Steel Dome Oven

[Wiley]

Re: Steel Dome Oven

Firebug, I have used 1/2 inch Hardiebacker to prototype a door for my WFO and found that as it gets near 500F it starts to give off a very unpleasant odor and it becomes quite fragile of the course of a dozen or so firings. In my case it lasted long enough to try out the shape I wanted which I then created in steel. I kept using it to see if the odor would eventually go away. It lessened but the door became so fragile it easily broke.

As you are thinking of having the sand against the cement board and it will easily get to those temps I would advise against using it. 16 guage steel is easy to work with, thick enough to be fairly easy to weld and yet light enough to be easily shaped, bent, sheared or cut with a saber saw. 16 guage by coincidence equals 1/16 inch or .0625 inches, for manufacturing .06 is the usual nominal thickness.

Hope this helps,
Wiley

[arren]

Re: Steel Dome Oven

Hello Friends.......
I just found your topic and I am interested in building a Steel Dome oven. I read your directions and they sound pretty clear. We'll see how our creation turns out...
Thanks

[arren]

Re: Steel Dome Oven

Hello to all

A domed-shaped oven relies on induction technology to provide heat. In particular, the oven has a dome or igloo shape, preferably modeled as an Italian dome oven, for use in a commercial pizza facility. The dome is made of a heat conducting and holding material such as concrete or stone. In the bottom of the oven, a magnetically susceptible plate is interposed between two layers of concrete. Beneath the lower layer of concrete, an induction coil provides the energy necessary to inductively heat the plate sandwiched between the concrete layers. In alternative embodiments of the present invention, additional plates are interposed between layers of concrete throughout the dome. Additional induction coils are provided proximate each of those plates.

Thanks for sharing

[jcsforager]

Re: Steel Dome Oven

Steel dome oven creators..

Just got my steel dome oven up and running and working great. Thought I would post my experiences in short for those who are headed this route. First and most importantly, my oven is working great and pizza, bread and other goodies are first rate.

What I did.

Oven is mounted on heavy duty trailer. Built a boxed frame out of 1 1/4 steel tubing with angle iron reinforced bottom. Wrapped this with metal lath, small stuff and filled the entire base with Vermiculite/portland cement mix. This is insulating pad. The outer dimensions of my frame is 58" which is the diameter of my buoy which became my oven cap. The internal dome is propane tank. 41" diameter. This rests on its own framing 1 1/4 inch tubing that is welded to the entire insulated box. The fire brick is set into the 41x41" frame on top of mortar/fireclay mix embedded on all sides with vermiculite insulated pad. The design of the inner dome I based on Kiko Denzers Earth Oven book which uses clay domes. Cut door at the 63%. Mounted steel dome and cut door and welded entrance door to this. From this point I welded rebar spikes around the dome, looked like a silver porcupine that I connected with wire. This was to give the fondu/ 1/4" minus basalt heat sink mix something to hold onto for the bumpy roads. Did the heat sink few inches thick and in 4 sections allow for expansion of metal. Foil under all of this to allow for slip. Having the rebar protruding from this made it easy to wrap all this with Kaowool and then more wire to hold it tight. At this point I capped the whole thing with my huge buoy. What I ended up with was a steel framed oven welded all the way down to the trailer. So far so good. Got the whole thing up to 50 mph other day. Time will tell how it holds up but only week link I can think of could by the firebrick inside but they are solid.

Some observations so far. Kaowoll is amazing. Outer dome is barely warm to touch with oven temp well above 600. Thermometer only goes to 600. Vermiculite/cement mix also is working well as bottom under oven is barely warm with firebrick blazing hot. The Heat sink principle seems so basic but I really didn't get it until I got this oven going and did my baking. To come out next day, 12hrs later and open door to find oven still at 150 degrees I started to see it all coming together. A well insulated heat sink. Seems simple but going through all the motions of building and following the principles makes much more sense to me now in practice. Have a steel door that I prop at an angle for bringing up to temp. When raking coals out I push the door in front of chimney pipe and against inner dome sealing in heat.

Now I'm making the oven look somewhat professional. And learning how to use it. Time/temps/wood used. Really amazing how such small about of wood can create so much heat. This project was built from salvaged materials, cutting metal with torches and hand saws and arc welding from a generator. Long road but well worth the pizza and bread so far. Now second phase will be to study longevity of trailer oven and all its parts.

