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Post by Deleted on Oct 20, 2014 3:03:19 GMT -8
Vermiculite and perlite can be used as volumizer,
but their properties are limiting the amount
and may require some protection of the surface from extreme heat.
For temperatures above 800°C consider them as voids,
without any structural support and you are on the safe side.
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Post by ericvw on Oct 20, 2014 15:59:14 GMT -8
Vermiculite and perlite can be used as volumizer, but their properties are limiting the amount and may require some protection of the surface from extreme heat. For temperatures above 800°C consider them as voids, without any structural support and you are on the safe side. Thank you for this insight, Karl, As the appearance of Davideaks kiln-fired riser shows, there was some gooey stuff involved. if perlite melts, and it's present through out the castable mix, would there be any to attempt by the molten perlite to migrate outward from the matrix, not totally unlike explosive steam spalting? I hope not, because I'd really like to include it in this next mix, but I will err to the side of caution!!!! Your sharing is much appreciated, Eric VW |
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Post by Deleted on Oct 21, 2014 4:10:37 GMT -8
Vermiculite may break in smaller pieces and perlite will soften,
but this means only that they cannot provide structural support at high temperatures.
The clay or whatever is used to embed vermiculite or perlite needs to be strong enough
to support the structure alone.
Lots of people are using them successful.
Even something destroyed in a kiln may work well enough in a stove.
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Post by PNW Dave on Oct 26, 2014 2:04:10 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. Thanks again Karl. From my limited research, I was under the impression that vermiculite has already gone through its exfoliation process (quickly heated to the point that it expands, correct?) before it is sold in stores for horticultural uses. I read that the vermiculite furnace is heated to approximately 1,000-1,500°F (540-810°C). Significantly lower than the temperature you mentioned, so, is vermiculite still susceptible to further exfoliation? I have fired a couple vermiculite test bricks to about 1200°F (650°C), but this isn't hot enough to know. Some updates and observations- I now have all four heat riser sections formed, two are perlite and two are vermiculite. The vermiculite mix requires much more of the furnace cement/waterglass/fireclay slip mix, about double what the perlite needs. Also, the vermiculite compacts to about 50% volume when rammed, so you need twice as much as would fill the forms with a loose fill (the perlite compacted about 25-30%), of course this is subjective to how hard you pack it, I tried not to compact it too much. Another notable difference with vermiculite is that when ramming, it can have a harder time adhering to the previous layer if it is packed too hard and the top surface is smoothed over. Fortunately I found this out with a test brick. The first vermiculite riser section I made, I started to run out of the adhesive mix and had to "bulk it up" with more furnace cement and clay slip (I was out of sodium silicate) in order to get the materials moist enough to stick together. Then, I hadn't secured the inner and outer forms well enough and they started to slip apart as I rammed the mix. I might need to remake this one. The second vermiculite riser seems perfect, I used minimal water when misting the vermiculite and sprinkling fireclay and had enough adhesive mix to get the right consistency. I had accidentally left a vermiculite test brick outside overnight and it got rained on. This one had not been fired, only left to dry then heated with a blowtorch until the surface was glowing red, on each side twice. The water softened the brick to a mushy crumbling mess, except for a thin layer on the outer surface that was sufficiently heated and remained solid. So I took a vermiculite test brick that HAD been fired (to about 1200°F) and plunked it into a sink full of water and left it to soak while I went to work. When I removed it from the water a few hours later, it had not softened and still had the same solid sound when tapped with a metal object. So thats a good thing. I just shut off the kiln, firing the second perlite riser to 1300. Looking forward to firing the vermiculite risers tomorrow (today). |
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Post by PNW Dave on Oct 26, 2014 16:47:05 GMT -8
More progress today. While the first vermiculite heat riser section is in the kiln, we prepared the location for the RMH and did some dry fitting. Dug a hole for the base of the core-  Spread a thin layer of multi-purpose sand-  Lined the hole with three layers of heavy duty aluminum foil-  Mixed up a huge batch of "fire clay coated perlite" including failed perlite heat riser sections (the furnace cement and the fire barrier from my original post, not including the riser section that melted in the kiln), leftovers from successful riser sections and new perlite, fire clay and thorough misting of water-  Tamped and leveled the insulating base, then laid a dry fit of the first course of red clay brick-  Then laid the fire brick floor and called it a day-  Feels good to be getting somewhere with this project! |
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Post by PNW Dave on Nov 5, 2014 4:04:09 GMT -8
Well, I've been pretty busy with work the last few days but was able to find time to get the core put together and do a test run. I still need to source one more 30 gallon barrel to set over the riser. The two barrels surrounding the riser will leave a 3-4" gap, which I can alter by building up a taller or shorter taper on the top edge of the riser. The lower barrel has the manifold attached and sealed already. It is a 12"x12" square to 8" round duct, as seen in the pics at the end of the video.
