Finally finished! Heat treat oven

D

Doc Shipley

Joined
Mar 7, 2009
Messages
254
I've been working on a heat-treat oven for a couple of months. It's finally operational, although I expect to make a couple of changes to it.

Specs:
Duralite 220VAC/4kW element
Auber ramp/soak PID controller w/ 40A SSR
Auber type K thermocouple and TC wire/fittings
Chamber: 17" deep x 6.5" wide x 5" high
Overall: ~28" deep x 18" wide x 19" tall (closed)
2300F soft brick

The door was designed to keep hot brick facing away from the operator and to prevent accidental closure. At full open, the door's weight pulls it farther open instead of closed.

The "To do" list includes a door switch to interrupt power when open and a counterweight system for that heavy-a$$ed door. :)


Oven_01.jpg


Oven_02.jpg


Oven_03.jpg


Oven_04.jpg


Oven_06.jpg


Oven_07.jpg


Oven_08.jpg
 
Looks awesome, I love the door, great design. Did you mortar the bricks together, if so what with?
Mike
 
Looks great, Doc! Glad you finally got it running. I really like your door design. Pics of the thing at temp are now a must :D.

--nathan
 
Beautiful job! Congratulations! How hot do you find the airspace is, say, four or five feet above the oven at operating temp? (I have a little little Paragon kiln I have not used yet and want to be sure I maintain a safe space overhead.)
 
Miles, I won't speak for Doc, but with my homebuilt oven, the air even an inch or two above the oven while at stainless temps isn't too hot to tolerate (touching it momentarily is another story). With my Evenheat (which gets quite hot on the outside while at temp), again the air even a few inches away from the oven is fine. That being said I'd allow at least a foot around every part of the oven for clearance and avoid putting anything heat sensitive/flammible within a couple of feet.

--nathan
 
Many thanks! I am not planning any contact with combustibles, but my kiln/oven is currently about 4 feet below the overhead rafters. I can move the oven outdoors, but would rather not. Also, however, would rather not burn down the shop. Wood ignites at temperatures between 375 and 510 degrees Fahrenheit....
 
Thanks, everyone!

I spent way too much time on it, but I'm very pleased. I'm thinking about either a spring assist or counterweights for the door (actually, I expect I'll end up building a whole new door and links), but it works fine as it is.

...I think. I haven't put a blade in it yet. :D

Miles Undercut said:
Beautiful job! Congratulations! How hot do you find the airspace is, say, four or five feet above the oven at operating temp? (I have a little little Paragon kiln I have not used yet and want to be sure I maintain a safe space overhead.)
Click to expand...

Miles, I ran it for several hours at 1950F the other night and could still touch it if I didn't linger too long. I was worried a bit about the rear being so close to the wall, but during and after that run I still couldn't feel any noticeable heating of the drywall. I agree with Nathan, though - a foot of free space all around and good air movement will be good insurance. I'm going to move the table out from the wall.

12345678910 said:
What did you use as a door gasket seal ?
Click to expand...

Nothing - it's straight brick to brick, planed flat. I decided that a 3.5" flat butt would block heat better than a narrow airtight seal. I guess it worked; at temp, there's no appreciable heat coming up from the door join.

Airbalancer said:
Looks awesome, I love the door, great design. Did you mortar the bricks together, if so what with?
Mike
Click to expand...

The floor and walls are mortared with "kiln cement" from the local pottery supply. No idea what it really is. The roof is just laid dry, as tightly fitted as I could get it. I wanted to be able to replace the element or make repairs if needed.

With the Auber PID on auto-tune, it comes up from ambient to 1200F at something under 40 minutes (I forgot to check it before that...) From 1200F to 1950 was just at 25 minutes. Let it run at 1950F for 3 or 4 hours, turned it off, and 10 hours later it was still at 345F.

I have another PID controller and some of sunshadow's $5 thermocouples. I plan to check the temperatures at various places in the chamber, like up front by the door, and see whether there's any variance.
 
drdoc said:
I think that's the highest praise a man could ask for!

But no thanks - I really want to get back to making knives. :)

If there's interest, I'll try drawing up the basic plans for it. AFTER Ashokan...
Click to expand...

That oven looks GREAT!! Good job drdoc!

I have an interest in the plans :)
I am not in a hurry at all...It would probably be a winter/spring project (after building a rotary phase converter)

Bill
 
Nice work. I am not sure what the last two pictures are of? It looks like rope in the heater coil grooves.

Thanks for posting.
 
PigPopper said:
Nice work. I am not sure what the last two pictures are of? It looks like rope in the heater coil grooves.
Click to expand...

The last 2 pictures are me bragging. :D

You're right - it's 1/2" nylon rope. The heater element came pre-wound from Duralite but not stretched to length. I needed a way to determine the exact length without test-fitting it over and over.

I ran the rope in the brick channels where the coil would go, marked the length, then taped the rope end to the vised end of the coil when I stretched it.

It worked, too; the heater coil fit on the first try.
 
Very nice. I would like to make one some time soon. Could you give an estimate of the cost of materials?
 
gga357 said:
Very nice. I would like to make one some time soon. Could you give an estimate of the cost of materials?
Click to expand...

It worked out to just over $500. And yes, really, there are 50 9" x 4.5" x 2.5" bricks in there. Total waste was 4 1" drops.

$180 - 4 dozen firebrick at $45/doz

$125 - ramp/soak PID, 40A SSR, thermocouple, TC wire & connectors

$65 - Heating element, 10ga high-temp wire, and Mullite tubing

$30 - Kiln mortar

$75 - Frame parts - Angle iron, square tubing, welding wire, misc. hardware

$10 - Stainless steel skin

$25 - cutoff & grinding wheels, welding wire, etc
-------
$510 - total

The prices listed include tax and/or shipping. I got the firebrick and mortar locally, and the stainless body was salvaged from a broken hotel housekeeping cart. Stuff like the LG6/30 plug, 10/3 extension wire, and box for the controller parts I had lying around, so maybe another $40-60 for incidentals.

I couldn't begin to tell you how much time I have in it, but I think I could build another one in 20-25 hours.
 
Thank you, such great information.

drdoc said:
It worked out to just over $500. And yes, really, there are 50 9" x 4.5" x 2.5" bricks in there. Total waste was 4 1" drops.

$180 - 4 dozen firebrick at $45/doz

$125 - ramp/soak PID, 40A SSR, thermocouple, TC wire & connectors

$65 - Heating element, 10ga high-temp wire, and Mullite tubing

$30 - Kiln mortar

$75 - Frame parts - Angle iron, square tubing, welding wire, misc. hardware

$10 - Stainless steel skin

$25 - cutoff & grinding wheels, welding wire, etc
-------
$510 - total

The prices listed include tax and/or shipping. I got the firebrick and mortar locally, and the stainless body was salvaged from a broken hotel housekeeping cart. Stuff like the LG6/30 plug, 10/3 extension wire, and box for the controller parts I had lying around, so maybe another $40-60 for incidentals.

I couldn't begin to tell you how much time I have in it, but I think I could build another one in 20-25 hours.
Click to expand...
 
From the looks of the pictures if you extended the back of the lower door hinge and put a counter weight on it would make opening the door easier.
Just me thinking again. :)
Lynn
 
I have seen the british blades tutorial, but if you would write up your plans


dimensions internal and external
ie brick layout
why so many bricks ?

and the door mechanism measurements...
I like that style
 
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