As the reverb furnace didn't seem to fit the bill, atleast in my poorly constructed tester, I still needed to find a better way to melt down mass amounts of cans. I read a little article about cupola furnace and thought I might try a variation of the theme.
I took my little freon tank furnace and added about 10 inches in height by cutting up another freon tank ( I cut off top and bottom and used the middle for my extension). I wrapped up the seams between the two freon tanks with a few layers of aluminum flashing I had on hand. To hold the entire rig together I added a jumbo hose clamp. It was pretty wambly. I added some firebricks to ring the interior of the new upper tube. I also cut a new hole into the bottom of the furnace and welded in a piece of angle iron that protruded out the front where I planned to place the ingot mold. The plan was: added aluminum scrap into the top, blast it directly with the burner, melt it down and it flows out the new bottom spout into nice shiny ingots....well not quite.
This photo shows the new angle iron spout which will drain the cupola with the ingot mold lying underneath. My burner is seen on the right side. I used some modeling clay and a piece of rebar to make a clay plug to seal up the drain spout until it is backed with molten aluminum. I figured to open and close this hole with the plug as I filled the ingot mold....
A close up view of the clay/rebar plug for the drain However I found as I heated the furnace up that the modeling clay was too wet....it started to spit and spall and generally fell aprt long before it could stop up any molten metal.
The beginning of the end....just as the aluminum started to melt I noticed that the furnace was starting to glow white hot. It appears as though one of the bits of scrap I put in the cupola furnace was mostly magnesium and the direct flame had ignited it. You can see the molten aluminum flowing down the spout and the ingots were starting to fill nicely...too bad it all was going bad.
I quickly shut down my burner but it was too late the fire inside kept getting brighter and brighter...I backed way off and thought about dumping sand in the top to cover the burn. Finally it burnt out, it got so hot it melted the welds holding the burner tube and it slumped down. I think the white powder all over the exterior of the furnace is mag oxide from the burn. The material inside the furnace was a big lump of drossy slag....maybe some day I might try to remelt it and recover several pounds of aluminum.
The glowing aftermath of the mag fire inside the furnace..see the burner tube slumped down from the failed welds.
A closeup of the failed burner tube...the interior is still glowing red hot but the shell is pretty well burnt up....time for another rebuild.
