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Post by PNW Dave on Oct 8, 2014 14:24:13 GMT -8
David - good stuff! What are your thoughts on using this mix for a core. Seems pretty durable, and much lighter than a mix that uses much more fireclay. I see you've opted to go with firebricks instead. Just easier to build, or other reasons as well? Why didn't you burn out the inner form? To reuse it? Thanks wiscojames! I definitely think it is a viable option for making a core. I've put my little L-feed test stove through some intentional abuse to see how this mix holds up to physical abrasion. Jamming fuel in against the back wall and scraping it around, I've even kicked the fuel into the feed a few times. It is wearing down, to be sure, but I think that should be expected. I will get a pic of its current condition for you (edit: the second or the third time I lit the stove, it was put out with water. I didn't want that to happen, but it was done. Surely that had a negative effect on the strength). I plan to make a batch of patching material, which will be the same thing except I'll first sift out all the largest perlite particles, and then kick fuel into the feed and see how it holds up. My mix does seem very durable for its weight, although the heat riser sections have almost half of the furnace cement and water glass mix as the little stove. Of course they won't have to withstand physical abrasion. I will probably weigh the next riser section I make before/after drying. I've opted to use fire brick for the core for a few reasons. The obvious one, overall durability and resistance to abrasion. Also to allow for trying out various core configurations, I will loose fill and lightly pack my "fire clay coated perlite" (no furnace cement or water glass) into the space between fire brick and clay brick. Then I can just dig out the perlite, reconfigure the fire bricks, and put the perlite back in. I will definitely try inducing a vortex in the riser by having the burn tunnel enter the heat riser off centered. I didn't burn out the inner form because I reuse it. The outer diameter of the inner form is tapered from 8.25" to 8.75". To taper the cardboard tube, I cut 16 slits with a 1/16" cutoff wheel on an angle grinder then taped around the circumference. 4 cuts almost the full length, 4 cuts a little shorter and 8 cuts even shorter. Then wrapped sheet metal around it and trimmed the edges. I put two screws through the from the inside and cut them off flush with the outer face. So the inner form is constructed, from the outside in, wax paper, sheet metal, tapered sonotube form, another tapered sonotube form made even smaller. This gives pretty good strength to resist ramming the perlite mix, and it's modular so I can easily take it apart if needed. It's just too much work and waste to remake every time.
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Post by PNW Dave on Oct 13, 2014 15:10:01 GMT -8
Here are a couple pictures of the wear inside the little test stove- Looking through the feed at the back wall- Looking down the heat riser at the back wall-
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Post by ericvw on Oct 13, 2014 18:18:21 GMT -8
Ahhhhhh, water poured into young testbed shows premature wear. Not cool! Nah, maybe not related at all! What's your next move? Eric VW
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Post by PNW Dave on Oct 13, 2014 21:46:00 GMT -8
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Post by PNW Dave on Oct 15, 2014 0:10:02 GMT -8
I fired up the kiln for my first time today! I have the first heat riser section in there, it has almost hit 1850F and I have an 06 kiln sitter in so it.... *flinches* It literally just now clicked off. HA! I also had an 06 cone and an 08 cone in there as well as a pyrometer for measuring the temperature. Now we just have to wait for it to cool down, I'm really anxious to see if it feels stronger than ever, or if it has become a fragile, crumbling waste. Either way, knowledge is gained. Warming up, this was maybe 600F. You can just see tip of the 06 cone- The 06 cone through the top peephole at about 1250F- Looking through the lower peephole at the heat riser at about 1250F- Pyrometer, just before starting to type this post- 06 cone- And the heat riser at 1850F- FUN!
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Post by PNW Dave on Oct 15, 2014 9:56:51 GMT -8
Awe man!
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Post by pinhead on Oct 15, 2014 10:20:20 GMT -8
Did it melt and slump or just break apart? It's hard to tell from the picture.
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Post by PNW Dave on Oct 15, 2014 11:07:41 GMT -8
Well, I think it slumped. This heat riser section was the first one I made, the mix was wetter than the rest and it developed large cracks along the full height during the initial drying. It appears that it came apart at these cracks, then started to slump. I think that if it didn't have those huge cracks it would have stayed together. The mix did harden and tapping it with a metal object sounds like a large hollow piece of ceramic. I'm still going to fire another one, this time at a lower temp, see how it comes out and maybe apply a hotface of plain clay slip and fire again. Up close, it kind of looks like a rice crispy treat-
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Post by pinhead on Oct 15, 2014 13:18:34 GMT -8
I'd back the temp off a bit; it looks like you melted the perlite!
