Author Topic: Sawed off cupola (Read 159437 times)

vtsteam · « **Reply #200 on:** July 10, 2013, 11:02:57 AM »

A few differences from the video -- mine doesn't have a perforated bottom -- it's completely open. Mine works with wood -- preferably 1-3 inches thick. And I used a circular lid.

Mine works even if the barrel you find has only one end on it. I also modulate the fire with the lid, and sand at the base once it is burning well. I try to keep it just slightly smoking -- a wisp or two -- rather than running it full out. I believe this gives a greater yield.

There is also some suggestion lately that it is helpful to retain some of the volatiles -- not sure if I subscribe to that yet, but I accept that as a possibility worth exploring. Also another heresy that pine charcoal is better than hardwood charcoal from a Japanese style sword making source. Though what kind of "pine" and "hardwood" have been compared is not yet clear. White pine and yellow pine are very different woods and fuels, as are cottonwood and red oak, for instance. So pine vs hardwood might be apples and oranges, so to speak!

Anyway, about to light off the second batch (if I can manage to light it) and the rain holds off. Everything was doused last night. My hardwood today is red maple and black (sweet) birch, for comparison sake.

BTW -- one could easily melt aluminum -- probably a sizable quantity -- in the heat given off during the charcoaling process. Thus a single load of wood could be used for two separate melts. You would have to find a way to suspend a crucible in the barrel (I've found that even 1/2" rebar across the opening sags like a noodle in the charcoaling heat) and a way to observe and remove it when ready. Sticking even gloved hands or head anywhere near the opening is not advised -- at least with a hardwood burn.

vtsteam · « **Reply #201 on:** July 10, 2013, 03:45:58 PM »

The sun came out and it got hot and muggy, so I started the charcoal burn. When it was just done, and I'd covered everything with sand, the clouds rolled in and we got inundated with rain.

The furnace area flooded, as did the charcoal barrel. I hope it didn't wash the sand down from the lid into the fresh charcoal below. Looks like it did from here....

This is the wettest summer I have ever seen.

awemawson · « **Reply #202 on:** July 10, 2013, 04:10:24 PM »

Bad luck. You need a simple bothy type building - four poles and a corrugated roof leaving the sides open to let you carry on playing.

vtsteam · « **Reply #203 on:** July 10, 2013, 04:29:33 PM »

Thanks, yes awemawson, that would be nice. But limited budget means even the galvy roofing would be difficult.

I'm doing better than local farmers, though. Almost none of the hayfields have been cut for the June hay. All turned brown and gone to seed. I don't know if they will be able to get it down and try for a second hay if this continues. They need a week of drying weather just to get out into the fields.

Between thunderstorms I ran out and knocked the barrel over -- was surprised to see most of the charcoal clean and dry. I salvaged enough and got it under cover to bring the total on-hand to 14 gallons. The furnace takes 4-1/2 to fill. So I may try it when the weather improves.

vtsteam · « **Reply #204 on:** July 11, 2013, 05:50:13 PM »

Rained this morning, but cleared by afternoon and was able to work while ground dried. Today's cupola work:

Added view ports to both tuyeres...

vtsteam · « **Reply #205 on:** July 11, 2013, 05:51:50 PM »

Added a support fixture to the lift rod for pre-heating the ladle:

vtsteam · « **Reply #206 on:** July 11, 2013, 05:54:16 PM »

It's just a scrap pipe nipple quickly carved into a sort of spiral with the hand grinder. Not a thing of beauty, but it works well.

vtsteam · « **Reply #207 on:** July 11, 2013, 05:58:59 PM »

It grips the rebar shank. Stays put even when I rotate the lid of the cupola as seen here, yet is easily removed with a twist and lift motion.

Today I also made up the sand bottom of the cupola. Everything is looking ready except maybe a formal means of moderating blast. Weather tomorrow is predicted at 30% chance of rain mainly after 5 PM, so I may have a go at cupola casting with with charcoal, second time around.

andyf · « **Reply #208 on:** July 11, 2013, 07:04:01 PM »

I'm just an interested observer of this topic; molten metal is well out of my league. However, it does occur to me that your weather reports aren't encouraging me to visit Vermont. It will soon be 40 days and nights; time to stop gathering animals two by two and charcoaling wood which might be better employed in building an ark.

