Polyurethane floatation foam - mold release?

[erikgreen]

I'm not sure if anyone has expertise with this, but I thought I'd give asking here a shot. I'm trying to mold a part out of floatation foam, the two part polyurethane type.

I want a specific shape of course, and carving the foam would be a huge waste, so I've made a mold out of MDF. It's covered with an epoxy coat, and ready to go, except I need to pick a mold release.

If I wax the mold like I would for fiberglass, then I'd have to find a way to clean all the way off the foam before I could paint it or glass over it. Not easy considering the porous nature of foam.

I was thinking of spraying PVA over it as a release film... anyone know if that would work?

Alternatively, how hard will the poly foam grab onto the epoxy coating? Could I risk using nothing?

I had also thought of lining the mold with plastic sheeting, 2 mil.. that would make removal easy, and I don't need that much detail in the foam anyway.

Erik

 

[jonesg]

Re: Polyurethane floatation foam - mold release?

A trash bag works.!

 

[ondarvr]

Re: Polyurethane floatation foam - mold release?

There's no mold release that won't mess the surface up for a future use like painting, even PVA should be used with wax.

Plastic (bags or whatever you have) works well, just tape it in place.

 

[Mark42]

Re: Polyurethane floatation foam - mold release?

Hi Erik! Floatation foam is sticky stuff. Don't even think of letting it come in contact with the mold, they will become one and the same.

If the mold is lined with plastic, the foam will stick to the plastic and the plastic won't come off the foam. If you want to paint it, then that won't work either because the plastic bag won't take paint.

It a tough one. Play around with thick mold release, maybe vaseline or something like that. Then you have to clean it off the foam, and that will be a problem too.

Let us know how this works out.

 

[redfury]

Re: Polyurethane floatation foam - mold release?

If you are going to paint the foam piece after it's removed, why not wax the mold and paint the mold, then pour the foam. Maybe I didn't understand exactly what you are doing, but it seems like you could get the results you want by molding it the way you normally would mold a glass part with gel coat.

 

[erikgreen]

Re: Polyurethane floatation foam - mold release?

I think I'm going to try plastic sheeting, which I'm hoping I'll be able to pull away from the foam once it's out of the mold. At least if I use thick sheeting I can probably get all the plastic off, even if I have to repair the foam shape afterward.

I could try to do a reverse layup inside the mold, but I think that's probably more trouble than it's worth, plus prone to difficulties like dealing with over-expansion of the foam or mis-measurement of volume, etc, and coordinating layup times on the resin, glass, and foam.

What I'm planning on doing is just casting a shape in foam, then popping it out, doing some touch-up on it, and putting a layer of glass and poly resin (with mat) over it to waterproof and puncture proof it.. so I could make a buoy, for example.

The other way to do this would probably be to cast a block of foam big enough to contain my desired shape, then carve the resulting block to shape. Too much waste and work if a mold will rough it out for me.

I also haven't found a source of polyurethane or any other high density closed cell foam in blocks or sheets that's cheaper than the liquid stuff... if anyone knows of a good source, let me know.


Erik

 

[ondarvr]

Re: Polyurethane floatation foam - mold release?

If you need to do any work on the foam after removing it from the mold it will be no different than carving the shape free hand. Foam is very easy to carve with even the simplest tools and in no time you'd have the finished shape you're looking for. You could fill a cardboard box, or even a garbage bag if it's close to the right shape and then become an artist and start carving. Polyester will eat the foam, so you need to use epoxy, but I think you knew that.

 

[jonesg]

Re: Polyurethane floatation foam - mold release?

another way to consider..
lightly spray inside of mold with 3m77,
line the mold with alum foil.

But if I already had the mold I'd just go ahead and make the part and fill with foam, it doesn't make sense to make a mold then start carving anything and glassing it later.

 

[oops!]

Re: Polyurethane floatation foam - mold release?

welcome home erik !!!!!!

id just carve the foam...!

im doing the same thing on a dashboard....really tricky peices......

i also looked into the procedures of speaker box building.....they use fleece ! and poly resin it.....then that would be your plug......

but for my dash...im going to carve the foam.....yuppers.....gonna be a sculpter!

cheers bud.......oh....and any pics of the shop?

 

[Tim Frank]

Re: Polyurethane floatation foam - mold release?

Probably out of my depth here, but....
The few times that I have used foam it stuck to fibreglass like ***t to a blanket.
Could you wax the mold, apply a coat of resin, then the foam?
The resin would release from the mold c/w the foam. Your foam part would be coated with resin and ready for paint.
As far as i can see the theory is OK, but since it hasn't been suggested by any of the glass gurus I have that nagging feeling that I am overlooking something embarassingly obvious.

 

[erikgreen]

Re: Polyurethane floatation foam - mold release?

If you need to do any work on the foam after removing it from the mold it will be no different than carving the shape free hand. Foam is very easy to carve with even the simplest tools and in no time you'd have the finished shape you're looking for. You could fill a cardboard box, or even a garbage bag if it's close to the right shape and then become an artist and start carving. Polyester will eat the foam, so you need to use epoxy, but I think you knew that.

I figured I could carve it easily, but I would really like repeatability in shapes... so I could make a pair of floats the same size and shape, for example.

ondarvr, are you sure polyester resin will eat polyurethane foam? If so I'll need to use a different foam, or maybe vinylester. I was planning on just coating the foam with a layer of glass using pigmented resin, no painting required (and low maintenance). I can't leave epoxy unpainted, though. I wonder what foam surfboards are made of?

Hmm.

