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I'm building an electric kiln to melt metals like lead aluminum, and maybe even copper.

I have no experience or professional knowledge on the subject.

I want to be able to reach at least 1100°C but currently, it reaches no more than about 150°C.

I currently use two nichrome wires in series that are a bit stretched.

I use two kinds of firebricks. One kind is white and lightweight - I use it for the cover on top. The other kind is brown and heavy and is used to build the kiln body, I also used high temperature cement for this.

The temperature is controlled via a PID controller with a temperature sensor and a solid-state relay.

I checked and the current through the wire is about 4.5 A at 220 V. So about 1 kW of power. The wire resistance is 50Ω.

The possible flaws I thought of:

  • Maybe I need more nichrome wires, or maybe to connect them differently (parallel or something.)
  • Maybe the kiln is not sealed enough.

Questions:

  • Why doesn't my kiln reach higher temperatures?
  • I would also like to know the ideal place for the temperature sensor.
  • How can I properly ground the bricks? I get a tingling shock from them.
  • Is it necessary to make grooves in the bricks for the heating elements?
  • I have some mineral wool, would it help to cover the kiln with it from the outside?

Pictures:

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winny
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Lidor shimoni
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    "bricks [...] cause I get a tingling shock from them" uhh... – TypeIA Jan 25 '22 at 13:42
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    What power are you putting in? What is the resistance of the nichrome element when cold? ditto when hot? And ... uhh ... yeah, you want ceramic standoffs holding the element safely away from the bricks. –  Jan 25 '22 at 13:51
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    Either you're not putting enough power into the kiln or you are losing too much through the sides and top. My guess is that you are not putting in anywhere near enough power at this point. – jwh20 Jan 25 '22 at 14:12
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    A kiln which gets to 1100C and is any larger than a thimble will need multiple kW of electrical energy turned into heat energy and decent thermal insulation to keep the heat inside the kiln. It appears that you have neither of those. You also need to electrically insulate your heater elements from the walls of your kiln if you want to stop that 'tingling' ... – brhans Jan 25 '22 at 14:21
  • Does the heating element glow brightly? – HandyHowie Jan 25 '22 at 14:28
  • @HandyHowie, when I use two nichrome wires in a series it doesn't glow. when I used only one wire it was glowing orange. – Lidor shimoni Jan 25 '22 at 14:32
  • @user_1818839 The wire(two wires stitched together) resistance is 50ohms. I'm putting in about 4.5 Amps at 220V. – Lidor shimoni Jan 25 '22 at 14:37
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    To give you a gut feel, compare your kiln with examples in your life. A range oven which does not get nearly as hot is still far more powerful than your kiln (though probably less insulated, but still). You'll have to do at least that well with power, heating elements, etc. – DKNguyen Jan 25 '22 at 14:59
  • You clearly need to connect the elements in parallel rather than in series. Have you tried that? – HandyHowie Jan 25 '22 at 15:05
  • Where did you get the elements from? Are they a part made for a kiln? – HandyHowie Jan 25 '22 at 15:06
  • @HandyHowie If 1kW is already being drawn in series going to parallel will trip the breaker but no way around it. Four times the power. – DKNguyen Jan 25 '22 at 15:06
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    I’m voting to close this question because about thermal dynamics, not about electricity – Davide Andrea Jan 25 '22 at 15:17
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    If it doesn't glow, the element alone is < 500C. Above that, you can easily translate colour into element temperature. And it goes without saying that the element needs to be hotter than you want the chamber. –  Jan 25 '22 at 15:20
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    a kiln that size would need at least 6kw to reach cone 2, more if the insulation is not great. – dandavis Jan 25 '22 at 18:04
  • @user_1818839 I'm a bit surprised. Are bricks that conductive? – DKNguyen Jan 25 '22 at 21:47
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    @DKNguyen Looking at them, I suspect soot (carbon) contamination may be related to the tingling. But you need the standoffs anyway to avoid thermal conduction. –  Jan 25 '22 at 22:13
  • " I get a tingling shock from ... the bricks." It's a warning that you should buy a commercial kiln before you kill yourself. But the dangers from tingling bricks are minor compared to the dangers of playing with molten metal if you ever get that far. "I have no experience or professional knowledge on the subject." This is a dangerous activity. You should get tuition in real life from someone experienced in working with molten metal (which I did, on an engineering workshop course). – Graham Nye Jan 26 '22 at 12:32

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