terry
Junior Member
Posts: 128
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Post by terry on Aug 1, 2015 13:06:33 GMT -8
best if you could screw the mold together. Line every surface with builders plastic, screw it together. Make the mix drier than you might think. Vibrate it and the seemingly dry mix will flow and settle. (I used a jackhammer! A bit overkill but I had it laying around. I placed the mold on a larger board and sat it on a large tyre, and very briefly jackhammered (only two or so seconds) a lump of loose wood on the board. The mix flowed nicely. I suppose if it were TOO dry it might not flow, but you'd be surprised how well a seemingly too dry mix will flow.
Then cover the lot with plastic, cling film, anything. Let it cure itself under the plastic, not 'air dry'.
Unscrew the lot the next day. That is if you wish to re-use the mold I suppose. If not, then yes I would still line it with plastic so it can properly cure and burn the mold out later. Burn it out too early and the escaping steam will no doubt cause cracking. If you do intend to burn it out then by definition it will take *that* much longer for the water to escape the casting before you can heat it.
edit..looks like you casted it before my response. hope it was successful
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Post by exoplasmic on Aug 2, 2015 7:18:28 GMT -8
Thanks for the procedure Terry. I wish I saw it before I casted (cast?). I covered both molds with plastic. But my mistake was that I didn't seal the wood mold for the port (but did in the box top). The wood side of the port had sucked water out of the mix and I noticed that it's friable / a bit crumbly. I can scratch it and dust will come off. The side that touched the plastic on top was rock solid hard. I'll still use it but the good side will face the fire box where wood might bump it. Hopefully the side in the riser will vitrify when I bring it up the full temp. I plan on take both pieces and putting them in my mom's kiln to cure. It's a programable electric kiln. I used a hammer drill with an unbalanced piece of metal in the chuck for vibrator. You are definitely right about the "dry" mix flowing with vibration. Wow. 55 pound bag takes 3.3 quarts of water. I added 3 quarts + 8 ounces or 3.25 quarts, and it seemed too dry. It wasn't. I also miscalculated the volume of the mix. I had to short the fire box top a small bit. It still meets the hieght specs perfectly but doesn't come close to the top of the metal wood stove frame I'm using. www.dropbox.com/s/z80137iw3j603f9/box%20top.jpeg?dl=0
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Post by exoplasmic on Aug 2, 2015 15:12:00 GMT -8
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Post by daniel on Aug 22, 2015 12:31:40 GMT -8
Hi,
I hope I finally got my message to the thread I wanted, the double bells accumulating heat from a batch box. Today I dry cut the batch box according to the base number dimensions list for a 8" (200mm) internal diameter riser. The riser should be 144cm (5' 12/16") - is this from the floor of the firebox? Above the riser there should be the first bell but I am not sure what are the restrictions I should follow as far as the location of the riser the height to the top of the bell and the space around the riser. I understand that for the gases to slow down after passing through the outlet whole there should be a widening of the space a number of times the diameter (don't understand this part) for the gases to have time to rise and not shortcut to the exit to the second bell. I am taking pictures as I go along and videos and will edit a clip at the end. I have to build the heater before the cold comes since I don't have other heating source.
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Post by satamax on Aug 22, 2015 14:17:16 GMT -8
From the floor of the firebox, yes!
A bell CSA (cross sectional area) should be at least 4 times the system size, in this case 8 inches, 8*8*3.1415926/4 so at least four times 50.26 square inches. Upper limit is given by the ISA (internal surface area). IIRC, 11M² for an eight incher, not accounting the floor, is the bell is made of accumulative material. 0,70 times that figure if made out of metal. Gap above teh heat riser, Peter advises at least one foot. You can get by with less. Or with more. You should never go under the CSA in ring projection. I'd advise to go for 1.3 CSA as the absolute minimum, when there's size limitations. You can increase the ring projection diameter making the end of you heat riser like a "trumpet bell"
By the way, where do you come from?
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Post by daniel on Aug 23, 2015 8:39:10 GMT -8
I am currently in Romania, I was living in the US, have been following up heaters for years. I participated in a build in Denmark years ago with mr. Flemming and Heiki.
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Post by daniel on Aug 23, 2015 8:49:29 GMT -8
Thank you for that clarification, about the widening of the space after the opening to the bell how wide is optimum if space is not a problem
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Post by satamax on Aug 23, 2015 11:02:47 GMT -8
Daniel, imho, no measurement, would it be width, lengh or height should be under the double of system size, so, 16 inches, for a 8 incher heat riser.
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Post by peterberg on Aug 24, 2015 8:10:13 GMT -8
From the floor of the firebox, yes! A bell CSA (cross sectional area) should be at least 4 times the system size, in this case 8 inches, 8*8*3.1415926/4 so at least four times 50.26 square inches. Upper limit is given by the ISA (internal surface area). IIRC, 11M² for an eight incher, not accounting the floor, is the bell is made of accumulative material. This has come by in another thread, there's a fat chance 11 m2 is too much ISA for an 8" batch box bell.
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Post by satamax on Aug 24, 2015 10:56:41 GMT -8
Yep Peter i remember. Tho, may be with a good chimney. I'm just giving rough numbers. People will have to dig into the forum. I can't do the library work for them!
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Post by exoplasmic on Sept 27, 2015 17:12:55 GMT -8
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Post by exoplasmic on Sept 27, 2015 17:21:47 GMT -8
I am building the bells to have 8m2 inside surface area (excluding floor). Maybe I'll waste some heat out the chimney. But I think it is best to have an excess capacity of hot air rising so that if/when worst a case condition of high winds or slow heat rising it will not cause system to stall and fill my house with smoke.
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Post by peterberg on Sept 27, 2015 23:49:31 GMT -8
With two bells, you are probably just right.
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Post by dustylfc on Sept 29, 2015 6:30:18 GMT -8
Keep the pics coming very interested to see how it turns out
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Post by exoplasmic on Sept 30, 2015 16:00:11 GMT -8
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