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Post by byronc on Nov 14, 2015 4:26:09 GMT -8
I picked up a 25 foot roll of 1 inch thick by 24 inch wide CFB / Ceramic Fiber Blanket insulation for my indoor 6" batch box RMH construction project. With lots of CFB insulation on hand it is tempting to use such to make the heat riser. The local refractory supplier stocks liquid Rigidizer, sold by the gallon USD 40.
To fabricate a rigidized CFB insulated heat riser I'm thinking of rolling the CFB into a tube shape, placed inside a round form of thin steel air return duct, large enough in diameter that the resulting I.D. will be 6.0 ~ 6.5 inches. The CFB is 1 inch thick but I could use two layers making the heat riser walls 2 inches thick, if that would make for better heat riser performance?
Anyone doing something like this and have any recommendations? How much Rigidizer does one "paint" onto the surface of the CFB (inside surface of the heat riser)? Or is it best to completely saturate the CFB with the Rigidizer?
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Post by spacevan on Nov 23, 2015 13:30:30 GMT -8
Hi i am also going this route i have some 1" r2600 ceramic fiber blanket on order. Have you built your heat riser yet? how did it turn out? I am planning on using rigidizer and after it has been fired applying a coat of itc 100. Hope it works.
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Post by byronc on Nov 24, 2015 7:16:00 GMT -8
Nope, not yet. My local refractory supplier only stocks rigidizer spec'd at 1800° F. So I'm looking into possibly using a castable refractory instead, something like kasto-o-lite 30 that has a 3000° F. rating.
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Post by spacevan on Nov 24, 2015 18:40:02 GMT -8
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Post by pinhead on Dec 7, 2015 19:10:17 GMT -8
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Post by tedwiersma on Dec 16, 2015 18:59:50 GMT -8
hi just wondering if you can add some vermiculite to the refractory cement to increase the R value.
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Post by oxbowfarm on Dec 17, 2015 7:31:44 GMT -8
You can, but it reduces the refractory nature of the casting. Perlite and vermiculite have lower melting points than high temperature refractory. In the backyard metal casting world people will build furnaces that have a refractory cement hotface and then back it with lower temp insulating materials. This is more complicated to do for a heat riser because the cross section is much smaller than a furnace body, but the heat stresses are also much smaller. I think high temp refractory is too mass heavy and cost heavy for a heat riser. If you want to spend money on high temp refractory for a heat riser it seems better to just go ahead and buy a high temp insulating mix like Kast-O-lite.
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Post by smokeout on Dec 25, 2015 10:14:48 GMT -8
Hi Everyone, I'm a fairly new rocket builder. I'm still on my first stove. Modified it several times though.
I first tried sand around a steel heat riser. good learning experience .
Next I put in perlite. The stove got hotter than hades, then burned up the perlite. So next I tried vermiculite . I got the same results as the perlite.
After destroying my first heat riser I went with sch 80 stainless steel and used rock wool for insulation. It didn't take long to discover the rock wool doesn't have enough insulating properties to achieve the temps I reached with perlite.
My question is, Will ceramic wool insulate as good as perlite on my SS riser pipe? thanks in advance for info . Just a great place to learn.
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Post by peterberg on Dec 25, 2015 13:00:23 GMT -8
Hi Smokeout, welcome to the boards.
Two inch of perlite with a very little bit of clay will insulate enough to reach freaky high temperatures. But you are in tricky territory now. When insulated properly, the stainless steel won't hold for several seasons. It will suffer from extensive spalling because of the high temperature, high oxygen and low carbon environment. In other words, it will corrode like mad. And by doing so, it will disturb the smooth inside of the riser by disforming badly.
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Post by keithturtle on Dec 25, 2015 17:43:40 GMT -8
And by doing so, it will disturb the smooth inside of the riser by disforming badly. Welcome smokeout. Peterberg has a very diplomatic way of saying "METAL IS DOOMED!" Figgered I'd save you the effort, Max! Actually, I've been focusing on a homemade castable refractory in molds to form the stack. One blend that shows promise is: 1 part portland cement, 1 part fireclay, 2 parts fine mason sand, 3 parts graded perlite [thru an 1/8" mesh screen], enough water to eliminate the voids when tamped. I build an identical stack with Kast-o-lite 2600 true castable refractory for heads-up comparison. www.jjmedina.com.ec/KASTOLITE_26_LI.pdf Still testing Turtle |
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Post by smokeout on Dec 25, 2015 21:41:30 GMT -8
thanks Peterberg and Keithturtle for the advise. I'm thinking I will try adding clay to my old perlite and put it back in and give her a whirl until she melts down. I have been reading like mad on the refractory castings you guys are building. I'll be attempting a casting soon.
