Sorry for creating another thread but needed one specifically for kiln setup questions. I can get a pretty basic kiln locally for pretty cheap. That just leaves a better control situation. I find these little controllers on egay that are cheap but they do not run a variable frequency to the heating elements. Is that how even the good ones work? Just keep kicking a contactor in and out and this is all controlled by the digital PID system with a thermocouple input?

I remember reading in my other post that a better thermocouple system may be needed and possibly one just to read direct metal readings. I am really just looking for something cheap and small to give it a go on some tests to see what I can do and can't do. I am looking to run approx 500-1000in3 of material in it at a time. I am really just wondering if these little kilns lack the power to get things up to temp in a reasonable amount of time. I am sure if I can prove things out, I will just buy a real heat treat oven but would still be nice to do small lots quickly when needed.

I am primarily targeting low alloy and tool steels. Specifically 4140, 4340, 8620, A2, etc.

"Is that how even the good ones work?" Not certain about kilns, but we use a lot of heaters for plastics machinery. They are relay output PID controllers, simple on-off. We use mercury contactors since they don't wear out due to cycling a bazillion times, but mechanical relay would work fine for something you are not using 24-7 (we use them on some lab equipment). We use PID controllers made by Love (Dwyer); work good, last forever. They come in many flavors, basically what the input is (type of thermocouple), and what the output(s) is/are. You want relay output (many are dual for heating and cooling). They also have alarms and such. They are cheap. I searched eBay for "PID controller" and found new ones under $50. They have a "learn" mode that will figure out the response rate of your process and in my experience, they will nail the temperature target dead nuts. They are simple and you will have no trouble figuring them out. Documentation is on the web.

I just use a couple of 25-amp solid state relays to control the 220v power to my heat treating furnace coil. With feedback from a Type K thermocouple it works great and was real simple to construct.

Thats 125-250#, its going to take a pretty substantial kiln to rack that much material without much stacking or piling.

I am a ma value there. The parts I am looking to do asap with it will be 1in3 x 150 so 45 lbs. Most other parts will be smaller too. Obviously if we had big lots to worry about, I would just send them out.

Viper,

I have done almost exactly what you are attempting to do. I converted a small muffler furnace that our Chemistry department had tossed. Those little muffler furnaces cost $1500 new! I gave it a second life as a heat treat furnace and "modernized" it with a simple inexpensive PID and SSR.
Had to make a new front panel out of sheet alu and a few other misc parts. If you need a better schematic and/or parts list just let me know and I will send you a full sized PDF.

This setup has worked fine for about three years. I plan on building a larger one at some point.

See attached images.

Just noticed that the schematic is all but unreadable when confined to 640X480 so here is a link to a PDF of the file (also includes parts list):
http://phobos.ramapo.edu/~dutidjia/F...od_schm-v2.pdf

-DU-

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Hello Viper heres my setup for heat treating up to 2000 deg. Its a Fuzzy logic controler and a solid state relay and a type k thermocople.

Its setup for 120 volts add another relay for 220 volts .Holds tempreture +- 2 deg. This is all you need to controll a large ceramic kin.

http://www.metalworking.com/dropbox/...ce-control.jpg

This is the setup I have , Controler with dc pluse output , solid state relay with dc input , and a thermocuple .This controler controls the tempreture buy turinng on and off the power to the relay and the relay is just a switch turning on and off power to the heating coils one second on one second off or 2 seconds on one second off to keep the correct tempreture setpoint thats why you use a solid state relay (switch that turns on and off with no moving parts ) a standard contactor turning on and off many times a min. would fail.


http://www.coleparmer.com/catalog/pr...sp?sku=8980202
Controler with dc pulse output

http://www.coleparmer.com/catalog/pr...sp?sku=8985002
Solid state relay with dc input

http://www.coleparmer.com/catalog/pr...sp?sku=0851680
2000 dreg.type k thermocuple

Good reading
http://www.coleparmer.com/techinfo/t...ers.htm&ID=698

Lower cost controlers from omega

http://www.omega.com/ppt/pptsc.asp?r...ies&Nav=autb01 CN4316-DC1-DC2
http://www.omega.com/ppt/pptsc.asp?r...660&Nav=heap07
http://www.omega.com/ppt/pptsc.asp?r...chb&Nav=tema07

Remember get a dc output controler and a dc input solid state relay and a type K themocuple. Setup is easy.