Expandable Foam Core

[sportfisher88]

Has anyone experience with constructing a hollow hull say 1-1/2" thick and then compartmentalizing into sections then filling with expandable foam? It seems to me this might save some time forming the foam, plus expandable foam would do a better job filling in voids. Provided of course that the sections are kept somewhat small with air escape holes, injection holes etc. and done according to manufacturers reccomendations - does the expanable foam keep a constant density?

[alexlebrit]

I haven't tried this yet, but it's preciesely what I aim to do with my semi-sit on top kayak design. I've found there seems to be different types of foam though, anything from the squirty foam in a can you can buy in Do It Yourself shops to stuff you mix up yourself and then run away whilst it turns into something out of Doctor Who.

I'm aiming for the latter as it seems to be a bit more liquid so you can pour it in, and it has a slower rate of expansion. Also because it's a small boat, made of three seperate hull sections and I can the idea is to stand each section on end, pour the mix in and then let it rise up through the bulkheads which will be at each 50 cm offset position. No doubt I'll use too much but that will just expand out the end and I'll trim it off.

I'll let you know how it goes though, and hope it doesn't pop my boat.

[johnnyv]

Generally with a polyurethane foam you will get a higher density next to container walls where it gets cooled, not really a bad thing.
Also poly gets a good chemical bond to cured epoxy if thats what you are using so the two are a good combo. Not the other way round though, epoxy doesn't chemically bond to cured poly.

[kerosene]

I have played with similar ideas in my head and the problem I see is that you spend X amount of time making the hull, fill it with expanding foam and your hull either cracks or distorts into a sphere....

Hoe do you control the expansion so that you don't break stuff.

[alexlebrit]

Well in my case I'm using a two part product that I mix up myself, and which gives me a fairly good idea of the volume of expanded foam. So as long as I know the volume I have to fill and as long as I make sure there's plenty of escape routes for any excess, voila no popping nor distortion.

[kerosene]

Could you mix carbon or glass fiber chips or strands to the mix?
I have played with the idea of form molded aluminum sturctures - cad design, water cut and hydraulic form molding weld pieces together and fill cavities with carbon or other foam enforced foam and one could get really strong and light structures

[alexlebrit]

Ok, possibly nto practical on a large scale, but for something small like a dinghy, sit-on-top kayak etc I wondered about filling the voids with a mixture of polystyrene beans and adhesive.

I had the idea when I sat down on a bean bag and it popped this afternoon, so I've got a mould going of beans mixed with diluted PVA glue, to see what happens.

I shall let you know what happens.

[BarendGrobler]

If epoxy dosn't bond with cured poly, what does, I mean, how do you get a bond for say a sandwich pannel between the skins and the core???

[BarendGrobler]

Can one get Styrene mixes such as the Styrene-Acrylo-Nitrile from Core-Cell???

[War Whoop]

Originally Posted by BarendGrobler

Can one get Styrene mixes such as the Styrene-Acrylo-Nitrile from Core-Cell???

No LOL it does not work that way!

[BarendGrobler]

Originally Posted by War Whoop

No LOL it does not work that way!

How does it work then???
No seriously; I don't mean let's coppy the core-cell way, I just want to know whether you get better stuff than the good old POLY?

Pardon my ignorance; what does LOL mean???

[War Whoop]

The SAN Plastic Foam sheets require EXPENSIVE machinery to produce you are dealing with a solid engineering plastic Like that in cigarette lighter bodies. Whereas the PU foam is a resin,blowing agent and so forth in a two part mix.

[BarendGrobler]

You mean they take a plastic and fill it with bubles in a molten state which then sets to form the foam?