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Monday, April 25, 2011

Smelting Aluminum

I'll have to admit that this was a whole lot more work than any money I ever got out of it.  Still, times are tough, and the price of metals are going up a lot faster than minimum wages.  At one time, I had a larger furnace to melt aluminum, but this one was a better design and easier to operate.  






Materials:

1. squirrel cage blower (from a home A/C distribution unit for example)
2. metal ducting
3. 55 gal steel drum
4. wire mesh
5. fire brick (special bricks that don't crack at high temps)
6. silicon carbide crucible (the melting pot)
7. Four 50lbs bags of refractory cement (special cement that doesn't crack at high temps)
8. Refractory mortar
9. Various scraps of angle iron / bolts / screws

Steps:

The wood burner-

1. Find a good refractory supply warehouse to get the firebrick, and refractory cements
2. Cut a hole in the side of 55 gal drum big enough to insert the metal ducting.
3. Also, at the top of the drum, make 2 1 ft. cuts straight down about a foot apart to open an exhaust port at the top.
4. Screw wire mesh to the inside of the 55 gallon drum
5. Coat the mesh w/ some of the refractory cement, but of course, leave the hole open
6. Bury the drum if you can, attach the ducting (running it underground about 4 feet)
7. Put an upwards bend in the ducting and set the blower on top.
8. Use more refractory cement to make a door for loading fuel 1ft x 1ft x 3in thick, with wire mesh in the middle to add strength and bolts stick out of the top so you have a way to attach a handle later.
9. Use heavy steel angle iron to build a square frame over the top to support the door in step 8
10. Cover the rest of the top of the 55 gallon drum (around where the door goes) with firebrick, but leave that one side open for the exhaust port.
11. coat the steel angle with firebrick mortar to protect it a little from the heat.



Furnace -

1. Build a foundation on the side of the drum w/ the exhaust port - ~3ft x 3ft
2. Build the walls up with firebrick about 2ft high, leaving one side open for door.
3. Build the door ... mine was angle iron hinged to a post w/ firebrick attached.
4. Build the 'top' (what holds the aluminum scraps while they are melting). It's going to be a large block of refractory cement with a depression to collect the liquid metal and a hole in the middle to allow the metal to drip into the pot below.
-make a cement form 2ft by 3ft by 5in deep
-make another wooden form that's 1ft 8in x 2ft 8in by 1.5in deep and cover it with plywood.
-place the 2nd form (plywood side up) in the larger form.
-set a short scrap of 3" pvc pipe on top of the smaller form
-drill 4 holes into to smaller form around where the pvc pipe is ... 1/2" from the pipe and equally spaced around
-set 4 bolts into the smaller form around the pvc pipe ... the threads need to be down, with the head of the bolts sticking up a couple of inches. These bolts will hold a steel plate over the top of the hole to prevent big impurities from dropping down.
-fill the form with refractory cement
-when the cement sets up a little, remove the pvc pipe
-when completely dry, remove the forms and flip it over
-drill holes in a 6in.x 6in. x 1/4in. steel plate to match the bolts sticking up
-put several washers on each bolt, and then attach the steel plate. It should be sitting off the bottom ~1/2 in.

5. Put the top over the walls of your furnace. There should be a gap in the back.
6. Build the walls up another 2ft with firebrick, but leave a 1ft wide window on one side. This is so you have access to clean out junk and slag that will accumulate on the 'top'.
7. Rig up a steel grate to prevent pieces from falling down the gap between the back edge of your 'top' and the back wall of the furnace.

Operation:

Sometimes I used a bigger crucible and just tilted it to pour the metal rather than picking the whole crucible up. Also, if you want to melt copper, bronze, or iron, you have to pack coal around the crucible. Still just fill the 55 gal drum with wood, but adding coal right around the crucible will raise the temp there enough to melt copper, etc. But, only add clean copper directly to the crucible ... it won't melt over the 'top'.

For aluminum, you can bust up old transmissions or whatever and add the pieces to the top. Oils and paint burn off while it melts. You will need to regularly scrape out junk and slag that can block the flow of metal through the hole.



Additional notes:


 I designed the form for the "top" a little better than what I described above. On the clean out side, I had the side wall shaped like a ramp to make it easier to drag irony bits and slag out of the pool of aluminum. I also had a little lip around the edge of the hole to prevent  irony bits from washing into the crucible.



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