#2 heat treat oven build

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
Messages
8,633
I figured with the interest in HT ovens I would document my second oven build here. We have outgrown our one oven and have ordered components to build a second larger one. With this oven I’m turning the bricks so the wall, floor and roof thickness will be 4.5”. I ordered 6 cases of k23s, all thy had in stock. I need 2 more cases for the door but that will come later. So looking at wanting around 8,000-10,000watt. Here is the brick layout I have sketched up. The roof and walls will be tensioned with all thread.

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I’m also going to run it off 480v because my big tempering oven is 480v. I had converted it to 240v but I was not able to get the heating capacity out of it. I scored this from work so I can’t complain. It will output 480v at 50amps.
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I’m still undecided on the door layout but I’m not having it open down like on my other oven. More pictures incoming as I progress.
 
I would make it side swing that will go all the way around out of the way.
The other choice is a "lift" type door the comes out about 3" and then rises up on tracks. This is how big commercial ovens work.
 
Mine has a side swing door that gets well out of the way, I like that feature. The door has a very effective "heat trap" as well, made out of some kind of mineral fibre. It's 8.5 kW, 400 V.
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Scaniaman said:
Mine has a side swing door that gets well out of the way, I like that feature. The door has a very effective "heat trap" as well, made out of some kind of mineral fibre. It's 8.5 kW, 400 V.
qaBPSPq.jpg
Click to expand...

I had thought about using wool for the door. It would cut down on the weight and be quite efficient at blocking heat.
 
Scaniaman said:
Mine has a side swing door that gets well out of the way, I like that feature. The door has a very effective "heat trap" as well, made out of some kind of mineral fibre. It's 8.5 kW, 400 V.
qaBPSPq.jpg
Click to expand...
Not to derail JT's thread, but I'd love to see a few more pics of your oven. Looks like a really nice build.
 
Sure, here are a few from when I first got it. Internal dimensions are appr 8.9x22.7x6.1". About 40" depth on the outside including the electric box on the back. Weight 200 lbs. Top only elements. I have the controller mounted on the back for practical reasons. Controller in the pic is getting updated to a Bentrup TC507 at the moment, has more segments. Old one only had 2.
Yes, I find it a solid build. I did have some bad luck as one of the elements turned out to be a lemon and went fzzzzzz on me recently. But it'll be up and running again by next weekend.
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Drew Riley said:
Not to derail JT's thread, but I'd love to see a few more pics of your oven. Looks like a really nice build.
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What type of heating elements does that use?
 
Natlek said:
I think that this is best door solution for HT oven ......
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that is the style I want to do. I’m tired of roasting gloves with my door set up. And I’m thinking I will go with wool for the door.
 
Now ... I was starting to think about buying an Evenheat sometime soon .... but this has me wondering how easy it is to DIY build one. Are there any plans out there that give a basic idea of the build process? (Keeping in mind that I do not have the capability to weld, and have never welded anything in my life......) ???
 
JTknives said:
that is the style I want to do. I’m tired of roasting gloves with my door set up. And I’m thinking I will go with wool for the door.
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If you use HT elements only on roof , maybe back wall with wool is clever idea ?
 
The specs say "KN25" elements. I take it they are the normal coil ones, just tucked away in the tubing in the pic. I didn't assemble or fix the oven myself, so haven't seen them actually. If you want more detail I can shoot the company that built it an email.

JTknives said:
What type of heating elements does that use?
Click to expand...
 
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Scaniaman said:
Mine has a side swing door that gets well out of the way, I like that feature. The door has a very effective "heat trap" as well, made out of some kind of mineral fibre. It's 8.5 kW, 400 V.
qaBPSPq.jpg
Click to expand...
Judging by the external dimensions and from this picture , it seems that they have use another one layer of isolation over the bricks ?
 
Scaniaman said:
The specs say "KN25" elements. I take it they are the normal choil ones, just tucked away in the tubing in the pic. I didn't assemble or fix the oven myself, so haven't seen them actually. If you want more detail I can shoot the company that built it an email.
Click to expand...
My current oven I ran only elements in the roof and love it. I put mine over ceramic rods but with that’s much of a span I was thinking of using fused quartz tubes.
 
I heat treat between 6 and 12 slip joint parts at a time in my tiny oven. I don't have a door at all. It is a vertical oven and I just have 2 brick pieces laying on top. In each of the 2 top bricks I have half a hole cut, and when put together they make an entire hole. I have an umbrella arrangement of kanthal wires that hold my parts, and when it is time to quench I just lift the umbrella out and dunk in the quench tank. Sometimes life is simple. I will never go back to not HTing vertical. It fixed my warping issues too, I haven't had a warped spring since out of 50 or so.
 
I thought about going vertical but was worried about the temp swing from heat rising. Also I do a TON of stainless knives In foil so that would problematic.
 
Yes, there's another layer of fire brick material in there. I guess there's a balance to how much insulation you want in an HT oven. Both too little and too much would have their problems with affecting rebound time to aust temp, and too little is obviously inefficient in other ways too.
If I work things really quick when inserting foil pack at say 1950 fahrenheit, I get a temperature drop to 1934 and overshoot to 1963. I am back an stable at 1950 after appr 4 min.

Natlek said:
Judging by the external dimensions and from this picture , it seems that they have use another one layer of isolation over the bricks ?
Click to expand...
 
Just a comment about the statement that "Heat Rises".

Heat does not rise … heat radiates equally oin all directions.
Hot Air rises because of lower density (actually, the heavier cool air falls).
In an enclosed chamber, the convection and "rising" of the hot air is minimal compared to an open environment like a large room.
The reason one end of a heated chamber (whether vertical or horizontal) may be slightly higher/lower temperature than another is primarily the distance from the heat source.
 
I thought about wool for my door,I ran out of bricks when building it and I had wool here,but read something about thermal mass difference and would lead to lower temps at door
 
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