Does insulation foam collapse in a pressure pot?

This may be a crazy question. I have a couple of forms made in insulation foam that I want to cast in resin. Will the foam collapse or deform if I use my pressure pot when I cure the silcone as I usually do for moulds?

I wouldn't think so, since it's porous. If it's coated it may be a problem. Can you make a test piece from some scrap?

I'll do a test piece if necessary, but I figured the RPF would have the answer!

Knightjar said:

I'll do a test piece if necessary, but I figured the RPF would have the answer!

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I am interested in the outcume. I´d say it strongly depends on the foam you use and dare say that styrofoam might change its form, while EPS, being pressurestable, should hold up.

I haven't worked with it in person but I would figure anything expanded, *eps foam, polyurethatne foam, latex foam* may have problems. It comes mostly down to just how much pressure they are under. Extruded foam should be fine because it dose not have quite as much trapped air bubbles which are what are going to cause you problems potentialy. If you are using urithane foam then I would go with the hardest you can ge or, if it is ok for it to deform in the vacum if it comes back to shape when done, the softest/stretchyest. You're only boned if the air pockets actually burst.

http://www.youtube.com/v/qiTnBHb-FXk?version=3&start=918&end=925&autoplay=1&hl=en_US&rel=0

As I understand it there are "open-cell" and "closed-cell" foams. I'd imagine that the closed cells trap gas/air wich reacts to pressure changes and therefore compress or expand the containing cells/the foam.
But I'd also like to see how severe this is at what pressures :confused

SciFiPropFreak said:

As I understand it there are "open-cell" and "closed-cell" foams. I'd imagine that the closed cells trap gas/air wich reacts to pressure changes and therefore compress or expand the containing cells/the foam.
But I'd also like to see how severe this is at what pressures :confused

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You're absolutely right about open-cell vs. closed-cell. Most or all of what we work with as far as casting materials is closed-cell, but some raw materials that we use for building and sculpting are open-cell. But usually if you're wanting to make a mold of an open-cell item, or a closed-cell item that has been cut or carved, you will have sealed its surface. So when you put it in a pressure or vacuum chamber, there are a couple of possibilities for what might happen: if you sealed it perfectly, and your sealing material can withstand the pressure change, you might deform the whole prop, or merely deform the sealant (which would give your mold a surface texture that wasn't there on the master at ambient pressure). If you didn't get a perfect seal, or the sealing material cracks under pressure, you might force some of the molding material into the pores of the model. Then you might have problems removing the model from the mold, possibly damaging the model or the mold or both. Even if nothing is damaged, the bits where the molding material was forced into the pores of the model will remain as little tags on the surface of the mold, creating defects in castings you make with the mold.

Regarding the severity of deformation under pressure or vacuum, it depends not only upon the pressure differential, but also upon the rigidity of the base material and any surface sealing material.

Thank you, that's pretty much the exact reasoning I had too, but figured it was worth asking in case anyone had any direct experience. I suspect I'm going to have to manage without pressure on this casting, but in the interest of science, I'll do some tests anyway.

So the rule of thumb would be something like:
If you can, avoid the use of foam when dealing with pressure moulding, but if you have to: The more rigid the foam, the better are your chances!
Right?

Reporting back for anyone following this thread. Raw blue insulation foam survived the pressure tank unscathed at 40psi. However when sealed with PVA and encased in silicone, it collapsed on itself by about 20%. So, it's probably fine to use for props/supports etc in the tank but definitely not good for use in a model to be moulded.

It might work if the bottom was left uncoated, and it was attached to the floor of the mold box with holes in it. This would allow the pressure to enter the piece from below. I had something like this happen recently, a solid wood master that I added a base to with styrene strips, creating a hollow base about 1/4in high. It was glued down to sheet acrylic which formed the floor of the mold box. Under pressure the acrylic cracked, but fortunately didn't affect the mold any.

Sorry it didn't work out for you, but thanks for reporting back with your results.