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Post by erikweaver on Aug 13, 2015 18:47:20 GMT -8
I know the tolerances are tight in Peter's batch box, but I'm not certain exactly how tight. I'm wondering if I really have to cut fire brick to fit exactly? My local fire brick measure 2.25 x 4.5 x 9.0 inches, and the splits are 1.25 inches thick.
I'm planning a 6-inch batch box, and I have recorded these as the given dimensions:
Width= 8-10/16" ( = 8.625 inches) Height= 12-15/16 ( = 12.9375 inches) Depth= 17-4/16" ( = 17.25 inches)
Dividing by 4.5 (the width of my fire brick, and half the length), gives:
Width= 8-10/16" ( = 8.625 inches) / 4.5 = 1.916666667 Height= 12-15/16 ( = 12.9375 inches) / 4.5 = 2.875 Depth= 17-4/16" ( = 17.25 inches) / 4.5 = 3.833333333
In modular dimensions (of my fire brick) do you think the following would be close enough?:
Width= 8-10/16" ( = 8.625 inches) ==> 8.0 inches
1. That's 0.625" more narrow, so I can bridge across the top ("roof") with a full brick for the top, and have a 5/16" overlap on both sides (just over 1/4").
2. Alternately, could I slightly in-set the top course of the side walls, so that I am able to increase that overlap to become 1/2" on both sides?
3. Second alternate, would be to raise the "roof" by 2.5" by keeping to the 8.625 width, then setting a fire brick split on it's side along the top of the third course, and using that as an overlap/ledge, upon which to place bridge splits to form the roof on top. (This seems like a worse option than in-setting the third course only 3/16" on each side.)
Height= 12-15/16 ( = 12.9375 inches) ==> 13.5 inches That's three full courses, 0.5625 inches taller.
Depth= 17-4/16" ( = 17.25 inches) ==> 18.0 inches The length of two full brick are 0.75 inches deeper; from what I've read that should be fine.
Overall, this would be slightly tall and slightly deeper, but a little more narrow. Not counting the angled bricks at the bottom, that changes the volume:
Original vol. = 8.625 x 12.9375 x 17.25 = 1924.857421875 cu.in. Proposed vol. = 8.000 x 13.5000 x 18.00 = 1944.00 cubic inches.
Second question, regarding the P-Channel:
Has anyone tried making the opening into the fire box for the P-Channel out of fire brick, instead of square steel tubing?
I am wondering if I could make the back wall (the one that separates the batch box from the fire riser) out of two or three layers of fire brick splits, so that I could cut the "trip wire" over-hang into the fire-box-side brick, and form the air-way for the P-Channel out of the remaining fire brick.
Thanks in advance for your thoughts!
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Post by peterberg on Aug 14, 2015 1:41:27 GMT -8
I know the tolerances are tight in Peter's batch box, but I'm not certain exactly how tight. I'm wondering if I really have to cut fire brick to fit exactly? No, that isn't necessary. In reality, the dimensions are a logically follow-up on the size of the bricks I was using. In Poland the fire bricks are somewhat larger as compared to the Netherlands. So the best way to implement a core was building a slightly larger one of 6.5" system size in order to fit the bricks. But all the dimensions were within a plus and minus tolerance of a couple of percentages. So when you want to make the width 0.6" narrower because it's better suited to your bricks please go ahead. A set-in at the top of the firebox walls wouldn't influence the dimensions much so that could be done as well. Actually I would prefer that because the top 2" of the firebox aren't very useful besides the fact it's better not to fill it up right to the top. So, there is some allowance in the dimensions, something like half an inch plus and minus. Your proposed firebox is slightly narrower but also slightly higher, should be no problem. Try to use as much uncut bricks as you can as long as the deviation is still well within one inch. The standard p-channel is done in rectangle duct as wide or slightly wider than the port. But it can be made in "firebrick art" as well, has been done before. The most obvious downside is that the secundary air isn't heated up as much and also a lot slower.
