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I am looking to print an HTD Timing Belt pulley to be used in a laboratory setting that can get very cold for extended periods of time. By "very cold" I mean adjacent metal chambers get cooled with liquid nitrogen to lower than -200 °C. For the purposes of having a threshold temperature tolerance, assume that the metal chambers coming directly in contact with the pulley may get as cold as mK close to absolute zero.

While it was my intention to print this pulley out of PLA, I am unsure whether or not it will be able to withstand negative temperatures of this magnitude or if it will become brittle--or something else will happen to the structure of the print when it experiences these temperatures. I am open to printing any other material if there are some materials that will hold up better than PLA for low temperatures. It is preferable for me to print this part instead of machine it for the sake of a deadline. I was also wondering if there is some infill pattern, infill density, or other structural print parameters that would help reinforce a printed part against becoming brittle when imposed to such low temperatures.

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    $\begingroup$ What plastics do you already know can take the cold soaks you describe? Perhaps thermosets rather than thermoplastics (which would suggest an SLA rather than FDM print)? $\endgroup$
    – Zeiss Ikon
    Jun 17, 2021 at 13:57
  • $\begingroup$ Do you know a thermoset that would be good to experiment with for testing out these low temperature constraints? $\endgroup$
    – John Marangola
    Jun 17, 2021 at 14:05
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    $\begingroup$ Not offhand, just exploring options. I don't work in cryogenics, I repair power tools. I thought it might be possible to just look up the properties of various plastics, like we used to do with the "Rubber Bible" -- CRC manual -- when I was in college ~40 years ago. $\endgroup$
    – Zeiss Ikon
    Jun 17, 2021 at 14:07
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    $\begingroup$ @PerryWebb Actually, most steels become very brittle when chilled, even well above liquid nitrogen temperature. There are recorded cases of cold-induced brittleness causing failures in building structures (under construction) at fairly ordinary outdoor winter temperatures. $\endgroup$
    – Zeiss Ikon
    Jun 18, 2021 at 13:51
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    $\begingroup$ Another example: a steel trashcan will usually hold LN2 OK, but a plastic trashcan will usually crack if filled with LN2. Teflon tends to hold up well at LN2 temperature. It would make good bearings but too slick for pulleys and a difficult melting point for printing. $\endgroup$
    – Perry Webb
    Jun 18, 2021 at 14:08

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I found this article which seems to suggest PTFE is a good choice of plastic for a cryogenic environment. I've read that there are PTFE filaments available for FDM printers, though there are some caveats. First, you will need an all-metal hot end; enough heat to melt a PTFE filament will melt the PTFE filament guide if it is in contact with the nozzle. Second, you will likely need to edit your printer's firmware to permit printing at the high temperatures required. Third, it may require some testing to determine whether FDM printed PTFE will meet your mechanical needs (shear strength, layer adhesion, etc.) and fourth, you might need an unusual build surface, since the polymers used for many existing surfaces can't take the temperatures needed for bed adhesion.

Finally, as with a PTFE guide tube in contact with the nozzle, at the temperatures required you need to be aware of and take precautions against outgassing by the melting PTFE.

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  • $\begingroup$ The need for higher extrusion temperature is what I would expect. However, that's assuming the same function between the brittle cold temperature and the almost liquid phase. $\endgroup$
    – Perry Webb
    Jun 17, 2021 at 14:54
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You could try PETG. PETG labware works down to -70, and there is a video clip where a PET bottle filled with liquid nitrogen that withstands appreciable pressure. But for whichever material is used, thermal cycling may be a problem.

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    $\begingroup$ Welcome to 3D Printing SE and thank you for your contribution. When you get a chance, please take the tour to understand how the site works and how it is different than others. $\endgroup$
    – agarza
    Jun 18, 2021 at 1:46
  • $\begingroup$ Thank you for the suggestion--I will try it. Unfortunately for my purposes, -70C compliance is essentially meaningless to me (of course assuming you did not mean 70K). The temperatures I am referring to are an order of magnitude lower ~ -459.67C. I am sure thermal cycling is a potential issue that could induce material fatigue characteristics. $\endgroup$
    – John Marangola
    Jun 18, 2021 at 21:39

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