Cryogenic Materials (Non-Metallic)

[dfly9891]

Hi,

What non metallic material is best based on the following (in order of importance):

1) Has a CTE as close as possible to stainless
2) Relative isentropic contraction properties
3) Hold a piston/bore O-ring seal with stainless separating vacuum space from helium space (140 psia and 200 K)
4) Low thermal conductivity (less than 1 W/mK)



Thank You.

 

[iainuts]

Hi dfly,

3) Hold a piston/bore O-ring seal with stainless separating vacuum space from helium space (140 psia and 200 K)

This didn't make any sense to me. Maybe you could explain a bit better.

Regardless, you might consider G10. Its CTE is about as close to Stainless as you're going to get with a material that has a thermal conductivity of less than 1 W/mK. Physical properties aren't perfectly isentropic, but they're close. If you'd like, I can post some graphs of properties.

 

[jedward]

look at glass filled
torlon, peek or ultem plastics

 

[dfly9891]

iainuts,

I was thinking of using G-10 NT from Spaulding Composites, so it's good to hear that I'm on the right track.

As far as #3 goes... I need to hold a helium tight seal with an o-ring touching the G-10. Spaulding says that they can get the surface finish down to 40 RMA, so with silicone o-rings they have helid vacuums agsinst the G-10 down to militorr values.

I would very much like to see whatever CTE/THERMCOND graphs you have relative to G-10 and other cryo materials.


Thank You

 

[dfly9891]

jedward,

torlon looks promising.... do you have any information on the behavior of this material at cryo temperatures?

 

[jedward]

no specific information re low temperatures and torlon

could a FEP teflon seal be incorporated? it can be used at liquid helium temp and at least modest pressures

 

[dfly9891]

jedward,

I think it can be used in this app... I'm looking into FEP Teflon now. Thanks.

 

[iainuts]

Torlon is a good material. You can get it reinforced with glass fiber or carbon fiber. You can also get it with various wear reducing additives. Solvay is the company that markets it, but they don't generally make it. You can purchase bar stock from Drake Plastics, whom I've used before and found to be a very good supplier. Solvay has the technical information on their site:

http://www.solvaysites.com/sites/so...lymers/Spire_Ultra_Polymers/Pages/Torlon.aspx

Their design guide has some information about cryogenic properties:

http://www.solvaysites.com/sites/so...ics Literature/DPG_Torlon_Design_Guide_EN.pdf

Drake Plastics is here:

http://www.drakeplastics.com/

I've done some minor testing with it. I dunked a small cylindrical part in liquid nitrogen, put it on a concrete floor and tried to smash it with a hammer. It held up extremely well, though other materials did also including PEEK.

 

[dfly9891]

iainuts,

Thanks for the info. I'm going to call Drake this week to make some final decisions.

 

[fang54]

good starting point on material properties:

Cryogenic Material Properties Database

http://cryogenics.nist.gov/Papers/Cryo_Materials.pdf

 

[dfly9891]

fang54,

I've read this paper a dozen times. It's a great reference! What I'm looking for is the same level of detail with non-metallics other than the ones covered in the NIST paper. The nist paper covers, polyamide, teflon, and G-10. The most suitable material among those three is G-10. But torlon has the most suitable CTE... I just wish I had the CTE as a function of temp as in the NIST documentation.

In the end I'll probably make this part out of 3 different materials and test.

Thanks.

 

[iainuts]

Torlon is just a polyimide based material, so you can use the Cryogenic Materials Data Handbook for such things.

Volume 1 is all metals (aluminim, SS, ... )

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD420407&Location=U2&doc=GetTRDoc.pdf

Volume 2 has the plastics in it.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD713620&Location=U2&doc=GetTRDoc.pdf

 

[dfly9891]

iainuts,

Huge thank you for your last post!!

 

[Burdy]

Glass filled Torlon will abraid the o ring.
B

 

[dfly9891]

Burdy,

Interesting. Would you say that any glass filled material will abraid o-rings?