Usually that time is the pot life, and they specify the pot size. Epoxy makes heat as it cures, and that heat raises temperatures more in the cup than it does spread out on the part. You would have to do an experiment to see how much more time you get on an open part and on a vacuum bagged part - cores and the extra plies all have some insulative properties. I have made parts with Gougeon 125/229 that took 90 minutes to be under full vacuum, and they came out fine. Oh, climate controlled shop 70-75F (21-24C) and modest humidity.My resins come from this shop : Buy Resins online at R&G I am using L hardener now only 40 or 60 min. Have tried to use some 210 min hardener, which is designed for infusion, it needs post curing, and if parts are not lay-flat position - you get thinner edges, and more resin in the bottom. Regardless of vacuum bagging or infusion. I did wait till colder times in our climate to test mine twin foil laminating - all looks like to be working as it should.
And - resin will get to its end of gelling time at 12 degree too. After 6-8 hours. So i may to use it with foam too. But this is for this resin only, have tried same trick with some other - 18 degree is a minimum.
Zip ties. Or some duct-tape.You have this massive solid core wing. Now what? How do you attach it to the airplane?
You won't need to remind TiPi of this. Here's the very nice build log for the SD-1 he's buiding, including a picture of the work the mice did to enlarge some holes in a stack of his stored XPS ribs.Why does exposed polystyrene foam bother me? If nothing else, it can get wet with solvents or invaded by rodents or birds.
While I'm deviating a bit - still within the large monolithic block discussion. Yup EPS. Coffee cup foam - as long as it IS fully sealed and away from fuel/UV/rodents...Expanded Polystyrene foam, coffee cup foam? I have used it for tooling. The beads barely are attached to each other. MAYBE if it is a nonstructural assembly with it fully contained with composites - Interior panels, inspection covers, glovebox doors...
We are talking about wing structures here, and the OP does not want any sealing layer of cloth and resin on the inside. Regular blue foam exposed gives me the willies, but white coffee cup foam?
Why does exposed polystyrene foam bother me? If nothing else, it can get wet with solvents or invaded by rodents or birds. Both cases mean the skin can lose its support and collapse. Seen it plenty in floating docks made of blue foam. Seen it in stored foam or partially completed airplane parts (exposed foam). I have seen a lot of stored airplane parts, and never yet seen one where a rodent has hollowed out a nest from a foam cored part fully wrapped in glass-epoxy or even closed out with dry micro.
There are a few ways to do it, but it can be a little different/more complicated with composite spars.You have this massive solid core wing. Now what? How do you attach it to the airplane?
It does sound like a possibly efficient process for rapidly producing wings in an industrial environment. Two-part pressure molding, the use of steam "popped" polystyrene beads within those molds, pre-preg-- none of that sounds like the kind of thing designed for a one-off homebuilt. But, maybe the FAA's interpretation of the 51% rule will eventually get relaxed enough that a kit company could send out the EPS-filled wings already skinned and ready for ailerons and position lights.The wing, which was the airplane's primary structure, would be built in clamshell molds. First, foam "sugar" would be placed in the mold. Live steam would then be injected to expand the polystyrene beads to the mold contour. The mold would be opened, the core temporarily withdrawn, and "B" stage fiberglass prepreg would be laid up on the inside surfaces of the mold. The core would then be reinserted and the mold would be closed, compressing the core slightly and ensuring even pressure on the laminate. Heat would then be applied in the usual manner to cure the assembly. The use of prepreg would avoid the weight gain problem of a wet layup and would prevent the laminate from becoming resin-starved. The process as a whole is simple, repeatable and cheap.
Still makes me wonder, Single use molds are a little easier in this day and age. Sheetmetal and disposable CNC'd inexpensive construction materials, If you can salvage sections (ie prefinished skin) from one mold to the next - it's not the worst method we've ever discussed here.It does sound like a possibly efficient process for rapidly producing wings in an industrial environment. Two-part pressure molding, the use of steam "popped" polystyrene beads within those molds, pre-preg-- none of that sounds like the kind of thing designed for a one-off homebuilt. But, maybe the FAA's interpretation of the 51% rule will eventually get relaxed enough that a kit company could send out the EPS-filled wings already skinned and ready for ailerons and position lights.
I'd suspect that Rohr used EPS rather than XPS primarily because it was a very fast way to fill that 3D shape. If the wing skin really needs the compressive modulus typically associated with a 60 PSI foam, then doing it in EPS will be heavier than XPS, not lighter (by about 1lb per cubic foot). Still, especially in the days before cheap CNC cutting, it would have saved them a lot of labor hours to just throw the EPS "sugar" into the mold and turn on the steam rather than shape a block of XPS.
Well, my hot wire cuts never seem to recede below the template protecting the foam, my guess is the kerf is about 0.050", which is more than the thickness of my skin laminates. I always use the template to protect the piece of foam I need the dimensions close on. When I keep the cutoffs to make saddles, I do not worry over this issue, the part core is to size under the laminate, and the supports are what they are.How thick is the "kerf" created by a hot-wire?
How does it compare to the thickness of a composite wing skin?
I ask these questions because I am considering using "scrap" foam as female molds while vacuum-infusing wings. By "scrap" I mean the outside of the block of foam that you just carved/hot-wired the wing panel out of. As soon as the airplane is complete, those odd-shaped foam blocks go to the garbage.
The primary tool will still be a large, flat and stiff table.
I doubt if these female molds will be smooth enough for final surface. Instead, my concept is to use "scrap" female foam as cradles to stabilize components ... against distortion created by vacuum-bags.
Yes, this might limit builders to curing only the top skin at one step. Then flip everything over and cure the bottom skin during the second step.
Granted.Wel, only if you have tube fuselage fittings. I have looked at a lot of homebuilts, and only a few designs (mostly Jim Bede designs) use round tube spars and fittings. Most use some sort of channel, I beam, box spar, etc, with the bending strength tailored along the spar to the expected bending moment. And they use bolts to make the connections.