Steel Dome Oven

[Wiley]

Re: Steel Dome Oven

John,
You've been busy gathering materials... Great!

Wow, a six foot sphere, that's cool!

So if I am understanding correctly you will have a 72" +- hemisphere and a 48" hemisphere. That gives us a 12 inch space all around if one hemisphere was set over the other. My first thoughts are that I would use the 48" steel hemisphere covered with refractory like I did, something on the order of 4 inches thickness. Then fill the remaining 8 inches or so of space with insulating material (perlcrete or vermicrete). Built like that the roughness of the roadway or bumps would not result in a pile of dis-associated bricks. Also you would end up with a wonderfully smooth and weather resistant outer shell.

As for the question of cutting thru the backing ring or leaving it and cutting above (like I did): My reasoning (right or wrong) for leaving the ring was that these hemispheres are stamped out on a huge press and probably have residual stresses as a result. Heat that metal up and there is a chance it will move to release the stresses; cut the ring and any stresses may tend to flare the cut open and make the base out of round, even if it's cold and get worse when heated. Because the ring goes completely around it is acting in part like a tension member, sort of like the chain around a dome. Regardless, the inner voice was cautioning: "Don't!", so I didn't, whether my reasons were/are valid or not. I didn't want to burden myself with those possibilities, I wanted a circle for a bottom not something out of round, and unflat. And I feel such a fool when the inner voice says "Don't!" and I go ahead anyway, and it goes badly as a result. Embarrassed to myself, for myself, :-|

So I would still suggest leaving the ring if you can. It does make for a little bit more work in shaping the liner bricks, but bricks cut easily with a diamond blade. And I designed my oven so they all could be removed and replaced if ever they needed to be. The transition will fill with ash and if you wanted you could fill it with a mix of fireclay and brick dust and it would be near on invisible.

Also part of my decision to have the height inside decreased by the thickness of the bricks was the size of the split rim I had available for an entrance. I worked the math and decreasing the interior height made it so the radius of the rim was close on 63% of the lessened interior height. Close enough that the WFO draws fairly well.

I think your idea of simply pouring an insulating pad upon a steel deck is good. No need for the weight of a concrete support slab. 4 or 5 inches of vermicrete should more than enough protect the base. And placing the firebricks ontop of that would be the way to go. I would consider the idea of rabbeting out a notch in the sides of the bricks so that they could be set and locked together with a tennon either of slices of brick or high temp mortar. That way the interior hearth would act as a single unit. No bricks working their way up on a bumpy road. That may or may not be a problem once the bricks are locked together with ash and such.

I would suggest sketching it all out roughly on paper figuring what heights you want (interior and entrance) and where and what you can use to make the pieces from.

Looks like you are headed IMHO in a good direction.

Bests,
Wiley

[jcsforager]

Re: Steel Dome Oven

Good ideas.. I've been working with wood as my medium as of late and your comparison regarding tension holds true for wood as well. I built a Yurt once, using a tension ring around the top to hold the structure tight and when I looked closer at your design I saw that leaving the band does seem more intuitive/stronger. I may go this way. Good to think of though as I'm buying 1/2 of tank, not entire one so I need to get the 1/2 with ring. I like the idea of adding insulation and then refractory all inside the Buoy. The Buoy itself is really something I want as the oven "look". Getting it to my place was a whole adventure in itself. The guy told me it was 48 in so I brought a 6' trailer. Was loaded into the back of the trailer but stuck and I couldn't get it out. Ended up learning to use a boom truck and a day of screwing around but.. I have a really cool oven cap. I also got a bunch of chain and all the 6 braid rope that held the buoy. Will come in handy I'm sure in some way dressing out the trailer.. You were right on the propane tanks, those things are built like tanks and will make a pretty solid oven core. Still more gathering to do and few steps back for learning some welding but will be giving you some updates. Thanks for the ideas!
john

[fireart]

Re: Steel Dome Oven

Wiley, what did you do before you retired? You must have been a Engineer of some sort but with hands on knowledge. Amazing work. Thanks for sharing.

[jcsforager]

Re: Steel Dome Oven

Wiley - This little forum is filled with goodies of knowledge! Been reading on the ceramic blankets. Looked it up on Ebay as suggested and found plenty.

Hoping to keep my weight down so I'm looking at this as an option. My previous post said my Buoy was 6'. It is 60" So I'm dealing with 6" of space, not 12" between inner dome and outer. Still should be enough for sufficient insulation. You used the Fondu as your refractory. Do you think a ceramic blanket would work on the dome?

