Subject: temperatures - how to?

From: [email-masked]
Date: 22 Sep 1996 06:37:54 -0700

Hi!
I've been reading, both in books and here, about heat treating, hardening,
annealing metals.
I have a Neycraft furnace with just the temperature indicator - no manual
controls.
My question: how do I go about doing something like this:
Heat to 900def F, hold for 10 minutes, remove and quench.
How do I know that the part has reached 900deg F? I only have an indication
for the furnace's temperature - not the actual part.
How long should I hold the furnace's temperature for the part to get an even
temperature?
As I don't know if things are working, I can't even do some  testing.
Can you help me?  Many Thanks eduardo haddad filho [email-masked]

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From: [email-masked] (Russ Kepler)
Date: Wed, 25 Sep 1996 16:40:36 GMT

In article <[email-masked]>,  <[email-masked]> wrote:
>Can you help me?

I didn't see any answers, so I'll give you my take: in general, the
rise in temperature in a furnace isn't so fast as to have really
unequal temperatures in the furnace, or at least not between the
pyrometer and the work.  If there is much of a difference you should
see it in a change in the on/off time of the heating elements.  This
is all assuming that the work is placed in the furnace with both in a
"cold" state.  

If you were to place the material into a hot oven then the heat time
would be a complex function of the temperature delta, work thickness,
ability of the furnace to hold temp, etc.  When you get into those
complexities I don't know how to suggest going forward, except to
repeat the suggestion that you look at the furnace cycle time to
maintain heat, and when that's back to the heated-but-empty time that
the material should be at the proper temperature.

-- 
Russ Kepler							[email-masked]

                    Please Don't Feed the Engineers

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From: [email-masked] (Spehro Pefhany)
Date: 26 Sep 1996 03:28:34 GMT

[email-masked] wrought:
: Hi!
: I've been reading, both in books and here, about heat treating, hardening,
: annealing metals.
: I have a Neycraft furnace with just the temperature indicator - no manual
: controls.
: My question: how do I go about doing something like this:
: Heat to 900def F, hold for 10 minutes, remove and quench.

Hmm... you could upgrade the control to one that ramps and soaks etc, but 
that would cost money (say $250-$600 probably). You can probably do ok 
manually if you are not using it much. 

: How do I know that the part has reached 900deg F? I only have an indication
: for the furnace's temperature - not the actual part.

At relatively low temperature like 900F, why not attach a thermocouple 
directly to the part? Assuming the part isn't too pathological a shape 
you will get a much closer number than measuring the air in the furnace. 

: How long should I hold the furnace's temperature for the part to get an even
: temperature?

This depends very much on the part and what you mean by "even". 

--
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Spehro Pefhany                                  "The Journey is the reward"
[email-masked]                          -------------------------------------
Fax:(905) 332-4270                    (small micro system devt hw/sw + mfg)
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From: [email-masked] (John Erdman)
Date: 25 Sep 1996 15:25:39 GMT

Hi Eduardo -

I assume from the temperature you are considering that you are wanting to
temper a piece that has been hardened.

For all practical purposes when you are tempering your piece, it doesn't
make any difference how long you hold it at 900 degF as long as you hold
it there long enough to get to "equilibrium".  

In my oven, it takes about 15 minutes for the temperature to come back to
the set point temperature after I've opened the door (I have digital
readouts). So assuming that yours has similar reheat characteristics I
suggest you preheat your oven to the desired temerature as indicated on
the indicator and then stick your piece in for a half hour or so.

If your actual hardness is even semi-important you should at least test
with some hardness files.

Regards and good luck,

John Erdman

-- 
John Erdman
Greenfield Machine Works
"Out in the Puckerbrush"