Rewiring a kiln for heat treating

[Johncco]

So just picked this up for $50 bucks off of facebook market place. The body and bricks look in good shape, a few little places I'll have to touch up with refractory cement. The wiring is all dry rotted. I planned on rewiring it. I just want to make sure I'm on the right track with my plans of rewiring.

The interior dimensions are 12"w x 12"l x 9"h. So thats exactly .75cubic feet of volume. Based on my research you want 5-8000 watts per cubic foot of space for a heat treat oven.
So I plan on wiring a breaker, a 220v pid and ssr and coils for a target of 5k watts. That will draw 22.7 amps and I need a resistance of 9.68ohms if I was doing one coil. The kiln has three coils so I'd like to use the guides it has. The guides are .4" tall and about
.75" deep. And total guide length is 72" give or take.
So if I want to use all three guides I would have to run my coils in parallel which means I need three coils that can stretch to 72inches with a target resistance of 30ohms to give me a resistance of 10ohms.
Have I missed anything? Am I on the right track?
Kiln https://imgur.com/gallery/ntWDu3N

 

[Stacy E. Apelt - Bladesmith]

The only issue is that it is a burn-out oven. It will work fine for carbon steel HT, but isn't built to run at stainless temperatures. Changing the coils won't change that.
Honestly, if it is running now, I would just use it for tempering and build a proper size HT oven around 18"x9"x6".

 

[Blackdirt cowboy]

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[Johncco]

The only issue is that it is a burn-out oven. It will work fine for carbon steel HT, but isn't built to run at stainless temperatures. Changing the coils won't change that.
Honestly, if it is running now, I would just use it for tempering and build a proper size HT oven around 18"x9"x6".

The Pyro meter on the kiln has a max reading of 2500f. The coils in it and the wiring are shot. Most of the wiring is dry rotted.

 

[Stacy E. Apelt - Bladesmith]

The 2500°F scale is like the 150 MPH speedometer in my car. It looks impressive, but means nothing. I have three burn-out ovens that have scales over 2000°F. None will get past 1800°F ... and it takes a couple hours to even get there. Trying to run them much above normal burn-out temps (1400°F max) will also shorten the coil life and lead to coil sagging. They go to 1500° just fine, but even that takes a little while. Burnout ovens are designed for slow heating rates and long burnout cycles. They are John Deere tractors, not Corvettes.

You could have a lab oven, which will get higher temps. They have different refractory.
Show us the details plate on the kiln with model and power ratings, please. That will help.

 

[Natlek]

The Pyro meter on the kiln has a max reading of 2500f. The coils in it and the wiring are shot. Most of the wiring is dry rotted.

Trying to run them much above normal burn-out temps (1400°F max) will also shorten the coil life and lead to coil sagging. They go to 1500° just fine, but even that takes a little while. Burnout ovens are designed for slow heating rates and long burnout cycles. They are John Deere tractors, not Corvettes.

You could have a lab oven, which will get higher temps. They have different refractory.
Show us the details plate on the kiln with model and power ratings, please. That will help.

If this is mine oven for which i pay only 50 $ i will invest little more money and modified it ........I will use half inch ceramic board as hot face and one inch ceramic board on top and heat element only on top.
Other way is to cut bricks to make the channel for heat element disappear and so i can use one inch ceramic board ...............

 

[Johncco]

I

The 2500°F scale is like the 150 MPH speedometer in my car. It looks impressive, but means nothing. I have three burn-out ovens that have scales over 2000°F. None will get past 1800°F ... and it takes a couple hours to even get there. Trying to run them much above normal burn-out temps (1400°F max) will also shorten the coil life and lead to coil sagging. They go to 1500° just fine, but even that takes a little while. Burnout ovens are designed for slow heating rates and long burnout cycles. They are John Deere tractors, not Corvettes.

You could have a lab oven, which will get higher temps. They have different refractory.
Show us the details plate on the kiln with model and power ratings, please. That will help.