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Post by erikweaver on Aug 14, 2015 3:26:23 GMT -8
Thank you very much Peter! Back to the sketch pad with confidence Very nice to hear that a bit of an in-set of the top course would be beneficial. I'll go with that design element for certain, as it allows the "roof" to be safely supported by several 9" bridging fire bricks. I can see I'll have to think a bit more about the P-Channel. With regard to the P-Channel, I am considering a combined modification, that has the entry into the fire box carved into the fire brick, and has a straight piece of square steel tubing fitted into that (and running along the top of the fire box "roof" as your diagrams show). That might at least help bring the temperature up a little more. I doubt I can do much about the slower velocity around a fire brick "trip wire" area, versus the steel tubing; given my ham-fisted "carving" with a diagonal grinder, and the fact that fire brick offers more friction to the air than does steel. Just thinking out loud, there is the laminar effect of the air along the face of the fire brick.... So perhaps the friction isn't the primary concern? Is carving the thin lip in the fire brick, to approximate the hanging lip/edge of the P-Channel, the tricky part? I'm just taking a gut feel guess, not based upon anything I can logically point to... but it seems that a longer smooth edge (something like an air plane wing, for example) leading up to the edge of the lip/protrusion of the P-Channel would not create as much turbulence/venturi effect, as compared to a sharper lip/edge sticking right in the middle of the airway. But the smoother edge would take accidental bumps from stoking fire wood, whereas the square edge, unless very wide (along the wide axis of the fire box) would break off more easily, largely ruining the effect. Also, the smoother edge would be easier to make using an angle grinder and concrete cutting wheel. Or: Just seat the barrel more effectively! But having said all that, after reviewing the thread images again last night, I think your solution may be easier as well as more effective. (No surprise to you, I'm guessing, lol.) I just have to design the barrel seating-seal in such a way that I can get right at the square tubing easily. My biggest concern is in replacement of this piece of steel tubing, which I want to be as easy as possible. I should be able to figure that out. I'll "think on that" as we say here in the Ozarks Once again, thanks!
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Post by peterberg on Aug 14, 2015 11:30:15 GMT -8
There are other solutions to replace the p-channel, like the S-portal and Matt's pre-port tube. Those are not as well tested as the p-channel and not as documented. Those are easier to replace but more complicated to make, though.
There's another solution available, commonly called the floor channel. It isn't thoroughly tested yet but documentation is very straightforward. This is doing more or less the same thing as the others and do consist of one straight piece of rectangle duct. About the same size as the p-channel, resting on the firebox floor between the slanted sides and stretching from the front to the port in the rear wall. It doesn't require another port size and it is *very* easy to replace. The only down side is that you have to check the ashes at the back end regularly. Of course it will burn out, stainless will hold for a couple of years. So it would be good to keep some spare parts.
The idea of the floor channel is old, from the rocket cooking stove and defined by Larry Winiarski in the eighties. I planned to test several shapes and sizes of this in the batch box rocket, sometime during autumn.
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Post by satamax on Aug 14, 2015 23:30:00 GMT -8
Erik, Peter has summed it all up. I don't know if you remember the tricks used in the range retrofit. www.permies.com/forums/posts/list/35569#344806www.permies.com/forums/posts/list/35569#344811www.permies.com/forums/posts/list/35569#344815Here you have the three posts in a row with the details of the firebox end, P channel etc. The P channel on that was easy the only part which needs to be the right size, is the "mouth" of the P channel, the rest can be bigger. So making a descending piece as i have done. Only three sides bent in a vice. it was pish easy to make. And then you could do a brick channel on top of the firebox ceiling with splits or full bricks. or whatever. I gathered the stainless steel from a restaurant fridge. As for the bricks, sometimes it's worth looking a bit further. Like ordering pizza oven slabs, or using pizza stones instead. Well, i can get localy some firebricks slabs 50cmx50cmX5cm thick. Theses would make nice firebox ends. Or ceilings. Stuff like this may be www.amazon.com/Pizzacraft-PC0102-Rectangular-Cordierite-Baking/dp/B005IF2YOWLooks pretty much like proper terra cota. You would have to check. This one drew my eye, tho it's expensive. www.notonthehighstreet.com/bigblueproducts/product/fireclay-pizza-stoneYou could use pizza or baking stones for the top, and end of the firebox. Or even, if lucky three splits for the end of the firebox. Not even having to cut anything. For the ceiling, if done with bricks, and the stove will be monolihic, i wouldn't bother much about cutting a ledge on the bricks. The rest of the stove will hold it, as long as the bearing surface is big enough. Or hold with wire, as i have done. Well, just trying to give you other options. Sometimes, spending 50 bucks to save you hours of headaches is a good ides. Hth. Max.
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Post by ericvw on Aug 15, 2015 4:45:04 GMT -8
erikweaver, can you get a hold of refractory and do a one piece roof, or is that not in your cards? I threw together a dry stacked FB batch in the back yard 2 years ago, and had to shrink some dimensions to utilize the bricks and it worked great- even full of air sucking gaps!!!
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Post by erikweaver on Aug 15, 2015 10:51:06 GMT -8
erikweaver, can you get a hold of refractory and do a one piece roof, or is that not in your cards? I threw together a dry stacked FB batch in the back yard 2 years ago, and had to shrink some dimensions to utilize the bricks and it worked great- even full of air sucking gaps!!! Hi Eric. I've thought about using a refractory pour, but I don't think I'll get around to that this year. Maybe next year, when I have less on my plate. This year I have to prep the area (finish enclosing the porch, with the concrete pad upon which I'll be building this), and I just don't think I'll have the time to want to mess around with pouring a refractory, and even moreso, rigging up something to vibrate the bubbles out.
