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Mini electric kiln project
#41
I have almost finished the outer design of my mini electric kiln for one blade.

The thickness of the white soft bricks is 3” and the additional grey insulation is 1” thick.

       

I have already received the ceramic holders of the heating elements and ordered the Sandvik heating wire Kanthal A1.

I am considering suitable temperature controller. They are some inexpensive models offered on Amazon, but I am not sure if it is the good choice.

https://www.amazon.de/Inkbird-Temperatur...X277WR072F

Jan


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#42
Mr. Jan, I'm pretty sure Amazon sells Omega PID controllers. If they aren't on Amazon, check out Omega's site. They have top quality stuff, and seemingly endless choices. Their salespeople are well trained to answer anything you ask.
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#43
be sure to get one of these https://www.amazon.de/100mm-Spade-Thermo...d_sim_60_3? and one of these
https://www.amazon.de/SSR-40DA-Halbleite...WPZSBYWKRC although I would look and see if there are any siemens SSR available for similar price. I would also look for a siemens temperature controller
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#44
Thank you for your tips Mr. Mark and Mr. Scott. Smile 

Omega is surely renowned brand, but the prices are 5 to 10 times higher than the inexpensive models on Amazon. Sad

Previously I received a tip for SOLO PID controller
https://www.automationdirect.com/adc/Sho...SL4896-VRE
Jan


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#45
I almost always get the most expensive doohicky I can find. I hate being disappointed worse than anything. I'm sure there are good PIDs and cheap PIDs, and they aren't one in the same.  Wink  

Now that I see your plan with the ceramic wire holders,  I have an observation for you, Mr. Jan.

I'm not a naysayer, but it seems like the heat from the wire between the ceramic and the brick has nowhere to go. Like the wire between the ceramic and the brick could get significantly hotter than on the open side. 

Do you think uneven wire temp could be problematic, especially since the wire isn't exactly free to move around? 

I am certainly no authority on the subject, but have you seen this type of ceramic wire fixture used like this somewhere else? Hopefully you've seen this in a really well engineered kiln.

Wishing only the best, of course.
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#46
Mr. Mark thanks for your concern about my kiln project. Smile 

What concerns the PID controller, not only brand defines the price, but its features also. The more advanced models enable PC connection to configure the controller and monitor the heating process.  Other options are several levels of ramp control.

The wire holder concept is widely and successfully used for decades in infrared heaters and industrial applications. I have used it in my home made enameling kiln, it worked well but was designed for temperatures below 650°C (or 1200°F). The wire holders were not in grooves but placed vertically in a cylindrical chamber.

Yesterday night when I was milling the grooves I was also worrying about the heat escape from the wire between the ceramic and the brick. I have made the grooves even more open to the chamber inside.
Having the heating wire coiled on the wire holders I de facto do not need the groves, but I have decided to keep them to prevent that one element heats the neighboring ones.

My decision the use the wire holders was not quite voluntary. The reason for the problem is the small = low power kiln and 240 V grid. The total length of the heating wire is 20 meters. The length of the minimally stretched heating element is some 3 meters and I am not able to accommodate this length into the walls of the small chamber. (For 120 V the stretched element would be much shorter.)

I am not sure that it will work well, I only hope it will. At this stage there is no way back for me.

Thanks for your support.
Jan


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#47
I have more confidence in your studious game plan than my limited experience, Mr. Jan.
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#48
Maybe we missed it somewhere in this thread Jan but what is the nature of the actual temperature sensor in your design? Thermocouple, thermistor etc.? Is it somehow built into your PID or is it some separate and remotely mounted analog device(s)? You realize, of course, that you have to be at least as old as we are to even know what an analog device is.
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#49
for a kiln like this, you would mount a thermocouple next to where the blade will sit and connect it to a display/controller(pid). you tell the controller the temperature you want and your hi/lo limits, lets say 1485*F +/- 15*F. the controller then sends a signal to a solid state relay that turns the power to the coils on or off.
if you wanted, you could hook the thermocouple up to an analog display and just switch the kiln on or off to keep temperature where you want it.
old analog stuff is amazing. imagine a system that could place a 2500 pound artillery shell +/- 25 yards on a moving target from a distance of 20 miles
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#50
Thanks for the info Scott. Never dealt with anything with temperatures this high before. Our hat's off to thermocouple manufacturers for making a sensor capable of accurately responding to temperatures in this range without melting the temperature sensor. On naval guns; isn't that something? Heaving Chevy Novas 20 miles into somebody's backyard and not just any backyard...your backyard. We suppose that if the sea was calm they could have knocked the lid off your barbeque grill and all with just a slide rule and a couple of hand cranks.
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