Oven looks like giant buoy with a chimney. Plan is to do personal catering. Thinking of names, any suggestions...

john

[JoeyVelderrain]

Re: Steel Dome Oven

that is a perfect little trailer, did you modify it any?

[Fish Wheels]

Re: Steel Dome Oven

Buoy's on Wheels Bakery

[jcsforager]

Re: Steel Dome Oven

Trailer was previously modified by whomever built it. It was a mobile home trailer that had been shrunk down but is super beefy. Craigs list score. Shocks may be a bit stiff but seems to travel better now that I have weight on it. Did end up cutting some pieces off, adding a few.. Main thing was attempting to get weight distribution correct. Built oven frame and then moved it back and forth a bit before welding it to trailer.

I bought this because of its height and double axle. I added the square beams that oven pads rest on that were 8" and pad is about 8" which gave me correct working height. I also designed this so a fork lift could remove oven if needed. Now that I am more familiar with welding I think one could frame up any trailer to the correct height without to much trouble but helps to start out up a bit.
john

[JoeyVelderrain]

Re: Steel Dome Oven

love it, more pictures please...

[randall4483]

Re: Steel Dome Oven

Wiley, Is the perlite for thermal mass or just insulation. I am building one like yours but it will be inside a structure so space around the oven is unlimited. Thinking of using 2 domes (putting slices in the outer dome to fit over tight) for thermal mass then using insulation of ceramic wool or other material. Do I need more thermal mass before the insulation?
Thanks,
Randall

[Wiley]

Re: Steel Dome Oven

Hi Randall,
The thermal mass in my WFO consists of the steel inner dome and the calcium aluminate/basalt concrete. Outside the basalt concrete is the ceramic kaowool insulation and outside of that is loose vermiculite (contained by the window screen then stucco). I didn't use perlite as I prefer working with vermiculite...I find it less irritating to my skin. But as for insulating properties it's pretty much a loss up between which is better. By using it as dry fill I have (hopefully) made best use of the insulating properties, anything which has cement as a binder would, I think, be less insulating as the cement binder would have poorer insulating properties than a simple void between the particles.

I think one would be pretty safe in saying that any mixture with perlite or vermiculite is going to fall under the heading of insulating rather than acting as a heat sink.

I might be mis-reading what you said but it would appear that you are going to try close fitting one steel dome over another. While I suppose this could be done I would think that there would be problems with differential expansion between the two domes as intimate contact between the two would be hard to achieve. I might be wrong in this but I am under the impression that heat transmission is better from contact as opposed to transmission by radiation. If there is any void between the two shells heat transmission would vary between where the shells are in contact and where they are not and this might prove problematic. IMHO I would think a dome with a refractory applied over would have less chance of problems in this regard.

The steel dome in my oven serves several purposes: it maintains the shape structually; it is damage resistant; and because steel transmits heat better than brick any point where heat is applied (say where flames lick the surface) the heat is spread out thru the better conductivity of the steel to heat a greater surface of the underlying refractory concrete. This is only important, I think/suspect, during fire up; once at temperature and the refractory is soaked/saturated there is probably mute difference between straight brick and a steel lined refractory. I have no empirical data to prove this, it simply makes sense to me and this is what allows my WFO to get to temperature as quick as it does. I did not assume in my design that the steel shell was a significant portion of the heat reservoir in my WFO although undoubtedly it does help.

Hope this helps,
Wiley

[waynebergman]

Re: Steel Dome Oven

Wiley....thanks for you postings. Enjoyed looking at your pictures and detailed explainations of how and why things are working for you. I am currently planing on building another oven for resale. I may want to build what I can in my garage and assemble on site for others. I have an oxy/ace welder and have an interest in things built out of steel. I may want to build my next oven fashioned after yours or perhaps a hybrid. Brick dome with a steel fabricated entrance, vent, and stack.
Couple of questions I have for you......
1. Have you used a fire brick oven to compare with yours to get a feel for pros and cons with going with a steel dome?
2.I will ask our local propane dealer if they have any old tanks....how much should I expect to pay for a 36" or 40 " diam tank?
3.I am on the Sunshine Coast up here in Canada and don't see spherical shaped tanks they are more like giant hot dogs....I guess I could use the two ends and recycle the middle part. Are the spherical shaped tanks that common?
4.I have a cutting torch with my welding kit....I would probably cut it open with this. Is there anything I should be thinking about saftey wise before cutting this open because of the tank being at one time filled with propane?