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Post by ericvw on Oct 15, 2014 15:57:44 GMT -8
Wow! What was the upper limit of the sodium silicate? I thought the gooey looking stuff looked like a previous "liquid state" sorta thing. But perhaps Karl will chime in.... EVW
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Post by Deleted on Oct 16, 2014 4:00:31 GMT -8
The sodium silicate needs enough high alumina clay for chemical marriage. Perlite is not a high temperature material suitable for direct contact with fire in a riser as it softens when it reaches temperatures of 850–900 °C. There schould be an inner layer of something more refractory, eg a high alumina clay and sodium silicate mixture.
If fired in a kiln enough time should be spend in the range of 450°C - 900°C to let all the chemicaly bound water escape without causing damage.
The cracks are likely caused by the furnace cement.
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Post by ericvw on Oct 16, 2014 18:49:37 GMT -8
Oh, he chimed in, didn't he David?! That Karl knows more about everything, than everyone knows about little! Bravo, Karl! (Off topic, what about this Ebola thing, Karl?) D-eaks, are you ready for the geopolymer recipes? I try to follow them, but goes right over my head! At the least, will you opt for the high alumina fire clay? Perhaps lower temps? It's all very exciting, I'm just thinking your kiln is too far from my backyard to help dry out my next castings! Eric VW
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Post by PNW Dave on Oct 18, 2014 12:10:23 GMT -8
The sodium silicate needs enough high alumina clay for chemical marriage. Thanks for the reply Karl, such an incredible wealth of knowledge here! Is Lincoln 60 a high alumina clay? Its composition is shown in the chart on this page- shop.clay-planet.com/rawclay.aspxI read somewhere that Lincoln 60 is not actually "fire clay", now I can't remember where it was written. Perlite is not a high temperature material suitable for direct contact with fire in a riser as it softens when it reaches temperatures of 850–900 °C. Ok, so I have now started to play with Vermiculite. With the same process as the perlite mix, I made a few vermiculite test bricks and dried them in the kiln last night. They came out well, although much more dense. Now I plan to make the bottom two heat riser sections with vermiculite. There schould be an inner layer of something more refractory, eg a high alumina clay and sodium silicate mixture. If fired in a kiln enough time should be spend in the range of 450°C - 900°C to let all the chemicaly bound water escape without causing damage. Perfect, the other night I fired another heat riser section to the middle of that temperature range. Then last night I applied a hot face of sodium silicate/fireclay/vermiculite fines (vermiculite sifted through window screen) and dried it in the kiln at low temp. I think it turned out really well, though it may not be thick enough. The cracks are likely caused by the furnace cement. Hmm, of course I just bought 3 more 1/2 gal tubs online, maybe I can return them to the local store. Although none of my other heat riser sections have had problems, the first one was mixed too wet, miss-handled and dried too fast. The cracks developed before firing. Oh, he chimed in, didn't he David?! That Karl knows more about everything, than everyone knows about little! Bravo, Karl! (Off topic, what about this Ebola thing, Karl?) D-eaks, are you ready for the geopolymer recipes? I try to follow them, but goes right over my head! At the least, will you opt for the high alumina fire clay? Perhaps lower temps? It's all very exciting, I'm just thinking your kiln is too far from my backyard to help dry out my next castings! Eric VW I'm still thinking about trying the simple geopolymer he suggested earlier, 80% calcined fireclay / 10% lye / 10% lime, mixed with water. I would drizzle it over vermiculite while mixing, using the same process as I've been doing. Trying to get just enough green strength to hold together until dried/cured/fired or whatever, but also trying to keep it as light weight and insulating as possible. Too bad about the distance, I'd like to see those next castings!
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Post by Deleted on Oct 19, 2014 2:47:36 GMT -8
The Lincoln clays are at the lower end of alumina content. But if a clay can be considered refractory depends not only on alumina content, as some inpurities may lower the melting point. High alumina clays should have around 40%.
Vermiculite has a higher melting point than perlite and a much higher softening point, but it starts exfoliating at 900-1000 °C.
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Post by ericvw on Oct 19, 2014 15:09:52 GMT -8
So don't add either vermiculite or perlite as a volumizer to insulating refractory? Just trying to extend the 55 lb bag I have towards another pour.... Eric VW
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