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Post by ronyon on Sept 23, 2017 19:07:53 GMT -8
I am using a variation on the "Mat Mix".
No clay, just high temp cement and Perlite.
But according to Paul(Wheaton):
"Perlite starts melting at around 1400. We have lots of perlite glass blobs from risers that had perlite."
I asked him if the perlite risers melted entirely or are they just replete with blobs of perlite glass,but his answer was indirect.
So I'm asking the board, Matt in particular,is perlite still acceptable in the core and riser?
Or is it just a bad idea with what we know at this point?
A brief search of the board shows Peter warning against it in the burn chamber.
Since the riser is hotter still, I would guess he doesn't recommend it there either.
Peter,you often advocate in favor of commercial refractory and against tge home brew stuff,so there might not be a diy product that meets your approval.
Donkey seems to favor cob with burn out material for insulative voids.
Anyone with experience with Perlite in their core or riser, please chime in.
My core is almost done, so no going back but going forward might change things.
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Post by matthewwalker on Sept 23, 2017 21:51:25 GMT -8
I've never had an issue with perlite melting or causing failure. I've never seen melted perlite gobs or runs in any of my stoves. My original perlite/clay riser is still in the big heater and still in use after 5(?) full seasons. I checked it last season, it shows no signs of deterioration. My feeling is that if some perlite is melting away, then it is leaving insulative voids, and in the unlikely event that does happen, I speculate that it only happens on the surface layer. I would not hesitate to use perlite anywhere in a core build.
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Post by ronyon on Sept 24, 2017 6:28:22 GMT -8
Hey,that's great! Thanks for the feed back Mat, I can now proceed with confidence.
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Post by pinhead on Sept 25, 2017 8:45:12 GMT -8
IMHO the "mix" will give you problems long before the perlite, itself.
OTOH, ceramic fiber blanket makes a much better riser than any perlite-clay mix.
To each their own, I suppose.
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Post by Orange on Oct 1, 2017 2:14:27 GMT -8
why don't we use solo perlite, like in the portable rockets?
the safe options are liapor and vermiculite.
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Post by coastalrocketeer on Oct 4, 2017 10:59:36 GMT -8
Loose perlite will work if you have a liner that will stay solid through the extreme heat over time... Otherwise loose perlite will follow gravity...
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Post by coastalrocketeer on Oct 4, 2017 11:30:01 GMT -8
The ceramic fiber blanket and board I've seen is rated to withstand regular use at 2300 or 2600C... It is used in pottery kilns that regularly attain these temps... And doesn't break down until at least 3000C.
You may be thinking of rock wool/roxul insulation.
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Post by drooster on Oct 4, 2017 11:59:54 GMT -8
... ceramic fiber can melt too above 1000C, just like perlite. ... Please do not write outright lies on this board. Unless your post is deleted someone might read it and believe it, and that would be a VERY BAD THING. |
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Post by Orange on Oct 4, 2017 12:39:49 GMT -8
Loose perlite will work if you have a liner that will stay solid through the extreme heat over time... Otherwise loose perlite will follow gravity... sure, all you need a cheap metal liner and pour in the perlite - easy work, great insulation, lightweight, disassemble  |
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Post by Orange on Oct 4, 2017 12:42:41 GMT -8
The ceramic fiber blanket and board I've seen is rated to withstand regular use at 2300 or 2600C... It is used in pottery kilns that regularly attain these temps... And doesn't break down until at least 3000C. You may be thinking of rock wool/roxul insulation. sorry, i was just looking at the first type on wikipedia, AES wool. other types can take the heat. |
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Post by pinhead on Oct 5, 2017 8:09:25 GMT -8
Loose perlite will work if you have a liner that will stay solid through the extreme heat over time... Otherwise loose perlite will follow gravity... sure, all you need a cheap metal liner and pour in the perlite - easy work, great insulation, lightweight, disassemble False. Metal is doomed in this configuration. It doesn't matter how thick or what grade - even if using stainless. It will be quickly destroyed and let your loose perlite pour into the stove. Been there, done that. There are many threads with numerous examples of that very failure. The low carbon environment of the heat riser combined with high oxygen and high temperatures simply steals the carbon out of the metal - which becomes brittle and flakes away. You should ignore what the youtube rocket stove builders tell you about this. METAL IS DOOMED. |
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Post by coastalrocketeer on Oct 5, 2017 9:35:41 GMT -8
Basically, anyone who is having a metal inner liner in the core, surviving more than a season or two of burns, is NOT achieving the efficient, extremely high heat combustion that is the MOST very basic trait common to all iterations of the "rocket" combustion core.