Oh, and Tim: The only problem with that idea is that any mold release I use will be hard to get off the finished foam object. So I'd have to chemically remove the wax or whatever, then paint. But I'd like to avoid painting anyway... I was hoping to develop a technique for making simple buoyant foam shapes with a glass coating, no paint, so I could make eg. a large custom buoy, or small raft, etc.

Who knew making a buoy would be this complicated?

Oops: Yep, I'm sorry I'm slow. I'm mounting a web cam in the shop, and putting the computer in there. I kinda doubt I'll leave the web cam on all the time though... you guys don't need to see me scratching my rear daily

PS: One more thought... what if I line the mold with dry cloth/mat? Then I just pull the cast block out, trim the rough edges, and resin the heck out of it to saturate the cloth? I suppose that'd leave sloppy cloth, bubbles, etc.

 

[ondarvr]

Re: Polyurethane floatation foam - mold release?

Now that we know some of the game plan the response will change.

Are you making a custom shaped float for yourself, or do you plan to sell them?

If you have extra materials and want to make some special shape for yourself then give it a try. If somebody else is going to pay you a bunch of money to make one, then do it. If you think this will be an easy and low cost way to make and/or market a float, forget it. The price of the typical orange float or buoy is so low you won't be able to compete, plus they won't look as good or hold up as well without more time and money invested.

 

[erikgreen]

Re: Polyurethane floatation foam - mold release?

It's just for me. Mostly because I want to do it, but partly because a really nice buoy is expensive, and they get beaten to death in Superior.

For example, a wreck mooring buoy is a sphere or teardrop about 18 inches across, with a quarter inch bar down the core, white with a blue stripe. Cost is about $200 delivered, and if it's near rocks, one solid storm will leave it in poor shape.

Not that I put out a lot of buoys, but it would be nice to just make one up and not care if it gets destroyed.

Then there's weird ideas I have... like making a custom streamlined float to keep my sidescan cable out of my props, or molding a life raft

But the real reason I'm doing this is I want to work with foam some more, and because I've never tried this.

Erik

 

[Mark42]

Re: Polyurethane floatation foam - mold release?

Erik!

How about filling one of those kids beach balls with floatation foam? Not the type you blow up, but the pre-inflated rubber balls about 20" diameter? They are fairly tough, with a thick wall. Pretty cheap too. Just go to walmart and look in the kids toys section.

BTW, when I cast the MFG emblems I make, sometimes I use WD40 as a release agent. Works well. Don't use silicone spray, you will never be able to paint whatever it contacts!

 

[erikgreen]

Re: Polyurethane floatation foam - mold release?

Okay, here's the summary of what I ended up doing.


I tested the foam with some plastic sheeting I had lying around, and it popped off easily and cleanly, even picking up the pattern on the sheeting (it's 1 mil "painter's dropcloth" type stuff).

So, I then used the sheeting to line my mold, taping it into place, and poured my large batch (I bought a 1 CF kit to try this out). I made sure to heat the cans of part A and part B in hot water beforehand, so I got full expansion.

Results were good. The foam leaked into a few cracks and touched bare wood or MDF in places, but other than that the whole thing popped out of my mold very easily.

It picked up the mold shape for the most part, but there were some "dents" due to bubbles between the plastic and the mold, plus some grooves from folds in the plastic.

All in all, a successful molding. Now I can do a little carving on it to try out shaping techniques, then I'm on to glassing it and destructive testing

I think for the future I'll probably just make molds out of wood and MDF, then use 3m Super 90 or 77 to line them with plastic sheeting without folds and bubbles. Window insulator plastic might be even better for flat surfaces, since I could shrink it for a nice smooth fit.

Curved surfaces and round shapes will be hard though, just to make and also to coat with sheeting. I wonder if you can get a plastic resin to spread on like paint that foam wouldn't stick to?

Anyway, for round shapes I'm going to end up sanding and carving the foam rather than casting. Cast to rough shape, carve and sand, then glass or paint. I might try a hot wire cutter in the future, or even a goofy idea like a "foam lathe" where I spin a chunk to cut round shapes.

Onward and upward.

Still not done with the workshop setup... I seem to do whatever is most interesting on a given night, so I haven't gotten it done yet Sorry oops.

Erik

 

[Tim Frank]

Re: Polyurethane floatation foam - mold release?

What about using release agent on the mold, then gel coat, and then the foam?

 

[erikgreen]

Re: Polyurethane floatation foam - mold release?

What about using release agent on the mold, then gel coat, and then the foam?

I need to have a layer of glass in there too. Gel coat alone is too brittle to protect the foam from puncture.

So I'd have to use gel coat, chopped fibers (or apply resin by hand after the fabric), then foam.

I'm thinking I'll just go with the plastic... it makes it easy and quick to make molds for the stuff.. no coating needed, just make an MDF or wood mold and glue/tape plastic to it. I'll have to see how the process of glassing the test piece goes though.. I'm wondering if I may need to use a vacuum process to get the whole thing covered at once.

Erik

 

[wca_tim]

Re: Polyurethane floatation foam - mold release?

pam olive oil cooking spray would probably be a decent mold release for many two-part polyurethane flexible or rigid foams... A small part will react with the isocyanate curing chemistry and the rest would wash off with relatively mild dishwashing detergent. Try test spot and see how it goes. If the foam formulation you are using sticks to your mold using that, there's others that will work a lot better, but won't be so easy to come by.

 

[jonesg]

Re: Polyurethane floatation foam - mold release?

Anuther way,
wax and spray release the mold,
paint with marine paint,
apply cloth and epoxy resin
and inject foam just as it cures.

 

[ondarvr]

Re: Polyurethane floatation foam - mold release?

I was kind of thinking the same thing. Spend a couple hours more on the mold and then just make it like a normal part, then every one you make is 90% done when it comes out the mold.