Sawed off cupola

[vtsteam]

Measuring capacity and charcoal this morning. Looks like, if filled to the brim, the furnace will hold 9.5 liters (a full US 2.5 gal bucket) of charcoal, which weighs 1735 gm, (3.8 lbs).

Somewhat more than half of the barrel is above the tuyere, but let's say the bed is less than half -- that gives me say 1.5 pounds of carbon in the charge. That should mean maybe 6 to 9 pounds of iron, depending on how well it melts (if at all!).

So, maybe start out with 6 lbs of iron?

[Rob.Wilson]

Must be getting very close to a melt in cupola mode  Steve 

I will keep my fingers crossed all goes well 


Rob

[vtsteam]

I could probably try it tomorrow, Rob if I could work on it straight from here on out. But commitments to work today and through the weekend, and Monday all day will push it off, I think. Weather has been perfect.

Tuesday prediction looks do-able.

Unless I can sneak it in Sunday evening....

[vtsteam]

[vtsteam]

Another two to check off the list.

[vtsteam]

Mixed up 50 lbs of new greensand tonight after supper. 50 lbs F60 quartz sand with 3.75 lbs Bentonite (ceramic grade) and 2 lbs water.

I put it in a wheelbarrow and applied the Strongarm (tm) muller first the sand, then water gradually, and finally the clay.

Wonderful stuff, very fluffy and uniform compared to my ten year old sand -- which was sand and fireclay.

Well, it stood me in good stead for a long time -- built my lathe and much else. But I think I'm really going to love this new stuff!

Funny how you can get excited over some sand!

[Rob.Wilson]

Hi Steve


  nothing wrong with having a sand fetish 


I hope the weather holds for you 


Rob

[vtsteam]

I'm more pleased with the new sand than anything else!  Keep going out and making little clumps of it and breaking it apart. Nice clean break. This stuff is pure white.

I must be nuts.

[vtsteam]

Well was able to sneak in a couple minor things after supper -- painted the handles different colors so I know what is what quickly, and won't lose a tool in the grass.

And I soaked some broken up steam radiator pieces in a little dilute muriatic acid for a couple hours to remove scale and most of the rust. Then rinsed and set out to dry. That's about 18 lbs ready to go --  3 charges @ 6lbs ea. in case they are needed.

Getting there little by little!

[Rob.Wilson]

Hi Steve

I like the easy find tools , very bright    , looks like you cant be far off now 


Rob

[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.....

[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.

[vtsteam]

I removed the charcoal from the bottom. Lining is perfect. No puddle of iron. But a fair number of frozen droplets mixed in ith the bottom charcoal. Here's all the metal removed from the furnace, arranged by melting range. Sifting this stuff out feels a little like an archaeological dig. 

[awemawson]

So you were close in temperature but not quite high enough. Either not enough air or possibly too much air over cooling the burn. I suspect the former as you have unburnt charcoal left. Did you get white sparks out of the top or only orange? Many cupola designs pre- heat the blast air using heat lost in the walls.

[vtsteam]

Thanks awemawson.  Air might have been a factor but the biggest problem was not enough fuel height -- at least that's what I think.

The charge burned through in at most a couple minutes. Didn't time it, but should be more like 5-10 minutes for the iron to drop through.

I measured the furnace and the 2" tuyere is centered 7" above the sand floor, and 11" below the top of the furnace barrel.

So that's only an 11" bed height. From readings, a lidded cupola furnace can get away with a shorter bed height. That may be true, but how much shorter? and charcoal would seem to require a higher bed height normally. So I think it might have worked with either coke, or more bed height.

So, options:

1.) I have a nice strip 10" x 48" of clean steel sheet that I can bend into a furnace extension. That would give me 21" of bed height as opposed to the present 11". It will be less of a "sawed off cupola" however, and I will have to modify the lid lifting mechanism as well as make the new extension. The space for a drop may now be insufficient under the furnace, but I suppose I could raise it on blocks, and or trench a little under it.

2.) I could make an oil burner pretty easily and run it as a waste oil crucible furnace, with no other modifications.

3.) I do  not think this furnace will work as a charcoal crucible iron melter -- though I could still try that. But I believe that would require a bigger bore to seat more fuel around the crucible. My crucibles are about 5" in diameter, and with a 7 " bore, most of the charcoal would have to be sitting on top of the crucible, and wouldn't drop past it. A plinth would also block fuel. Wish I'd made the bore larger -- that would have helped the cupola mode as well, I think.  I don't know if crucibles are ever set floating, to drop with the fuel -- that would be the only possibility I think, of melting iron with charcoal in a crucible in this furnace.

[Rob.Wilson]

So close Steve 

Stick with it I no you will crack it  ,,,,,,,,,,, at least you have had iron and fuel in yours unlike yours truly 


Rob

[vtsteam]

Thanks Rob!! I'll keep going. But I'm starting to lean toward oil, just to see some liquid iron without doing another week of work. Feel like that's cheating, but I can always make the charcoal cupola extension, too.

It has also been threatening rain off and on all day -- rained last night. So out of a mixture of curiosity mixed with frustration at the weather, I thought I'd try a quick crucible run with my remaining charcoal and about 2 lbs of iron pieces. It seemed to me that I had more crucible side clearance than I'd remembered. So maybe it would work.