The other way to look at it, is that anyone who is building a REAL rocket, with a combustion core that is metal lined, is building something with a short service life, and effectively disposable... The waste of disposable culture is something most of us are trying to move away from... But if your stoves are made entirely from items already in the waste stream, I suppose the environmental karma is rather neutral in the thing having a limited life.
You CAN however, use metal as forms that burn away over time assuming the insulated material around them holds it's shape after the metal disintegrates.
This presents issues with some lower heat areas not completely disintegrating, and how to deal with larger chunks of metal that may fall to areas where they are not easily removed, but block proper gas flow through the stove.
Much better to use cardboard painted with wax, or some other combustible or otherwise removable form material combination to make forms.
Hot face interior liners that you need to depend upon to hold insulation in place long term HAVE to be made from high temp refractory materials.
Preferably lightweight insulating ones.
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Post by Orange on Oct 5, 2017 11:32:18 GMT -8
I wasn't precise - metal for outer lining of heat riser, just to hold perlite.
The riser is of course made out of refractory. Top of the riser is sealed so gases do not enter perlite section.
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Post by coastalrocketeer on Oct 6, 2017 0:50:54 GMT -8
That could certainly work... Although you would need something like 6 or more inches of perlite to match the 1" ceramic fiber blanket inside a 10" metal stove pipe held by just being slightly over the required circumference in width, that another forum member came up with. I can't remember who... But it was genius.
Your idea will certainly work... The difficulty of it versus other methods may present some hands on learning, and possible new invention of method/material/process that solves challenges with it and creates a whole new way to make rocket stoves.
I did not mean to discourage you.
I will say, that in looking at loose fill myself, I determined that making a refractory liner that would stand up to the heat was an issue. I decided it's best place was as a fairly insulative, moisture resistant, and air permeable "floor" under my whole core and heat bell design, and around the core as additional insulation.
My core design will most likely be based on Matt Walker's insulating ceramic fiberboard Jtube core, feeding to a bell chamber with a large (open) tank of water enclosed on 5 sides by it... Coiled heat exchanger copper piping in this tank will collect heat for a closed loop hydronic system with radiators and/or in floor piping.
The exterior of the tank, and bell chamber housing it, will be insulated with rock wool or other non combustible insulation, and the shed around it will be constructed entirely of non combustibles.
A long feed will allow bundles of sticks tied with jute twine to be stacked 6' high for (hopefully 3-4 hour burns) capped at the top with a hinged lid on a chain so that any flash of hot gasses that may occur is not near hands or face... The air intake will not be down the feed tube (which will be capped), but straight in line with the burn tunnel.
An added safety on top of it being an open tank hot water system, will be a pair of floats that close the intake of the rocket core, and the exhaust of the bell if water level drops below tops of heat exchange coils.
This also prevents an uninitiated user from firing up the stove if the "heat ballast" water is not present.
[That's my plan, which will probably take 1k in total including building the shed, for everything outside the house, unless I can scavenge more of the materials. Already have metal roofing and siding for shed.
Planning on starting with buying Matt's core plans and ceramic fiber board from a local vendor he referred me to. Going to experiment with the basic fiber board core design and my intended modification sans water and bell as soon as I get those two items.
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Post by pinhead on Oct 6, 2017 5:49:48 GMT -8
A long feed will allow bundles of sticks tied with jute twine to be stacked 6' high for (hopefully 3-4 hour burns) capped at the top with a hinged lid on a chain so that any flash of hot gasses that may occur is not near hands or face... The air intake will not be down the feed tube (which will be capped), but straight in line with the burn tunnel. I hate to be the bringer of bad news, but this won't work. What ends up happening is the low velocity inside the vertical feed tube allows convective heat to enter the tube, dissipating heat and burning the fuel in a low-oxygen environment. It will be smokey and unmanageable. There have been various examples posted over the years but I can't seem to locate the threads right now. In my own personal experience, even having a "chamber" for a clean-out at the base of the feed tube was dubious unless it was completely filled as to make the classic J shape. |
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