Andy

vtsteam · « **Reply #209 on:** July 11, 2013, 07:53:28 PM »

We're really not responsible Andy, we get our weather second-hand from New York state.

vtsteam · « **Reply #210 on:** July 11, 2013, 08:17:31 PM »

Here's an ark, of sorts, I built 22 years ago in Vermont. Took it 1700 miles down the coast and across the center of Florida. Lived aboard, off and on for 10 years in Florida and later Louisiana. Finally towed it back to Vermont, and used it as a base camp on land while building my present house.

Launch day, November 1991:

Interior:

Base camp ten years later back in VT, October 2001. Frost is on the field again.

vtsteam · « **Reply #211 on:** July 12, 2013, 06:44:53 PM »

Tried the cupola on charcoal today. Even with the extension the charcoal burned down very quickly. A few minutes and it was down 18 inches. Melting was more thorough than last time but not good enough. The melt froze in the well -- never went completely fluid. I did have one small stream of metal start out the tap hole before freezing . \

Here I'm getting ready to chip out the blockage. I never did get to bod it off. The bod rods are at the ready in the cinderblock in this picture, and the ladle is heating on top of the cupola. The flame had been impressive out the top, but by the time this picture was taken it had died down as the cupola had burned most of its fuel.

I did try a second charge after refilling with charcoal, but had no better results. In the end I dropped the bottom and chiseled the slag off the barrel.

vtsteam · « **Reply #212 on:** July 12, 2013, 08:03:32 PM »

When the cupola cooled off enough to remove the extension, I pulled the tuyeres off, plugged up the far one with bod mix on the inside, remade the bottom, installed the new oil burner, and the plinth. Brought up the compressor, the oil and kerosene, and tried an oil burn. Figured I might as well try to fill the mold I'd made while the main furnace body was still hot.

But, no luck there, either. The new burner had an air leak in a silver solder joint, so wouldn't draw the fuel. Just bubbled in the container.

So I took the burner apart cleaned it and re-brazed it. Took two tries to finally get rid of the leak. Tried it again, and it seemed to work, but wasn't drawing fuel as well as the first one had. Not sure why -- maybe there is a blockage in the jet. There was definitely enough draw for kero, but waste oil draw was weak.

I probably could have melted with kerosene, but it was getting late and general discouragement was taking over. Decided to just put everything away and call it a day.

vtsteam · « **Reply #213 on:** July 12, 2013, 09:54:47 PM »

I think I'm going to stop the charcoal cupola experiments for awhile and just melt iron with oil.

My feeling about the charcoal side of things is that it would really need a much larger bore for increasing the heat available to a single charge. You really can't just go upwards -- most cupolas fit several charges in a taller height. That wouldn't work here. You basically need more charcoal between each charge, and the only way to do that is to increase bore.

I think mine might have worked with a much smaller charge than the 6 pounds (x 2) I tried. Maybe 2 or 3 pounds. But then the well is far too large for that quantity (7" dia x 8" high) so it wouldn't be hot enough to keep it fluid.

I'd say that to successfully melt iron with charcoal -- in usable quantity -- I would want something about a foot in bore diameter, minimum, whether a crucible furnace or cupola. The well on a cupola would be short -- the tuyeres much lower than in coke melting practice, and a higher bed height.

I don't think my 7" cupola is going to work with charcoal therefore -- maybe with 2 pounds of iron it might, but that's a lot of work both in construction, pour preparation, and fuel making for such a small quantity of metal. And I bet it would pour cold.

I'm pretty certain it would work with coke, and it is proven as a crucible iron furnace with oil. Aluminum and the copper metals should be doable with charcoal. Or propane.

I'm pretty much "burned out" on furnace experimentation and construction at this point -- other than finishing up the oil burner tank and piping.

Maybe in the fall I may try a short big bore charcoal iron crucible furnace using a half 55 gallon drum -- I would still like to melt iron with charcoal at some point, but I think my cupola days are over.

Rob.Wilson · « **Reply #214 on:** July 13, 2013, 12:03:23 AM »

Hi Steve ,

Dont be too disheartened , It was a valiant effort too try and get a charcoal fired cupola to melt iron,no one could have done more .

, Step back ,take a break, you have been at this project for a wile now , spend a bit time on another project

At the end of the day you still have a very capable oil fired furnace

Rob

awemawson · « **Reply #215 on:** July 13, 2013, 04:01:17 AM »

Steve,

Bad luck with the melt - you've put a lot of effort into this.

- you are re-charging with fuel as the burn progresses aren't you? - when I've seen cupolas working they've all had to have several re-charges of fuel to get up to temp then several fuel / iron batches added as the melt progresses.

