heat treat oven help

[808blades]

I’m in need of some technical assistance. I built a heat treat kiln using a design I found online. Everything works great but I am having trouble with the element. The first one burned.about 20 minutes into my test run. I built a new one but it stretched out about 6 + inches after my 30 min test run. It was sagging out of the grove anywhere it wasn’t pinned. Am I using to thin a gauge? Any thoughts/ advice on this would be greatly appreciated.


The kiln is 2.5 inch fire brick inside dimensions are 11 in deep 4.5 in tall and 3.75 in wide. The element is approx 40 in stretched ⅜ in inside dia coil made out of Kanthal 22 gauge wire. Below is how I’ve got it wired.

 

[Hubert S.]

That is really thin wire. Google "kanthal handbook" to get a pdf with recommended surface loads for different element types.

I used 16ga wire for a 1,400W element and it seems to be holding up fine, but 14ga would probably be better.

 

[Jax knives]

Without knowing exactly the wattage you are shooting for. I would suggest you use 16 gauge wire.

I would also suggest you use a door switch that interrupts the ( neg control side) SCR's when the door is open. You don't want the elements on when the door is open.

If I remember correctly: I run 14 gauge (3/8 dia) with 16.9 ohms at 240 volts around 3500 watts give or take.

 

[808blades]

Without knowing exactly the wattage you are shooting for. I would suggest you use 16 gauge wire.

I would also suggest you use a door switch that interrupts the ( neg control side) SCR's when the door is open. You don't want the elements on when the door is open.

If I remember correctly: I run 14 gauge (3/8 dia) with 16.9 ohms at 240 volts around 3500 watts give or take.

Thanks so much for the info. How would I wire that door switch in given my wiring diagram?

 

[Stacy E. Apelt - Bladesmith]

The door switch goes in the wire from either terminal 6 or 8. It interrupts the SSR ON mode and shuts off the power to the coils. Use a limit type roller switch for the door switch.