new heat treatment kiln - great results

[Kevin Colwell]

Hello Everyone,

So the idea for this kiln goes way back to Don Fogg on this forum and his old website. I was using a vertical barrel kiln for high temp heat treatment, and an electric evenheat for tempering and spheroidizing. I wanted a way to heat treat outside when quenching would happen, due to oil, flames, martempering with hot oil, etc. None of those things will happen in my basement.

 

Well, I could not get the vertical barrel kiln to get closer than 40F top-to-bottom. No good when it is a 36" barrel and I am making 30" blades with tangs. 

 

Plus, I wanted a kiln that I could just go to and use, and not have to tweak for an hour until it worked optimally.

 

So, I took Don's idea of the horizontal ht kiln, and I tweaked it slightly.  I added mild steel baffles that are pushed up against the back end/bottom of the barrel. They leave about 4" in front, and about 1" on the sides. With the burner, a 3/4" T-rex aimed off to one side, the thing worked amazingly well. Much better than I had hoped. I put a thermocouple about 6" from the entry port, and another about 8" from the far end. They were within one or two degrees C of each-other. I was amazed. I believe that I actually built a better kiln than I could buy.

Vertical kiln with burner to show how it began.

 

Stand made from scrap wood, of course, and barrel horizontal.

 

Covering it all with rigidizer and satanite. I also put in better wire supports for the kaowool. 

 

Here is the inside with the baffles. The burner port is in the lid, down near the bottom of the barrel, under the baffles. The idea is that only convection can heat the top. 

You can see the thermocouples and also the burner pointed off to one side. This made a HUGE difference. Don't point it straight down the barrel. The rebar goes through both sides of the barrel, and it holds the mild steel plate that forms the baffles. Two plates, so I can adjust how much room on either side.

 

 

Yes, I didn't believe it either.

 

 

Here is another to prove that I wasn't just picking one time they were coincident. I wanted to take them up to 850C but I had to go cook dinner for the family. Still, this is far better than I had hoped. 15 inches apart and about 3 or 4 inches difference in height within the furnace.

 

Edited July 19, 2021 by Kevin Colwell

[Bill Schmalhofer]

Very nice. I’ve been thinking on how to modify my long heat treat forge as I have a horrible temperature differential. Mine’s vertical now but I’m moving it to horizontal. Nice idea with the plate baffles. How thick are your plates?  I’m assuming the temp probes are under the baffles, or is the burner under the baffle?

Edited July 19, 2021 by Bill Schmalhofer
Addition

[Kevin Colwell]

burner is under the baffle, the temp probes and the sword hang in the top over the baffle. That way, only convection can heat the top part. Don Fogg, a long time ago, figured out that the top layer of air in a setup with the burner at one end and a port to put swords in through at the top of the same end would equalize well across the entire barrel. All I did was add baffles to his design, because in his there was often about 30F difference between the middle and the two ends of the barrel. I wanted to do better than that, so I added the baffle. It is just 3/32 mild. Actually, it has two plates stacked on each other, so I can slide them around and play with the width of the openings. One is 1/16th and one is 3/32. I don't think thickness matters. Just that something traps the heat and only lets the hot gasses out in scattered form. Also, aim the burner sideways so the flame wraps onto one of the walls. If you aim it straight down the kiln, the far end will be way hotter.

Edited July 19, 2021 by Kevin Colwell

[B Bott]

Nicely done. I think I will steal your idea :-)

Do you happen to have a pic of the way your burner is mounted?

Edited July 19, 2021 by B Bott

[Kevin Colwell]

It isn't really, "mounted." It is just pointed into a 2" square hole at the very bottom of the lid. Look at the pic of the barrel with a ladder in front of it. The burner is sitting on a firebrick and just slid a little into the kiln. Light it outside, aim to right, and slid it in some.

[B Bott]

I see it now. Thanks for the info.

[Pieter-Paul Derks]

I use something very similar, although mine doesn´t have the baffles, onw swords the temperature isnt perfectly even, but for (big) knives it works flawless.

I was also amazed how well this works for such a simple setup, I almost never use my electric kiln anymore, the drum furnace is just way faster to heat and gives no decarb issues.

 

 

 

[Kevin Colwell]

I use the electric kiln for tempering and spheroidizing/annealing. The two make a good combination to get the various things done. You are right about decarb. I tested the edge of the sword, which I had draw filed after forging. The whole length of the edge was hard as glass. No decarb that I could notice, after three grain refinement cycles and a hardening cycle. 

 

 

Notice how uniform the color is. There is just a bit of decalescence or recalescence happening above the tip if you look. Just below the bold that holds the leg of the post vise to the arms. 

 

 

This is a different grain refinement cycle. Notice, not as hot. Same thing.

 

 

Here is the quenched sword (it lives) over the drawing of what I am supposed to make. I missed a tad.