I realize the importance of allowing room for the metal to expand and the blanket seems like it would allow this. Coat of foil/2-3" blanket/2-3" perlite mix? Looking for ways to stay light on my wheels... I'm also playing with idea that if I did cut dome from bottom ring up for the door to then have a few welded joints around outer edge of each dome connected to either metal framing or brackets extending to metal framing that will secure dome for road travel and preserve integrity of sphere..

john

[Wiley]

Re: Steel Dome Oven

John,
Please correct me if I have something wrong in what you said you have already gathered. You have a 60 inch sphere and at this point do not have an interior hemisphere. I would think in the best of possible worlds a 40 inch dome (like I have) would give you 10 inches of space between the two hemispheres for refractory and for insulation. Figuring 4 inches of refractory would leave six inches for insulation; and depending upon your pocket book you could go with 4 inches of ceramic insulation and two inches of vermicrete or three inches ceramic and three of vermicrete you would probably have more than safe temperatures on the outside of the sphere. Perhaps all vermicrete would work but I would try to go for as lean a mix as possible if I went that route. A fair bit of leeway there, I mean if you came up with a 38 inch dome that would be fine and a 42 inch would still be good.

I don't think I would be as enthusiastic about a 48 inch inside a 60 inch. My thinking is that I wouldn't want to go less than 4 inches of refractory heat sink and that would only leave 2 inches for ceramic blanket. And I would think you would be more "forced" into using the blanket. Probably still work but I suspect you would feel some heat on the outside shell after a while. How much heat is the question? So I would attempt to find a smaller interior dome and if you don't have any success (or they want too much) then go with a 48" if you have access to that.

So, if I understand correctly and you only have the one sphere/hemisphere at the moment I would suggest calling Pennisula Recycling at 360-379-9404 and asking what they have on hand in the way of half propane tanks. A man named Ed is the owner and his cell is (or used to be, people seem to swap providers alot) 301-1229 and I'm guessing that's still area code 360 as I don't have anything indicating otherwise in my roll-a-dex. Ed is willing to barter, dicker and horse trade whereas the ladies in the office think of the operation as more of a business...which I guess is what it is supposed to be. Another option is to call the various propane distributors and see what they have in the way of reject tanks (Suburban Propane in PT seems to always have a stack in the end of their yard). Depending upon your ability to "smooze" you might get a tank for little or nothing.

Good hunting and keep me posted. I have a 48 inch full sphere so if you have no success we could probably work some sort of trade. What was the length and size of chain came with the bouy? This year I am scheduled to swap out the top chain on my mooring. But like I said I would first try for a smaller dome.

Bests,
Wiley

[Wiley]

Re: Steel Dome Oven

Fireart,
Thank you for the kind words. No, I'm not an engineer. What I did before I retired depends upon what time (year/month) of which one inquires. My father was a Professional Metalurgist and worked as a Materials Engineer most of his adult life and so I was exposed to that sort of stuff all my early life. He worked in the auto industry and then for Lockheed, I was also exposed to all that comes with such a life: layoffs, threats of layoffs, up and downs in the industry and such like. It wasn't what I wanted and so early on I opted for a different route for my life.

I've lived my life like a dog wandering down the road stopping to sniff any any bush that attracted my interest. Instead of living to work, I worked to live. And I liked to travel and experience different cultures.

I've always been a quick study and curious about how things work and how things were done. So lots of countries and lots of different jobs doing lots of different things. I've spent alot of time on and around the water and boats. It worked for me. I invested what money I made early on and let it grow. Married at 39 (to a wonderful woman with four daughters and far poorer than I) and retired at 49 1/2. I'll be 60 in a couple of weeks.

Years ago I happened to overhear a conversation at a party where my wife was asked what I did. I'm still pleased with her answer, "He does what is needed next."
Bests,
Wiley

[jcsforager]

Re: Steel Dome Oven

You are correct, I do not have interior dome yet.. But I have one picked out, Navy City metals in Bremerton has one that they are willing to cut and sell me 1/2 @ .50 per lb. Was going to get maybe next Wed? The big question as you mentioned is how much heat would I feel on outside w/ only 6"? I'm wanting as much room as I can get but laying out my pizza pan inside a 40" would still leave plenty of room. Do you feel limited at all with the space your 40" dome has? I talked w/ Ed last week and they don't have any tanks but he said keep checking. I've seen a few other tanks around, I may just slow down a bit and see if I can find a smaller dome. I got a bunch of chain but it has been chopped into many small sections...

thanks,
john

[Wiley]

Re: Steel Dome Oven

John,
I don't feel limited at all by the capacity of my 40 inch. Although I am not skilled enough to bake more than one at a time at present there is definitely enough room to bake two or more at a time. I plan on getting into baking bread in my oven this spring/year (bummer, it snowed again this am :-( and planning on being able to bake 10 to 12 round loaves at a time in my oven. So a 40 inch closely fits my needs.

I have a friend with a WoodStone WFO that is 60 inches inside diameter and he rarely uses it as it take so much wood to get it up to temperature. So as one would expect there is no universal right sized oven it depends upon the need. What is your expected need?

