A Homemade forge for casting aluminium
This homemade forge came about because I was making a homemade jet engine and found I had to pay serious money for large pieces of aluminium.
The air intake of the engine is machined from a 1 inch length of 4 inch diameter bar - I had to buy a minimum length and even on eBay it cost me £30 just for a 4 inch length.
After machining almost half of that away to get the shape I needed, I found myself looking at the scrap I was producing in a different light. That's a pile of spent money laying there!
So, I started asking myself 'how difficult can it be to make a forge to recycle aluminium?'
First thing I needed was something to hold the fire - okay, I've got some left-over bricks from when I paved the drive so I laid those in a circle.
I have an air blower that I made from an old vacuum cleaner (I use it as a starter for the jet engine), so I laid that by the circle of bricks and connected it with a length of old steel pipe. Then I lit a fire in the circle of bricks and piled on some coal I had handy.
While the fire was warming up, I got an old gas cylinder and cut it in half for a crucible. This is one of the disposable gas cylinders you can buy from welding supplies companies. They usually contain argon, CO2, or propane and are quite substantial lumps of metal. I drilled a couple of holes in the rim so that I could hook a wire through for lifting.
For the mould itelf, I made a wooden box frame, a couple of inches deep, placed it on a table with the pattern in the middle and filled it with builders' sand, which I rammed firm with a lump of wood. Note the strip of wood nailed to the inside edge to help stop the sand falling out when the mould is turned over.
Oh, and I sprinkled talcum powder over the table and pattern to act as a release agent. That's the white coating you can see on the surface of the mould. (Made it difficult to photograph though)
I already had a pile of scrap aluminium, offcuts, swarf, lengths of old window frame, greenhouse fittings and even an old saucepan, so finding the raw material for an ingot was no problem. In fact, I had more than enough and when the pour was done, I still had a lot of melt in the crucible, so I quickly poured it into an old baked bean tin that I had handy (You can see it standing by the gloves in the top picture). That made another sizeable ingot that I can use or re-melt sometime.
Casting metal is usually done using a wooden 'pattern'. So I made a simple disc out of some MDF and gave it a good coat of wax. I added a hole in the middle to insert a woodscrew that I used to lift the pattern out of the mould.
No photo of the forge in action I'm afraid, I really had too much on my mind at the time to take photos. The aluminium melted quite quickly when the crucible was just beginning to glow red at the bottom. I though at first it wasn't melting, but when I prodded it with a wire, the bits of aluminium metal sticking up just collapsed into a pool. I think it was being held in shape by the oxide layer
Here's a shot of the mould, pattern and resulting ingot, taken after casting was complete. To my surprise, I didn't need to destroy the mould to get the ingot out. It simply fell out when I turned the mould over.
The result wasn't perfect. The surface of the sand in contact with the hot metal has caked and lifted a little, spoiling the appearance of the ingot surface. You can see the bottom of the ingot in this picture, and the corresponding surface of the sand.
Still, I got what I was after - a lump of recycled Aluminium!
The ingot after machining the surface.
The large defect to the left of centre is part of the original ingot surface that I didn't completely machine away, so ignore that. Apart from that defect, you can probably see that there is some porosity in the finished surface. It doesn't machine as cleanly as fresh aluminium either, the swarf comes off as crumbs instead of nice turnings, but hey- who cares? For non-critical jobs like the engine air intake I was working on, the odd small defect in the surface isn't important.
The important thing is that it works and I don't have to pay big money to get a useable piece of Aluminium.