Next will be running the duct into the half-barrel bell and seeing if the dead end bell will be sufficient or if I'll need the chimney to be at the far end of the bench (I hope for the dead end bell to work).
I was pretty impressed with the roar, even with such a small amount of wood and the flames barely even making it into the burn tunnel.
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Post by Daryl on Nov 6, 2014 0:24:27 GMT -8
Wicked. I haven't seen a video yet that showed such a little bit of wood making a roar.
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Post by PNW Dave on Nov 8, 2014 16:10:26 GMT -8
Wicked. I haven't seen a video yet that showed such a little bit of wood making a roar. Right?! Although it wasn't the same after putting on the barrel, due to reduced draft speed. I think my final design will bring back some of that intensity. We'll see. Last night I placed the barrel over the heat riser and clamped it to the lower barrel (both 30 gallon), connected the manifold to three half-barrels and put up an 8' chimney on the far end of the barrels. This does not follow the final design exactly but gave me a rough idea of the performance. The roar was significantly less impressive. Draft was sufficient but it was on the edge of fire creeping up the feed. I might change the feed tube to be made of my perlite or vermiculite heat riser mix. I don't mind patching it up on occasion. As Matt has said in another thread, any mass in the feed is not recommended, it should be insulated. I've noticed that the firebrick splits really absorb heat and stay hot for quite a while. Over about 3 hours of burning a mix of seasoned split firewood and green unsplit left in the rain wood. I got a pretty deep buildup of glowing embers. 2-3 inches deep. I don't think that is optimal. The top of the barrel reached around 550F and the naked half-barrels got to around 220F at the highest spot (the half-barrels weren't level) and about 170F at the lowest. I intend to have each half-barrel "step up" half an inch or so towards the dead end, so heat will tend to accumulate there a little more. Exhaust was clean and was nearing 200f (I think) at the inside wall at the top of the chimney. The exit from the half-barrels wasn't necessarily down low, just an elbow coming out the end of the last barrel. I intend for the exit to be a plunger tube and on the same side as the entrance to the bench. The first barrel will not actually be cut in half, instead a full barrel will be buried to provide a large space accommodating both an inlet as high as possible on the end of the barrel and the exit will be an elbow inside the barrel, plunger tube style, coming out right under the inlet (see pic). After the system cooled I removed the barrel to check on the riser sections, they are holding up perfectly. Tapping on them, they sound "dry and hollow" and feel very light weight. It's all very encouraging, seeing full-scale proof of concept in person for the first time. I just wish I could dedicate more time to the build, but work and life take priority.  |
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Post by PNW Dave on Nov 15, 2014 15:50:21 GMT -8
Here is a video of the test burn described in my previous post. The video also shows the structure I am building to cover the RMH (please excuse the horrendous mess). The main structural part is done, proper roofing is done, I have the insulation and 5/8" type X drywall ready to go up as soon as I have the time. Then the interior walls will be covered in reclaimed pallet boards to make it pretty, we have already broken down 30 pallets but I'm sure we will need more.
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Post by pinhead on Nov 17, 2014 14:01:11 GMT -8
Add a P-Channel to that puppy!
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Post by PNW Dave on Nov 17, 2014 15:40:05 GMT -8
Add a P-Channel to that puppy! Definitely! First I need to cut the firebrick that overhangs the feed and fabricate a section to increase the height of the feed by 3-4 inches. |
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Post by PNW Dave on Nov 26, 2014 18:39:25 GMT -8
Finished the pallet board walls. Dug a hole to half-bury the first barrel in the bench bell. Tilled a trench under the half barrels.
That half-buried full-barrel will have both the hot air input and a plunger tube for cold air exit, on the same end. I hope that the trench under the rest of the bell will help the cooler gases travel towards the exit without too much disruption of the hot layer above.
Slowly but surely this project is moving forward!
Video-
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Post by matthewwalker on Nov 26, 2014 19:07:03 GMT -8
Looking really good there Dave! Can't wait to see it go.
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Post by PNW Dave on Dec 17, 2014 18:19:20 GMT -8
Not much progress recently, been busy with work, then... A wind storm came along and...   So I removed the tree to asses the damage  Supported the roof with a 4x4 "T" and a floor jack, removed the hurricane ties and 2x4 hangers and then jacked up the roof to replace the broken 2x4 with a 4x4. Then lowered the roof onto the new beam. Then replaced the two 2x6 edge cap boards.   Next I need to replace a truss or two and replace a few rows of shingles. Sigh. Then it's back to the RMH, where I'll be fitting the exhaust reheating barrel and connecting it to the bench for a proof of concept run. Which I would have been posting the results of right now if it wasn't for that tree. |
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Post by DCish on Dec 17, 2014 18:59:19 GMT -8
Ouch! ...and glad you weren't there at that moment...
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