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Post by pyrolyse on Jan 9, 2017 8:19:50 GMT -8
Which parts of a Batch Rocket absolutely need to made from refractory materials and which do not?
I am aware that the fire chamber and heat riser preferably should be made of refractory materials, but is this because we want a higher temperature or because of durability? Or both?
Also, how about bells? Does the first layer of bricks closest to the actually fire need to be refractory? Or is regular brick OK? Also, does this have to do with the placement of the bell(s)?
Is it more critical to use refractory if the bell is directly above the heat riser? Is it less critical if the bell is fx on the side, like a heated bench etc?
I know, that´s a lot of questions. I just want to be more knowledgeable about this area, and I have seen conflicting things around the forum.
Pyrolyse
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Post by drooster on Jan 9, 2017 9:34:58 GMT -8
Which parts of a Batch Rocket absolutely need to made from refractory materials and which do not? I am aware that the fire chamber and heat riser preferably should be made of refractory materials, but is this because we want a higher temperature or because of durability? Or both? Surely it is more about withstanding than wanting? If the higher the temperature the more complete the burn, and the more efficient the heat from fuel is ... then very high temperatures will destroy everything that is not refractory quality. |
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Post by peterberg on Jan 9, 2017 10:52:19 GMT -8
The core, i.e. firebox and riser, should be made out of high heat resistance material. It isn't uncommon that refractory material which is specced 1200º C as maximum service temperature becomes red hot every time the heater is fired, especially the lower half of the riser.
In bells, everything that's above the level of the riser end should be refractory material as well. To be sure, I would extend the fire bricks two or three courses lower than the riser end. The rest of the bell could be built out of normal bricks. I know of several personally that are built out of unfired loam bricks for the lower parts and is staying whole. There's no need to use fire bricks or other refractory close to the firebox as long it is out of the path of the hottest gases.
Directly above the riser is answered above. Every other bell or bench or whatever can be built out of normal red bricks, single skin or double skin if you wish to do so. Normal bricks are fired at 1000º C, half of that figure is concerned to be a safe limit.
In order to avoid cracks it would be best to build the whole of the heater as double skin OR a thick layer of cob plaster with lots of straw in the first layer.
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Post by pyrolyse on Jan 9, 2017 16:18:06 GMT -8
Thanks for the in depth answers, Peter.  |
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Post by pyrolyse on Jan 12, 2017 11:16:04 GMT -8
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Post by peterberg on Jan 12, 2017 12:27:39 GMT -8
The specs looks good, but most of the time they'll crack because of expanding irregularly. You could avoid cracks by making one, just one slit, lengthwise, that should be enough to keep is as a whole. That 4 cm thickness is a hindrance, it'll make the riser high mass but once heated up there's no difference. But for the rest: specs are good, surrounded by insulation it would go like... a rocket?
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Post by pyrolyse on Jan 12, 2017 12:58:30 GMT -8
We certaibly do want it to go like a rocket! The reason for me asking is that I'm looking for alternatives to IFB bricks, because they seem to be virtually non-existant on the Danish market (and importing will probably be very costly). Could ceramic fiber insulation held in place by something work? Is that the same as the Superwool you frequently refer to, Peter, or is that some other material? |
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Post by peterberg on Jan 12, 2017 13:40:55 GMT -8
Ceramic fibre insulation is the form of a blanket is the superwool I am referring to. It's a product of Morgan Thermal Ceramics. The difficulty here is that the material isn't rigid by itself so it could release tiny fibres while in use, which is irritating for eyes and lungs.
So that makes the refractory tubes a realistic alternative, 250 DKK is equevalent to 33.62 Euros. Not really cheap but good enough when the stuff is staying in one piece. The only thing you can do is buy a couple, use it in a heater core and check again after a heating season. Don't forget to apply that slit I mentioned, or even better, do one with and another without. The same firm is also selling superwool or something like that.
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Post by pyrolyse on Jan 12, 2017 15:03:02 GMT -8
How about a homemade riser from vermiculite, clay, water and refractory cement, would that be more ideal? And if so, should it be as thin as possible or are the insulating properties of vermiculite good enough for a relatively thick riser?
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Post by peterberg on Jan 13, 2017 2:24:01 GMT -8
Vermiculite will melt in the riser I'm afraid, especially in the lower part. So this shouldn't be a permanent solution. Personally, I'll stay away from home concoctions and buy refractory castable which is specifically designed for this sort of goal.
Recently I got my hands on some Gouda Refractories Golite 135. Specced to 1350º C maximum service temperature and density after drying at 110º C of 1400 kg/m³, which is about half of normal concrete. Worked remarkably well without additional insulation.
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Post by pyrolyse on Jan 13, 2017 4:37:54 GMT -8
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Post by peterberg on Jan 13, 2017 7:34:39 GMT -8
It looks like something similar as far as temperature goes. But is it as light as what I mentioned? Støbemasse, could that be translated as ramming mass or is it casting mass?
Price would be around €78.- per 25 kg bucket, quite steep!
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Post by pyrolyse on Jan 13, 2017 8:33:11 GMT -8
Yeah, that´ s the problem, there is no information about the weight of the material. "ildfast støbemasse" is the Danish equivalent of "castable refractory". I think I´ll ditch that product, because I just found a Danish refractory company that casts both pre-made refractory elements, custom refractory elements and has IFB bricks and normal dense firebricks: www.hasle-refractories.dk/ . |
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