Tempering question

C

CoryS

Joined
Apr 23, 2020
Messages
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Can I setup a schedule on my kiln to temper at say 325 for 2 hours, turn off for 4 hours, and then temper again at 325? Or will the slow cool down in the heavily insulated kiln effect the temper?
 
I don t know if you can set up your kiln to do that , but I know that temper should be done immediately after quenching .....both cycles .Long interval between cycles ? I don't believe it's good ..............
 
It doesn't work well to do what you describe with a HT oven.
It would probably work sort of OK if you built a programmable controller for a toaster oven and used it to do the tempering. They cool down pretty quick. Something like 2 hours
at 400F; 1 hour at 80F (effectively off); 2 hours at 400F; OFF
 
Stacy E. Apelt - Bladesmith said:
It doesn't work well to do what you describe with a HT oven.
It would probably work sort of OK if you built a programmable controller for a toaster oven and used it to do the tempering. They cool down pretty quick. Something like 2 hours
at 400F; 1 hour at 80F (effectively off); 2 hours at 400F; OFF
Click to expand...

thank you Stacy! Could you educate me on why the slow cool down effects the temper?
 
CoryS said:
Can I setup a schedule on my kiln to temper at say 325 for 2 hours, turn off for 4 hours, and then temper again at 325? Or will the slow cool down in the heavily insulated kiln effect the temper?
Click to expand...

If you're asking if the "quench" rate after temper matters it shouldnt. In other words after those 2 hours there is zero difference between taking it out and dunking it in water, taking it out and letting it air cool or simply turning off the oven and letting it cool down slowly. Speed of cooling really only affects the hardening step.

You do want, however, it to get down to room temp between tempers so youll want to make sure if you leave in the oven to cool off it actually cools to room temp before ramping it back up for your second temper.
 
One concern I have about this is the PID overshooting the target temperature, especially if it is operating in a range it is not tuned for. I use a PID that does double duty on a lead pot and it overshoots by twenty degrees on the tempering oven if it is tuned for the lead pot. Even if it is tuned for the oven, there is some slight overshooting on the initial heat up. I always let it get up to temperature about half an hour before I plan to put the blades in. Might not be an issue with your controller, but could not hurt to check before attempting this.
 
Hubert S. said:
One concern I have about this is the PID overshooting the target temperature, especially if it is operating in a range it is not tuned for. I use a PID that does double duty on a lead pot and it overshoots by twenty degrees on the tempering oven if it is tuned for the lead pot. Even if it is tuned for the oven, there is some slight overshooting on the initial heat up. I always let it get up to temperature about half an hour before I plan to put the blades in. Might not be an issue with your controller, but could not hurt to check before attempting this.
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I was worried about this as well, but the evenheat with TAP 3 controller seems to hit it with no overshoot. Even in the ramp as fast as possible mode.
 
Without verifying that with a separate thermocouple, I wouldn't trust a heat treat oven to be accurate at tempering temps.

Am I wrong?
 
Keith Nix said:
Without verifying that with a separate thermocouple, I wouldn't trust a heat treat oven to be accurate at tempering temps.

Am I wrong?
Click to expand...

a good controller can be calibrated at at least two set points. Mine is dead on in the 3-400s.
 
Good on you, Cory. And Larrin is spot on, verify that with a quality thermometer...
 
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