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I Forge Iron

Digitally Controlled Vertical Heat Treat Furnace

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Here's my newly completed heat treat furnace, and have yet to see a furnace that is like it or that can do as much. Just put the paint job on it this afternoon.

It is digitally controlled with a PID controller, which takes in a temperature reading from a k-type thermocouple and then operates a gas solenoid valve to regulate when the burner is fired to regulate temp.

It has about a 40" blade capacity (built it so I can start getting into swords again. I had put aside the long blades until I got a better HT setup). The blades hang vertically into the burn chamber (this is a pretty uniqe design feature that I havent really seen in other furnace designs) which really cuts down on the warping and sagging that can occur when heating and trying to manuver a red hot piece of steel horizontally. And here's the kicker, it will operate at BOTH high temps, for heating blades to critical, AND at low temps for tempering. Ran tests at both 1550 F and at 400F and it operates great.

From my initial testing it looks like I can maintain temps within about +/- 10F of the set temp (which is quite good). From the initial test, looks like it produces pretty even heat (from what I could tell by eye) over the entire length of the furnace. It has a pretty awesome rising heat vortex from the way the burner is mounted that distributes heat pretty evenly along the length of the chamber.

I've still got to run more tests with it and play around with settings to get it fine tuned, but so far it works great!

And now for Pics

First up is the Burner manifold. Sidearm burner, solenoid, and the pipe that runs parallel to the burner is the pilot light jet.


One of the burner manifold mounted


Front view.


Control panel (still need to wire in a switch)


I'd be happy to answer any questions about the furnace, its design, construction, etc.

I'll also try to get some pics of it running when I get a chance.

Hope you enjoy


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Back in the 1980's Tom Maringer used a custom digitally controlled vertical electric furnace with inert atmosphere for doing his large swords; at one time he was trying to sell it.

It could do ramping and a lot of tricks for heat treating high alloy tool steels.

Good ideas never go out of style...

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Dave, boil a spaghetti noodle for about 10 minutes and then pick it up by the end---how straight is it? For big blades like swords their weight will deform them if they are being manipulated horizontally. Hanging them vertical during heat treat helps keep them straight.

If the column is closed in use then there is less issues with convection (and oxidization); but you are right that can be an issue. OTOH many folks are still heat treating in forges and the heat is not evenly distributed in them either.

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The vertical setup allows the blades to hang vertically where gravity will aid in keeping things straight rather than working against you, as Thomas mentioned.

As far as heat uniformity, it maintains pretty consistant temp throughout the entire length of the furnace. This is due to the fact that I have the burner mounted roughly tangentally to the inside of the the inside of the furnace, the velocity of the hot gases generated by the burner are directed by the furnace walls into a spiral. This rising spiral carrys the heat all the way around the chamber as it rises (not just up and out). The interior volume of the furnace is also pretty large which allows heat to even out pretty evenly and not develop hot spots.

As for marketing them, I'd think about it, but I have no idea where I could get a consistant supply of furnace bodies for them (this is done out of an old 100lb propane cylinder from the scrap yard) at a cheap enough price (new cylinders are pretty expensive). That and I don't really have a whole lot of extra time on my hands.

I considered buying a more expensive PID controller with ramp and soak capabilites, but I dont need anything like that at the moment and wanted to keep things as inexpensive as possible for the moment. Thats something I can always upgrade later. I could also turn this into a high temp salt pot pretty easily as well, pretty much just drop in a ss pipe with the salt, and move the thermocouple. But thats all down the road.

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Well you start by calling up all the propane companies and telling them you need old tanks that have failed test and are being junked and tell them WHY and what you are doing with them and that you will pay scrap rate.

Then you figure out how to stay ahead of the piles you can accrue.

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