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Post by erikweaver on Aug 15, 2015 11:31:45 GMT -8
Satamax, thanks for the suggestions. I was thinking I would form my fire brick wall between the fire box and fire riser similar to what you have done. And yes, maybe able to get by with out even cutting fire brick. Which is nice, but it cuts really pretty easy with my angle grinder and masonry wheel (although it does throw a ton of dust in the air doing so!). I've not yet found a fireclay pizza top of a useful size here in the USA. I'll keep looking. Same thing goes for the refractory sleeves. I can find them listed by big corporate whoesale web sites, but I have not yet found someone willing to sell just a few pieces. But I'll keep looking around, and see if I get lucky It is nice to know that you had decent success with your P-Channel. I am playing around with ideas along the lines of those you have suggested in your post. I'm still in the sketch pad phase! Far easier to re-draw my plans 100 times than re-build the real heater twice! lol
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Post by johndepew on Aug 15, 2015 18:04:55 GMT -8
Earlier this year, I was looking at the idea of using ceramic fiber blanket (which I can get locally quite easily) with a silicate rigidizer to make my own ceramic riser sections. I haven't gotten too far into that process, but its an idea worth considering if you can get those materials easier than refractory sleeves.
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Post by erikweaver on Aug 16, 2015 5:57:59 GMT -8
Earlier this year, I was looking at the idea of using ceramic fiber blanket (which I can get locally quite easily) with a silicate rigidizer to make my own ceramic riser sections. I haven't gotten too far into that process, but its an idea worth considering if you can get those materials easier than refractory sleeves. If you end up doing that, I think it would make for an interesting thread, so I hope you keep us all updated. I certainly would like to know how you make them rigid, and how well it holds up during use. Here's my plan, and a couple of questions... I just ordered a roll of ceramic fiber rated at 2300 F. It measures 1 x 24 x 300 inches. ($114 USD found on eBay.) I'll use this to wrap the fire brick split fire riser (shaped to an octagon), and 36-inches tall (four 9" fire brick splits, standing tall): 1. Cut the inside edges of the fire brick splits to a pencil line, approximating the angle for an octagon (360/8= 45/2 = 22.5 degree angle cuts, on each brick). I'll have to see how brittle my fire brick is, and decide how deep to make these 22.5 degree cuts. Off hand, I'm thinking perhaps an inch, which will leave 1/4 inch of uncut brick on the back side. Just kind of guessing that will be strong enough that I won't knock the 1/4" edge apart shaping the brick and building the fire riser. If that breaks too easily I'll only go 1/2" deep for my 22.5 degree cut. 2. The joints I will fill with a 1:1 (fine masonry) sand:fireclay mix, then wrap with bailing wire (similar to Satamax's images, linked to above in his post) to hold them steady while I build each layer. I think that'll hold it in place (anyone think this is a bad idea?). QUESTION 1: Would be wise to mix in some amount of refractory cement to the sand:fireclay mix? Will that better ensure my octagon-shaped fire riser stays intact? Good idea; or more trouble than it is worth? And I may rebuild this the following year, increasing size if it doesn't keep the approx. 1,350 sq.ft. house warm enough, so maybe this makes taking the brick apart more effort than it is worth? 3. Wrap the fire riser with three layers (for 3" total thickness) of the ceramic fiber blanket (rated at 2300 F). The roll I'm buying is 24 inches wide, and the fire riser is 36 inches tall, so I'll alternate the 1-foot cut, top on one layer, and bottom on the next, etc. Each layer will take more material (1" larger radius each wrap) so that approximately (2*pi*r): 1st layer/wrap (8.5" diameter: 6" fire riser + two walls, 1.25" fire brick) = 26.7 = approx. 27 linear inches (circumference). 2nd layer/wrap (10.5" dia.) = 33.0 = approx. 34 lin. in. (circumference). 3rd layer/wrap (12.5" dia) = 39.3 = approx. 40 lin. in. So, 27+34+40 = 101; and 101 x 1.5 = 151.5 lin.in., leaving about half of the ceramic wrap for stuffing cracks here and there, using to help seal the bottom of the barrel, ceramic glass viewing port, etc. Plus, there will be some additional extra ceramic wrap, because the part of the fire riser that is against the back wall of the fire box is not wrapped. This will leave about a 5.5-inch air gap, 2.25-inch along each wall of the barrel (24" barrel dia. less the approx. 12.5" dia. of the fire riser). Really, estimating 2.125" (2-1/8") air gap would be safer, because the barrel is actually just a little smaller diameter than 24-inches. So I think I should have adequate air flow inside the barrel. But I don't think I should try putting on a 4th layer of wrap, because that would reduce the air gap along the walls of the barrel to just over 1-inch (est. 1.25"). QUESTION 2: Is the 5.5" air gap sufficient (est. approx. 