - but not impossible

Lastly, if you're using the foam directly on your car -- you can attach the mounting brackets exactly where you want them - fastener and all
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