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Overdrive a kitchen oven for Tempering?

Johann

Johann

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May 20, 2020
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Triangle area NC
Anyone ever do it? Looking to get 650*F.

I've just dipped my toes into the heat treating of 1050 steel for use in Reenactment Armour. I've got a venerable kiln running again that does the 1650*F needed to harden the steel but it takes forever to get to the lower temperature after that effort to do tempering. I'm working in relatively thin steel. .030- .093 for most of it.

Having stuff sit around hardened but not tempered is a recipe to have things get cracked while they are brittle. Either from internal stress or accidental impact. Last time we did it we used the home oven to stop temper at 500*F to help with that while we waited about 3 hours for the Kiln to stabilize to *650. Doing it earlier than that had pretty wide temp fluctuations we tried to mitigate by opening the lid.

I figure a PID controller, temp sensor and solid state relays like what I am driving the kiln with should drive the temp as well as it is doing with the kiln. But what I do not know is if the element in an oven can actually get that hot.

Anyone done anything remotely like this or have suggestions on making this work with a Kitchen stove? I can pick one up at Habitat for $50 and it would be handy for other shop projects like heat forming Kydex. Any other suggestions are welcome as well. Kiln is 18"x18"x18" so looking to have a similar capacity.


The stuff I made below was commercially heat treated but had to ride to Seattle which doubled the cost.

dHM3RtCl.jpg
 
No tech for you until you do a build thread for this stuff!!!!

That is so cool would love to see how you make that. You never know we may need to relearn how to make armor like this in a few years the way the shit is going nowadays :lmao:
 
Thanks man. The breast plate is .075 so it would have been musket proof in it's day. One day I'll make up some blanks and test it with one of mine. Here is a build thread for what you see in the pic. It's based on some historic armour from Augsburg Germany in roughly 1585. It is already on an armour centric forum I frequent.


Now give me some tech! :flipoff2:
 
Any self-cleaning over can hit those temps easy. I think you will have no problem doing it but you'll probably wanna run an air gap around the stove unless you wanna blister the paint off you walls. Stoves are meant to be touch-able on the outside when they're ~500 on the inside. Crank the temps higher than that for sustained time periods and you will likely get hot enough to have problems with a "normal kitchen" type installation. You will want to disable the lock on the oven. Self cleaning ovens made in the last ~30yr have a temperature controlled lock (electronic on the new ones, probably just a bimettalic strip on the old ones) that won't let you unlock at temps above what the normal cooking temps go to.
 
I have seen videos of people modifying regular ovens to go hotter for Pizza, Generally you would bypass the ovens controls and use a PID controller and solid state relay. Keep in mind that the ovens insulation and wire routing are meant for lower temps so it may be best to build a larger outer enclosure with more insulation, especially if you plan to leave it unattended.
 
arse_sidewards said:
Any self-cleaning over can hit those temps easy. I think you will have no problem doing it but you'll probably wanna run an air gap around the stove unless you wanna blister the paint off you walls. Stoves are meant to be touch-able on the outside when they're ~500 on the inside. Crank the temps higher than that for sustained time periods and you will likely get hot enough to have problems with a "normal kitchen" type installation. You will want to disable the lock on the oven. Self cleaning ovens made in the last ~30yr have a temperature controlled lock (electronic on the new ones, probably just a bimettalic strip on the old ones) that won't let you unlock at temps above what the normal cooking temps go to.
Click to expand...
So an oven old enough to be non digital would crank up higher than cleaning mode if the temp lock is disabled with its normal temp control knob or would I still have to put in a new controller? No big deal if I do.

I'll certainly air gap the stove when in tempering mode. I do the same with the Kiln. Mostly so we can lift from it safely. Same with the propane forges I run for various metal heating & pounding.
 
MigGunslinger said:
I have seen videos of people modifying regular ovens to go hotter for Pizza, Generally you would bypass the ovens controls and use a PID controller and solid state relay. Keep in mind that the ovens insulation and wire routing are meant for lower temps so it may be best to build a larger outer enclosure with more insulation, especially if you plan to leave it unattended.
Click to expand...
Yeah, I may gut/reroute the wiring to get it isolated from the heat. I can get more kaowool to add insulation if needed but I probably would not run it in place against the wall.

Really just looking at the oven being a premade steel box with a door that I will modify for my use. Hmmm. May need to go shopping at Habitat this afternoon!
 
Johann said:
Yeah, I may gut/reroute the wiring to get it isolated from the heat. I can get more kaowool to add insulation if needed but I probably would not run it in place against the wall.

Really just looking at the oven being a premade steel box with a door that I will modify for my use. Hmmm. May need to go shopping at Habitat this afternoon!
Click to expand...
Yea honestly just a metal box with a door an element and some insulation. I would just plan on PID control, they are cheap and easy enough and probably much more accurate than the ovens controls anyway because you can put the probe exactly where your work is going to be. I would not be worried about the element at all, it is going to be much hotter than oven temperature no matter if the oven is set at 350 or 650.

I would keep an eye on the door seal at the higher temp but I imagine they have a pretty good safety factor built into those.
 
ovens aren't very temperature stable
you end up with a wide range of temperatures
fine when you're okay with over-drawing the temper down further than you'd want

its because they aren't well insulated and the element is only on the bottom and floating in open air
kilns got the element wrapped all around the chamber and they got all that thermal mass of the firebrick directly on the element
 
We have an old oven at work for doing just this. They replaced the control with a temp control out of McMaster Carr.
 
[486] said:
ovens aren't very temperature stable
you end up with a wide range of temperatures
fine when you're okay with over-drawing the temper down further than you'd want

its because they aren't well insulated and the element is only on the bottom and floating in open air
kilns got the element wrapped all around the chamber and they got all that thermal mass of the firebrick directly on the element
Click to expand...
I'll have to pay attention to that. My kiln is a top loader and it loses heat pretty quickly when open. Less important in this one since we just leave the piece in there till it hits the high temperature we want.

I was hoping to tie the upper broil element in with the bottom bake one to help with uneven heat and loss. I think I am good as long as it does not swing high.

I have fire brick I can add for thermal mass. Not a bad idea.
 
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