Why is it that all the things i make involving heat are small?
There's the coal forge, that was fairly diminutive, but i digress.
by-tor the snow dog asked me if the coal forge got hot enough to do glasswork. ( http://www.instructables.com/id/EG8B14NNJJEYMW0DC9/#CEXLBVSRGSWEZ7BDCQJ ) Basically, it does, but i wouldn't recommend it, because the hot coals will stick to the glass ans it'd be manky, so i decided to make a clean, hot-burning furnace using what i had lying around.
There's the coal forge, that was fairly diminutive, but i digress.
by-tor the snow dog asked me if the coal forge got hot enough to do glasswork. ( http://www.instructables.com/id/EG8B14NNJJEYMW0DC9/#CEXLBVSRGSWEZ7BDCQJ ) Basically, it does, but i wouldn't recommend it, because the hot coals will stick to the glass ans it'd be manky, so i decided to make a clean, hot-burning furnace using what i had lying around.
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I used the Refractory glop i sued for the coal forge -i'll keep using this until i find something better, IF i find something better- and a can. The can should hold about half a kilo and, even with the refractory taking up some of the space my torch was still struglling to heat all of it up, so if you want a bigger hotspot, you'll need a bigger can,obviously, and more torches for the heat, but that presents some new problems because you don't want the torches to overheat one another. This can held 540 grams of grapefruit. Because the can has to be emptied first, choose something you'd like to eat. If it's beans, work outside.
I used the Refractory glop i sued for the coal forge -i'll keep using this until i find something better, IF i find something better- and a can. The can should hold about half a kilo and, even with the refractory taking up some of the space my torch was still struglling to heat all of it up, so if you want a bigger hotspot, you'll need a bigger can,obviously, and more torches for the heat, but that presents some new problems because you don't want the torches to overheat one another. This can held 540 grams of grapefruit. Because the can has to be emptied first, choose something you'd like to eat. If it's beans, work outside.
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It was based on this, but a little simpler. You'll need Perlite (availible in the gardening section, DON"T get vermiculite), silica sand (plain, clean sand, often sold as playbox sand), portland cement (sold in big bags at some hardware stores, outside. You will probably need help because an average bag weighs 90-something pounds), and bentonite (cheap kitty litter, oil absorbing clay, etc., it doesn't need to be powdered, although that would be better.).
Combine one part perlite, one part silica sand, and one part bentonite.
mix well and add a small amount of water, just enough to make it moist. let this sit for 30 minutes, mix again, add a little more water, and let it sit for 45 minutes. Now add one part portland cement, and mix more water in. You are looking for a moist/wet crumbly-ish texture. Grab some in your hand, and squeeze. If it holds well, then you're done. If it is too crumbly, add more water and test again. Remember, it is not supposed to be as wet as normal concrete, so don't add that much water.
This is like all concretes with portland cements, it hardens by a chemical reaction (hydration), so adding more water will not keep it soft forever, so mold extra into bricks or plinth blocks (they hold the crucible up in gas foundrys; look at the bottom of the page).
In order for it to turn out pretty, and work well, you need to ram the refractory. I used a small dowel. First, make your bottom layer, then center a pvc pipe in the can, standing up. This will form the interior space. Ram the material in layer, ramming 2 or 3 layers, and then compacting it hard, repeating until you're done.
I used a 2" pvc pipe, and left about 1/2 to 3/4" on each side( I was using a small coffee can). When I was done, I waited 5 minutes, then pulled out the pipe with pliers.
I forgot to say that you need to ram with the pipe (the one going to the propane) in when you ram the material so it will leave a hole. So do that.
I've found it to be an easy formula, although you need to start the torch on low and run it for about 15 minutes to drive off any moisture left from before, before you crank it up to operationg temps. This only needs to be done once.
Today I was able to melt some aluminum, using it vertically.My crucible was a small steel match holder that I- I mean my friend, actually broke. My only power source was a regular propane tank.I I might post pics if I get around to it. I poured it into a small ingot, using small channel iron (actually steel).
I'm thinking of making an instructable on the refractory, small forge, and a helium tank foundry. The foundry is the only one not completed.
Also, I found that when measuring out the materials, using a plastic cup is a good way of measuring. I each part is +3/4 of a plastic cup, then you'll have just enough to complete the forge (in my case). Don't cut it short!
I hope you appreciate this because it took me a long time to write this comment (I type slow).
Vermiculite is a superior product for making firebrick refreactory.
The refractory mix is composed of Portland cement (1.5 parts), silica sand (2 parts), perlite (1.5 parts) and fireclay (2 parts). The first three components are mixed together thoroughly.
Thats the formula.
However, its not as great as i thought it was at the time, now that i have tried different refractoires(that post was about a year ago).
Also, portland cement is a flux at high temperatures. Most people say to skip the portland.
I use Kaowool now. Its cheap, and truly great for a small gas forge like this. You might want to look into it.
If not, see [www.backyardmetalcasting.com/forums] for more info, or comment back.
this would make an excellent tempering forge for small/med knifes, punches, chisels and the like.