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Thread: Air blower for charcoal fueled furnace

  1. #1

    Air blower for charcoal fueled furnace

    I finally got around to testing my furnace after months of the deep freeze here. It was quite a disaster, but not completely unsuccessful. I am new to this and it was my first burn ever. I decided to started with just beer cans to see how it worked (to save my good aluminum for later). So, I think the problems I had were due to two major factors. First of all, it is hard to find good charcoal here in the off-grilling season. The only place close to me that had it was a very thin light weight wood charcoal. 20170311_142647[1].jpg. The second problem was that I was using my shop vac with the hose attached to the outlet as an air blower. I think that it was way too strong. I basically ended up with a crucible full of charcoal, and the charcoal was burning extremely fast. I had to replace it 3 times. Today I built a new blower from an old stove hood 20170311_141705[1].jpg(haven't tested it yet as I need to get better charcoal and I burnt out my crucible (a small cooking pot) on the first try). So my question is, how strong should the force of air be? The shop vac seemed way to strong, the stove hood seems like it might be a little weak. Also, I am wondering about the placement and length of the tuyere. How easily or hard could it be adapted to change to a propane burner? Also does it stick out too much in the inside?20170311_141602[1].jpg(also notice that I use sheet metal rolled up the form the inside chamber, when I was ramming the calcium alum cement the sheet metal wasnt strong enough and formed a misshapened form. And the last question. I noticed that there was some deterioration of the hot face close to the tuyere, is this normal?? 20170311_141622[1].jpg. And, as I said earlier, it was not completely unsuccessful. I managed to get one ingot out of the burn (if you can call it that, it didnt quite fit the only thing I had handy for a mold at the time) 20170311_224810[1].jpg. That was about 10 beer cans.
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  2. #2
    Administrator Site Admin
    Join Date
    Dec 2005
    Huatulco, Mexico
    An old hair dryer is perfect for a charcoal furnace. (New ones work too.) You want one that can run with no heat. Yard sales, thrift stores, Craig's list, your wife's bathroom when she is out shopping. A good thing about them is the round snout. A 2 inch hose fits over it perfectly.

    When I die, Heaven can wait—I want to go to McMaster-Carr.

  3. #3
    Senior Member Tobho Mott's Avatar
    Join Date
    Oct 2013
    Ottawa, Ontario, Canada
    +1 for using a thrift store hair dryer for your blower. I even had to use a dimmer switch on mine to turn it down even lower that it can normally go. With such fine charcoal lumps, maybe you need more blower than me to push the air all the way through the coals to the top of the furnace though. Tuyere width also affects how hard to ideally run the blower - when the flames blow out of the vent hole, you are giving it too much; ease off and watch them retreat just inside. Try to maintain as deep a bed of coals beneath the crucible as you have room for to break up the airflow and prevent crucible-killing cuttting torch effects.

    A grate above the tuyere will really help the air circulate evenly; I think I this will be especially important given your tangential tuyere angle. Which is burner-ready as-is if you ever want to convert to propane. I'd pull it back a bit and keep the pipe out of the bore of the furnace, put the end even with the wall or just a little back from it so it will be out of the fire somewhat, then it won't burn up or melt off so soon.

    A little charcoal in your crucible won't hurt anything; if anything it may protect your melt from oxidizing. Just skim it off with the dross.

    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

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  4. #4
    Senior Member
    Join Date
    Jan 2012
    Buffalo, NY
    The blowers you see on oil and gas burners are performing several functions: to physically cause air and fuel to mix by creating turbulence, at to provide oxygen for combustion of the fuel itself. In a charcoal furnace it only needs to provide combustion air. The only force needed is to distribute the air adequately through the charcoal bed. Additional force and volume only create problems like the rapid consumption of the charcoal and a blowtorch action which can not only burn a hole right through a steel crucible but can also damage a ceramic one. I use a hairdryer as mentioned above. Anything larger is more than you need. With the use of a grate above the tuyere I've actually had the furnace melt a steel crucible of aluminum with no blower at all. I was just letting everything sit with the blower tube pulled out while I was finishing up a mold and when I went to put the blower back in the metal was already liquid. So yeah, a shopvac is definitely too much.
    You are indeed ready for propane now. Your pipe is too far in but the excess will go away on its own. You could probably gently grind it away with a die grinder so as not to traumatize your hotface with heavy grinding, but a couple of sessions running hot and lean with propane would probably burn it away pretty quickly. An overly oxygenated charcoal fire will burn it away too.
    That little bit of surface flaking is no big deal. I would say that your furnace is pretty early in the game and hasn't seen much of the punishment that's yet to come. I don't know what calcium alum cement is, but if it's going to fail it's better that it does it as soon as possible so you can fix or rebuild it and then get on with the show. It looks ok for now. There isn't much you'd be able to do about it anyway.

    Great progress so far!


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