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  • PeterW
    replied
    Re: Steel Dome Oven

    I've been watching this with interest, and I'm really impressed with the re-use of old stuff...!

    One think I did think, is expansion of the steel. This might sound an odd suggestion, but why don't you add a thin layer of a compressible fibre insulation, such as 10mm of rockwool before the outer refractory..? It will allow the steel to expand but not crack the casing..?

    Just my 2p

    Cheers

    Peter

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  • Wiley
    replied
    Re: Steel Dome Oven Update

    I got a few days off and managed to get some work done on the WFO and figured I should post an update as to progress. Attached are some photos:

    First shows the entrance (half split rim) welded onto the dome. View is from the top. Photo is out of order date wise as the original got lost somewhere's.

    Second shows the dome inverted and ready to cut out the entrance itself. Entrance was welded to the dome before any cutting to minimize distortion of the dome from the welding.

    Third shows the back weld of the inside of the entrance. Entrance had to be cut before back welding in order to weld to the edge of the dome.

    Fourth shows the weld but ground and sanded to make for smooth flow of hot gasses in exiting the dome.

    Fifth shows setting the dome back into the shop. It's easy with the right tools, in this case an excavator :-)

    Next I'll grind the bottom of the entrance to the height of a standard firebrick and then build the transition/support piece to the chimney.

    In order to slow the heat transfer from the steel dome to the front of the entrance I am planning on cutting the entrance so that it is essentially two arches. When finally assembled the outer arch will be spaced about one inch away from the arch that is welded to the dome. That space will be filled with insulating refractory. This is for safety, otherwise I can imagine the outer edge of the entrance getting quite hot.

    If all goes well, I should be able to "test fire" the dome in a week or so to be sure it draws and (if necessary) make modifications before cladding the dome with refractory and setting on the platform... which I haven't built yet :-)

    Wiley

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  • Wiley
    started a topic Steel Dome Oven

    Steel Dome Oven

    This is what I am doing in the way of constructing a somewhat different WFO. It will still have a brick hearth and the actual design is not unusual, only the materials of it's construction are different. I'm going to try and stick to using commonly available recycled materials because (to me at least) going into detail about a project using truly unique one-of-a-kind materials, while perhaps interesting, is of limited use to others who might be so inclined to follow and build one of their own. That's providing, of course, that this works, which I believe it will or I would not be spending my time, money and energy on the project.

    I'll try to add lots of photos. Suggestions as well as comments are welcomed.

    First off this oven will be using one half of a condemed spherical propane tank. Tanks are condemed for various reasons, a common one being the serial number and spec plate has become separated from the tank. Once separated a tank is condemed and cannot be reused for propane. I got this one from our local scrap metal recycler. In point of fact, I got two, one a half tank with a diameter of 40" and a full sphere with a diameter of 48". The 40 inch one is what I'll be using in big part because it is aready cut in half and because the size is better for my use. The thickness of tank is approximately 5/16 inches.

    This dome will serve as the interior surface of the oven. Refractory material will be exterior to this surface, with insulation outside of that, just like a typical WFO. These tanks were constructed of two hemispheres welded together. Where the weld is made there is a backing plate, in this case a backing ring. This backing ring aided in the welding because it allowed for higher amperages to be used in joining the halves resulting in a better weld (since it could only be welded from one side). The sphere was cut in two on one side of that backing ring and as a consequence when cut, the two halves were not equal. The half I have has the backing ring so that it is slightly larger than a true hemisphere. See photo of backing ring. The addition of the backing ring makes the interior height of the dome 20.75 inches.

    This is all boring but the reason I included it will make more sense in a bit (hopefully).

    So that will be the interior of the dome itself, a steel dome. But what happens where the interior makes the transition to the entrance/doorway and the entrance itself? My answer is one half of a steel "split rim" off a truck. This one came gratis from our local Les Schwab tire dealer. It was the biggest I could find with an interior diameter of 22.5 inches. That makes for a radius of 11.25 inches. This radius would be the height of the doorway/entrance to the oven. Split rims are thicker than conventional "clincher" rims, and this one is approximately 1/4 inch thick.

    Now according to Alan Scott and others, in a correctly proportioned WFO the height of the doorway should be 63% of the height of the interior of the dome. So how far off are we with these two pieces? The height of dome (20.75 inches) minus the thickness of a standard firebrick (2.50 inches) creates an interior height of 18.25 inches. 63% of 18.25 inches is 11.497 (basically 11.5 inches). Height of split rim entrance 11.25. So matching the half split ring with the half dome is within 1/4 inches of being correct.

    So it seems a straight forward matter of welding a piece of 1/4 inch steel plate to the bottom edge of the split rim (which will make the height of entrance to height of dome proportion correct); then welding the rim to the dome; cutting out the entrance/doorway and back welding the join. Then fitting, welding and cutting a suitable transition piece for the chimney. Followed by setting the whole assembly on a suitable raised base and covering with refractory and insulation etc. and finishing in a more conventional way with a layer of stucco.

    For refractory I'm planning on using "traprock" or basalt (which is available locally) with LaFarge "Fondu" as cement. Per suggestions on this forum I am now expecting to use about 3 1/2" thickness of refractory. Insulation will be first a blanket of Frax (kaowool) and then a couple of inches of vermiculite and Portland cement.

    Thoughts or suggestions anyone? I'm looking for ideas on the transition piece to the chimney, thanks.

    Bests,
    Wiley
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