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Post by mmcc73 on Dec 16, 2014 10:21:05 GMT -8
Hi - I'm planning to make a cast core and riser for a rocket stove heater for a workshop. I'm going to be roughly following what Matt Walker set out in his videos for making the casting material, but I'll be using Vermiculite instead of Perlite. I live near a McMaster-Carr warehouse, and they sell vermiculite in two "textures" - fine (like grains of sand) and medium (like grains of rice). The fine grade is listed as having more absorbency per unit volume.
Any thoughts on which would be more appropriate for this application?
Thanks, Clark
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Post by pinhead on Dec 16, 2014 10:58:02 GMT -8
IMO it doesn't make much of a difference - the measured volume will be the same. The only difference you may see is in the surface texture.
Again, IMO.
The biggest disadvantage I see in using vermiculite vs perlite is its compressibility. This must be taken into account when packing/pouring the mix.
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Post by PNW Dave on Dec 17, 2014 11:58:23 GMT -8
I think you should get the larger particle size
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Post by DCish on Dec 17, 2014 13:27:49 GMT -8
Ditto to both pinhead and Dave. As I understand it, vermiculite takes on more water, so you have to adjust your mix to account for that. Since it crushes more easily, you lose some of the insulating value. And at the end of the build you would be having to drive the extra moisture off. So while perlite and vermiculite may be comparable as dry fill, once you start mixing and manipulating, that changes.
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Post by PNW Dave on Dec 17, 2014 14:51:21 GMT -8
I agree about the compressibility...
When making my heat riser sections, I found that the vermiculite mix I used compacted to about 50% volume when rammed. So I needed to make at least double the amount measured by loose filling the form (lightly packed).
I also noticed that vermiculite is more susceptible to "layering". Meaning that when ramming, the mix won't adhere well to the previous layer and during/after drying it might separate easily at these layers. This is because the vermiculite will pack down to form a very smooth surface unlike perlite which maintains a rougher surface. To combat this, I added smaller amounts at a time, rammed less-hard and not as thoroughly, compared to ramming a perlite mix. In other words, lightly ram only a little at a time, instead of pouring in a lot and trying to pack it in hard. I hope this makes sense.
The perlite sections needed about 25-30% more than the loose fill measurement.
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Post by wiscojames on Dec 17, 2014 16:18:51 GMT -8
Using what Matt and Dave have shown us, I made a riser using an 8" cardboard footing form inside of a small oil drum. I thought that I would try to make it lighter by using something along the lines of Dave's perlite and waterglass mix. Of course, it ended up being a little different, by necessity and experimentation. It was something like 15 gallons perlite (rammed to ~12 gal) + 2 gallons fireclay (misting and adding a few times, mixing on a tarp in between) + 1 gallon sodium silicate + 2 gallons clay slip (milkshake consistency) + 2-3 gallons chopped straw. I thought maybe the tensile strength of the straw might help hold the interior together, in the absence of furnace cement. I now suppose that most, or all, of the straw gets burned away. But maybe not? It sure does insulate well. I made a door (~2" thick) out of the leftover, and the heat of the fire was not detectable on the outside of the door. Take this for what it is (not tested under fire more than an hour) but I like the mix. Next time I take the barrel off, I want to weigh the thing, but even before I dried it out, it wasn't too much to carry by myself. After I burned out the form, the inside was smooth and seemed very hard. Also, as has been said before, it doesn't need to withstand a lot of jarring, etc. Ans being somewhat familiar with vermiculite and perlite through landscaping and greenhouse work, I tend to think perlite would be the right material for the application. I know the thing is 'rustic' to put it generously, but I'm learning some good things, and hope to use the knowledge gained to makesome good things this coming year, in slightly more favorable conditions (35 and drizzly makes it all less fun). Thanks to everyone who contributes to this open source knowledge forum!
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Post by PNW Dave on Dec 17, 2014 16:56:42 GMT -8
Looking good Wisco! I bet your heat riser provides excellent insulation and performs very well! Do you have a thread discussing this build? I didn't see one, but am interested in seeing more.
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Post by wiscojames on Dec 17, 2014 18:01:28 GMT -8
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Post by mmcc73 on Dec 17, 2014 20:06:28 GMT -8
Thanks for the information all. I was poking around the McMaster-Carr web site, and found that they carry this product at $86 for a 50 lb bag: www.mcmaster.com/#9876k1/=v2k2h1From the MSDS, this seems to be the product in question: firearmor55inc.homestead.com/I was thinking about starting from equal parts Vermiculite and fire clay, and adding some of this stuff (say half a bag for the core, half for the riser) to help it stick together. Any thoughts? Thanks - Clark
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Post by coastalrocketeer on Dec 23, 2015 0:35:11 GMT -8
Thanks for the information all. I was poking around the McMaster-Carr web site, and found that they carry this product at $86 for a 50 lb bag: www.mcmaster.com/#9876k1/=v2k2h1From the MSDS, this seems to be the product in question: firearmor55inc.homestead.com/I was thinking about starting from equal parts Vermiculite and fire clay, and adding some of this stuff (say half a bag for the core, half for the riser) to help it stick together. Any thoughts? Thanks - Clark Wow! - other than the fact that it's over $100 a cubic foot, that stuff looks amazing! I really want a sample to play with! My thought would be to use a roll of ceramic wool with 1" over my desired inside radius and put a nice 1" layer of that inside, and thinner over the top and outside to provide a stiff, 5000+ degree rated liner/form holding coat for the ceramic wool. Or could be cast into a 1/2" thick inner (and outer?) riser walls and filled with perlite in place. Stable to 5000+ degrees and apparently one test used a 2000 degree flame on a 3-1/2" thick piece and opposite side was only 243 degrees after 12(!!!) hours! Does anyone else think this stuff has serious potential?
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