# PTFE



## Mo deller (Jan 22, 2010)

I have a scrap box of plastic and was wondering if there is a positive way of identifying ptfe.

Peter ???


----------



## Noitoen (Jan 22, 2010)

PTFE is a dull white, feels soapy, and is denser/heavier then other plastics.


----------



## rickharris (Jan 22, 2010)

FWIW

Density PTFE (lb/in³)
	unfilled 0.078   25% Glass filled 0.081   25% carbon filled 0.075

(g/cm³) 
    unfilled 2.16   25% Glass filled 2.25  25% carbon filled2.08		

Same for Polyethylene

Density (lb/in³)
	LDPE 0.033  HDPE  0.035   UHMW 0.034

(g/cm³) 
    LDPE 0.92  HDPE  0.95  UHMW  0.93


http://www.boedeker.com/ Useful site with lots of information


----------



## Mo deller (Jan 22, 2010)

I have some that is I would say milky white and does feel a bit slippy to touch. I would guess it is ptfe but I have no experience so wondered if I could be fooled by something similar. 

Rick, I dont know what to do with all the numbers. I guess there must be a formula to work it out from weight and volume but I have no idea how to do it.

Thanks
Peter


----------



## Noitoen (Jan 22, 2010)

The numbers are easy. Just fill a graduated measuring cup with some water, drop a chunk of the material you want to measure, determine the water displacement in cu/in, weigh the piece and calculate the density.


----------



## Mo deller (Jan 22, 2010)

;D Yes I can do the drop it in some water and weigh it bit,it's the calc I dont understand. What is the formula?


----------



## Mo deller (Jan 22, 2010)

Ok I think I have it. Mass divided by volume = density. I get the impression that's very basic and in reality it is more complicated.


----------



## solver (Feb 4, 2010)

How about simple rubbing-test? If it's ptfe, it should be quite slippery against for example brass or steel.


----------



## charlesfitton (Feb 4, 2010)

A technican at my place of employ showed me a neat way to identify plastics 
- a burn test.

Some won't stay lit, some smoke a lot, some drop small burning gobe of fire - I'm sure there's a chart somewhere on the web.

Marry up the characteristics with the chart and Roberts' married to your Auntie...

f


----------



## Mo deller (Feb 5, 2010)

I just had a google and found that if I poke a soldering iron into ptfe it doesn't drip and should smell of burnt hair.
Added to feeling slippery I think should get some positive id there.

Many thanks
Peter


----------



## solver (Feb 5, 2010)

Burning ptfe isn't recommended, since it forms very hazardous gases.


----------



## Mo deller (Feb 6, 2010)

solver  said:
			
		

> Burning ptfe isn't recommended, since it forms very hazardous gases.



I appreciate your concern and I half expected someone to raise the health issue. I am well aware that burning any plastic is not to be reccomended but will a quick prod with a hot object done outside just to verify things be that bad?


----------



## solver (Feb 6, 2010)

If proper precautions are taken, I suppose it can be done. 

Some info about ptfe: http://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety

Using respirator mask isn't exaggerated. If you inhale that smoke even bit, it gets you in a quite bad shape almost immediately.

I have done that mistake, and hope others don't do it. Safety first.


----------



## Mo deller (Feb 6, 2010)

mmmmmmm I dunno, I think I'll stick to the rub test then. 
This has made me wonder how much it gets heated inside an engine but we could go on and on. It's a small amount but if you happen to be sensitive to it that is irrelevant. 
With all the stuff that is going on in the world I think we are all doomed anyway, doomed,doomed I tell yeee ;D

Anyway safety issues noted,thanks.


----------



## AdShea (Apr 30, 2012)

I know this is reviving an old thread, but one easy indicator of PTFE over HDPE or PP is that PTFE sinks quickly in water, the others don't (just look at the density).


----------



## Todd... (Jun 4, 2012)

getting ptfe above 300 degrees F will emit a gas and cause "ptfe flu" 

had to do my senior design project using the stuff, easy to machine but a pain to work with non the less


----------



## steamer (Jun 4, 2012)

Yes...the "flu" I suspect is a result of Phosgene gas.  PTFE needs to be turned more slowly than most plastics so that it doesn't overheat and break down....but it's not that hard to do.  The other by product I believe is Hydrofloric acid.....KenI will be along with a complete and correct assessment... ;D

DON"T SMOKE WHILE TURNING THIS STUFF!

Dave


----------



## Blogwitch (Jun 4, 2012)

PTFE machining gases whilst smoking produces phosgene gas. Which in turn forms hydrochloric acid and carbon monoxide in the lungs.

Burning Viton produces hydrofloric acid, which kills any living cells on or in the body it comes into contact with. Usually it is easier to amputate the whole limb quickly rather than attempting to treat the affected area, as it spreads with ease throughout the body. It also eats it's way through glass.

These are two of the most dangerous 'plastics' that we can use in our shops.


John


----------



## Maryak (Jun 5, 2012)

Bogstandard  said:
			
		

> PTFE machining gases whilst smoking produces phosgene gas. Which in turn forms hydrochloric acid and carbon monoxide in the lungs.
> 
> Burning Viton produces hydrofloric acid, which kills any living cells on or in the body it comes into contact with. Usually it is easier to amputate the whole limb quickly rather than attempting to treat the affected area, as it spreads with ease throughout the body. It also eats it's way through glass.
> 
> ...



Thanks for that Bogs :bow: I wonder how many of us knew that ??? I sure didn't.

