This is my little blast furnace, it’s just two coffee cans that are lined with a mixture of bentonite clay, sand, and a handful of sifted concrete. I usually just melt down aluminum in it, but Im pretty sure that stuff like copper or brass might be possible if I try to get it hot enough. I just use charcoal as you can probably see in the pics, and with the right design, it can get to temps hot enough to make heatsinks and other aluminum stuff to melt down quite easily, within 5-10 mins usually. Im not sure what mine runs at, but Im guessing it’s anywhere from 1200F-1500F.
It’s made with two coffee cans, one with the hole in the bottom of the can, and have around an inch thick lining on the outside of the refractory mix listed above, that is used as the lid, and the bottom is the same except the hole is in the bottom is in the bottom side of it, which a 1 inch stainless steel tube from an old broken broom handle or mop that I found, which in turn is attached to a fan blower that came out of an old computer, dell optiplex gx260 or something like that I think. The bottom part that holds the charcoal tends to get alot hotter than the top, and you have to wait for a few hours to let it cool down before you can even touch it to put it all away. The top part, it gets pretty hot also, but the refractory does a good job of keeping the heat inside of it, and not letting much escape so with my welding gloves on, I just pick the lid can up and set it on a nearby firebrick when Im ready to add more scrap aluminum, fuel, or ready to remove slag and pour.
The fans in those systems are really handy for this purpose, but when you attach 12v to them, they only go full blast for a second, then they run really slow. This is due to a temperature sensor inside of the fan assembly that causes it to run at the speed the computer needs to keep the cpu cool, and when it gets hot, it causes the air temp to rise, so the fan automatically compensates for that. That’s no good for this kind of work, so if you look above the sticker, there’s a little pannel that looks like electrical tape, and if you peel that off, you’ll find the thermistor, just take your soldering iron and solder the pins of the thermistor together, just using a solder blob to jumper across the pins. That will cause it to run full blast all of the time. Ive had many many hours of it running at that speed, and it never got above room temperature.
I just use a tin can and melt the stuff down in it, it seems to work for one or two melts usually, but just depends on the can really. I made my own casting sand (greensand) out of play sand that was really cheap at lowes, and ground up cat litter, and it seems to do pretty good, just make sure to run the sand through a sifter first before you try casting anything or you’ll find that it has some pretty large pebbles in the sand that you didnt see before and will make large pockets in your casting.
Here’s a video of it running, I love the flames shooting out of the top. :P
If you ever get into this stuff, make sure to test your aluminum scrap that your wanting to melt down first with just normal vinegar, some aluminum has magnesium in it and trying to melt something with magnesium in it tends to turn into a really bad day for you. It has an ignition temp at around 1200F, which is where aluminum melts, and burns at around 6000F, which will act like thermite and burn right through your crucible, and probably your furnace splashing molten red metal and glass all over the place at your feet.