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Author: Subject: Recasting teflon
roamingnome
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[*] posted on 13-6-2008 at 12:38
Recasting teflon


I have a large assortment of PTFE stoppers mainly, and Ill use some,

but if they can be ground and recast into a more useful shape like a thick tube or teflon beaker this would be great.

melting of some plastics causes shrinkage

Has anyone melted teflon to fatique?

[Edited on 13-6-2008 by roamingnome]
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Eclectic
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[*] posted on 13-6-2008 at 13:55


I don't think you can melt PTFE.
Most items are made by press/sinter of the powder.
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[*] posted on 13-6-2008 at 15:16


There is a fine line between melting and decomposition (to deadly gases such as HF and fluorophosgene). You must operate on that fine line which is around 330°C to cast it. Decomposition will already be taking place to some degree at that temperature and I believe you will need a good fume hood and scrubber system. I have melted very small amounts of PTFE before but have not cast anything. It would require constant heating. In industry it is injection molded at somewhat below its melting temperature, like pretty much any other thermoplastic. If you can set up presses and molds for injection molding, that is the best way to do it.



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Panache
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[*] posted on 13-6-2008 at 17:56


It won't flow even if you can dance on the ever so thin line kilowatt mentioned, so casting is impossible. i understood teflon to have too poor a melt flow index for injection moulding and that machining or sintering the powder is about it, hence the expense of anything manufactured from teflon, except teflon tape which is reasonably inexpensive.
Best thing is to drill your stoppers into shavings and using the teflon 'wool' for everything under the sun in your lab.


[Edited on 13-6-2008 by Panache]




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[*] posted on 13-6-2008 at 18:48


IIRC, PTFE goes "gelatinous" at the "melt" temperature (the "fine-line"). If you had the proper mass to fill a two-part mold, you could heat it until gelatinous, then press it between both halves of the mold (heated at the same temperature as the melt and then cooled in some controlled way) to cast the object that you want.

I really like the PTFE "wool" (it does turn very nicely, beautiful in a drill press or end-mill) idea, though, and will definitely keep that in mind.

Cheers,

O3




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[*] posted on 13-6-2008 at 19:23


http://www.sciencemadness.org/talk/viewthread.php?tid=2090&a...



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roamingnome
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[*] posted on 14-6-2008 at 18:42


well it seems then, that simply buying 1-2 inch stock is the most direct and safe way of making a microwave cavity.

If scrap PTFE from grindings/millingings/shavings is used, the polymer chain length would then be shorter.

This would effect the polymers property's in some way for sure. Something maybe interesting, but not for moderate pressure conferment.

[Edited on 15-6-2008 by roamingnome]
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[*] posted on 14-6-2008 at 22:07


I would like to add that I have tried to melt and "recast" teflon before via conventional heating and determined it to be all but impossible. The "liquid" point and decomp. point are so close that they seem to happen simultaneously.

It always gets "charred" and really never fully "melts" because of that.




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chief
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[*] posted on 10-7-2008 at 17:32


A lot of chemists are said to die of teflon-overheating- accidents; it's said to be very painful too.
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[*] posted on 10-7-2008 at 22:33


Quote:
Originally posted by chief
A lot of chemists are said to die of teflon-overheating- accidents; it's said to be very painful too.


What accident ensues when teflon overheats?




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[*] posted on 11-7-2008 at 00:32


Quote:
Originally posted by chief
A lot of chemists are said to die of teflon-overheating- accidents; it's said to be very painful too.


I've never heard of chemists dying because of PTFE over heating. Canaries and other birds kept in kitckens have popped off when teflon coated non stick frying pans are left on. The worst I've heard of is 'polymer flu' where you get flu like symptoms from exposure to the very small amount of dangerous products given off if the PTFE is burned up.

I'll have to do a search for teflon related deaths when I get the time. Can you reference any links to such a situation?




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[*] posted on 11-7-2008 at 10:53


Quote:

Canaries and other birds kept in kitckens have popped off when teflon coated non stick frying pans are left on


I go to this lady at work, hey cool your useing cast iron pans, and she says its for the birds....
after giving here a puzzeled look she explains that yes they die

but teflon flips the eggs good, any toxin cant be good for us in the long run though

anyway...
"Several lines of evidence have suggested that hydrolysis of PFIB and resulting production of hydrofluoric acid may be responsible for pulmonary damage"

Overheating of PTFE generates fumes of highly toxic PFIB and poses a serious health hazard to the human respiratory tract. PFIB is approximately ten times as toxic as phosgene [2]. Inhalation of this gas can cause pulmonary edema, which can lead to death. PFIB is included in Schedule 2 of the Chemical Weapons Convention (CWC),

teflon: a blessing and a curse
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[*] posted on 11-7-2008 at 12:09


Also, heating PTFE generates TFE (a great way btw to get tetrafluoroethylene "IF" you know what you are doing). In high concentrations, TFE when exposed to oxygen deflagrates creating a LOT of energy as well as CF4, C, and other CFO species. Meaning, if it's in high enough concentration and is exposed to oxygen (or any other radical for that manner), it will go boom (has about the same power gram for gram as TNT if I remember right).

For this reason TFE is dangerous stuff and I wouldn't recommend ANY amature chemist messing with it. Typically it is stored in a cylinder with ~20-50 wt% CO2.

Most TFE polymerizations are controlled emulsion or solution polymerizations where the TFE is slowly bubbled into the pot, thus there is never a high concentration...and these reactions are done behind large blast shields.
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