Sparks!

I've got two full trash bags of smashed aluminum cans floating around and I'm and starting on a third. I know I could haul them to a recycling center, but I never seem to get around to doing it. So instead I decided that I should melt them down and cast them into something useful. Besides, I've always liked playing with fire.

I started doing some preliminary research on smelting/casting aluminum a couple of years ago. The first few websites I found went on at great lengths on how to build a furnace etc. etc. I was wondering where I could buy a crucible, fire brick, refractory cement, green sand and all the rest of the "stuff." A couple of months ago I ran across another web site that basically said "Start simple. Charcoal, an old stainless steel pan and a hole-in-the ground with a forced draft will work." I saw another site about the same time where the guy was using two old coffee cans as a furnace. So I decided to start simple.

I have regular bricks and crushed limestone gravel from building garden paths (see a couple of posts ago). I also had a pretty big ceramic flower pot. I did have to do a hasty transplant of the plant into a bigger plastic flower pot, but it needed replanted anyway.

So I created an air passage with bricks that have holes in them, set the flower pot on top, built a brick box around the flowerpot and filled it with gravel. Oh and I set the whole thing on a 2 foot by 2 foot concrete paver from a sidewalk that I removed. (You can see another paver sitting beside it.)

I also needed a lid. There were also some round concrete "stepping stones" through one of the flower beds. They usually sink under the dirt anyway and there aren't enough of them to make a useful path so I thought I'd use one of them as a lid.

However, the lid needs a vent or the charcoal won't burn. So I drilled a series of holes in the stepping stone with a masonry bit and then chiseled out between them -- or I tried to chisel out between them. I got halfway through the top side, flipped the stepping stone over and was about a quarter of the way through the back side when I hit it a liiiitle too hard and split the first one into three pieces. I think the real problem was that I left it on some scrap 4x4 that I had used to prop it up when I was drilling the holes. I think I would have been OK if I would have just put it right on the floor when I was chiseling.

Luckily I have more stepping stones.

On the second try I put one hole in the (approximate) center of the stepping stone, put a nail through a board to spin the stepping stone around and then put the whole thing on the drill press, instead of using a hand drill and eye balling it like I did the first time.

Theoretically this would make a perfect circle of holes around the pivot. That is if the pivot axle (the nail) wasn't smaller than the pivot hole and the drill press chuck wasn't welded on crooked by a previous owner (can't expect much from a $20 drill press), and the masonry bit wouldn't deflect off of the gravel in the concrete. But it was close enough.

I chiseled it on the shop floor the second time and it worked.

The blower is from an exhaust fan that was in the ceiling of my workshop before I replaced the drop-ceiling with drywall. I wired a three prong cord to it several years ago to use it to re-distribute heat from my fireplace insert. It was only marginal in that task but works quite well as a forced air draft.

I was worried that both the flower pot and the lid would crack from water turning to steam while in use. To try to prevent this I built a couple of twig fires in the "furnace" to try to slowly dry out the flower pot and the lid out. The lid held up quite well. The flowerpot wasn't so fortunate.

I actually have a couple of burnt doughnut shapes in the lawn where I absentmindedly put the lid down on the grass after taking off of the top of the furnace.

It took me a week or so to get to this point because of various other projects, company visiting and rain. Hot ceramic/concrete and water don't mix gracefully. I'm not fond of picking shrapnel out of myself so I waited for a day with no rain.

So on the appointed day I started a small fire in the flowerpot with paper and twigs and three or for pieces of charcoal. I let that burn down to just charcoal while I hooked up the blower, dug out the face shield and welding gauntlets and set up a splatter screen.

Then I stuck my crucible in the furnace and put charcoal all around it. That was actually a mistake. The charcoal needs to be around the bottom of the crucible where the aluminum is.

I didn't think that it was going to get hot enough to melt the aluminum at first. But that was mostly due to only a little bit of the charcoal burning. After I got the rest of the charcoal going it got plenty hot enough.

My crucible is a stainless steel kitchen tool holder I found at my local we-sell-everything store. It was about $8. I drilled two holes in the sides toward the top so I can put a wire handle on it to pour. I also bought a stainless steel slotted spoon with a long handle to skim off the slag. It was $3 or $4 dollars. That's all I bought for this project other than the charcoal.

I still don't have any green sand to do any real casting yet, but I was just trying to smelt the aluminum down into ingots. Lots of sites say to use an old, steel muffin pan to make ingots. I only have one muffin pan and it's a pretty good pan. So instead I cut the tops off of four aluminum pop cans and put them in a box surrounded with sand.

That worked OK except that I over-filled the first one and it instantly melted the top of the can and ran across the sand and into the grass. No great loss. I've an acre and a third of grass. One little bit I won't have to mow. Though it does make for an interesting "ingot".

The can that I didn't over-fill came out OK. The can on the left above has slag that I scraped off the top of the melt the can on the far right only has a drop or two of aluminum in it.

I did get a lot of slag. About 50 to 60% of the volume is slag. I think a lot of it was because I was melting pop cans. Before you get a pool of aluminum going most of the can just oxidizes. After you have a pool of aluminum to push them into, you seem to get less slag. And the vinyl burning off the cans does stink. I stayed out of the smoke as much as I could.

I got about a pop-can full of aluminum all told. That was basically one 5-gallon bucket full of smashed pop cans and 1 aluminum gutter nail. Next time I'll start with one of the "ingots" from this time, so I expect to get less slag. I'll probably just be doing ingots again next time. The time after that I'll probably try some real casting.