Mental note to self........"Don't have one last scratch of your privates, when burning Viton." 

Best Regards
Bob


----------



## Tin Falcon (Jun 5, 2012)

Hmm interesting conversation. brings up some interesting points. 
1) know the material you are working with. Know the hazards. that is What MSDS sheets are for they are readily obtainable and available as pdf files. download and print. follow recommended precautions. 

2) smoking in and of itself is not healthy the cigarette companies enhance the tobacco with nasty chemicals . to even call the stuff in cigarettes tobacco is to call sawdust/garbage board aka mdf wood. I would expect burning mdf in a fire expels some nasty gasses as well. 

3) some plastics are made with phosegene,burning it releases phosegene. 

4) phosegene a chemical discovered during world war I. A chemical warfare agent , smells like freshly mown hay.Causes dry land drowning. no antidote. exceed exposure levels it will kill you. made by reacting chlorine (poison) and carbon monoxide) another poison. 

5) OSHA regulations prohibit eating drinking or smoking in work areas that contain potential harmful or hazardous material or chemicals. also these materials are not permitted in designated eating areas/break rooms. 
6) popper practice of industrial hygiene including following recommendations on MSDS sheets prevents chemical exposures.

7) most of us here machine in our own private space we call a shop. we set the rules and enforce them or not. we are responsible for our own saftey. work safe ladies and gents.
8) do not forget this is supposed to be fun ;D
Tin


----------



## Ken I (Jun 5, 2012)

steamer  said:
			
		

> Ken I will be along with a complete and correct assessment...



No I won't - I'll stand by everthing written above as Kosher.

Take care.

As to the original question - if it feels soapy, dense and a soldering iron won't mark it its probably PTFE - most old hands will identify it a such the instant they pick it up - nothing else feels quite the same.

Ken


----------



## abby (Jun 5, 2012)

Hydroflouric acid is used in it's 30% state mixed with concentrated sulphuric acid for the polishing of lead crystal after cutting.
The cut crystal is literally rubbed by hand in baths of the above with heavy duty rubber gloves the only protection.
Operators are invariably splashed but I know of none who have suffered losing limbs or de-calcified bones.
Hydroflouric acid is also used mixed with ferric chloride as a pickle for heat treated stainless steel again operators get splashed , this is inevitable in an industrial enviroment but again I know of no-one who has suffered what we are lead to believe can happen from burning a small amount of PTFE.
I use Viton o'rings in my steam engines , they carry no hazard , I am unlikely to set fire to them and savour the smoke.
I machine PTFE and again there is no hazard, use very sharp tools and the "swarf" will be in one long piece , very easy to place in your dustbin , it does not get hot during machining.
Don't be frightened by such claims and warnings , by the very nature of what we do workbenches and hands will inevitably be contaminated , do the obvious and you will come to no harm.
It is not good to smoke - period , it is less good to smoke whilst working !
If making dust wear a mask , wear eye protection where applicable and wash hands before eating or smoking.
When it comes to machining alloys containing Beryllium or Cadmium well that's a different story.


----------



## steamer (Jun 5, 2012)

Hi Abby,

My Comments were not intended to be "alarmist". I use teflon for the piston rings and Viton for Orings on my steamlaunch running at 160 psi saturated steam ( about 377 F ) and have had no issues with it or any of it's by products for at least 10 years...I've lost count actually.

But I know what to look out for....so I am aware.

I stated my comments more towards the lines of the novice who might turn it WAY too fast (hard to do actually) or waives a torch at it intentionally or not....thereby making them aware of a potential problem.

I have plenty enough to do without being anyone's Nanny, I can assure you.

The message of "Just go slow, and think about what your doing" is what I was trying to get across.

As a wise friend of mine put it..." Safety is an attitude"

Dave


----------



## Blogwitch (Jun 5, 2012)

After reading Abby's post, I decided to do some searching of my own, and it seems that I was wrong, up to a point, about the effects of hydrofluric acid.

Please read the two following links to explain.

http://emedicine.medscape.com/article/773304-overview

http://www.hse.gov.uk/mvr/priorities/fluoroelastomers.htm

Unfortunately, I was passing information on from 'bogus' sources that I had come across when checking my own shop for H&E problems with the materials I use in there.

But, in my defence, I also saw genuine cases of large hydroflouric acid burns while searching on the web, which caused major amputations and even death.

John


----------



## rleete (Jun 5, 2012)

Better a healthy respect for that which could happen, rather than a disregard of all warnings.


----------



## steamer (Jun 5, 2012)

rleete  said:
			
		

> Better a healthy respect for that which could happen, rather than a disregard of all warnings.



YUP!


----------



## Tin Falcon (Jun 5, 2012)

I agree . No one here is saying do not machine ptfe/teflon in the home shop. and no one is saying not to use vton o rings in the home shop. all chemicals have some risk if improperly used. 

check out this web site http://www.dhmo.org/facts.html
Tin


----------



## Ken I (Jun 6, 2012)

The point is both PTFE and Viton produce extremely hazzardous gasses when burnt.

I have no problem with machining PTFE or using Viton - for that matter I used to use copious amounts of Beryllium Copper - simply be aware of the dangers.

As is the case for most hazzards - the extreme risks are generally overstated (but nontheless real) - for the inexperienced or unwary etc.

If you use a known hazzardous material look up the hazzard sheets and get specific advice wrt your application before proceeding.

Ken


----------



## steamer (Jun 6, 2012)

Like I said ...Ken would be along in a minute with some good advice.... ;D

 :bow:


Dave


----------

