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Posted: Thu Dec 31, 2009 2:05 pm
Does anyone have any ideas on building a small cupola furnace? I have several books on doing this, but they are all built on the basis of being fired by coke. I have seen somewhere recently that there is a cupola being built that uses propane (or at least I think). What I would like to do is build one that uses propane if possible that would be environmentally friendly. I don't know if I am imagining the propane cupola or not but I swear that I have seen one somewhere before. Any ideas please let me know.
Posted: Thu Dec 31, 2009 3:39 pm
A Cupola furnace is designed to burn solid fuel mixed in with the iron feed stock or scrap steel. This way in contact with the carbon based fuel it will pick up and hold the carbon in the iron, as the driplets flow around the burning fuel. Today we use processed coals, in antiquity they used charcoals from heavy wood. The Chinese go back many centuries with iron and bronzes smelted from oxides with these methods. These Eastern skills predate European metal working by many hundreds of years.
To my knowledge there is no Cupola design for using gas. There are furnace designs for crucible, and hearth type melters, reverbatory furnaces, that are used for iron and bronzes.
Posted: Tue Jan 05, 2010 2:06 pm
Not a cupola, but here's an oil-fired iron furnace: http://artfulbodgermetalcasting.com/
. I know of no propane furnace that will melt iron. The oil, BTW, burns very
clean, and you can use veggie oil if you'd like.
Posted: Wed Jan 06, 2010 7:35 pm
Um, actually I do own two. But honestly they have to run very hard to melt iron, and degrades the crucibles pretty badly. The silicon carbide has a long life with Al, less so with bronze and only about 20 or so heats with iron, they burn away so bad. That is where a cupola has the advantage. The fuel is in contact with the metal, so it heats faster.
Posted: Thu Jan 07, 2010 1:13 am
steamin10 wrote:Um, actually I do own two. But honestly they have to run very hard to melt iron, and degrades the crucibles pretty badly. The silicon carbide has a long life with Al, less so with bronze and only about 20 or so heats with iron, they burn away so bad.
Lots of things working against you when you use a crucible furnace for melting iron, even if you have success. For one, the chemistry of the iron changes drastically, often yielding iron that is too low in carbon, so it won't machine. White iron is the name.
Both silicon and carbon are readily absorbed by iron when it's molten, so the crucible is literally dissolved by the charge.
The best possible scenario is to melt with induction, where there is no change in the chemistry. A cupola yields iron of various descriptions, but that's it, regardless of the feed stock. A great melting furnace, no doubt, but drastically limited, and very dirty to operate.
Posted: Thu Jan 07, 2010 10:06 am
Harold is biased to his induction furnace, which is used quite a bit in small cast shops. Iron castings are normally produced in electric arc furnaces, and reduce iron and steel scrap into 'synthetic' iron, as it comes from working steel backwards. In any event he is correct on the cupola, it will only give you high carbon iron, that has its own limits. Because the work time in a small crucible is very short, to make additions and blow off some carbon and do a pin test for latent carbon, By the time you fool around with it, it is cold or frozen, and must be commited back to the crucible furnace. I have done this, and it is not fun. I got white iron edges at any rate, so I dont have the wand for magic answers.