2.125" gap along the walls of the barrel, and the insulated fire riser)? Or would I be better off either (a) compressing the 3" thick insulation a little bit, or (b) just using 2" thick ceramic insulation on the fire riser? NOTE: I anticipate a top gap space of approximately 16" above the top of the fire riser, to the interior top of the barrel. 4. The ceramic blanket will be held in place. With what, depends what I find for little expense. Given I do not expect the interior temperatures to be high enough to melt metal, I have a lot of options. I could just tie it together with bailing wire; I could wrap it with chicken wire (which I think is a light-gauge galvanized wire, twisted into roughly octagon square about 1" size); or if I get lucky, I may be able to find a section of 12" duct pipe at a local home surplus store (a ReStore for Habitat for Humanity). Inside the prototype I built last winter (a 6-inch j-style, not a batch box) the 12" dia. cardboard tube I used to hold the perlite:fireclay mix held up reasonably well; while the top part of it did get hot enough to fall apart, much of it held it's shape for a couple months of use. Based on that experience, and from what I remember folks here saying, I'm expecting anything metal I use to hold the ceramic fiber blankets should work fine. Note: I've caught some math errors, if y'all see more, please let me know, lol.
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Post by patamos on Aug 16, 2015 9:51:18 GMT -8
Eric, one thought regarding the floor P channel that Matt has recently applied (derived from Larry's L-feed cook stoves...) is to use firebrick splits as a base for the side walls inset slightly from the sidewalls. Then place a metal plate on top of them to serve as the firebox floor.
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Post by erikweaver on Aug 16, 2015 10:21:16 GMT -8
Eric, one thought regarding the floor P channel that Matt has recently applied (derived from Larry's L-feed cook stoves...) is to use firebrick splits as a base for the side walls inset slightly from the sidewalls. Then place a metal plate on top of them to serve as the firebox floor. That would certainly be easy to implement. I'm thinking using that metal plate to form the "roof" of the fire box (not the floor)... with the high oxygen content flowing along the roof of the fire box, and the lower temperatures, as compared to the fire riser, I'm guessing that metal may last a fairly long time up there? One could then either weld a length of channel iron on top of that plate, or just lay a length of square tubing along, shaped like Peter's air-intake feed.
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Post by peterberg on Aug 16, 2015 11:39:04 GMT -8
Hmmm... Using a steel plate on the floor or as the roof of the firebox will lead to disappointment I'd think. Such a plate will buckle like mad and and will leak dramatically, especially when applied as the firebox ceiling. Using a steel rectangle duct as floor channel would avoid this deformation. patamos, I wasn't aware of Matt having applied a floor channel to his stoves? That is to say, other than as the horizontal duct for his pre-port tube. erik, a 2 inch side gap would be sufficient. Fixing the superwool in place with chickenwire is done earlier, it seems to hold well. Normal hard firebrick splits are sturdy enough, fixing those with bailing wire would be sufficient. Perhaps you'd better not to use fireclay-sand to make the riser leak free. Using air-setting refractory caulk would be ideal and you don't need much.
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Post by erikweaver on Aug 16, 2015 16:39:26 GMT -8
Thank you for clarifying those points, Peter! I'll trash-can the metal fire box "roof" idea And I'll add some refractory caulk to me list of materials to obtain.
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Post by patamos on Aug 19, 2015 9:13:02 GMT -8
Peter, regarding Matt's 'floor channel', i could be using the wrong terminology. Yes i am referring to the horizontal duct for his pre-port tube. As you have also mentioned elsewhere… when he went to the double half risers in his 'riser-less core' the secondary air intake channel very much resembled the lay out of the Larry Winiarski's L-feed cook stoves. I have been building L-feeds by casting the side walls each with a 1/2" ledge to support the metal plate upon which the fuel load sits. But have found this relatively less durable than setting 1.25" splits in the same position. For 4" and 6" L-feed cooking a 1/8" or thicker metal plate holds up well enough to justify its simplicity of replacement. But for the added heat of a batch box set up i cannot say. And am inclined to defer to your more experienced opinion.
Eric, regarding caulking the seams, one technique i have been having success with is mixing sodium silicate with fine sand and enough water to make a medium-thick paste. This can be smeared on by hand with surgical gloves or the like. I've heard Karl mention that so si can start to denature around 900c and potassium silicate closer to 1000c (if i recall correctly). And i cannot say i have subjected my risers to much more than those temps. But so far it has proven to be simple and strong.
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