The Shop > Metal Stuff
Sawed off cupola
vtsteam:
Thanks Rob. Tomorrow was the day planned, but had a little setback this evening. Part of the lid flaked off while it was hanging off to the side. I patched it tonight, but the real problem was that I didn't add enough water to the clay/sand mix when I originally rammed it up. Most books say to keep it relatively dry, similar to molding sand. But every time I've done that on a furnace lid or repair I get flaking. I think it ought to be mixed thinner like mortar -- then it seems to stick well. It does shrink, and sometimes crack a little with more water, but it's usually solid.
The problem with this lid is it's 4" thick, as is the furnace lining. And it really doesn't get vitrified except above where the bore is. The rest just stays clay and sand.
I'm thinking that a much better way to do it would be to arch the inside upwards (hollow it) so the rim is the only area of contact with the furnace barrel. Then the whole top would be exposed to the heat and vitirify. Plus you'd have a little more room for fuel. I bet the arch would be just as stable against flaking as a shape, if not more so. Being in compression. And the lid would be lighter in weight. There's just a lot of wasted uncooked material in it now. So if it flakes again, I'll do the arch thing.
Anyway still lots to do if I'm to try an iron melt tomorrow -- the blower isn't sorted ( I do have my fan -- but without motor, and a choice of a small shop vac, and an older larger one). I might skip my fan for the first try and go with a vac. But still need to pipe it and make some kind of blast gate/control. Need to mix bodding. Should have done that today.
And need to mould a pattern in the new sand. Don't just want to pour ingots if this actually works!
Dental appointment at 11 -- and thunderstorms predicted for late afternoon. But it could all happen tomorrow..... :zap:
vtsteam:
Well, gave it a go, but it didn't work. I'm not sure how badly it didn't work because I decided to just kill the blast and close it up instead of drop the bottom. The tap hole was never closed, and nothing issued from it. I doubt I melted iron. From the looks of it through the peep hole I got the iron bright orange and that was it. We'll see tomorrow when it's cool. Big thunderstorm right now.
I think the problem is not enough height even for a single charge cupola -- or -- using charcoal instead of coke. It might have worked if either of those two had been changed, but the combination didn't provide enough heat for long enough time to melt.
It looked to me like the charcoal charge burned through in only a couple minutes before the metal had dropped (hot but intact) to the level of the tuyere. Too short a time. It should be more like 5 to 10 minutes. So that would mean more height for a deeper charge. Or coke, which probably doesn't burn as fast, being denser.
I would also think the tuyere could be lower in this type of cupola, and the bore could also be larger for the same amount of melt.
Oh well.
I can remedy the height by adding an extension, though this will mean modifying the top lift.
I also think two tuyeres would be better than one so the bed doesn't burn with a slope -- that tends to drop the iron even faster, as it slides down hill toward the tuyere. Stewart Marshall suggested that a single tuyere could work on a small 7" cupola -- so I tried that -- maybe this would also be more true for a coke charge than a charcoal charge. But I think performance would definitely be better with two tuyeres when using charcoal.
Charcoal tends to blow out the top very easily with a strong blast, again coke probably does this less since it is denser. Flying embers limits the permissible blast pressure -- I don't want to start a forest fire.
The good things about today were getting practice at a full iron run through. Getting the ladle lined and heated. Practice with the botting, and seeing how the whole thing should work.
I think it may work with a taller rig. I still don't have any access to furnace coke. The other possibility would be to oil fire the furnace as a crucible melter. I'm pretty sure that would work.
ironman:
Think of the Wright brothers, it took a while for them to deal with the problems they faced. In the end they did fly and had no internet to help them. In my first melt with a cupola I got lucky and had lots of iron coming from the tap hole but I used a cold crucible to pour the iron. Cold iron does not work very well. Cupolas have a steep learning curve, everything has to be right for it to work.
vtsteam:
Thank you, ironman! I'll have to think about what to do.
vtsteam:
What I found this morning:
It was up on top of about 7 inches of un-burnt charcoal. Extinguished when I shut off the openings. I don't think there is any metal pooled at the bottom, but it's too hot in there to get the charcoal out yet by hand to find out. Still hot at the bottom 16 hours later.
Lining looks in perfect shape, and the top fired well. Yesterday I chipped away at older parts of the top and relined so the top had the concave shape I wanted. I think it fired all the way across. So that's a plus.
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