Attempting to make a high temperature melting oven.
I need to go to 1600C to melt Magnetite. The quantity of
material I need to melt seems to rule out an Arc furnace,
perhaps not, want to melt about 200cc.
Was thinking of using graphite gouging rods as the heating
elements and drive them with a 180Amp welder. Graphite is
good to 3000C in an atmosphere of CO.
Could a simply fuel gas like propane/butane be substituted for the CO to stop the rods from oxidizing. Graphite won't go much above 1200C in normal
atmosphere withoud oxidizing.
Are there any good sites out there explaining what refractory insulating materials are good to go to theses
temperatures. I have a good supply of Graphite blocks but
while they will take the heat I thing their thermal conductivity is too high for this task? If one was to obtain
a quantity of SiC sharpening stones (square, like bricks) would they do on the inside layer of the oven to take the big heat.
Kanthal A-1 heating elements are good to 1400C which is
getting close to the temp. I need. I could probably sinter
at 1400C
Now if I could get my hands on some that Molybdenum Silicide would solve alot of problems. It is good to 1600C.
Perhaps I am simplifying too much!
All pointers, ideas welcome.
Cheers,
Dann212AX7 - 1-2-2007 at 19:36
Alumina and silica based refractories are suitable. Get a sack of insulating castable.
Fuel gas will work if there is enough energy to sustain radicals. Probably, letting in a little oxygen will help. Enough will be had by leakage
through the refractory and joints. Lots of radicals also has the side effect of producing soot, which you probably don't want. Likely you'll want to
trim the right amount of oxygen, perhaps by using a gas burner set for a variably rich flame. Certainly, such an excessively reducing environment
will result in a lot of FeO and Fe.
The problem with graphite is it becomes less resistive at high temperature. I don't remember what the complete resistance vs. temperature plot looks
like, so I couldn't tell you how much a problem that is.
I wonder if microwave and/or induction would be capable of melting magnetite.
Timnot_important - 1-2-2007 at 23:13
Problem I see is that you're heating iron oxides in reducing conditions, I think you'll end up with metallic iron.
Magnetite has been used as a susceptor in microwave melting of metals, temperature limiting when the magnetite starts to flux the ceramic.
You can melt your magnetite easily with a propane fired-furnace. I know this is very possible because when I melt iron, the oxide on top of the melt
is a liquid. I use kaowool for my insulation (about 3") and 1" of 3200F (1700C) alumina castable refractory for the furnace walls. While running at
2100F/1200C the outside of the furnace is about 100F/40C, so it insulates very well. Expect to come to temperature @ 12 psi propane gas in about 20
minutes. To keep your magnetite from being reduced to iron, run your furnace lean. Melt your material in a clay-graphite crucible that's been washed
with either ITC296 or with some sifted refractory powder (alumina slurry).
It costs me about 30 USD a bag to get for 50 pounds (22.5kg). I sell the kaowool, you can U2U me about it if you like.
You don't need molybdenum disilicide elements. They're expensive and temperamental. They do get to about 1700-1800C though.