The only one I've personally attended (rather than seen on film) the fellow had many buckets all pre-prepared - some just coke, and others coke / iron / limestone mixes all weighed out.

NeoTech · « **Reply #216 on:** July 13, 2013, 04:20:46 AM »

Thats still a great furnace however you choose to fire it. =)

vtsteam · « **Reply #217 on:** July 13, 2013, 05:04:39 PM »

Thanks greatly, Rob, Andrew, NeoTech!

You make it useful to report this kind of thing.

Andrew, in answer to your question yes I did keep adding charcoal, -- I went though all of the charcoal I had -- but only after I realized it had evaporated so fast. And even later added a second metal charge (which didn't help anything). I went through 14 gallons of charcoal. The furnace had been preheated with wood for an hour with blast on, and charcoal, as well as a heat soak period with metal.

Just as observations which may help others on this particular path, I do believe that the iron layer tended to choke up the exhaust and force it out the tap hole. The tap hole was left open to look for the first iron, per most cupola books. But it hardly showed up. I do believed the open tap robbed some heat from the upper cupola and kept it low -- near the tuyeres -- but probably there just wasn't enough heat altogether for the quantity of metal. If there'd been an excess, fire would have come out of every nook and cranny! Well maybe the lid contributed to this upper restriction problem. The lid also tends to stop you from adding -- you can't see what's going on inside, and don't want to cut the blast to check, while melting. So maybe the lid was part of the problem, too.

I should some day try it with the lid off, and try melting a 3 pound charge. But don't have the motivation right now. Not saying it would work, but might be useful to just see what the difference was.

I'm going to work on the oil fired side of iron melting in this furnace. I really want to do some casting and think less about the furnace construction itself. Thank you all again.

(Shot of one fused chunk of cast iron found in the drop -- shaped roughly like the well. About 5 pounds.)

awemawson · « **Reply #218 on:** July 13, 2013, 05:08:57 PM »

Steve,

Have a beer or two - sleep on it, finish off a few more bits awaiting 'round tuits' , then come back afresh. I bet it'll work then

Andrew

Mayhem · « **Reply #219 on:** July 14, 2013, 12:24:12 AM »

Bad luck Steve but I'm glad you are placing this part on the back burner and not giving up completely.

I'm having similar issues with my babington burner. It worked when I had it cobbled together with retort stands and clamps but is behaving badly now I have it in a self contained unit. I played with it a little yesterday and think I may be on to something but who knows

I look forward to seeing your results of using the oil burner, as if I cannot get the babington burner to work I will be heading down that path.

vtsteam · « **Reply #220 on:** July 15, 2013, 12:40:24 PM »

Thanks both of you! Perhaps another cupola some day, and maybe even a try or two with this one in a few months time if I thought there was value to it.

This furnace will continue to melt iron at present as an oil burner. We'll see where we go with that -- plenty of scope for improvement there. That first pour must have been beginner's luck! Anyway I'll open another thread for it as an oil burner if anything interesting comes up.

Cheers!

tom osselton · « **Reply #221 on:** July 16, 2013, 02:35:58 AM »

Vsteam have you tryed a bigger blower or maybe another vacum one for each tyure by the look of your pic it came close to melting it may just be low blast presure.

vtsteam · « **Reply #222 on:** July 16, 2013, 08:24:37 AM »

I suppose it's possible Tom. But charcoal embers were flying out of the top as is -- I have a burn on my ear to prove it.

Maybe more air rather than more pressure. One possible way to do that would be to leave the lid off to reduce back pressure.

I also don't think the well was hot enough. not sure what to do about that except lower the tuyeres.

One more thought -- charcoal is supposedly hotter burning than coke. The problem is that it burns so fast. Maybe larger charcoal would be better. I tried to mimic coke size (3/4") for this size furnace (7") but maybe that was a mistake. Larger pieces burn more slowly, plus they let air through more easily. Maybe that would compensate for the charcoal characteristic of too much too quickly. A flash in the pan...

Lots to think about.

Meldonmech · « **Reply #223 on:** July 16, 2013, 10:12:08 AM »

What a fantastic effort, you have achieved a great deal and aquired invaluable experience. I know you must be disheartened but am convinced you will succeed after you have had a break from it. Can't wait for your next attempts. The build has been both interesting and informative.

Well Done David

vtsteam · « **Reply #224 on:** July 16, 2013, 07:44:19 PM »

Thanks so much, David!

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Author Topic: Sawed off cupola (Read 159437 times)

Rob.Wilson