May 14, 2020 - 12:25pm
Steel lined wood fired oven
Re: steel template inside liner
I'm making an oven with a 2:1 elliptical 1/4" thick steel dome. I want to lay brick around that using it for template and support, and then blanket insulation, and then chicken wire and concrete cladding, and then a sheet metal outer shell for weatherproofing. The inside is 42" dia. It will sit on a 3" steel reinforced concrete slab with 2" of refractory concrete on that, and then 4 1/2" X 2 1/2" X 9" firebrick on edge for the floor.
What about the disparity in expansion rates between the steel liner and the masonry surrounding it. I'm thinking about avoiding something catastrophic (late at night, always). Any concerns there?
I've seen Utubes about building dome ovens with wood scaffolding on the inside. after the brick dome is built on top, the wood is then burned out.
There's also the bit about how the bricks radiate heat back downward after the oven is fired. Having steel between the bricks and the food is going to change that radiating dynamic.
I copied this from a thread in another forum on this subject:
I think you will find that it heats faster and obtains a more even heat distribution than straight bricks or cast refractory. This is because the steel has a higher conductivity of heat than does the straight refractory. Thus the direct heating of the plate from the fire more quickly spreads the heat to a larger area and more efficiently transfers the heat to the underlying refractory than heating the refractory alone and having that heated refractory conduct the heat to surrounding refractory. Likewise when shutting up a steel plate lined WFO oven to equalize the temperature when baking "equalization" of internal heat occurs more quickly. The better re-radiation of the steel plate lining also will cause the hearth to heat quicker during fire-up.
I'm encouraged. Any thoughts?
I don't have enough formal education to know if I should buy into that reasoning from the other thread.
If there is not enough air space between the dome and the brick above it, thermal expansion of the metal dome could crack the brick.
If there is enough air space, it would insulate the brick from the metal dome, and the brick would take longer to heat up. The air layer would attenuate the heat transfer from the interior metal dome to the above brick.
If the air layer were not uniform, there would be hot spots and cool spots. Conduction is a better heat transfer than convection.
It seems that if an interior metal dome were cost effective, we would know of commercial wood fired ovens that use them.
There might be a reason why this wheel has not already been invented. But... I don't want to discourage your dreams, ingenuity, or sense of adventure.
This page is worthy of browsing: http://heatkit.com/html/bakeoven.htm as is the main page: http://heatkit.com/
I’m not smart enough to know the answer to this. But I’ll also throw into the mix the consideration of how much thermal mass 1/4” thick dome of that size is. Might be worth to calculate how long it would take to heat soak that and a percentage of the refractory above it to your desired baking temp. Might be quite a lot.
I mention this as I’ve built a number of rocket stoves and recently made one with thick wall pipe. The idea being that once heated it’ll retain temp better. It does, but man was I surprised by how long it takes to heat up fully. So not sure if there’s any applicability for you application, but just thought I’d throw it out there.