Oven heating element mounting & TMI

[rgray]

My latest project has been a heat treat oven.
There is a ton of good info out there and I studied it for quite some time.
I never really liked the elements in the grooves in the bricks...people talk of them shifting and having to staple them in...one guy went so far as to pin them in with porcelain rods.

Liking the porcelain rod idea..I went in search of them...My idea was to cross the top of the oven with the rod and have the element wound around it...they are kinda expensive and the site also had fused quartz tubes...they will take the heat and are quite cheap.

Not knowing if i would be able to cut and use the quartz (comes 48" lenghts) I ordered both porcelain rods and quartz tubes. Rods are 3/8 x 12"...quartz tubes I ordered are 1/2 x 48"

The quartz tube is easily cut with a diamond wheel. I turned it in my lathe in a collet and held a dremel with diamond wheel against it to cut it.
I did this same thing with the porcelain rod. it is much harder to cut, and eventually I ended up just scoring it and snaping it off to save on diamond wheels. If a nice end is not needed or perfect lenght it can be wraped in a paper towel, put in the vise and just snapped off.

My oven is 18 x 9 x 6.5 inside. So a full brick wide with side bricks standing on end. This leaves the top a full brick wide. I closed it in by pining bricks together with 2" lenghts of the 3/8 porcelain rod. 9" side to 4.5" side. Refactory cement was used between bricks also.

The quartz tubes are set into grooves in the top of the wall bricks. The elements are wound from 16ga kanthal. I did math till my head hurt figuring the elements out. I think I figured I needed 35 feet so I cut 37' to give some extra to double wind the end etc.

After testing and 2 heat treatings (4140 @ 1575 & W1 @ 1425) my elements measure 11 ohms.
I have a full 240 volts in the shop so pulling 22 amps and output is 5236 watts.

Winding the elements took more math 56 turns then leave 4" then 56 turns etc....Each set of elements when done had to be taped in place so it could turn with the 1/2" rod in the lathe while winding the next element. It's all one element but on 4 quartz tubes.

Bottom of the enclosure is 4" square x 1/4 round rod rack (cut from clothing display chromed rack) on top of it is a piece of .060 aluminum sheat. 1/4" superwool 607 blanket on the alu sheet and then the fire brick. Sides are two layers of the super wool so 1/2" and I put 4 layers on the back so 1". Top also got 2 layers. Steel sides and top were cut from our old kitchen oven (soot streaks are from welding the 4 square rack to it) the back is left open so the electrics stay cool.


On to the TMI
5 minuits from cold to 1200 deg.
7 min from 1200 to 1575
At 1575 Temp at back 74 deg
side 71
top 74
door 97
under door 178
bottom 69
top brick above door 77
left side of door 92
right side of door 99
angle iron on door 79
thermo couple housing 120
Wire conector/element 150
SSR 82


24 minuits after shut down(oven now at 1000 deg)
back 89 deg
side 101
top 108
door 187
under door 205
bottom 103
top brick above door 142
left side of door 165
right side of door 178
angle iron on door 150
thermo couple housing 153
wire conn/element 124
SSR 77

One hour after shut down (oven at 705 deg)
back 105
side 119
top 127
door 181
under door 215
bottom 123
top brick above door 150
left side door 172
right side door 172
angle iron on door 159
Thermo couple housing 160
wire conn/elements 114

Outside temps all went down after 1 1/2 hours and temp inside was 590 @ 2 hours 535 @ 3 hours 450.

 

[LJP]

rgray, interesting stuff for sure.
Do you have controls to regulate the heat?
How much did it cost to build?
How is the door made? And how is it hinged?
Did you just google it to find the information you studied to get started?
More questions as I think about this more, I am sure.
Definately interested in all your comments about how it works in the future as well.
Thanks, Larry

 

[rdhem2]

Bravo, fun stuff. Many moons ago i worked for a contractor who was every slum lords best friend. We not only repaired the house wiring but all electrical equipment inside.

In those days coiled wire resistive heating was very common with brands like Cadet, Commodore, Thermador and King being very popular. Then we could just get no-chrome wire pre coiled in a plastic bag. You told the salesman what you had for type of heater, voltage, wattage, and amperage. He would come back with the element ready to go.

We would then lay a piece of string along the path of the element wire being careful to keep it accurate. Then with the help of a buddy to hold string and element you would stretch them both to the same length then wind the element back to the ceramic support being careful to not let the wire ever cross itself. A couple terminations, burn the oil off and you were in business. These elements were made by Chromalox Co. and I'll bet are still available as the company is still in business.

Good study of the dwindling heat over time.