50 cents a pound including cutting sounds like a reasonable price especially if you can be there when they cut the tank. It'd be great you can choose the half you want the ring on etc. They'll probably be cutting with propane not acetylene so if you can sweet talk the guy into cutting wide from the line you will end up with a nicer edge after grinding. If they cut with arc air you will definitely want a wide from the line cut. The old rule "cut wide and grind to the line" definitely applies if that's the case. I got a PM a day or so ago from a man with domes that are closer to your need but he's located in the east and shipping would be impractical and costly.

My top chain is 20 ft of 1/2" chain and only constraint is it needs to be able to pass thru the inside of 2" ABS DWV pipe.

Bests,
Wiley

[randall4483]

Re: Steel Dome Oven Test Fire

I've taken several photos of the intermediate steps but figure unless the oven works they are not really that valuable. So today I assembled the pieces I have built on the driveway in front of my home and had a test fire.

So lots of things were "mock-up", the bricks on the hearth are old red bricks and in order to insure some sort of air-tightness I packed sand around the outside of the dome itself. The chimney was something I found at the recycle center (see where I shop :-)

I am including a photo of the three pieces before assembly. Also I would like to know (even though the photo doesn't show it) I did get a small wisp of smoke out the front, is that common or do I need to consider rebuilding my transition piece... in this case the hoop band that connects the chimney to he FWO? Thoughts and opinions welcomed.

Wiley

I thought in your earlier pics you had welded the rim onto the dome? Now it shows 3 pieces. Is the chimney piece made from a rim also or fabricated curve? What kind of work did you do before you retired? Very nice work.

[Wiley]

Re: Steel Dome Oven

Randall,
Sorry that the posts are unclear. In post #2 in this thread I do have the rim welded onto the dome. Subsequently I cut the rim such that the flanged end of the rim was separate from the portion welded onto the dome. That is sort of visible in the last photo in post #11 where there are three pieces spread out. Here's what happened between the photos:

The reason I cut the flanged portion from the rim welded to the dome was to create a thermal break. The dome gets hot, way hot and if the outer rim portion was part and parcel with the dome it was going to get very hot too. So my thought was to break that direct flow of heat with the strip that holds the transition to the flue. So heat has to flow out of the dome then over a strip of frax paper (Frax paper is a compressed ceramic material that looks like blotter paper...think kaowool compressed into a thin sheet) and into the strip or strap of steel that holds the transition then back thru the frax to finally heat the outer rim section.

Here's what I did (warning: probably confusing, although not meant to be)

Yes, there are three pieces, The dome with the welded on section of rim ; the transition section with the flue ; and the outer rim. The reason was stated above. Now I wanted to create the bent piece such that it matched the curve of the rim. So I tack welded a strip of metal to one edge of the rim (bottom edge) and bent it over the rim. Now anyone who has tried to bend a piece of metal over another can attest that when you let go the piece you bent didn't retain the bent shape but springs back in sort of the needed shape. That's not what we want so there is a way around this... heat the metal as you bend it and give it several smacks with a 48 oz hammer as it is being bent. For heat I used a carbon arc torch which is the easiest and cheapest way to get a real hot pressure-less flame (near 3000F). It runs off a welder and save for protection from the high intensity ultra violet light it generates and radiant heat it is a very neat tool. So bend the strip over until it reaches the opposite edge and tack weld it there. Now go over the whole bent strip get it good and hot with the torch and allow it to slowly cool, when it is cold it will retain the exact curve of the rim.

Now set the dome up so that it is level and determine the top of the strip of metal you bent. That is where the center of the flue will be. Lay out the flue and in the inside (nearer to the dome) drill 1/8 inch holes where the inside corners of the flue will be...only the two inside holes (there being four corners in a rectangle you are drilling the two nearest the dome). Next cut and weld the pieces of the transition together. Don't worry about cutting out the actual flue hole yet, having everything solid makes welding straight forward and fairly easy.

Ok still with me? Now drill four holes for flat headed bolts that will eventually hold the transition piece to the rim/dome section. I positioned them so they were about an inch up from the bottom on each side and then fairly close to the flue (two each side). The flat heads will be on the inside of the rim with the threads projecting thru the rim and then thru the welded transition piece.

Now grind out the tack welds that held the strip of metal to the rim. The strip will separate but retain its shape. Next mark and cut the rim into two from one edge to the other. This cut will be straight and end up being the front of the opening of the flue. Now mark and cut the rim and cut out what will be the flue passage thru the rim. That's why we drilled the corner holes that locate the exact flue location. However, (and here's where I expect to loose you) the flue hole thru the transition measured 3 x 9 and the section I cut from the rim/dome measured only 2 x9 the extra space is created by the outer flange rim being forward of the rim/dome piece...that's the thermal break area! Then cut out the section of the transition that will be the flue. Now lay the frax on the rim and push the flat headed bolts thru the frax. Cut away the part that would obstruct the flue and place the welded transition on the rim/dome and bolt down. The outer section of the rim that has the flange is supported by the base bricks and is held in position and captive by the transition piece. The thermal break allows for the dome to expand and contract as it needed as it heats in the completed WFO such that the dome can be very hot and not break the weathertight seal of the flange to the dome exterior.

