The Shop > Metal Stuff
Oil fired crucible furnace
vtsteam:
Cast this morning, with the new crucible, and just opened the mold. Not perfect, but a visible improvement. defects are fewer and smaller.
The crucible exterior looks shiny and new, the interior has some slag I couldn't scrape out, but i believe it probably has done well, too. It's too hot still to look at closely, and I'm letting it cool slowly in the furnace.
The slag was relatively compact and manageable -- not as nice as with flux added -- but much better than it had been with the old crucibles.
Total furnace run time was 1 hour 5 minutes. Actual melting time was 45 minutes, as metal wasn't added until 20 minutes after the furnace was lit.
Definite progress on all fronts. Photo of casting below:
awemawson:
Steve,
I used to bring the charge of iron and the furnace up to heat together, inverting an old crucible over the main one to allow more metal in the uncompacted state which would run into the lower crucible and avoid flames impacting and oxidising the melt thus forming more slag. Not sure that your furnace is tall enough for this approach though?
vtsteam:
Andrew, it isn't tall enough, although i did earlier make a top for the crucible out of fireclay and sand, and that actually worked. In fact it stayed perfectly intact through a couple of melts unlike those old crucibles! Had me thinking maybe I ought to make my own.
But the top wouldn't allow additional metal -- just what would fit.
This time I figured I'd follow Morgan's recommendations -- they say to bring it slowly to a red heat before adding metal, then give it full blast.
I've tried that method twice now. And the odd thing about it is, I get a faster melt that way than I do filling the crucible from the start. And use less fuel. :scratch:
I'm thinking that my furnace has lots of thermal mass to heat up -- unlike one with fiber blanket types. The walls are 4" thick so it still insulates well. But it takes awhile to get up to temp. Not lots of heat necessarily . Just time. In fact lots of heat probably just blows up the stack until things warm up.
Same thing for the crucible. Takes time. But takes less time if nothing is in it. Then when everybody is hot enough and radiating red heat, add metal and pour on the coals.
I dunno. Somethings happening to make it faster. I guess that's as good a theory as any!
NeoTech:
been thinking of making crucibles as well.. my mom work as a professionaly pottery..maker.. *what the hell its called* Ceramics.. person..
Anyway, she has a machine to make clay.. And then i found this .. man.. And his crucible making endeavours. =)
vtsteam:
I've seen that one before Neotech. It seems like a lot of work considering he is just using it for aluminum. A steel crucible with sand and fireclay lining would work as well, and most, including me, just use iron or steel alone.
Now if that crucible could be used for iron, that would be different! I don't like his tall tubular shape much, and I don't have a pottery wheel to make a bilge style crucible, so I would want to coil form it. But maybe it would be possible. He does use graphite in the mix, which seems to indicate he was thinking about the higher temp metals. Just confusing that he eventually just pours aluminum with it.
Vince Gingery wrote a book on crucible making (also using a press) which I have. But I don't believe he uses graphite, and also he says that it isn't for melting iron.
I believe that the only reason I'd ever venture into ceramics to build a crucible would be for iron. Everything else can be melted in clay lined iron or steel, which are much simpler -- and safer.
An iron melting cupola furnace has a very great advantage in that it doesn't require a crucible. Just a clay lined ladle. It also has a great melt rate. The only problem for me is that (so far) it requires coke, which I can't get.
I may try charcoal again in a bit -- with new ideas.....
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