Electric oven problems

[Otonel]

First I want to wish you a happy new year! My problem is that I built an electric oven for thermal treatments, especially for stainless steel blades. I took the dimensions and parts after a tutorial on YouTube, my problem is that the temperature rises quickly to 700 degrees Celsius then slowly to 850 and to reach 1000 degrees Celsius it takes over an hour. I'm thinking of improving the insulation to the walls that heat up to about 70 degrees and to change the length of the kanthal wire. The measured resistance of the wire is 47 ohms, which gives me a power of 1103 watts for 225V. What do you recommend I do to quickly rise to 1050 degrees Celsius as I need?

 

[Stacy E. Apelt - Bladesmith]

Welcome Otonel. Fill out your profile so we know where you live and a bit about you.
I assume from the voltage and temps you gave you are not in the USA. (Actually, I don't know any country with 225V mains, but the range for many areas is 220-230V)

The issues are:
Too low power - 1103 Watts is not a very powerful oven
Too little insulation may also be an issue. However, most ovens get pretty hot on the outside. A 70°C exterior could use more insulation.
Not waiting long enough - many low power ovens take a long time to heat up to max temp.

Most all the issues are related to the 1103 watts power. Most knife HT ovens are over 2000 watts.

A lower resistance coil would help it heat faster. Lower the resistance to 25 ohms and it will double the power to 2025 watts.

 

[Otonel]

Thanks for the answer, very useful, I measured the voltage at the socket and that's why I put 225 V, as I live in Europe the voltage is really between 220-240V. I will calculate the required resistance for 22 gauge wire or I will try to measure the resistance of the wire on different lengths to see where to cut it to get 25 ohms

 

[Stacy E. Apelt - Bladesmith]

25ohms was just a round number I used for calculating. Anything in that range will be a vast improvement over your 47ohm wire.

Use a resistance calculator for the Kanthal wire and determine the length and gauge needed. You already know the length from the last build, so all you need to do is pick a thicker wire.

 

[Otonel]

I don t fiind a free calculator resistance for my Kanthal wire so I use my pencil , the resistence for 1 feet of 22 gauge wire is 1,31 ohm at 68F so to obtain 25 Ohm I need only 19 feet of wire not 33 like I use

 

[Stacy E. Apelt - Bladesmith]

Gauge and wire length are also determined by coil diameter. Your new coil will need to be as long as the old one to fit in your oven.

Search the internet under "Kanthal coil calculator" and you should get many sources. There are aslo many old threads in Shop Talk on the subject. Use the custom search engine in the stickys to find them.