Unlike many other forges this one can be reasonably used in a residential environment without attracting undue attention from the neighbors. It's not particularly noisy and doesn't project huge fiery jets. It doesn't require permanent construction or a specialized installation. It can be put together, used and torn down in a single afternoon.
I really like many of the propane designs I saw but most people don't have a propane burner or nozzle assembly to spare so I decided that design which leveraged existing BBQ technology would be more widely useful.
The mandatory note: I believe the insurance company add that says 25 burned down their houses attempting to deep fry turkeys. Don't be an idiot.
No blow dryers were injured in the making of this instructable if would be nice if folks who tried this exercised great care and caution and no humans get injured in trying to do this.
Step 1: Bill of Materials
23 ordinary red clay bricks. I had some used brick laying around but new brick from Home Depot costs about 17 cents each. You can get firebrick if you want (I didn't). The concrete bricks would probably be okay but I can't speak to that.
An ordinary blow dryer. You can pick up a cheap one at Walmart or Target for around $15 or you can use on that you have. It will not be damaged or changed in this process.
A coat hanger
A BBQ grill at 18 inches in diameter. When all was said and done I used the top grill from my Weber, you will learn more about this decision in the next step.
Charcoal or biochar briquets, the charcoal must be sufficiently formed to rest on the fire grill.
A 30oz steel can. I happened to use Rosarita Refried Beans, this is a standard super market can size and almost any 30oz can should do. A small size may be used but for this design the 30oz is appromiximately the largest size that can be accomodated.
A catalog or magazine, preferably with slick, glossy pages ( clay paper ). We actually only need one page from it which will be damaged in the process.
A long handled tea spoon or small ladle for removing slag.
A 1 foot or so piece of steel pipe of approximately the same diamater as the blower tube on the blow dryer is convenient. Different diameter pipe may be used but if so a smaller diameter should be chosen.
A 2 foot or so wooden stick or pole that can be used in handling the crucible.
A can opener. I didn't show all the tools needed but I'm showing off the fancy, shmancy one I have...
Okay now if we've got all the bits together let's make a furnace...
Step 2: Laying the groundwork
The bricks are layed out to create an air chamber the size of, well, one brick. The pipe fits loosely between its guide bricks and will be removed temporarily in a later step.
This assembly serves to isolate the forced air feed (blow dryer) from the heat of the fire. Since heat goes up the air feed and blow dryer are placed below the burn chamber. This, in combination with the forced air assembly insulation seems to protect the device adequately.
Note how the pipe just projects into the chamber. I experimented with various things and it seemed like this assembly got the most even air flow through the firebox.
This layer will also hold the fire grill. The firebox sits above the air chamber and the grill used to hold the charcoal in pace. My grill had a supporting wire rod running down the center so you can see how I used the recess created by the pipe and the gap between the two bricks in the back to so that it lays flat and doesn't get bent by the weight of the bricks above. I used a grill big enough so that the outer wire supporting rod didn't impact the forge. Everything used in the forge should return more or less to its original purpose.
Step 3: Assemble the firebox and chimney
The chamber will hold the burning charcoal and crucible which we will make in the next step. The size of the melt chamber can be varied and performance will vary in a large part based on the air capacity of the input feed device (blow dryer or other device).
Now that we've got the furnace in place let's quickly put together the crucible which will hold our feedstock.
Step 4: Arthur Miller where are you?
Now I happen to have...okay, my wife has, this really cool can opener that removes the lid and the top seam so that the can has a tidy and much safer edge. If you do not have such a wondrous device then take a file and file down the inside edge of the can to obtain a smooth lip.
Take the coat hanger and clip off the long straight section across the bottom. Now take your drill and drill two 1/4 inch holes across the diameter of the can. This need not be exact but should be pretty close.
