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Post by SentencedToBurn on Dec 24, 2016 9:18:11 GMT
Oh crap I didn't realise it was gonna take that long. Yup no worries, I'm in no hurry, I'd rather dry it out properly. Until then I'll probably mortar up the bricks on the sides of this.
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Post by SentencedToBurn on Dec 27, 2016 0:27:24 GMT
While the vermicrete is drying out, getting ready for the walls and the arch over the door. Made the door template, measured up the bricks, the number of them I need ot make the arch, and a few half-bricks for the walls themselves. To chop the bricks I used a masonry disk to make cuts around the outside, then instead of buying a wide chisel, used an old leaf spring, made a sharp edge with a grinder, a single wack with a sledgey and it's split perfectly. Works really well, just did a slight bit of grinding over the middle to smooth out the cut.
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Post by 5leafclover on Dec 30, 2016 12:17:46 GMT
Loving your build Chas. Something very fresh about the design, and I'm a teensy bit envious of your steel working abilities.
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Post by SentencedToBurn on Jan 1, 2017 10:15:32 GMT
Haha thanks mate. Welding up thick stuff like this is easy, when it comes time to dealing with something like 0.8mm sheet then I can only spot it.
It's been super sunny and hot here, so I think the vermicrete block is plenty dry now, going to do the base and hopefully the first 5 layers of the wall tomorrow. Must remember to add the hinges as I go, they're meant to be concreted in.
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Post by SentencedToBurn on Jan 5, 2017 6:56:10 GMT
So we've had some real sunny days (apart from a few when I had to plastic everything up), so I decided it was time to do the walls, and the arch. All went pretty well, given it's my first time doing any kind of brick work. I screwed up the spacing a few times but managed to keep all my stuffups in the back left corner where you won't see it. The hinges measurements were spot on so the doors went on sweet. And the arch didn't come out too bad even though the width of the doorway was a bit wider than I initially estimated (hence the gaps around the template. I never accounted for the mortar, which I'm sure is the noobiest mistake anyone can make, but something to learn for next time. Still, so far so good. The roof is going to be the real challenge, at least here I've already learnt at least a few basic things.
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Post by downunderdave on Jan 5, 2017 22:28:16 GMT
Barrel ovens require either buttressing or bracing of the side walls to prevent their collapse. Because a dome is self supporting its popularity over the centuries is testament to its preference as a home oven. For baking bread the barrel oven is more suitable because for the given floor area you can load in more bread, being able to place loaves closer to the perimeter. Having a very high vault increases the volume of the oven, but does not increase floor area, so you may find your fuel consumption will be higher than if you had a lower side walls. This shouldn't be too much of a problem because your oven is small. For cooking pizzas though, the vault being so far away from the pizza, will probably result in difficulty cooking the top quickly. The low dome neapolitan ovens of Naples are an example of the opposite of your oven design, where their objective is to cook the pizzas extremely quickly (around 90 sec) There are quite a lot of barrel oven builds at community.fornobravo.com well worth a look at to address the buttressing/bracing issues of barrel ovens. ps. hope you used a refractory mortar or home brew rather than a portland cement/sand mix.
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Post by SentencedToBurn on Jan 5, 2017 23:50:42 GMT
Thanks for the info Dave, just looking through that forum now.
And yup, I actually ended up buying fire mortar, it ended up being just slightly more expensive to buy it premixed rather than getting all components myself and mixing them etc.
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Post by SentencedToBurn on Jan 15, 2017 1:54:35 GMT
Ok, after reading on the barrel ovens (thanks Dave), figured I definitely need reinforcement if I want to be confident that the oven will stand strong. I made a basic frame which I'll cover with some 1.5mm sheet next weekend, the top part is the base for the chimney. The frame itself is the bottom part where the bricks will lay on top. I'll have to cut some wedges into bricks to make them fit the wall and the top of the roof too. Also calculated the expansion rate of the steel frame (2.3mm increase when going from 20C to 400C, although I don't think it'll get that hot), so won't be cementing the bricks which will sit on the wall, but will just have them resting on the edge (hence me cutting a wedge into bricks). So when the frame expands, the bottom will just lift off slightly without cracking anything. Will post next set of pics in a few weeks it'll be pretty clear on what I'm doing I think.
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Post by downunderdave on Jan 15, 2017 3:40:08 GMT
The main problems with steel in kilns and ovens are twofold. Firstly the huge difference in conductivity between steel and refractory means that the steel will expand quite rapidly against the refractory causing greater expansion and stress. More so if the steel is on the inside and the refractory surrounding it. Some people think that because steel and concrete are used in conjunction with one another in heavy construction and because their expansion is similar the same must hold true for ovens and kilns. In the case of a concrete bridge for example, at ambient temperature the concrete surrounding the steel reinforcement will be at the same temperature and any temperature change will be so slow and minimal that the different thermal conductivities of the two materials does not create a problem. This is not so with a kiln or oven where the temperature rise may be over 300 C/ hr. Secondly steel corrodes and the rate of corrosion is accelerated by heat, so unless stainless is used there will be problems down the track. I have owned and operated many kilns and nearly all of the failures have related to corroding steel. Kilns are subject to higher temperatures and corrosive gasses from clay changing states, but the same principle applies with ovens. Just be aware of all of this as you "design and build as you go"
Also, if you use an updraft system for your flue, much of your heat will go straight out the chimney as the flame rushes straight for the flue. The beauty of a cross draft system is that the flame rises to the roof, heating it, before being drawn down and sideways exiting out the flue.
