Plastics for low temperatures 2

[CADShark]

I need to find a plastic that will hold up in a -300 degree F. enviroment. It will not be a constant exposure but a frequent interval of every 12 hours for about 1 minute at a time. I know teflon is good for low temps but it also needs to be a moldable plastic.

Does anybody have any suggestions?

Thanks in advance,
CADShark

 

[patprimmer]

Does it need to stand any load or impact at this temp, or just withstand the thermal shock.

At -184C I think almost all thermoplastics will go to their brittle phase. Wether or not this generates breaks from thermal shock will depend on design and rate of cooling as well as material choice.

I have never seen data for less than -40 degC, so in the words of Captain Kirk, maybe you are about "to bravely go where no man has gone before".

I will see what I can dig up from my old data.

Maybe other injection mouldable flourocarbons might do the job

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[PrentP]

Not true Pat - the ban has been lifted. See

http://www.millenniumchem.com/Produ...r_Whats+New/Cadmium+Pigments+Whats+New_EN.htm

Good News for users of Cadmium Pigments



Regards,

Peter P

 

[PrentP]

Sorry, This should have been in Plastic molds/fabricating engineering.

Regards,

Peter P

 

[sealguy]

PTFE can be compression molded and FEP, PFA, PCTFE can be injection molded (melt prossible). No other plastics, that I know of have better low temperature properties.

 

[CADShark]

Pat,
No stress involved, just thermal shock. I have other machined metal parts contained within the plastic but there Coef is higher.

Sealguy,
Forgot about the PFA's and the PCTFE. We need the plastic to be injection moldable.

Has anyone dealt with VESPEL or LUSTRAN? I heard they are good for low temps too.

CADShark

 

[patprimmer]

I have never seen a plastic with a co-efficient of expansion lower than most metals. The plastics are normally higher by a factor of about 10, are you sure you have not lost a decimal place somewhere.

Also the plastic will almost certainly go through a second order transition in the range from ambient to -184C, which will cause it to contract somewhat more than the co-efficent of expansion would indicate as it passes through that phase change.

I think sealguy gave you your answer with the injection mouldablr fluorocarbons. Why don't you ask their manufacturers for details.

The figur's you need are co-efficient of expansion and elongation at break, for both properties over the temperature range involved.

Problem is I expect no one has tested for this.

Can you get test plaques or pices of barstock of the canditate materials, drill a hole the appropriate size to allow for mould shrinkage in one of them, heat the plaque, and super cool an insert, place the insert in the hole, allow the whole deal to normalise overnight, then cool the part to -190C



Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[gambro]

We used to make a bag for storing items in liquid Nitrogen (at something like minus 192°C). The bag was made of Kapton foil (Polyimide foil with PTFE layer, manufactured by DuPont). We injection molded the connecting ports using Teflon PFA (DuPont) which were then welded onto PTFE-layer of the bag.

 

[eliassen]

Look at a TICONA material, UHMW-PE, it can work wll at -253
degree celsius. I think this will be cheaper than Teflon, and work better too.

Ståle Eliassen

 

[DeGlaas]

I aggree with Eliassen. I saw tests at DSM Engineering plastics where UHMWPE was used in combination with liquid Helium at -269 °C. It still had usable impact strenght. You need a PE with very high molecular wight though, because lower weights will decrease ability to withstand low temperatures.
Keep in mind that it has high CTE, and relativly low mechanical strenght.

 

[samuelT]

Try Hytrol by Dupont, Toughest stuff on the planet. It is a Copolyester elastomer. Can inject but tough to push.

 

[samuelT]

Sorry that was Hytrel not Hytrol

 

[patprimmer]

Thermoplastic Polyester elastomer's like Hytrel and Arnitel are quite tough at room temperatures, but what are they like at -300 F, as requested in the original question?

i know they are good for ski boot parts which need reasonable impact strength at -40 deg C, but thats a long way from -300F

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.