HomeRoast Digest


Topic: reminder about tc insulation (5 msgs / 115 lines)
1) From: Jeffrey Pawlan
I have posted this before but it seems that there are new home roasters who did
not see it.
Do not use teflon covered thermocouple wire in a coffee roaster, especially in
an air roaster which has higher temperatures than any drum machine.
Teflon melts and becomes highly toxic well below 460 deg F.  That is what killed
astronauts in a shuttle fire many years ago; not the fire. It will poison you
long before you can taste it.
I use double kapton covered thermocouple wire in my computer controlled
roasting systems. This is quite safe for food and imparts no chemicals or taste.
It will not melt below 600 deg F.
Also safe are fully enclosed stainless steel probes. However, they have a long
lag in response time as stainless is a very poor conductor of heat.
Jeffrey Pawlan
Pawlan Communications

2) From: Dean
I hate to argue with Jeffrey,  but the references I find suggest that 
Teflon PTFE and Teflon PFA both have melting points substantially higher 
than indicated--around 600-620 F.  FEP (sometimes described in the 
Teflon "class") is around 520 F melting point.  Omega rates FEP at 
392F--so no good for a roaster.   They rate TFE at 500 F.  The Kapton 
wires sound like they'd be fine--Omega says up to 600F is probably OK.  
Omega probably sells as much TC wire as anybody, so should know what 
they're talking about....
As to the astronauts killed in a shuttle fire--I don't remember 
that--the Apollo 1 tragedy, yes; and while arcs from damaged Teflon 
insulation was suspected as  the source of the fire, this was never 
proved, and TFE was not likely the source of the toxic fumes.
I use the Fiberglass insulated wires (without the blue tape on the end) 
that came with the theromometer and they've held up well in my Rostos. 
They might shed a bit, so that's something to think about fi you enjoy 
worry.  I also have a SST probe, and as Jeffrey indicated, it's a bit 
sluggish.
For coffee roasting temperatures I wouldn't worry much about PTFE or PFA 
melting or igniting.  Not before the beans.... :-)
Dean
Jeffrey Pawlan wrote:
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3) From: James Raven
If you want to argue, ask Jim to argue.
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ribes) go tohttp://sweetmarias.com/maillistinfo.html#personalsettingsWindows Live Hotmail and Microsoft Office Outlook  together at last. =
Get it now.http://office.microsoft.com/en-us/outlook/HA102225181033.aspx?pid=CL10062=6971033=

4) From: Brett Mason
LOL - way too funny for midnight CST...
On 10/27/07, James Raven  wrote:
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-- 
Cheers,
Bretthttp://homeroast.freeservers.com

5) From: Aaron Scholten
Teflon does give off toxic fumes when overheated, burnt / etc etc.    
However the amount on your tiny little while is not enough to really 
panic over.... unless you are a canary of course.
I believe I know the TC wires you are talking about, and the shields 
have various melting points depending on the application.  Is it teflon, 
or a nylon derivitave?  either way I do remember it was a #$% to strip 
back when hooking up T/Cs to the bed furnace.  If it overheats a bit id 
think it's just kind of 'melt back' on the wire a bit, exposing a bit 
more of the TC wire which really wont hurt too much.
Aaron


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