Looking forward to seeing your progress.
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Post by SentencedToBurn on Jan 15, 2017 19:55:13 GMT
The main problems with steel in kilns and ovens are twofold. Firstly the huge difference in conductivity between steel and refractory means that the steel will expand quite rapidly against the refractory causing greater expansion and stress. More so if the steel is on the inside and the refractory surrounding it. Some people think that because steel and concrete are used in conjunction with one another in heavy construction and because their expansion is similar the same must hold true for ovens and kilns. In the case of a concrete bridge for example, at ambient temperature the concrete surrounding the steel reinforcement will be at the same temperature and any temperature change will be so slow and minimal that the different thermal conductivities of the two materials does not create a problem. This is not so with a kiln or oven where the temperature rise may be over 300 C/ hr. Secondly steel corrodes and the rate of corrosion is accelerated by heat, so unless stainless is used there will be problems down the track. I have owned and operated many kilns and nearly all of the failures have related to corroding steel. Kilns are subject to higher temperatures and corrosive gasses from clay changing states, but the same principle applies with ovens. Just be aware of all of this as you "design and build as you go" Also, if you use an updraft system for your flue, much of your heat will go straight out the chimney as the flame rushes straight for the flue. The beauty of a cross draft system is that the flame rises to the roof, heating it, before being drawn down and sideways exiting out the flue. Looking forward to seeing your progress. Thanks Dave, this morning I've gone and bought an anticorrosion temp resistant spray I used on exhaust headers a few times in the past. That stuff is "meant" to work to 800C, and in the past when I used this same spray it didnt burn up or flake off for years, although I don't how how hot the headers got. So I'm figuring if I coat the hell out of the frame in this spray it'll prolong the life of the roof. I'll try fill as much of it on the inside of the box section as well. I am also a bit concerned about the expansion rate so hoping that my plan of not connecting the roof bricks to wall (but only having them rest on them) will prevent any expansion fracturing. But will see when I get to the actual build. Also I've looked up the cross flue design, makes much better sense, Lucky the frame I'm using allows me to move it forward quite a bit, so I don't need to redesign anything. Great suggestion thanks, because initially I was just gonna chuck the chimney right in the middle and that ofcourse wouldve reduced the heat absorbtion.
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Post by SentencedToBurn on Jan 22, 2017 5:04:58 GMT
Decided to use box section instead of sheet steel to make all supports for the bricks, and sorted out the chimney area on the front of the roof. Will add a few more brackets that sit on the wall and then will coat it with the heat resistent spray to at least give some corrosion protection.
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Post by downunderdave on Jan 22, 2017 19:52:03 GMT
This set up is still a simple updraft oven. It will work, but you'll have flames coming out the chimney. To create a cross flow design you need to place the chimney or flue in front of your arch. The oven would then operate much better.
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Post by SentencedToBurn on Jan 23, 2017 2:42:17 GMT
This set up is still a simple updraft oven. It will work, but you'll have flames coming out the chimney. To create a cross flow design you need to place the chimney or flue in front of your arch. The oven would then operate much better. Oh crap, ok, because I moved the chimney as far forward as I could within the original roof frame, i missed the part about it being infront of the arch. I dont think I'll be able to alter it now since the arch is already build and it's infront of the actual base. My plan is to have the fire right in the very back, so hopefully that'll help heat the bricks up a bit. Also with the chimney made of bricks (I'm planning to do it about 6 bricks high, so that's 115x6=690mm) these bricks will also heat up and transfer some of the heat to the base, if the flames end up going out the chimney.
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Post by SentencedToBurn on Jan 28, 2017 1:33:22 GMT
Have put up the side of the roof today, and did most things I can do without mad brick cutting. I'll let this set, and will then sort out the back wall with the triangular shapes, fill up the gap above the arch (will have to work out how to do it best without making it look crap), and will add a few levels to the chimney. My concern is the frame, I couldn't make it so it's not cemented along the bottom to allow the frame to expand. I did my best not to actually cement the bricks to the frame, which I think mostly worked, but the issue is I think will be whether the expansion of the frame will cause any cracks between the walls and the roof.
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Post by downunderdave on Jan 28, 2017 3:40:11 GMT
If you are worrying about cracks then leaving the structure uninsulated will be a greater contributor to the structure cracking than your steel frame, but firing the oven will reveal these issues for you.
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