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Heat Treat Oven, homemade one-off

Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
Power: 110 V, draw about 13 A
Temp: 2300 deg F max
Element: Kanthal A1
Heat Control: PID controller, SSR, k-type thermocouple, all Hong Kong stuff from eBay; the controller face is the black square at the left end of the oak board
Bricks: soft refractory brick from Sheffield Pottery, Mass.; outside the layer of bricks is a 1 in thick layer of vermiculite board;
Outer cage: bronze brazed (O/A) weldable steel angle and steel expanded sheet; cage remains cool to the touch during firing

The four bars forming the support rack at the floor of the oven are 304 S/S (thanks Ray Behner); they must get softish at max temp, but they support the part in its foil envelope OK.

HeatTreatOven_a.jpg



HeatTreatOven_b.jpg



HeatTreatOven_c.jpg
 

jimboggs

Stainless
Joined
Sep 4, 2007
Location
Clermont, Iowa
Marty,

Very nicely done! May I ask how much did it cost? how much time? What is the work piece max size? I've considered doing something like this only one a much larger scale and making it oil fired. This would give me the ability to fire entire machine castings prior to weld repairs, plus I suppose a guy could harden beds/ways and the like. Something small would be nice too, however, for centers, spindles, etc.

Would you be willing to provide a simple drawing and parts list?

Thanks,
Jim
 

Marcibb

Hot Rolled
Joined
Mar 5, 2009
Location
Alabama
Nicely done

Nicely done, I have already purchased the same or similar controller module and plan to build one this summer.

Marci

:cheers:
 

David Utidjian

Titanium
Joined
Jun 30, 2006
Location
Wayne, NJ
Nicely done Marty. I especially like the support rack bars which would get the heat and temp pretty consistent all around the part.

Only problem I see is where to put the lid when the system is up to temp and one has to take the lid off. It will ignite just about anything even partially flammable at a considerable distance. So... where DO you put the lid when adding/removing parts?

I made one out of a salvaged muffler furnace from our chem dept. The coils are embedded in the walls so no contact with metal parts inside. I added the PID, SSR, and other doodads to modernize it.

-DU-
 

Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
Oven - responses to above comments

David Utijian - Re where to put the hot cover: The top two photographs show a freestanding rectangular platform sitting on the bench next to the oven. This is on 1-inch legs, and was made to put the hot lid on after removing it from the oven. There is enough room on it alongside the lid for tongs and a couple of small hot doodads.

gzig5 - Re cost: I did not keep a ledger, but I would guess something under 225 would be right. The controller, thermocouple, and element each ran about 30 bucks, the SSR about 10 bucks. The bricks were a bit under $4 each (less than half the McMCarr price), and the refractory mortar another 20. The angle and expanded sheet were from the local hardware store.

.RC. - Yeah, made just for my own personal shop use, not as a for-sale item.

jimboggs - Re time: Didn't keep track of hours, but as is often the case with these things, the very great majority of the time spent went into planning, figuring, & thinking about things. Having gotten the first one done, the actual construction time for a second one, which I'm not planning to do, would be two full days once all the materials are in hand. You'ld want to leave the mortar to set at least a full day, undisturbed, after doing the brickwork.
Re size: The interior of the oven measures 8.5 in long, 4 in wide, and the usable z-distance above the rack is 1.75 in.
Re availability of plans & parts: Leaving aside the fact that I have no set of plans and no official parts list, I am really reluctant to say too much, since I don't know that my construction decisions are the best ones. I designed this oven pretty much as I went along, and my purchases of parts were mostly governed by what I stumbled across using the internet, not by a careful analysis of costs or features, although my friend Larry did do a pretty sophisticated study of element wire gauge, coil diameter, and gyre pitch. I'm not trying to hide any secrets by evading the plans issue, and would be glad to answer any specific construction questions that pertain to this oven.

scatter cat - If I understand your suggestion correctly, your concern is electrical hazard from touching the element terminals. Where the two ends of the element wire lead through the oven wall to the outside, they travel in a small ceramic sleeve. Right at the outside wall of the oven they connect to the hookup wire, which is wire with high-amperage insulation that can be bought from pottery kiln manufacturers. The connection is mechanical, by means of steel cuff-shaped connectors I made up in which the wires are clamped together by means of setscrews. If you look at the bottommost photograph of the three I posted, you can just see the upper one of the two element connections. The round white thing at the oven wall is the outboard end of the ceramic lead-through. The shiny grey material which appears continuous with it is a goobered-on coating of JBWeld, which bonds well to the ceramic tube and to the initial portion of the insulated hookup wire, and which is non-conductive. You can touch it without getting shocked.
 

Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
Yes, 2300 F. Not sure willbird if there is something hiding behind your word "stable", but I would say that with the PID controller functioning in auto-tune mode, any temp you select is maintained with very little fluctuation. I have not tried to push things beyond 2300, since that gets into territory that is out of spec for the element wire and the bricks, and maybe other components as well. 2300 as a max does it for high alloy steels, e.g., tungstenized HSS for metal-cutting tools.
 
I would guess 2300F since that what it says in the second line of the original post.

I would guess you did not see the word "stable" in my question, that might come from being a rude and arrogant so and so.

I asked about "stable" because ambient temp had an impact on a tempering furnace we had at one past employer...it would hit higher stable temps in hot weather than it would when the shop was 50 degrees F.

So I would guess your furnace could hit a higher stable temp at 100 F than at 50 F ambient temps.

Bill
 

wippin' boy

Diamond
Joined
Sep 14, 2005
Location
il.
very nice machine
but
if i were building it i believe i would build a side load device
with a swinging door for some already mentioned reasons
i think the top loader is more of a "youch" monster
and your size would allow you to use a single brick for a ceiling with no real arch required
i would also put the coils in a slight recess to avoid incidental contact
 

gwilson

Diamond
Joined
Oct 1, 2006
Location
williamsburg va
I'd recommend a front opening furnace,as the very high heat is going to roast anything near it when the top lid is taken off. It might need you to wear full heat protecting clothing to manage to extract anything from the furnace. Our 2300 degree furnaces were hard enough to get close to with tongs to extract things at full hardening heat. I kept low down when taking stuff out of the kiln, to let the heat rise away from me,but the radiant heat was still pretty hot!

The furnaces we had at work were Paragons,and just used ordinary strap hinges on their doors. The bricks were wrapped in stainless steel sheet to give something to screw the hinges to. They could have used a layer of insulation,too. They cooled down too fast to anneal some metals.

The coils in ours were also exposed. Over the years,the coils began to creep out of the back corners of the kiln. The newer models had vertical ceramic rods in the back corners to keep the coils from creeping out. Yes,you don't want to touch those coils!
 
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Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
willbird: Thanks for clarifying your "stable". I had not thought about ambient temp at startup being a relevant variable. Interesting. I will keep it in mind.

USMCPOP: I happened to get the components you mention from a fellow called Marco Wong, who can be reached via the website Home Page. He does business on eBay under the seller name lightobject. If this doesn't get you to the right place, post again and I will try to dig out more definitive info.

wippin' boy: It probably isn't clear from the photographs I posted, but the coils were in fact recessed in grooves in the sides of the bricks. The outsides of the coil gyres stand no more than a 16th or so proud of the plane of the bricks' walls. The grooves were produced using a ball end mill in a router, with the mill end sticking up vertically through a hole in a table, wood-shaper fashion.
 

Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
USMCPOP: For some reason, the website address I wrote in my message above came out reading "Home Page". Here is the website address in a different format - www dot lightobject, followed by dot com.
 








 
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