Jaydee
we have the same foam here in the states except its pink.
-Dan
Dan,
Yes we have a Pink Foam too, never tried it though.
They need to be tested to see what they could be used for,- - lots of time needed!!.
John.
I worked on a Human Powered airplane in college and we did an extensive evaluation of both the blue and pink foams. The pink foam was found to be superior in terms of lower density and had no adverse properties in terms of reactions to resin, etc.
If you look closely at this picture, you will see that the upper skin of the wings is pink:
http://www.dfrc.nasa.gov/gallery/photo/Daedalus/Small/EC88-0059-002.jpg
This foam is excellent for creating shapes which can then be glassed. We used a computer driven hot wire foam cutter to cut extruded airfoil shapes out of blocks of this foam. But it could easily be worked with sandpaper or other shaping tools…
- Will
Will Gorgen
There are basically two types of “common” foam here in the US
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The white stuff that looks like little beads mashed together. In fact, when broken, there are little beads all over. This is “EXPANDED” foam and worth very little in the r/c building process. While extremely light weight, it has virtually no structural strength, and is very susceptible to most paints, solvents and resins other than epoxy. If you take a piece and paint it with regular spray enamel, the surface will “pit” and will resemble the moon’s surface - lots of craters. It is usually associated with styrofoam coolers and bait buckets !
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the other common foam is “EXTRUDED” foam and this is what here in the US we see for basement and wall exterior insulation. If is of very fine density, cuts easily with power tools, shapes easily with power and hand sanding, and if you use a template and hot-wire, the surface results in a smooth and shiny appearance that doesn’t take much epoxy to fill. This comes in various colors - I am familiar with pink, blue and grey. Available at most home centers. This also is susceptible to polyester resins, and some paint/solvents. If you try to use common automotive “BONDO” - the Methyl keytones used for hardner will attack the foam and cause “Moon Surface” as well. Once covered with a barrier coat of epoxy resin (of cloth/resin) products containing solvents will not attack the surface.
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There are a lot of “stuctural” foam products that are used for underlayments for roofs and floors. This stuff is high density and rather expensive. Also it usually has some type of foil vapor barrier attached which also limits it’s use for r/c models. Divinicell and similar foams are high density and manufactured for marine use in big boats. Usually fairly expensive too.
Use of foam for modeling made in-roads for the aircraft and sailplane r/c groups, as it was easy to shape and very light weight. My prototype MulitONE was made from a shaped foam plug, that was hot-wire cut in sections, glued together and then covered with a release tape. A tip to reduce epoxy absorption, is to use an old household iron and set on low (warm) setting. Run iron over the surface and it will smooth and seal the surface to eliminate a lot of resin being absorbed by the rough finish after sanding/shaping. Also, one can adhere very thin wood veneer to the shaped foam to project the look of a wooden boat.
Foam is subject to breakdown by UV rays (sunlight) and the “pink” color with turn a very light yellow/tan color. It will abrade eaily and you will have a powder in your hands. It needs to be protect by paint, varnish or epoxy pigments to prevent breakdown of the surface.
The last type is the “sprayed foam”, used in interior home insulation or sprayed inside closed areas to be filled. Too expensive to have your own setup, and if done by a friendly insulator, be careful because as it expands, it could ruin your mold. I’m not familiar with that type, so if you use it, be sure to post on how well it worked.
One very positive benefit of using foam, is the speed in which shaping can be done, and if the design doesn’t work, a lot of time is not lost as it would using traditional balsa strip building methods.
The only concern/issue using foam, is the need to plan ahead and provide hollowed areas for radio gear, etc. and perhaps the need to imbed wood pieces in areas of very high loads such as shroud, stay attachment points. This can be added after the first layup of glass cloth, by using a router to make an opening for the base material for attachments. Don’t forget to leave room for rudder control rods, etc. as well.
In closing, not to dispute Will’s post, but I believe that when the term “resin” is used, we are talking epoxy, not polyester? I have never found regular polyester resin to be “foam friendly” - but I could be wrong. Will - can you clarify please?
Yes Dick, you are right about the resin.
We only evaluated the pink and blue foams for the various epoxy resins we were using on our project. It was very stable with all the epoxies we tried (7 or 8 different flavors). As someone else (might have been you Dick?) noted earlier, you can eat out the foam with acetone. We did this on occasion for various purposes. It is not a very controllable process, but could be used to create a small cavity through a small hole in the fiberglass where shroud attachments are needed which can then be filled with epoxy or some other material that would be suitable to screw chainplates to.
As far as the liquid two part foam, you can buy this at hobby stores. I have used this to create mountains and such on a train layout. It is pretty neat stuff and can be poured into a mold so long as the mold is not closed (the mold needs to have a substantial opening to allow the foam to expand through before it solidifies). You have very little working time with this foam as it tends to begin expanding while still in the mixing cup. The expansion goes very quickly. But the foam has the consistency of shaving cream when it is fully expanded. Then it takes a little time (a few minutes) for it to harden. So you can work it a little in its expanded form. THe final form is very sandable and appears to be quite a bit lighter than the pink or blue foam.
I have not tried any resins with this foam (like I said, I used it to create mountains on my HO train set). But perhaps the container would indicate what you can put onto it after it has hardened.
As far as some of the higher density foams like divinicell, clegucell and the like, you might want to visit your local boat builder. They might have scraps of this stuff that they would otherwise throw away that would be appropriate sizes for bulkheads or other purposes in our size boats.
Dick, I don’t know if Jason Brown still runs the old Johnson Boatworks up on White Bear Lake. If he does, I bet he would supply you with all the high density foam you could ever need. I know him pretty well, so if you need an introduction, let me know. I think Tony Johnson (no relation as far as I know) could probably get you “in” as well…
- Will
Will Gorgen
Two pound per cubic foot polyurethane foam can be used with polyester resin but one of the the best systems is one pound per cubic foot styrene foam and epoxy. Dicks idea with the iron sounds like it might work real well since the sanded foam surface can hold alot of resin…
UPDATE:I’ve been told that styrofoam will absorb some water over time even if well glassed…
Doug Lord
–High Technology Sailing/Racing
I used a foam in a “spray” can to glue the foam onto the wooden spine of my Schooner, but the expansion caused problems as it cured, I wrapped a long piece of cloth around the parts being “glued” and pinned the ends to hold it in place.
Using heat to smooth the surface of sanded foam, could result in some shrinkage, so would need to be allowed for in building, but a low temp should be ok.
The “planning ahead” also was a problem, I got round it with a soldering iron with a piece of stiff copper wire round the Bit, to extend it and shape the holes.
Again there is quite a bit of shrinkage when “heat cutting” like this.
John.