i guess I will learn how this forum works as I go. I DK how to follow a thread and then come back later to read more. thanks again guys
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Post by ringoism on Jan 22, 2016 2:42:22 GMT -8
And by doing so, it will disturb the smooth inside of the riser by disforming badly. Welcome smokeout. Peterberg has a very diplomatic way of saying "METAL IS DOOMED!" Figgered I'd save you the effort, Max! Actually, I've been focusing on a homemade castable refractory in molds to form the stack. One blend that shows promise is: 1 part portland cement, 1 part fireclay, 2 parts fine mason sand, 3 parts graded perlite [thru an 1/8" mesh screen], enough water to eliminate the voids when tamped. I build an identical stack with Kast-o-lite 2600 true castable refractory for heads-up comparison. www.jjmedina.com.ec/KASTOLITE_26_LI.pdf Still testing Turtle Peter, a few years back when I was in the conceptual stages of my all-steel portable rocket for the Himalayas, you'd suggested 310-grade SS as a likely high-temp candidate - have you actually tried this subsequently and had it fail? At the time, couldn't find that, and built with what I did find. My 3-1/2" system is pretty regularly running orange-hot in the riser (as of course it should), and lacking any supplemental mass, it is often run many hours on end. My cheapo 25gauge (0.5mm) 404(304?)SS riser, ceramic-wool-wrapped, is in its third season now, and upon removing it for inspection a few days back, I found it completely intact, with only light scaling now on the lower end (which wasn't there earlier). No actual burn-through, but even if it did, I don't think it would matter since the surrounding 3" insulation would more or less seal it - meaning, it's not going to cause trouble till the whole structure collapses, which I imagine would take another few years (likely to test that theory). Meanwhile, for version II, I found some 17ga. 310 sheet here in India that I'll be using for my burn tunnel top and sides. It costs around $10/kilo, which seems pretty feasible. I figure if the more standard grades can last a few years, high-heat-specific ones ought to be capable of at least twice that (by which time all of us tinkerers would have built new stoves anyway)... That said, my riser will now be (square, assembled) 1" ceramic fiber board (found that now, too), maybe wrapped with a 1" layer of the same "supercera" blanket. Since the board has it's own structure, the SS liner is unnecessary. Anyway, vs. 310, 309 is similar (high-chromium, both grades "superior at temps exceeding 1800F (982C)", and 446 can apparently be used at "temps approaching 2000F (1100C)". There are a few proprietary grades (2111HTR, Haynes 214 = 1260C, etc) that are even better. That would seem enough in most cases. I suspect that even grades intended for the 900C range (330, 321, etc) could often work, depending on the particular design/environment/gases/moisture levels present. The moisture content seems sometimes quite important, some grades corroding quickly with any moisture in the oxygen, while in dry environments forming something like a protective film. Metallurgy is not my strong suit, incidentally. There's just a ton of stuff out there, though, and it seems hard to imagine that one of them wouldn't work long-term in a rocket-stove environment. AtlanticStainless.com claims that "no order is too small" which would seem to suit DIY project folks. -Eric |
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Post by ringoism on Jan 22, 2016 3:09:36 GMT -8
I went with sch 80 stainless steel and used rock wool for insulation. It didn't take long to discover the rock wool doesn't have enough insulating properties to achieve the temps I reached with perlite. My question is, Will ceramic wool insulate as good as perlite on my SS riser pipe? thanks in advance for info . Just a great place to learn. One additional note is that schedule 80 pipe is going to have a lot of wall thickness. Mass is one issue, since it's going to take a long time to heat up and thus for the stove to be optimized re: efficiency / emissions - maybe part of the reason you weren't reaching the same temps? But there's another thing: I seem to remember reading something along metallurgical lines where high-temp scaling actually INCREASED with thickness, I think because the differences in temp across the cross-section of the metal exacerbated the issue (?). As mentioned, my standard-grade SS riser liner is only 0.5mm thick, and after three years would seem to have a good amount of life left in it. And 0.5mm (25ga) is plenty strong enough to hold up a couple kilos of ceramic blanket. Possibly one of those things where "bigger" (thicker) isn't better. -Eric |
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Post by peterberg on Jan 22, 2016 5:49:46 GMT -8
Peter, a few years back when I was in the conceptual stages of my all-steel portable rocket for the Himalayas, you'd suggested 310-grade SS as a likely high-temp candidate - have you actually tried this subsequently and had it fail? No I didn't have the opportunity do try it. What I did in an early stage of testing using a bog standard stainless steel pipe as the riser with 2"of loose fill vermiculite around it. The thing was used occasionally over the span of 3 years and during a very long session the riser collapsed and the thing started smoking like a heretic. (That last part is a Dutch expression of something which is smoking to the extreme. Something to do with death sentences to the stake, no doubt.) That particular pipe was a SS 304 part, same thickness as yours. It was used for a 6" batch box, by the way, which is quite different temperature-wise as compared to a tiny J-tube. |
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