As I stated in my original post I Plan on completely rewiring it, all the wiring is dry rotted on it, I plan on a new pid controller, new ssrs. New coils. The data plate on the side says 110v but it has a 220 plug on it so it's been rewired.

 

[Natlek]

I

As I stated in my original post I Plan on completely rewiring it, all the wiring is dry rotted on it, I plan on a new pid controller, new ssrs. New coils. The data plate on the side says 110v but it has a 220 plug on it so it's been rewired.

What Stacy is trying to say / at least I understand that way/ is that you have wrong bricks , that brick in that oven have higher thermal conductivity then K23 bricks ordinary used in HT oven and you will have problem with time to reach high temperature ....
Search this topic from our member @PEU ..............bricks make difference , that s why i suggested ceramic board inside ...... of course if Stacy is right about bricks.
https://bladeforums.com/threads/heat-treatment-oven-wip-peu.1314585/

 

[Stacy E. Apelt - Bladesmith]

Pablo's build was the best I have ever seen.

 

[Johncco]

What Stacy is trying to say / at least I understand that way/ is that you have wrong bricks , that brick in that oven have higher thermal conductivity then K23 bricks ordinary used in HT oven and you will have problem with time to reach high temperature ....
Search this topic from our member @PEU ..............bricks make difference , that s why i suggested ceramic board inside ...... of course if Stacy is right about bricks.
https://bladeforums.com/threads/heat-treatment-oven-wip-peu.1314585/

Ah that makes sense. If I add the ceramic board on the inside it'll reduce my interior dimensions and I'll no long be able to treat large chef's knifes. I guess since manufacturer is out of business the only way I'll know for sure is to wire it up and see if it gets up to temp.

 

[Natlek]

Ah that makes sense. If I add the ceramic board on the inside it'll reduce my interior dimensions and I'll no long be able to treat large chef's knifes. I guess since manufacturer is out of business the only way I'll know for sure is to wire it up and see if it gets up to temp.

If that not work you can cut bricks from heat element side of bricks to make room for ceramic board and to keep internal dimension same .

 

[Stacy E. Apelt - Bladesmith]

It is too small for a large chefs blade. I would say you need an 18" oven to do those. 12X12" will hold a 7-10" blade with sufficient room. The diagonal is right at 16" and you want two inches to the walls and 3" to any corner.

 

[Johncco]

So I started on the kiln, took the top off and found that it had vermiculite on the top and ceramic fiber insulation on the sides of the ifb, decided to replace it all with new wool. Installed new coils, and wired it all up. Ohmed out at around 11.5 ohms, with the 235v my plug produces its right around 5k watts. Did a test run to 1000f, 1400f, 1800, then 1950. Works perfect, takes about 15 minutes to get to temp at full power but plan on doing slow ramps. After 15 minutes at 1950 outside temperature is between 120-140. So far so good. As far as large chefs knife, I meant 8inch chef's. Total length should be around 13 inches which should still give me a little space between the walls and corners.

 

[FredyCro]

It is too small for a large chefs blade. I would say you need an 18" oven to do those. 12X12" will hold a 7-10" blade with sufficient room. The diagonal is right at 16" and you want two inches to the walls and 3" to any corner.

Stacy, do I also need to keep these distances in my oven that has top and bottom hidden elements or could I use full length?

So I started on the kiln, took the top off and found that it had vermiculite on the top and ceramic fiber insulation on the sides of the ifb, decided to replace it all with new wool. Installed new coils, and wired it all up. Ohmed out at around 11.5 ohms, with the 235v my plug produces its right around 5k watts. Did a test run to 1000f, 1400f, 1800, then 1950. Works perfect, takes about 15 minutes to get to temp at full power but plan on doing slow ramps. After 15 minutes at 1950 outside temperature is between 120-140. So far so good. As far as large chefs knife, I meant 8inch chef's. Total length should be around 13 inches which should still give me a little space between the walls and corners.

That sounds promising. You could also do WA handles or framed style handles for large chef knives if you need a inch or two on the blade length.