Electric kiln build project

Discussion in 'Furnaces and their construction' started by Sillytrain, Feb 6, 2020.

  1. Sillytrain

    Sillytrain Copper

    I’m going to be starting my first electric kiln build here in about a month.

    This is what I’ve picked up so far for the project:

    Inkbird ITC-106VH PID Temperature Thermostat Controllers Fahrenheit and Centigrade AC 100 to 240V K Sensor Solid State Relay

    High Temperature k-type Thermocouple Sensor Ceramic Kiln Furnace with connector plate 2372F 1300C CR-02

    uxcell Heating Element Coil Wire AC220V 3000W / AC110V 750W Kiln Furnace Heater Wire 7.2mm 800mm 2PCS

    Uxcell a14062000ux0866 2.5mm2 Flexible Heat Resistance High Temp Wire Cable 3 Meter Long

    I think I’ve got the construction process down from the tutorials I’ve watched except for a few details that I’m trying to research to figure out:

    1. How to properly power the pid. I tried to follow instructions and I thought it was rated to be able to hook it straight up to a 110v outlet but that instantly burnt out the pid... not sure why.
    2. I’d like it to be able to get up to 2200f to be able to double it as an electric forge for melting and pouring copper. Is that feasible to accomplish?
    3. If so do I need heavier gauge coils?
    4. What kind of voltage&amps I need my electrician to setup for me on my dedicated outlet to sufficiently power it to those temps.
    5. What’s the optimal material to line the kiln with. There are a lot of options and opinions out there. Curious to have you guys weigh in based on your experiences. I have a stainless steel drum from a washing machine that I’m considering using as the outer frame for the kiln.
    Thanks in advance for any advice you guys can give.
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Although your calling it a kiln, per your item 2 I take it your primary intention is to use it as a melting furnace, correct? I really like mine. It is 8.5kw and uses two resitive coils. There is a link to the build in my signature. Just scroll to the electrical section of the build.

    To me 220vac is clearly the way to go. 3000w at 220vac is 13.6 amps. You might want to consider at least two of those coils. 3kw might be a little wimpy depending upon how much you want to melt. What are the interior dimensions of the furnace?

    I started out with IFB and would probably still be using it to this day had I not splashed Al on the coils. That will cause them to alloy and fail in short order. That led me to build this:

    http://forums.thehomefoundry.org/index.php?threads/furnace-fail-reconstruction.209/page-3#post-3660

    The dense castable version is virtually indestructible but much more massive than the IFB furnace and consequently takes longer to initially heat, but holds its heat very well. That is unfavorable if you usually do only one melt per casting session and perhaps favorable if you do multiple melts. I still have the dense castable module, but then built this low mass liner.....which is great and my clear favorite!

    http://forums.thehomefoundry.org/index.php?threads/muses-about-a-low-mass-electric-furnace.607/

    Of course since building it I've conceived a much simpler way to achieve same. I can elaborate if you are interested.

    Not sure what could have happened there. For safety reasons I would usually use a low voltage control circuit but my furnace has 220vac panel controls.

    What gauge are the coils you purchased? Heavier gauge will be more durable but you will need a longer coil to get enough resistance for your power range. My coils are 14ga and you can see a simple winder I made in the links I have posted. Winding your own coils in cheap and easy. Here is Kanthals handbook.

    https://www.kanthal.com/globalasset...-elements/resistance-alloys_s-ka041-b-eng.pdf

    Here is where I buy my resistance wire by the pound.

    https://www.euclids.com/index.php?cat_id=159

    If you have Kanthal (FeCrAl) coils that temp would be in range but IMO 2200F is too low for copper melting/casting as you need to be above melt temp to pour and cast. If your coils are the more common NiCr 80/20 you're probably stuck with aluminum. FeCrAl has a max operating temp of nearly 2600F but must be derated down to about 2350F when coiled wire used in a 3-sided grooved slot.

    Resistance loads are pretty easy going. I'd say you could get by with a supply circuit that was 25% higher ampacity than your furnace requirent. If you were running 0ne of your coils at 220vac a common 20 amp circuit with 12ga wire would easily suffice. If you ran two coils I'd say probably 40amp min but why not 50amp?.....only cry once!

    I have a lot of bells and whistles on my electric furnace controller. Here's the build:

    http://forums.thehomefoundry.org/index.php?threads/electric-furnace-controller.458/#post-9345

    Insulating Fire Brick is pretty hard to beat and that's why most kilns are made from it...... 2300F or 2600F rated material and it's easy to cut and work with. You could also use refractory fiber board and achieve about the same performance as my low mass furnace. You need to give some thought to how you will design the coil shelves to retain and protect the coils. You also need to give some thought to safety to address the electrocution hazard which is why I have the bells and whistles on the panel to give visual status of power to the coils and multiple means of electrically isolating the coils before I reach into the furnace with tools.

    Best,
    Kelly
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    ..........one more thing, you need to reduce the temperature of the heating element before it connects to the electrical conductor. The usual method is to use a twisted length of two or three strands of your resistive wire, run that through the furnace wall insulation into ambient air and then connect to high tempt conductor like MG appliance wire.

    https://www.prowireandcable.com/hi-temp-125c-538c/mg-mica-glass/

    The twisted pair/triplet of resistance wire reduces the resistive heating and the distance removes it from the hot zone. If you don't do an effective job, the resistance wire will alloy with the conductor and fail.

    Best,
    Kelly
     
  4. Jason

    Jason Gold Banner Member

    There is very little difference in cost between a 30amp or 50amp circuit. Keep in mind, you may not be able to let the wife run the electric dryer and kitchen oven while you are up at 2000 in the kiln.

    So you already burned out your PID? WHOOPS!! On the label it should say what the input is. Keep in mind, the pid monitors the temperature and it's output simply drives a relay. That relay is what does the job of switching on and off the kiln.

    Here is an excellent thread that will teach you more than you need to know about a pid, how it works and what to do with it. http://forums.thehomefoundry.org/index.php?threads/kiln-pid-controller-retrofit.340/
     
  5. Peedee

    Peedee Silver

    Can't see how you could kill that PID without stuffing mains voltage up the thermocouple connections. Did you get a dud unit?
     

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