Thanks Wayne....Garden Bay BC

[JoeyVelderrain]

Re: Steel Dome Oven

I have a cutting torch with my welding kit....I would probably cut it open with this. Is there anything I should be thinking about saftey wise before cutting this open because of the tank being at one time filled with propane?

Thanks Wayne....Garden Bay BC

OMG !! NOOOOOO!!!!!

[ThisOldGarageNJ]

Re: Steel Dome Oven

4.I have a cutting torch with my welding kit....I would probably cut it open with this. Is there anything I should be thinking about saftey wise before cutting this open because of the tank being at one time filled with propane

I have done this with a 20 gallon tank... this is how i did it..

1. let it sit in the sun for a few days with the valve open (this is supposed to purge any gas)
2. I removed the valve and filled it with water and drained making sure aany gas was pushed out by the water.
3. I cut mine using a 4" cutting disc on a grinder, Only because this is what i had available

just be careful... obviously

Mark

[Wiley]

Re: Steel Dome Oven

Hi Wayne,
Thanks for the kind words on my little thread. I'll try to address your questions in order.

11. Have you used a fire brick oven to compare with yours to get a feel for pros and cons with going with a steel dome?

I have not had benefit of the experience of using a brick dome similar to the one in the Forno Bravo plans. I have had hands on experience both with a commercial WFO (Woodstone 60 inch) and neighbors cob ovens. I have also had some small experience watching others using a very large WFO which was quite primitive by the standards we are building today. IMHO a WFO is basically a hole in some sort of heat holding non combustable medium in which a fire is built and food cooked either with the direct heat or with the retained heat to the fire. Beyond that basic one has alot of room to be creative and be as high or low tech as one desires or is able to achieve due to contraints of locale or pocketbook or ability. One thing I really enjoy about Forno Bravo Forum is the lack of people who are zealots/fanatics in what qualifies as a WFO. I really enjoy the diversity of WFO's represented. It would appear that each WFO is a bit of an individual, and how two identical WFOs act/perform can be dramtically altered by something as simple as orientation to prevailing wind. I am a bit amazed that no one else seems to be able to make or has a WFO that "pants". It's alive!

As for cons of the steel dome: biggest I've encountered was once in order to make steam for bread I tried spraying water against the dome. I ended up with a batch of lightly speckled bread. Sprecked with what appeared to be rust spots. After the oven had cooled I ran my hand over the interior surface and the surface had no loose rust. I suspect the rust came from some sort of fairly intantaneous reaction of the water with the super hot steel. Ever since that experience I have achieved the needed steam by spraying water into a cast iron pan which I heat right along with the firing of the WFO. Spraying water upon the brick hearth or a dome I think is asking for potential problems with spalling and degradation of the surface...I could be wrong there may be no ill effects of doing so but I won't chance it with my brick hearth.

Other than that I have no problems. I find that I can be fairly vigorous with cleaning out the coals and ashes with my rake. Scraping along the dome and getting out as much as possible. This is something I would not recommend with a cob WFO and suspect one needs to be gentler than I am with bricks as well.

As for the a large pro I don't have any anxiety regarding cracks. I read how some are disheartened when their creation ends up with crack(s). Cracks seem inevitable or at least very common with a brick WFO and it is rare to find any WFO of antiquity without repairs. Ovens of antiquity were built with poorer materials than are available today and were used much more frequently so any direct comparison is hard to support. Cob WFOs are by their nature ephemeral, and a bit more delicate, if they meet ones needs then I think they are fine.

2.I will ask our local propane dealer if they have any old tanks....how much should I expect to pay for a 36" or 40 " diam tank?

