Heat treat oven build

J

JustinWoody

Joined
Nov 10, 2017
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25
Building a heat treat oven. I am running 110/120v, (not sure which). I have the Auberins PID controller with ramp/soak, a 40a ssr with heat sink and k type thermocouple. Inside space of my oven is 4" tall, 5" wide and 18" deep. My element is 50' of 20g a1 kanthal wire coiled at about 5mm id.
I habe no idea what a sticky is, or how to find it so my question is, does anybody have a good wiring setup for what i have?
What may need to be changed to make this work better? I am sure bumping up to 220v will be one suggestion.
Auberins has not been very helpful. They did not send out a manual with the PID controller and the one i downloaded from them leaves a lot to the imagination.
Any help would be great!
 
I built one that is very similar to what you've described. I ran the coils in three loops wired in parallel and pinned them to the sides and top of the cavity. I didn't stretch my coils as everyone says you should so I had to pin them quite a bit (I used wire for that, just pressed into the firebrick) because they initially wanted to move around a lot at temperature.

With the amount of wire I used I am right around 15 amps. I plug this into a 20 amp circuit in my garage (you can spot them by one of the slots in the socket being T shaped). It works fine, and I've been using it infrequently for several years. It takes around 80 minutes to get up to 1500 F. That last 200 degrees takes forever. So this is quite workable for carbon steels (10xx, O-1, 5160, etc) but probably takes too long to heat up to do stainless steels which want to be closer to 2000 F.

In retrospect if I'd added a 4th loop on the floor of the chamber I would probably be in better shape.

I used a cheap Chinese PID controller and thermocouple. I think the thermo couple only goes to 1800 F -- again, fine for carbon steels but not quite enough for stainless. And I calibrated it using ice water and boiling water -- ghetto but it works. I have a fan blowing over the control box to keep the relay and controller cool.

I've not had a heat treatment that didn't work as intended using this oven with 1095 and O-1 steels and quenching in 140 F warm canola or peanut oil.
 
What gauge wire did you use zhyla?
I wish i could show pictures of what i have so far. I think it will turn oit nice. I just got a wiring diagram from a guy on fb in the group bladesmiths for beginners. I also sent a picture of the wiring diagram back to Auberins that they gave me in the "manual". The diagram doesnt show any wires going to the ssr except one shows the hot power in going to the element. I will see what they have to say. I may call an electrician and see about getting a 220v ran into my garage. I do want to get into stainless as i want to build kitchen knives as well.
I have 3 1/2 knives waiting to be heat treated now, all oit of 01 steel and i want to make sure my heat treat is spot on. These are gifts to family, 3 hunting knives and a pairing knife for my wife.
 
For the heating coils I don't remember the gauge. They were Kanthal brand but that's all I remember. For the main wiring I used a computer cord and connector like you'd have on a computer power supply. Internally I think I just used some standard romex cable and cut the individual wires out of there. And then regular like 22 AWG stuff for connecting indicator lights and other low voltage stuff in the control box.

The tricky part is connecting the wires to the coils. You can't solder or use normal things like wirenuts because it just melts. I used a threaded rod and nuts for that. Wrap the wires around the threaded rod, crank the nuts down on either side to pinch in place.

As far as wiring the relay... I mean you really need to understand how all this works or you're going to get yourself killed. The relay just opens or closes based on the input voltage to the switch side of it. I think mine just gets a 5V DC input (might be 12V) from the PID controller. You can play with this and just like wire up a light or something so you can understand what's going on.

So the PID controller takes readings with the thermo couple and then flips the relay (SSR) on and off at a certain "duty cycle" -- initially on all the time, and as it gets close to temperature it will transition to on some of the time and off the rest. Kind of like your house thermostat but more intelligent.

I would totally do 220VAC if you're going to heat treat a lot (it will heat up in like a quarter the time) or if you want to do higher temp steels.
 
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