Not quite so structural foams?

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tr7v8

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The movie special effects people use something called "green death foam", which is a typical Hollywood FX nickname.

In the real world, the stuff is also called "floral foam" and it is sold (here in USA) as small blocks of foam for florists to stick flower stems into, to make a small display. They put candy skewers and other things into it, to make an attractive presentation. Most Craft and Hobby stores here sell it, Walmart and many others here.

Find a local flower shop or floral display maker and see if they have it, it is medium green in color, very light, and very rigid. Very fine "grained". Probably not as good for a "real" aircraft structure because it will fracture more easily than the common aircraft foams. Also, podiatrists (foot doctors) use this material to make a mold of your feet, they have you step onto a block of this, and it leaves a perfect impression of your foot, arch, etc.

The "green death" name comes from the fact that when you sand it, it creates a very fine and highly irritating dust, so the Hollywood guys making monsters and movie props and such get covered with that dust and have to be sent through a car wash afterward :)

So absolutely wear a dust mask, eye protection, etc. But epoxy resins should not melt or soften it, and it will surely work for a non-critical part. They come in smaller blocks, which means you may have to glue a few of them together to make the size you need. But you won't have to buy a huge expensive block either.
This is known as Oasis is the UK, has a similar consistency to honeycomb sweets.
 

RSD

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Many thanks to everyone for all of the great information - very much appreciated as getting supplies here is not as easy as it is in the U.S. or New Zealand - N.Z. has a big boat building industry that we don't have here unfortunately.

Will post some pictures of the finished product once it is done.
 

Lendo

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Billski mentioned he use Polystyrene for his fuselage mold, that is also used locally but they use a 'high density' Polystyrene and CNC the shape.
I do know of one plane in Australia that made the wings out of glassed solid high density Polystyrene, that was some years ago and I can't remember the name at this very moment.
George
 

Bill Welter

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The local Hobby Lobby sell two kinds of green foam, urethane which is soft, and polystyrene which is a bit tougher. Urethane is very easy to shape, and you can top with poly fiberglass resin and it won't deform. Perfect for making bucks or molds. LongEZ fuselage uses urethane foam, wings are polystyrene. But just the kind from Hobby Lobby...
 

Vigilant1

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I've managed to located an importer of high density XPS that seems reasonable - they are located only two miles from my factory and are happy to deliver to me - happy days! They have only been there about a year and the only thing they do is import this XPS - the specs seem good for what we want - http://www.thermostruct.com.au/wp-content/uploads/2019/07/ISOMAX-300-XPS-BROCHURE_JUN19.pdf
It is probably worth a shot. 2 observations:
1). 300kpa (44 psi) is better than the typical home center XPS we see (15-25 psi), but it is less than the higher grades oh Highload XPS. But, it might work for your "slice it into thin sheets" idea.
2) Some foams contain additives that result in poor bonding to epoxy. You'll just have to try it out to see.
Good luck!
 

RSD

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It is probably worth a shot. 2 observations:
1). 300kpa (44 psi) is better than the typical home center XPS we see (15-25 psi), but it is less than the higher grades oh Highload XPS. But, it might work for your "slice it into thin sheets" idea.
2) Some foams contain additives that result in poor bonding to epoxy. You'll just have to try it out to see.
Good luck!
Cheers Vigilant - I hadn't given additives causing a problem a thought but... - fingers crossed!
The importer said that the 300kpa (44 psi) is guarenteed for all thicknesses, but the 50mm thick is actually about 450kpa (66 psi I think) - which is probably pretty reasonable?

Have grabbed a pack of 25mm, 40mm and 50mm so far. First project will be to make a lightweight cooler box for the boat.
 

Vigilant1

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The importer said that the 300kpa (44 psi) is guarenteed for all thicknesses, but the 50mm thick is actually about 450kpa (66 psi I think) - which is probably pretty reasonable?
.
RSD, I'm not sure what you'll need as a low-cost replacement for thin (e.g 4mm) PVC foams. The 15-20 psi stuff is what is typically used for the thicker single massive cores, and does fine. For the thin sandwich approach you are considering, the PVC cores (e.g Diab Divynicell H80) that are normally used have compressive strengths of 200 psi or more (so, approx 1400 kpa). This may allow for a thinner laminate outer skin that can still survive normal handling/hangar rash.
 

