Hello. I´m building a heat treating oven. Firebricks and that stuff.

It is small and I have based my calculations in other brand new ones that get around 6.000 watts per cubic feet (I use metric, so this calculations is an effort haha). So, I´ll go for 7.000 watts/cubic feet since mine will be worse isolated than those. Mine is 0,248 cubic feet so 1.700 watts aprox.

I = 1.700/230 = 7,4 amps So the heating element, made of khantal wire has to va a resistance of R = 1.700/7,4^2 = 31 ohms

Until here, everithing is correct. But I see a oven calculator that says that I can go with 1 heating element of that resistance or go with 2 heating elements in parallel, each one of 62 ohms, what makes sense because the total resistance will be 31 ohms, but each one only disipate half of the power, so I don´t think that they get red/yellow hot. I mean, this furnace is supposed to operate between 500-950 ºC (932-1750 ºF) so I´m not sure I could reach these temperatures if I go for 2 elements. Or maybe only 1 element will be too much.

I have found another calculator for the temperature https://jacobs-online.biz/calc2.html and for the 60 feet of 18 WAG wire needed (with onlye one heat element of 31 ohms) it says that the wire will heat at 230 volts to 371 ºC (700 ºF) and doesn't make sense for me.

Any help will be wellcome

Thank you

Best regards

 

Many time ago my friend who is a advisor Graphic learn me to use Photoshop. He gave me one good advice. I use this advice in many aspect on my life. I was learning to use filters on Photoshop and he tell me to "make it extreme" . When you apply a filter do first 10% then 90 % this way you will see what this filter is doing. Then you can change the % of it. So, in your case lets "make it extrem". And lets say you will use 1000 elements and the total resistance will be 31 ohms . You will have 1.700 watts aprox but the temperature will be lower then. This because the same amount of heat will be dissipated from a bigger element.

 

I built one similar to this:

Only 1 element

 

Thanks for your answers. So I´ll do try an error until I get that red/orange color

 

@Irving
The father of my boss made a bigger one with natural gas. The melting pot was about 15L and it become cold very fast when you remove it from furnace. I was thinking that if i need it in the future I will add a small electric heater around the melting pot to add heat while it's out from furnace.

 

Ok after some research the question is the watts per surface unit. In kanthal wire the maximum desirable value is 2,5 watts per square centimeter. Above that the heat is too much