Price of a decommissioned tank would vary with locale and condition. In conjunction with your question regarding cutting a tank our local scrap metal dealer has a contract with several propane companies in California to recycle their old decommissioned tanks. It seems from what he told me that the liability issue was too great for them and so they were willing to pay to have them hauled to our local guy and pay him to take them. He won all ways, paid to transport, paid to take and then sold the scrap when finished. So finding a decommissioned tank in California might prove somewhat of a problem. I would suggest being creative in your search, Craigs List and scrap metal dealers, posting at the "wanted" ad your local Grange Hall, farm feed supplier etc. Get creative and I wouldn't be surprised that you find one or more at a acceptable price.

3.I am on the Sunshine Coast up here in Canada and don't see spherical shaped tanks they are more like giant hot dogs....I guess I could use the two ends and recycle the middle part. Are the spherical shaped tanks that common?

The sperical tanks are old school being built mainly right after WW2. Cylinderical tanks will work just as well and you might find a decommissioned one with elliptical ends. These are beingcoming more common and would be a very nice way of making a low vault WFO. As for recycling the center part, cut it into foot or so long sections (called "pups" in pipeline speak) and give them to your neighbors for fire rings or sell them.

4.I have a cutting torch with my welding kit....I would probably cut it open with this. Is there anything I should be thinking about saftey wise before cutting this open because of the tank being at one time filled with propane?

People watch too much TV. Yes, you can blow yourself up although I think you would have to be unusually unlucky or plain stupid. I have watched the guy at our local yard cut up an old tank (I happened to be there when he was doing so..just lucky to get to witness the final act to his process). His process was simple (although don't pass it on to the people in California or his tank deal might dry up): Hopefully the tank will read empty on the guage otherwise you will have to connect up your BBQ and use up remaining propane. Open the tank and allow whatever residual gas is left in the tank to vent off. Leaving the valve in the open postion, the day after the tank has stopped discharging thru the valve use a pipe wrench and unscrew and remove the valve. Leave the tank open for a couple of days. And what happens next I witnessed: Walk up to the tank with a lit torch and pass it over the top where the valve screwed in. Nothing happens. I asked him if he ever had anything happen when he did that and he said once there was a slight pop.

OK, so here is something else important: Propane is odorless so to make it detectable it is scented. The scent is a fliud which is not as volatile as propane and over years it can settle out of the fluid propane. Once the propane is gone the scent can remain as a fluid in the bottom of the tank. If one carelessly upturns a tank and the scent spills on the ground the spot where it spilled will smell like a propane leak for a very very long time. Same for getting it on your clothes. Nasty stuff, although one's mind runs to all sort of creative uses for such (all of which would get one in deep trouble with the powers that be).

So the usual disclaimers: don't do this at home, your mileage may vary, those doing this are trained professionals, do not attempt without consulting your physician etc etc. Do what seems logical to you, if filling the tank with water seems like a good idea then do that (although how you are going to move and deal with 500+ gallons of "contaminated water" is another issue). Place a air hose connected to your compressor and let it blow air into the tank for several hours, drop a couple of pounds of chipped dry ice into the vented tank. Lots of ways to get to the end result. Just remember the tank is much more dangerous with a couple pounds of propane in it than at any other time.

Hope this has helped, use your head and you shouldn't have any problems,
Wiley

[waynebergman]

Re: Steel Dome Oven

Thanks Wiley, this has helped a lot. I will look into tanks in the area here and proceed with design ideas. I will post some drawings for feedback on a new thread when I get closer to starting the project.
In my area, Vancouver Canada what I would propably go with to act as your fondu and basalt is a product I used in my last oven called "Moldit-X", it is also sold as "Devils Puddy" but much cheaper in the bigger bags where it is called "Moldit-X". It is good for filling large gaps and the folks that sell it say it would as your fondu. It is fairly reasonable at $30.00 for a 55 lb bag. It doesn't set up as fast as the fondu but nice to work with. I wonder if mixing into the mortar a bunch of busted up fire bricks into the mix would work as the basalt did for you. Do you have a feel for how the fire brick would compare to the basalt in an application like this?
Also wondering about making up a couple of molds to hold a pour of the above to make components like dmuns geo dome. These pieces could kind of float over the steel dome for expansion issues. The dome itself could be the underside of mold while making these components. Then insulate. I am a ways off for staring this project but thinking of different ways tackle it.....wayne