RSD

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RSD, I'm not sure what you'll need as a low-cost replacement for thin (e.g 4mm) PVC foams. The 15-20 psi stuff is what is typically used for the thicker single massive cores, and does fine. For the thin sandwich approach you are considering, the PVC cores (e.g Diab Divynicell H80) that are normally used have compressive strengths of 200 psi or more (so, approx 1400 kpa). This may allow for a thinner laminate outer skin that can still survive normal handling/hangar rash.
Hmm - will have to work on that still... lots to do... not enough hours in the day...
 

ScaleBirdsScott

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In an annoying case, I live directly across the river from the Dow plant that makes all of their Styrofoam, but yet it's actually quite difficult to source locally that I've found (though there must be someone)
The plant and its open dock storage area is literally less than 2 miles distant. One could build a Huckleberry Finn type of raft, float across the narrow part of the river (thankfully we're upstream of the nuclear subs) and then have a kind fellow throw one of the many, many, many billets of foam stacked in tall piles onto said raft. Round trip journey might beat simply driving a pickup around to the casino bridge and back down the other side.

Or, in another way, maybe one could get a helpful helicopter to fly over, pluck a block of XPS, and then simply drop it (gently) into a welcoming back yard. It's tantalizing close, those piles of blue blocks lying unassumingly, just waiting to be turned into something.

I have mostly used the pink foam, ironically enough, since that is easy to find at Home Depot of which that's the next-closest source, and the closest that will sell single boards.

I'd love to try this flotation billet stuff, if it's got a bit more resistance to crushing than the straight wall insulation board. Would be perfect for my use if I could get a block 4-6" thick. Just a shame for it to be trucked to some far off depot or wherever, only to have to pay for its return journey.
 

TFF

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I figure you do it James Bond, swim across the river with a duck camo hat on your head, jump on the bank, throw the billets in the water and ride them down stream. Actually find someone who works in the plant. Ask if the have a defect pile and if you could have some of it.
 

plncraze

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ScaleBirds, have you tried calling the sales office at Dow to see about becoming a rep? Sort of like what you have with Verner. Back when the Thorp T-18 was big the builder's association did that. I know that the "common" DuPont blue foam seems to have disappeared from my big box stores.
 

ScaleBirdsScott

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Well if I ever get to needing more than one or two blocks every 6 months I'm all game to sign up. As it is, I try and limit my need for using foam to just basic mold making.
 

litespeed

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Cheers Vigilant - I hadn't given additives causing a problem a thought but... - fingers crossed!
The importer said that the 300kpa (44 psi) is guarenteed for all thicknesses, but the 50mm thick is actually about 450kpa (66 psi I think) - which is probably pretty reasonable?

Have grabbed a pack of 25mm, 40mm and 50mm so far. First project will be to make a lightweight cooler box for the boat.
Excellent Idea, the billet makes a incredible beer box, easy to shape and sand, holds the epoxy well. Makes a extreme esky that also doubles as a life raft- make sure you have a good seal and proper lid lock mechanism. And ropes on the outside to hold on.

Nb* Aussie fisherman are often rescued in the ocean clinging to their best friend- The esky. We might down beers when fishing in leaky boats and forget radios, vests etc- but we always have a esky. In esky we trust. We are not talking a little one either but around 200 litres is common, so approx 300lt displacement. Add ropes and a crew of 6 can float and stay together safely.

And holds a lot of cold beer or fish.

In have made one my self, just from cheap styro fish boxes, double walled into a nice big cube. Mine is dodgy and only has glass on the inside, The outside is covered in fibre tape then two layers of silver bubble wrap- wear sunglasses. It reflects heats amazingly well and the beer is cold for days.

The billet foam will make one awesome esky. Far better than anything money can buy. Also a great experiment in the foam.

The billet foam is worth the extra money and when coated is strong beyond most expectations. No other foam shapes anywhere near as well, as per usual, wear safety gear.

It machines the best as well and when right looks like a perfectly sanded MDF. A trimming router does a great job and can be used to lay in pulltruded carbon rods for example. I have made model rc aircraft with it before and also with full sized boats. Even a sharp blade gives a lovely cut- you will enjoy playing with it.
 

SVSUSteve

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Actually find someone who works in the plant. Ask if the have a defect pile and if you could have some of it.
We got some that way (more than we ever needed or asked for) by telling a company that we could use the “scratch and dent” stuff to teach CAP cadets about composites. I will ask our aerospace education officer who we got it from. Technically, I am the one who got it donated (the joke is that I can get anything donated...which is good given that I work for a nonprofit) but I don’t remember who from.
 
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