Push the piece of coat hanger through the two holes. Take the remaining coat hanger piece and bend the two shoulder bars down so that it forms a long hook. When we are forging aluminum this hook is used to remove the crucible from the fire by placing it under the wire rod and lifting the crucible from the furnace. It also forms a pivot point so that the aluminum can be poured into the mold.
Okay, now that we've established our place in literary history let's put together the forced air blower
Step 5: The blow dryer assembly
Remove the pipe from the furnace. Arrange the blow dryer and the pipe so that they sit level. In my case blow dryer had protusions on both sides and I had to put a cloth under the pipe so it would sit level.
Take a page from the catalog or magazine and fold it into halves or thirds until it forms a strip a couple of inches wide. This will be used to connect the pipe to the blow dryer without a physical connection. That will reduce opportunities for heat transfer. Additionally the paper serves as an early warning indicator if heat is presenct, then the blow dryer can be turned off and the assembly removed from the heat to safety.
Tape one strip securely between the two tubes (blow dryer and pipe, see picture). Wrap the strip tightly around the joint several times then tape it securely at the ends. The paper tube now forms a surprisingly strong joint between the two devices to create a single apparatus.
Okay, now we're ready to put it all together and melt something....
Step 6: Assembling and Charging
Place the blow dryer so that its air intake is away from dust and dirt. A small towel or piece of cloth can safely be laid under the blow dryer to provide an even safer environment. The towel will get dirty so there's no free lunch.
Place a few rows of charcoal on the fire grill until you fill up the gap created by the first row of bricks.
At this point if you hang the crucible in the fire box chamber it should fit nicely with the bottom of the crucible just above the charcoal. The crucible should hang freely in the furnace chamber and not rest on the charcoal itself.
Preparation of the feedstock depends on what you're using. I used soda cans so I cut the tops and bottoms off using a pair of scissors (not the good ones!) and then smashed the remaing tube flat and folded it a bit. This allowed me to feed in the body seperately from the tops and bottoms.
There is much advice on this, however what I found is this. Cut up a bunch of small pieces and place them in the crucible. When things heat up this melt they will form a pool of molten metal. This will take much larger pieces conveniently. There are limits to this but you can think of preparing feedstock in much the same way as preparing a campfire. First comes the tinder, then the small logs, then bigger logs.
Okay, now we've got a furnace, we've got a loaded crucible lets smelt some aluminum...
Step 7: Smelting and Casting Aluminum
If you use on those charcoal starter devices with newspaper or whatever get your coals started. Otherwise remove the crucible and spray on a good dose of starter fluid. No need to go crazy, it won't help. Use the same sort of amount you would use the start the charcoal in your grill.
Light the charcoal and, holding the crucible the extended rod ends, place the crucible back into the furnace. **CAREFULLY** drop in additional briquets up to about the level of the crucible rod. Don't over pack, you can always drop in more briquets later.
Take the last two bricks and place them **CAREFLLY** on top of the furnace to form a chimney. They should be placed so that the center of the furnace forms a square framing the crucible. (see picture)
As things heat up the feedstock will begin to soften and then melt. As the metal melts addtional feedstock can be **CAREFULLY** added to the crucible. Eventually you will have either fed in all your feedstock or the level in the crucible will be "full". I wouldn't overfill the crucible, if it gets half full go with that until you a clear idea of how exactly things will go.
Dross and slag will float to the surface of the molten metal. I removed this using a long handled tea spoon. ( see picture ).
Once you have a nice crucible of silvery molten metal ( more or less ) remove the two chimney bricks from the top of the furnace. Hook the crucible rod with the coat hanger hook and lift the crucible out of the furnace. Tilt the crucible to pour the aluminum using the wood piece to lift the bottom (see picture), this approach provides pretty good control on the pour.
In this case I used a muffin tin as the mold. It was handy, worked and readily discharged the aluminum ingots in an interesting muffin shape ( sort of ). As you can see from the picture I've done two melts with this and didn't actually get a full muffin because I ran out of feedstock.