Machinable thermally insulating foam for containing liquid nitrogen

[alansimpson]

I am doing some cryogenic experiments and need to make some special shaped baths to contain liquid nitrogen for short time.
I have to be able to machine to complex shapes to fit around apparatus. Have been using a rigid foam(PU I think, for building insulation) about 100 mm thick and cutting on milling machine to shapes around 200 mm X 150 mm and coating in epoxy and glass fiber cloth. Messy and weak but works OK

Dewar that holds liquid nitrogen seems to be insulated with a LDPE foam.

Could anybody recommend an cryogenic insulating material I could cut on milling machine to various shapes

 

[Eltron]

Does it have to be foam? Why not just use HDPE?

Dan

http://www.eltronresearch.com

Dan's Blog

 

[btrueblood]

Urethane foams in various densities are certainly machinable, and should hold up ok to LN2. I have used styrofoam "ice chests" (the cheapo ones from a grocery store) as LN2 containers before, and the insulation layer in some commercial LN2 dewars is just that, although with a stronger polymer shell layer for support and damage tolerance.

Neither PE foam nor styrofoam are very machine-able. A more typical construction technique is to form the shell from sheet material, and inject (or pour) urethane foam into the hollow interior (or steam-expand styrene foam pellets). Polyethylene sheet as a cover for injected/expanded PU foam would be a pretty good combo., I'd think.

 

[IRstuff]

While styrofoam isn't machinable, per se, it is formable. If you get a nichrome heater wire, you can cut and sculp your desired shape.

TTFN

FAQ731-376

 

[unclesyd]

We always used high density Styrofoam for nearly all our bench containers for LN2 in under 1 liter quantities.

I know locally that cryogenic shipping containers are Styrofoam with a heavy duty corrugated paper board cover.

I was involved in project where we did machine some special containers from modeling or pattern board. These materials are mostly urethane foam of various densities. You could use the low density material to machine and then insert in into a Styrofoam shell.
I definitely would give Freeman a call

http://www.freemansupply.com/RenShapeModelingan.htm

 

[Eltron]

Everybody should have some Renshape laying around their shop. Great stuff.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[btrueblood]

"Everybody should have some Renshape laying around their shop."

And a good vacuum cleaner.

 

[alansimpson]

Can't find any renshape in Europe. Can you recommend an alternative?

Thanks

 

[btrueblood]

Alan,

Renshape is "just" urethane foam in various densities. (I'm sure there are some benefits to the real McCoy, besides fancy coloring agents . The lower density urethane foams will give better insulation properties, at the expense of structural strength/stiffness, and vice versa. Talk to a local machine shop or their tool supplier, a plastics supplier, or shop material supplier. Some other terms used for the stuff include "butter board" and "prototyping foam".

 

[btrueblood]

Oh, and Huntsman appears to be a distributor of the stuff in Europe.

http://www.huntsman.com/

 

[unclesyd]

Aside from Huntsman as posted above you can check out any one that supplies "core" materials. They will normally carry several type of foams and you will find tooling board normally listed under the polyurethane section. Along with the mill supply stores another source is the big marine
supply stores.

If you have to bond the PU foam make sure you follow the manufacturer's bonding instructions.