I made a top for the crucible out of sand/fire clay mix -- a patty. I put the iron pieces in the crucible, sprinkled in a small amount of sodium carbonate (aka soda ash, aka washing soda) and filled the crucible to the rim with charcoal pieces and covered with the top.

Then I lit the furnace with about 1/4 full charcoal, applied light blast to get it going, added more charcoal, more blast, etc until almost full. Then added the crucible and surrounded and covered that with charcoal.

Then I put the furnace cover down, applied blast, and after about ten minutes the crucible had dropped to the plinth. I then re-filled with charcoal, applied blast. When that burned down, I then re-filled with charcoal and applied blast. So charcoal three times total. Time was about 30 minutes from start.

The crucible was glowing orange in the furnace. I maneuvered the top off, and the internal charcoal was also bright orange. Couldn't see past that. I pulled the crucible out of the furnace and simply poured the contents out into the ingot mold.

Unfortunately it was just bright orange pieces of iron. No melting, but close, I think. If I hadn't run out of charcoal, a 4th or 5th round might have done it. The furnace did have to start from cold, and it does take an hour to heat the walls up. This was only a half hour, and the walls above the halfway mark weren't glowing. Normally with more time I pre-heat with a wood fire.

I'm pretty sure if it had been bronze it would have been molten even now, so I guess the crucible side of things still has possibilities.

[awemawson]

Years back I had an oil fired furnace. A Morgan No. 5. The burner was simple in the extreme. I used a central heating circulating pump to push red diesel through a small jet (0.8mm if I remember correctly, but it was a long time ago. The air blower produced 150 inches water gauge pressure, and if tested running on the foundry floor had a habit of sucking up small bits of grit and embedding them in my ankles! - it was powered by a 2HP motor. Fan was a 'shrouded radial blade type' of about 28" diameter and 4" wide. Lighting consisted of dumping an oily rag into the pit having lit it, turning on the fan, heavily choked back (simple gate valve) and slowly opening the oil feed. Then it was a case of adjusting the oil and air just as you would the gas and air with a bunsen burner to get the right flame colour. Flame was maintained by the glowing furnace and crucible.

Had to stop using it when my neighbour sold the bottom of his garden and a house was built 10 foot from my foundry 

[vtsteam]

Wow, awemawson, that's heavy duty! Too bad about the neighbor. 

I happened  to have just about everything needed for a Kwiky style burner so I'm making one up right now. We'll see if it's man enough to do the job 

[awemawson]

Mine was like this only slightly bigger and oil fired:

http://www.canfieldjoseph.com/foundry/furnaces/mms/gasoroilliftoutcruciblefurnace.pdf

Some useful data in that link

[vtsteam]

Nice furnaces!

I guess mine would be about 1/4 the smallest capacity listed. Though I think the warm up time (from experience) is about the same -- you need an hour to get my furnace up to temp with its traditional refractory  4" thick lining.

Among other problems so far, I don't believe I've properly warmed up the furnace in my last few tries. I should plan on at least an hour of full blast to get the walls glowing. Once it is up to temperature, It will become more economical of fuel, and more than one melt would probably be a good idea once it's hot. It takes a long time to cool down afterwards. It just needs to be handled and thought of in a more old fashioned way. Particularly with charcoal.

[vtsteam]

Small things completed on the furnace today - it threatened rain most of the day.

First, I drilled out the rivets holding the cupola tuyere plate on, and removed the tuyere. This will be held on with screws in future so I can substitute an oil burner here, now, yet convert back when operating as a cupola, which I still intend to do (and with charcoal.)

A couple problems re. this oil conversion presented themselves -- the tuyere hole is centered 7" above the bottom, and it is also directed 90 degrees to the bore. Ideally for an oil burner it would be near the bottom and directed tangentially to the bore.

I didn't want to put another hole in the casing and lining. It would be difficult to make a diagonal (tangential) hole through firebrick on edge without really tearing up the lining. Also I don't want additional holes to fill when used as a cupola. That inner surface and well need to be tight.

After thinking for awhile, I solved both tuyere position problems (I hope) by simply adding about 3" of sand to the bottom, and using a half fire brick oriented vertically as a plinth. The brick is located and oriented so that it acts as a deflecting vane to give a tangential swirl to the burner flame. The furnace is tall enough that raising the bottom and adding the brick puts the crucible right where it should be with clearance under the lid and supported just above the burner entry. So that looked good.

I also completed the burner jet -- several parts needed to be silver soldered. I then tested and adjusted the atomization of the burner jet with water, and briefly with waste oil @ 30 lbs of air pressure. No attempt at fire yet, but it draws oil very well and atomizes it. I'm confident it should flame.

I still need to locate the burner jet assembly into a pipe casing and then mount that to the furnace Also, connect the blower, which will probably be my small shop vac.

The only drawback I can see to this kind of oil burner is that it requires an air compressor as well as a blower. But mine is on wheels so not a big problem to bring to the site. There are simpler burners out there, but just thought I'd try this one.

I would really like to put the heat on tomorrow but we have 100% rain predicted tonight and tomorrow, as well as severe thunderstorm warnings. So it's unlikely I can.

I may make the 10" cupola extension ring tomorrow indoors, for use when I try to melt with charcoal again as a cupola.