Whew, if you followed that in one reading I'm amazed, Sorry to be so long winded and blow by blow.
Wiley

P.S. Last work before I retired was to gut a single story Victorian house (about 1/4 of the interior all the way to the dirt/basement) and rebuild. New joists, floors, plumbing, gas lines, wiring etc.etc. Finished with new oak floors and sheetrock, new thermal windows, clear fir panel doors the whole works. Did everything but the sheetrock myself. That was both my Victorian houses..my first and my last it took two plus years ugh!. Also delivered a 65 ft trawler thru the canal and up from Panama to Seattle as mate/engineer/navigator one summer and worked as an engineer on a fish buyer in Bristol Bay the next, so I had some fun too.

[jcsforager]

Re: Steel Dome Oven

Hi Wiley,

Thanks for all the info! They are cutting the tank either way as they sell them to folks for BBQ's. I think I may hold off and go for a smaller one, 40" or so. All your points are convincing and I do want to consider firing time for a larger oven. Once I get the bug for something, such as this and start looking I usually find just what I need. Fun poking around all these yards as well. I wouldn't be suprised to find what I need tucked away in the woods around here. Plenty of people seem to have an obsession with collecting "stuff", piles of it. I was thinking of this as I lugged my new buoy, chain, a huge block, and other stuff associated with the buoy back to my home. All treasures I say! This is what I told my wife.

Keep your eye out for domes...

thanks,
john

[randall4483]

Re: Steel Dome Oven

John, I have a 41" OD with the backer ring on it that I would sell for a $100 but I'm a long way from you so I'm not sure what shipping would be. My zip is 38017
Wiley, thanks for that very detailed explaination of the thermal break and rim.
After reading a few times I think I understand fully.
Also, still thinking about what you said on the steel floor welded to the dome. My wood stove is build like this and it gets much hotter without warping. Of course the floor is smaller. I make fire pits from these domes and never leave the backer ring and cut flames in the sides and I never had any of them become distorted so I don't think anyone needs to worry about it much.
Randall

[randall4483]

Re: Steel Dome Oven

Wiley, does steel hold heat longer than the refractory? I was thinking of making the dome 2 layers thick. One dome on top of another then add the refractory. Of course I would need to slit the top dome 3 or 4 times to let it slide over. What does the aluminum foil do that you put on top of your dome before the refractory?
Thanks,
Randall

[Wiley]

Re: Steel Dome Oven

Randall, Although I do not have any figures to prove this it is my opinion that steel does not hold heat longer than firebrick, I believe that it conducts heat faster and that a solid steel oven would actually cool down sooner than a totally brick WFO. That's given that insulation would be the same etc.

The purpose of the aluminum foil was to cause a slip surface between the steel dome and the refractory molded over it. I don't have the calculations at hand but if I remember correctly if the circumfrence of the dome was a straight length of steel and if one heated it from a reasonable ambient tempreature to around 900 F degrees the length would grow something on the order of 1/2 inch. Pi x D gives the circumference so the diameter would grow something on the order of one third of one half inch or one sixth inch. Not much, however, that expansion is real and needs to be reckoned with. The refractory is going to expand as well but the steel will heat faster as it's closer to the heat source and I don't have any figures as to how much the refractory will expand. So by creating a slip surface between the steel dome and the refractory (and segmenting the refractory) I can control more or less the expansion. As the oven heats and everything expands the cracks between the segments grow and as if cools they contract. I think I included photos of the cracks somewhere in the thread. I heat cycled the oven several times to prove to myself that the oven was "working" as I wanted before continuing with the kaowool and etc. covering. I also placed strips of aluminum foil between the segments so the expansion cracks were more likely to form there than elsewhere.

I will admit I had some concern that the oven would expand and when it cooling the refractory would hangup and remain in the expanded shape leaving a gap betweeen the steel dome and the refractory. In my case the refractory cycled as I wanted and expected. I'm not sure if it had hung up there would be a problem with heat transfer to the refractory from the steel dome or not, but the worry turned out not to be warranted on my oven. I add that because I don't know of another WFO like mine and one is a pretty small sampling from which to make a definite statement.

Hope that answered your question, if not ask again and I'll try again :-)
Wiley

[randall4483]

Re: Steel Dome Oven

Thanks, Is that just regular cooking aluminum foil or thicker stuff? If so, where do you purchase it. Approx. how long does your oven stay hot? say from 700 to 250? Once you remove the fire.
Randall