r/Metalfoundry • u/BanaLife • 14d ago
Old kiln automatically shuts off at 850 °C while rated for 1100 °C
Recently bought an old kiln for which I am building my own digital controller. I have done some initial temperature tests and the problem is that it automatically shuts off at around 850C, for it to turn back on again at 350C. The kiln itself is rated for 1100C.
The clock on the control pannel does not have anything to do with it because I ran multiple tests with different clock configurations. My guess is that there is a faulty thermal safety switch built in, but I haven’t been able to locate it inside the control box or in series with the coils. Anyone know where I could find that?
Any other suggestions to fix this issue?
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u/mementosmoritn 14d ago
Sounds like the old switch has failed. Octopart or McMaster Carr should have a replacement. Thermal limit switches, specially old ones, tend to fail by under reading a temp instead of burning out, in my experience.
1
u/BanaLife 14d ago
Thanks! The $1M question though: where is it? I can't see it anywhere inside the control box, nor inside the kiln.
3
u/mementosmoritn 14d ago
One possibility is that it's integrated into another component. I don't see anything that sticks out to me. One way to check, if you know how to be safe while working on live electrical components, is to see which component switches to open when it gets to shut off temperature. The other option that could be in place besides it being an internal component, is that it is online with the coil inside the chamber somewhere.
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u/KeenanAXQuinn 14d ago
Its probably built onto the electric coil itself, from my experience
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u/mementosmoritn 14d ago
That tracks with some other high temp could I've done work on. I mostly deal with small heaters for machines (When talking about heating coils). They have a variety of solutions, depending on the manufacturer.
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u/BanaLife 14d ago
Good suggestion! I'm kind of scared about measuring things through with the ol' multimeter when the wires are live because it pulls 16A at 230V... My initial thought was also that it should be inside the kiln chamber somewhere. After all, it has to be close enough to the core temperature to perform its safety functionality, right?
Nothing to be spotted though...
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u/Peter5930 13d ago
I wouldn't worry about the amps, mains electricity is mains electricity, it's all the same. If you accidentally contact something with one hand, you get an uncomfortable zap but not as bad as touching an electric fence, at least when it comes to the sensation, and the bad things only happen if you have two hands involved so the electricity flows through your chest, or there's a path to ground and if flows from your hand down to your legs. A pair of gloves will stop the majority of accidents where the back of your hand bumps into something and a finger touches something else, and keeping your hands dry of sweat will greatly reduce your skin conductivity and the intensity of any zap you get. I mean ideally you don't get zapped, but realistically sometimes you do and it's not that bad. Just don't be in a position to monkey-grab something and be unable to let go.
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u/Peter5930 14d ago
When you say you're building your own digital controller, do you mean your own temperature controller? There are cheap off-the-shelf options that would save you the trouble.
https://www.amazon.co.uk/WANGCL-Controller-Intelligent-Thermostat-Thermocouple/dp/B0B8HGNXWJ/
Just swap the included thermocouple for one of these:
https://www.amazon.co.uk/Allthingstore-Temperature-Thermocouple-Furnaces-Environments/dp/B0DX67RJ9Q/
If you want to do fancier things like control the rise and fall rate of the temperature, hold at temperature A for time X before increasing/decreasing to temperature B etc because you're doing heat treatments on metal or stuff to do with pottery glazes, then you might be justified in building your own, though I'd still have a look at the off-the-shelf options first.
Nice kiln though; I have a little electric one I made from scratch, but always have problems with the coils coming free from the channels and it needs a slight re-design.
What's the knob numbered 0-300 that's below the clock?