[TheForge] Forge temps

[Bruce Freeman]

First, go to this website:
http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=tc_colorcodes
Look in the "Maximum T" column and select a thermocouple wire with the
lowest suitable  maximum temperature.  I suggest K, for example. (Read
the column "Comments Environment" for details that concern you.  For
example, in a gas forge with the flame blowing out all the holes, the
environment inside is "reducing" and a thermocouple that can't
tolerate a reducing environment won't last long.  If the flame is
completely inside the forge, then the environment is oxidizing.  If
the thermocouple is only placed in the forge for short periods, this
won't matter.  The thicker the wire , the less this matters, so favor
the smaller-numbered gauges.

Now consider either bare wire or ceramic insulation for the thermocouple:
http://www.omega.com/pptst/BARE_SH_DH_OV_ELEMENTS.html
For example, sh-1-14-K-12 will run you about $20 for a 1-foot length.

You will need a millivolt meter.  This one from  HF is great, and
despite the price on this webpage, has been selling for $3 at HF
stores recently:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899

IF you can connect the thermocouple directly to the MV meter, then
you're almost home free.  If not, then you need extension wire.   For
precise measurements, you need extension wire of exactly the same
composition as the thermocouple (so you don't make new thermocouples
at the junctions).  This is only about $0.62 per foot, but they want
you to buy 100 ft.  The gauge of this wire doesn't matter at all.

SO, you might just keep the junctions at room temperature or close to
it, and just use copper wire as your extension wire.  This will
introduce errors, but these should be small if all extraneous
junctions are at room temperature.

Finally, you'll need a mV vs temperature chart for your type of thermocouple.
http://www.omega.com/thermocouples.html , or for the type K, measuring
in deg. F:
http://www.omega.com/temperature/Z/pdf/z218-220.pdf

What this chart tells you is that at about 2000 F, the thermocouple
will give you about 45 mV - easy to measure on the mV meter.
You take your measurement, then come back to this chart to read the
temperature.  Skip the "1" to "10" across the top, and just read mV in
the "0" column, which will give you deg.. F within 10 degrees.


On Fri, Apr 3, 2009 at 7:38 PM, Bob Willman <blcksmth at wcnet.org> wrote:
>        One could use Tempil sticks. They are accurate and reasionably
> priced.
>
>
> Bob Willman
> Bowling Green, Ohio
> The Eagle's Anvil
> WB8NQW
>
> -----Original Message-----
> From: theforge-bounces at mailman.qth.net
> [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Mark Novak
> Sent: Friday, April 03, 2009 6:12 PM
> To: theforge at mailman.qth.net
> Subject: [TheForge] Forge temps
>
> How do y'all measure and control the temperature of your respective forges,
> for accurate annealing? I don't have a pyrometer that goes over 1000ºF, but
> I got ahold of some S-7 I'm going to use for center punches and which needs
> to be annealed at 1500-1550ºF for 20-25 minutes (for a hand tool of this
> size). I have no idea how hot my crappy atmospheric propane forge burns, let
> alone how to maintain a somewhat consistent temp.
>
> Help!
> Mark Novak
> Fireworkspdx.com
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-- 
Bruce
NJ

The total lack of evidence is the surest sign that the conspiracy is working.