Heat treat oven question

S

scott wheeler

Active Member
I have a propane forge for doing carbon blades (0-1 1084) and it seems to work pretty well. I recently had someone ask me to HT some A-2 so I'm thinking of building an electric heat treat oven. Obviously can't do that one in the forge. I have found numerous plans and sourced all the parts either on the internet or locally. I'm comfortable with building this except for the wiring. I plan on using two elements in series (240 Vac Kanthal Heating Element - 2300 °F Max) with a PID controller, ceramic thermocouple and a 25 amp solid state relay with a heat sink. Where I'm getting conflicting information is about the SSR's. I'm being told that I need to use two relays for two elements. Any schematics or help would be greatly appreciated.
 
I can't help on the wiring, as the mains supply is different here , but you mention "240 VAC Kanthal heating element"

Are you using 2 of them in series?

I don't know your situation, but if you are following Andy Gascoigne's HT Furnace plans from way back, he used 2 of the 115 VAC elements connected in series and powered them with 230 VAC (UK mains Voltage). As I understand it, the supplier later started selling a single 240 VAC element (which was basically a double-length version of the 115 VAC one). This has led to some confusion and I am aware of a few builders using a pair of the 240V elements, connecting them in series and finding the oven will not make temperature because it only produces one quarter of the original design power.
 
True. I am one who found this out. If you are ordering the element from Budget Casting use only one of the 240 volt. I used two and could not get the oven to temp. I removed one and stretched it to the maximum manufactures recommendation and the oven is working great. One coil one SSR.
 
The BIG reason for 2 SSR's (or any relay) is safety. When using 240 VAC there is 120VAC on each leg to ground (ground can be you). If only one SSR (relay contact) is used, when the SSR is not calling for heat (open circuit) there is still 120VAC on the coil.

With that said, if you open the door while heating, you're under the same situation, UNLESS you have the door safety switch that removes power from coils any time the door is opened. Safety folks do recommend this switch in all cases.

Good luck - wiring isn't hard at all. Buckroo has a good wiring setup on his oven. There are a couple of threads here with good wiring diagrams..... but how do you know the good vs bad when doing a search?

Ken H>
 
I believe I understand better now I know the coil will be live even when the PID isn't calling for heat. I guessed what confused me is I found a tutorial from Budget Casting Supply and they show two elements wired in series for a sixteen inch deep chamber. Unfortunately it uses an home oven type controller and not a PID so it's wired direct. Buckaroo I think I'll try one element and size the chamber accordingly. Timgun do have a link to Andy Gascoigne's HT Furnace plans? Thank everyone this is what I looking for!
 
I am pretty sure the plans you'll have seen were Andy Gascoigne's, as they were also on the BCS site for a time. His original thread on British Blades was back in 2004, so it's a fairly old document. It can be found at:

http://www.freewebs.com/knifemaking/HT FURNACE.pdf

It used an infinite controller. I doubt there were affordable ramp/soak PID controllers available back then. Ten years is a long time in electronics.

There is a sticky on BB that has links to all the DIY HT oven stuff: http://www.britishblades.com/forums...ng-a-Heat-Treatment-Oven-Information-Database.

It's probably worth spending the time to work through it, even though much of the electrical stuff will not apply to you. For various reasons, the price difference between a commercially-made unit and a DIY one is much greater over here than in the USA, pushing many of us towards the home-build.
 
timgunn said:
I am pretty sure the plans you'll have seen were Andy Gascoigne's, as they were also on the BCS site for a time. His original thread on British Blades was back in 2004, so it's a fairly old document. It can be found at:

http://www.freewebs.com/knifemaking/HT FURNACE.pdf

It's probably worth spending the time to work through it, even though much of the electrical stuff will not apply to you. For various reasons, the price difference between a commercially-made unit and a DIY one is much greater over here than in the USA, pushing many of us towards the home-build.
Click to expand...

Thanks Timgunn, Yes its worth it, my cost when all is said and done will be just under $300 US. Would love to have an Evenheat or Paragon but it's not in the budget, plus I get the satisfaction of doing it myself.
 
Finally getting around to gathering the components for my heat treat oven build. I wanted to post a deal I found on fire bricks. If your near Reading PA I got a box of 25 9 X4 X 2.5 inches 2300 degree soft bricks for $55.00. They wont ship but you could pick them up at George Snyder Refractory contractor.
 
Finally getting around to gathering the components for my heat treat oven build. I wanted to post a deal I found on fire bricks. If your near Reading PA I got a box of 25 9 X4 X 2.5 inches 2300 degree soft bricks for $55.00. They wont ship but you could pick them up at George Snyder Refractory contractor Clarion Street Reading PA.
 
That is a GOOD price on those brick - being able to pick them up will keep the cost of oven to a reasonable cost.

Ken
 
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