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ALU melting

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NormanV:
Will, I built a foundry when I lived in the Falkland Islands and buying refractory cement was definitely not possible. It was possible to buy 1 kg tubs of ready mixed fire cement but to build the whole foundry with that would have cost a couple of hundred pounds. Instead I bought four pots of it, thinned it down with water and mixed it with "grog" that I made by breaking up and passing through a 1" mesh sieve a load of fire bricks that I managed to scrounge. It turned out to be entirely successful, no cracks appeared in it even after many firings. The lid was made of the same stuff in a sheet metal ring with wire reinforcement criss-crossing it.
For moulding sand I used sand from the local sand dunes mixed with fullers earth cat litter.

Eugene:
Will,

I'm doing the planning for a foundry too; one of the better internet sources for all things home machinist is "Mikes Workshop" as per http://mikesworkshop.weebly.com/furnace.html

The mix he used in his set up is .....

1. Portland cement - 1 part by volume
2. Clay - 1 part by volume. I used clay based cat litter. This is available from most supermarkets
3. Perlite - 7 parts by volume.

Looks simple enough and details of the mixing procedure are given on the site; I think I'll go with this procedure.

Eug

vtsteam:
No, do not use portland cement., it won't last, it will calcify. That occurs at 600C or about the melting temp of aluminum. Use of Portland cement by amateur foundry makers has been an ongoing problem ever since Lionel Oliver first put up a portland cement furnace on his website in the early 2000's -- however he at least used a flowerpot liner (clay) so not as bad as people who use portland cement directly with no protection for the material.

Plaster of Paris (gypsum)  is MUCH more refractory -- it's used in bronze casting as a molding material -- bronze pours at a lot higher temperature than aluminum melting temps -- Mattinker can tell you and has personal experience.

Also in industry, plaster of Paris pouring basins and liners are used for even iron. Plaster of Paris has a high insulation value there, which is why it is used -- see Steve Chastain's molding books for references to this. And on the popular internet video scene, plaster of Paris is used in numerous small benchtop forge videos and ripoff videos. One of the more popular is mentioned in the intro to this thread's flick.

As I said, my objection to this video is not with the furnace body, but with the cavalier disregard of coatings combustion products.

I've just built a new furnace with a plaster of Paris sand mix, so if you want to know how well it works, I'll be able to tell you shortly

There are other references to using Plaster of Paris with bronze on sculpture casting art sites.

vtsteam:
Also, you can melt aluminum in practically any furnace composition that will stand the heat -- a woodstove for example with hot embers in it, a hole in the ground, a woodfire, loose or bound bricks, a steel box or barrel, etc. People make a big deal out of it, and that can be fun, buying expensive stuff, and doing high tech things, but if you don't have money or access, you can still melt ALU.

vtsteam:
I just looked at the Mikes workshop furnace, and pretty much guaranteed that the Portland cement on the inside face has calcified and it's the clay and perlite that is now holding it together in the hot area. Still, if it works it works. The cement cures quickly to form, so useful that way, but you do need clay and perlite to make it work. Many have tried pure portland cement furnaces without understanding and those have failed over time or if overheated -- brass melting, etc.

I'm hoping that the sand/gypsum mix will allow bronze melting and steel forging as well as aluminum melting.

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