 

[rgray]

rgray, interesting stuff for sure.
Do you have controls to regulate the heat?
How much did it cost to build?
How is the door made? And how is it hinged?
Did you just google it to find the information you studied to get started?
More questions as I think about this more, I am sure.
Definately interested in all your comments about how it works in the future as well.
Thanks, Larry

I got the control,thermo couple, SSR, and ssr heat sink from light object.
PID : http://www.lightobject.com/JLD612-Dual-Display-PID-Temperature-Controller-P43.aspx
T-couple : http://www.lightobject.com/High-Temperature-2370F1300C-10ft-Ceramic-K-type-Thermocouple-P411.aspx
SSR : http://www.lightobject.com/Search.aspx?k=essr-40dac
SSR heat sink : http://www.lightobject.com/Search.aspx?k=ssr40a

Those 4 items with shipping cost $115.00.
The fire brick cost me $182.00 with shipping and came from ebay. Shipping cost was as much as the brick. I used 26 bricks.

The quartz tubes and porcelain rods cost $150.00 w/shipping. I bought 8 porcelain rods and two quartz tubes. I have 6 of the porcelain rod left over and one quartz tube. The rods were $13.47 and tubes $9.68, so $46.30 plus shipping for what I used. Gotten from Advalue technology http://www.advaluetech.com/

The kanthal wire came off ebay for $29.50 for 78 feet so lots of extra there.
The insulating blanket came off ebay for $48.00 for 20 feet quite a bit left over there also.

So I spent $524.50. Would be about $100.00 less if I knew the quartz tubes would work and the porcelain rods could probably be eliminated by using a smaller quartz tube to pin the bricks together. (I call them porcelain rods they are called Alumina rods on the website)

The door is simply 3 bricks glued together with refactory cement and surounded by an angle iron frame on the outside. The bricks are refactory cemented to the frame and there is a 2" porcelain rod pinned into the bottom of each brick for a little insurace they don't fall out.
It is hinged with 1/4" bolts to the same kind of angle iron that is screwed to the side of the oven.

Yes I googled and got alot of info. The build by Ray C on this site is what got me started. Just type "heat treat oven" into the search box on this site and threads on heat treating as well as oven building will come up.

Here's a pic of the back of my oven. Left it pretty open so the electonics would say cool (dosen't seem to be an issue at all and I may close it in later). The PID is upper left, thermo couple lower left. Other pic is top of oven. only thing out the top is the PID display. Not sure why the third digit didn't show up in the photo, but it is there. Not a very good camera angle I guess. It is sitting on a board on top saw horses at the moment, so I just held the camera above my head and snapped that photo. I will get wheels for it and it will go on the floor eventually.

 

[rgray]

Good study of the dwindling heat over time.

Thanks... It's nothing exacting...just a cheapy IR temp gun.

I did a batch of 4140 and then to temper I use a small kitchen counter top oven. One of those christmas presents the wife never used once. So brand new for me to temper in.

It's a Delondhi 1500 watt. it measures 18 x 11 outside and 12 1/2 x 8 inside.

I did the same heat measurements on it at 350 deg
top 140 deg
door 180
right side 85
left side 160
back 78

Made me feel good about my heat treat oven. The right side is where the controls are and why it was cooler there.

 

[LJP]

Thanks for all this info. Great project! On my to do list.
Let us know how things go using it.
Larry

 

[rgray]

Wow haven't kept up on this. Been almost a year. I have used the oven quite a bit. Probably average once a month. Not sure if that qualifys as quite a bit, but it is just a hobby for me.
Moved it into a less used part of my shop. Had to install a new outlet there for it.
The floor where I moved it is wood.
Made a few throwing knives, and learned that I really should have a hole drilled somewhere in the knife to attach a stainless wire for retrieval/dunking. Figured I'd just hang onto the handle end with pliers and if there was a soft spot there it would be ok.. All fine and dandy till I dropped one fresh out of the oven (0-1 at 1500 deg) It is really hard to pick that up off a smooth wood floor. Ended up with a couple of burnt spots on the floor before I could get it back into the pliers to dunk it.
Bought a little surface grinder between centers attachment on ebay and had to make the dead center as it was missing...pic is of it at the 1200 preheat temp...not nearly as exciting as at 1500 but there is not much time for snapin pics when ready to dunk.

 

[rgray]

The stainless oven racks are also to small in diameter on the cross wires. They just flatten out under weight. This lets a heavy object get to close to the bricks and can leave a mark on the material where it didn't get up to heat.

I will build a rack from 1/4 or 3/8 stainless. Wondering if a stainless plate on top of the rack would work to give an area for small parts. What thickness will be needed? I have some 4130 plate that is .100 thick, is stainless required or would this work?

I reshaped the oven racks in the above pic and added a second set to get the bars closer to keep the small part off the bottom. The bars on the original rack are very krispy from the repeated cooking. This makes me think alittle thicker plate may be good and survive longer.

Pic of some of my heat treat projects, the 1" boring bar was done with 2 others and the 3 of them easily flattened the rack down to the bricks, the circular marks are the result. Built from 0-1 bar.

The circular cutters cut automotive valve guide tops for positive seals, the larger one is a hole cutter for a press frame, they are 0-1 steel.

The tap handles are 4140 bodies and W-1 handles, all done at the same time this was the largest number of pieces I've cooked at one time, very busy when it comes time to dunk them all. Been trying to sell them on ebay without much luck.