Recommendation? Heat Treat Oven Element Calculations

[SLC_Blades]

I’m in the process of ordering everything I need to build a 240v single-element heat treat oven and I’ve finally reached the math part. I’ve heard that the standard wattage per cubic foot in a heat treatment oven is ~5000 (average of even heat products). My oven will be relatively small, with inside dimensions of 13.5” x 4” x 4” or 0.125 cubic feet. In order to achieve a wattage per cubic foot of 5000, I’d need a mere 625 watts. To me, this seems incredibly low. This will require approximately 92 ohms of resistance, or 44 feet of 24 gauge kanthal wire to achieve. A resistance of 92 ohms seems quite high, and I’m not entirely sure if I could stuff 44 feet of kanthal wire into a relatively small oven. Would it be detrimental to increase the wattage per cubic foot significantly?

Thanks!

 

[koduu]

Well, your oven could easyly be not quite as termally isolated, so i would use additional power, in that size, mb 1-2 kw. However, i would also advise you to avoid direct radiation from the coils to the thermocouple and the steel. This meanseither wery well designed grooves or some sort of a muffler/ shield.

 

[JTknives]

Well, your oven could easyly be not quite as termally isolated, so i would use additional power, in that size, mb 1-2 kw. However, i would also advise you to avoid direct radiation from the coils to the thermocouple and the steel. This meanseither wery well designed grooves or some sort of a muffler/ shield.

I dont mean to be rude or call into question your experance with ovens. But if the oven is built properly with direct line of site to the elements it will be fine. This is why we pre heat and let the oven soak for some time befor using it. The key is having the heating elaments evenly spread out so the chamber has the same watt density along the surface. My oven has the elaments all along the roof and it is very even. Once it's up to temp and good and soaked the elements will cycle on and off rather quickly. The thermal couple will show elevated temps much faster then the blade will.

If you need any help with this and the math let me know and I will fire up the ol excell spreadsheet I made to calculate my oven.

 

[scott kozub]

You may have already seen it but I did a thread on building a 220v oven here.

https://www.bladeforums.com/threads/diy-heat-treat-oven-build.1576402/

Should have what you need plus you can learn from my mistakes. The oven has been awesome and heats up very fast. However I know keep a 4x1x12" steel bar in it to act as a heat sink. Takes about 1st to heat up and get stable.

 

[DAMNENG]

Just some food for though.
AWG 24 wire will not hold up well, I would suggest AWG18. it is .515 Ohms per foot.
For the power you need why go 240Vac 120Vac at 10amps will give you 1200W. This will require about 23 feet of AWG18.
Wrap it on a 5/16" wooden dowell using a hand held portable drill. Wind tight and stretch to length when finished. Leave the leads at the end twice as long as you need them, then fold them back on theirselves to reduce the resistance in the leads to half. This keeps them much cooler than the heating portion.
Jim