bquirky
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My new Kiln
Gday Gents,
Ive been wanting to get myself a less shambolic way to make pitch/copper powder electrodes for a while so i finally decided to make myself a small
kiln to run at about 600-800 degrees C
and this is what i came up with.
First i wound the nichrome element around a cardboard former
Insert the former into the flowerpot
setup the 2nd former in the flowerpot
pour the fireproof cement into the 2nd former
Let dry for a week
fill the remainder of the pot with regular cement
let dry for a 2nd week
and I fired it up for the first time tonight.
it draws about 4 amps at 70 volts i found that it took a few hours for the remaing moisture and cardboard formers to burn off. it can heat a piece of
copper placed in it to red heat relitivly easily so during the week i should get my first chance to try and make an electrode.
ill post an update when i have some more results 
    
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Picric-A
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That wire supplying the bottom of the NiCr wire seems awfully close to the area of heat, sure there is not risk of it burning/shorting/melting?
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Paddywhacker
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Where is the payload placed? ... I don't see an opening.
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bbartlog
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If I'm seeing it right, the opening is the hole in the bottom of the flowerpot, so the space being heated is just a small cylinder that you can stick
a tube/pipe into for heating.
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bquirky
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Yes It is upside down in the photographs I should have taken one from the top !
It is ment to accept a metal tube about 15mm in diamiter and 100mm long from the top.
yeah that wire is fairly close.. i think the insulation will probobly burn up but its not near anything to short against so it might be ok.
When it was first run the outside of the terracotta pot was just a bit to hot to touch I should probobly find a more quantitive way to mesure the
tempratures.
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chief
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Whatfor would the "pitch/copperpowder"- electrodes be useful ?? Never heard of such ...
Wghen designing a electric furnace usually the nichrome-wire leads all the way into a cold and uninsulatet area at the outside of the whole thing,
==> since no contacts hold too long in the heat ...
Also: As long as the supply-section of the nichrome-wire leads through any insulation, wherefrom it can't give away heat,
==> it must be thicker, to set down the wattage at that section ...
==> ... else it will burn/melt within the insulation at the first occasion where you try to reach a higher temperature ...
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bquirky
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I Know many people far far smarter than I have been working on this for hundreds of years. BUT.......
I'm using copper as a lower cost alternative to nickel in secondary batteries effective electrode design and construction is the 'art' to the
endevour so i nead to get the right mix of solid carbon,soluble salts to make pores, and the active copper that changes volume during cycling.
I'm hunting bulk $/Kwh performance without using heavy metals.
Ive found a way to handle zinc migration that is acceptable to my application, that is a combination of carbon zinc intercalation and sepperator
geometry
Now im looking for the right electrode recipe. I have been using gas flame to date but its just not practical to hold a metal tube at 800 C for 6
hours using gas.
So thats why ive been messing with the kiln.
Your comments are very useful and ill keep them in mind when the time comes to make a larger MKII or when this one croaks and i have to remake it
I do have the nichrome wire doubled up at each end but i really should have run both ends of the nichrome out of the cement.
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densest
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Quote: Originally posted by bquirky  |
I have been using gas flame to date but its just not practical to hold a metal tube at 800 C for 6 hours using gas.
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There's a lot of "it depends..." in that statement... though I don't know what volume or shape you're trying to hold at 800C, the biggest "it
depends" is your budget. If it's under US$50, you're probably on as good a track as any. If you're having fun, ignore this.
For any approach, insulating the kiln well is your first priority. No matter how accurate or fast your heater is, if the heated volume loses heat too
quickly or unevenly, your product will not be good.
Are there any used hobby pottery kilns available in your area? Lots of people take up hobbies like pottery and then give up, then they sell the kilns.
Any kiln capable of cone 6 (which is pretty much any pottery kiln) will be able to go well above 800C. The limit is the heating elements (nichrome)
which fail above about 1100C.
If you are comfortable working with minor plumbing and gas fitting work, you could make an accurate gas-powered furnace. It would be controlled from a
thermocouple inside the kiln.
Heating controllers are often available on EBay for under $US75. Omron is a good manufacturer as well as Omega and some others. They have relay
outputs which could control a gas valve (get one that is "pilotless" or otherwise will operate with zero pressure differential, since some require the
gas pressure to operate, and fuel gas supplies are low pressure for safety which will not operate a piloted valve) which are usually available for
about $US10 or so. Put a pilot light which is always on (a small or smallish burner) to ignite the gas. Just use teflon tape to seal all the joints.
In the US, sealants rated for natural gas (methane) use are colored yellow. Propane, being denser, requires less stringent qualifications for the
sealant.
For a version which would require some computer knowledge but less money, you could use a valve as above which was controlled from a computer. The
very simplest version would cycle on and off a set percentage of time without measuring temperature. I think futurlec.com sells drivers which could
operate the valve from the computer parallel port. Fancier versions would use a thermocouple or other sensor, digitize the value, and use that to
control the flame. If you have some electronic expertise, you could use a timer chip (like the ubiquitous 555 timer and its clones) to regulate the
on-off cycle with a control you could set. For a closed loop all-analog design which would regulate to a specific temperature, a thermocouple to
voltage chip from Analog Devices AD594/595 is under $US9 and op amps, etc, would run another $US2 or 3.
There may be mechanical (using a gas-filled probe and bellows to regulate the gas flow) gas oven controllers which would work at 800C. All the ones I
have seen have soldered parts which might fail at that temperature depending on the actual alloy used to solder. One with a stainless steel probe (not
copper) would almost certainly work at that temperature. EBay might have one available at a price you can afford.
Just some thoughts - if the electric kiln works, good for you!
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