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Home Metal Casting
and Machining
Page 4
WARNING! Activities on these pages about foundry work are very dangerous. The chances of having a fire, causing injuries, or even dying are very good if you are not careful. I am not a professional foundryman, and will not attempt to disclose all hazards. If you choose to try this hobby, every precaution must be taken to be safe.
Which fuel for foundry furnace?
After the first charcoal melt there was a “B” model charcoal coffee can furnace with improvements over the “A” model straight coffee can with holes in bottom. It was the standard coffee can furnace with holes in bottom shown above, but with addition of second coffee can attached to bottom to create a “plenum” to help evenly distribute blast air to bottom of upper can. Metal from a third can was used to provide the strip that fastened the two cans together using some standard sheet metal screws shown in next picture.
Some
weight would be added to bottom can for stability. Beyond that
there were ideas for a “C” model charcoal coffee can furnace which would
have been some insulating refractory and a lid to retain more heat, but the
entire charcoal program was dropped in favor of electric kiln technology 
when I found the used mini kiln at a local ceramics shop for a steal at $100.
There seems to be continuing interest in which furnace fuel is the best choice for those just getting into casting or those wanting to take it up a notch. Here is my view on this subject for what it is worth. A charcoal furnace is a good cheap start for someone wanting to try casting or just do some occasionally but for someone that is going to do more than just occasional casting, charcoal can get expensive as a furnace fuel. Many seem to go to propane, and it has some advantages like fast melts from a cold start. While I never built or used a propane furnace, what I read was you had to make your own burner (no big deal) but the burners used for melting used a lot more fuel than your standard bar-b-que. It sounded like the folks using propane were getting a few melts per tank of propane which is somewhere around $20? The kiln I bought uses 12 amps at 120 volts which comes out to around 14 cents an hour. It never runs out of fuel, reaches a max temp of around 2200 degrees according to the manufacturers website (plenty hot). Melting is slower than other fuels but much cleaner. I usually let it warm up for a little over an hour before I start. In the mean time I am working on getting molds ready. I also speed up the melts by preheating the ingots on an outdoor propane stove.
For those who want or need to build an electric furnace, Dave Gingery did write a book on how to build one called LI'L Bertha A Compact Electric Resistance Shop Furnace. While I didn't build an electric furnace, I did make and test some heating elements out of both mig welding wire and aircraft stainless steel safety wire. Heating element wire can be purchased and is called nichrome wire. Nichrome is nickel/chromium shortened I think. Hmmm... nickel chrome steel sounds like what stainless steel is made of. I coiled up the wire by using a piece of rod for a form and made it a length to give the resistance I wanted to keep current flow (amps) at the rate I wanted (E divided by R = I). I'm sure there is some difference between the nichrome wire and the stainless steel safety wire but for my test both the regular steel mig wire and the stainless safety wire got red hot.
Another foundry fuel that I would like to try soon is waste oil. I have seen many nice waste oil foundry setups on the internet lately. Melting metal with free waste oil says "gettin one over on the man" all over it! From what I have read, waste oil burners are tough on furnace refractory so the free fuel might be offset a bit by the increased refractory maintenance but it would still be a sweet setup. Some are melting cast iron with them as well!
Induction melting foundry setups may also become a regular part of home foundries in the future. I saw one on Youtube where someone was melting a small crucible of aluminum and it said estimated wattage used was 2 or 3 hundred watts!
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