Cupola furnace ?

Sounds like work to me, but it will make great youtube content when your fire dept shows up!

 

"Iron Melting Cupola Furnaces" by Steve Chastain shows how to build a 10" ID furnace capable of 700+ lbs /hr.
"Building Small Cupola Furnaces" by Stewart Marshall describes a little 7" and also a 10". The 7" It is probably capable of 300 lbs/hr, but the drawback is the individual taps are not large enough to hold in a pouring shank while another heat is melting in the well.
Before I went oil fired, I toyed with building one, like Jason says it sounds like work.
The ratio that keeps coming up is 10 lbs of iron to 1 lb of coke.

 

Here is the one used locally at the Metal Museum.

Not sure of the exact size, but perhaps 30" in diameter on the outside.
They seem to fill two of the insulating style ladles per tap, and I would guess each ladle is at least 100 lbs. since it takes two people to handle it, sometimes three.

I would guess the inside bore is maybe 16"-18".
Note that it is a cupolette, not a cupola.

I can quiz them on the exact dimensions and capacity if you want that info.

 

For all the difficulty in starting and running a cupolette, I think it would make more sense to just build a furnace.

I would recommend a stainless 55 gal drum for a shell, and a use a #70 bilge Morgan for about 200 lbs of iron, or a #100 bilge Morgan for about 300 lbs of iron.

If you want speed, use a stacked vertical dual oil burner, each burning perhaps 2.5 gal/hr oil.
Separate the burners vertically by about 6 inches.
A single burner would actually do it, perhaps a 3" burner tube, and maybe two delevans in a single tube.

I would guess 1.5 hour melt time for the #100, or perhaps 2 hrs.

Use a crane lift, and a cart pour.
I have seen small commercial foundries that work this way with one man.

A cupolette could perhaps be run by one person, but would be 10 times the work of an oil-fired furnace, for very little gain other than bragging rights.

.

 

I have Stewart Marshall's book.
You can have it; I think I still have it.
I bought it before I found out that coke is not normally available in these parts.

Edit:
I also found a written description of how to operate a cupola.
There are some things you can do wrong, and the melt can freeze up if you are not careful (this happened to one of the local art groups a few years back).
You may also need an oxygen lance if your tuyeres get clogged.

.

 

Stuart Marshall has the best overall information and Chastain got most of his ideas from Marshall and refined the design for better efficiency. I think it would take a team to melt, tap and pour iron from a cupola. I think the guys at Tannehill Furnace usually have at least five guys and or gals for a pour. Usually two taps and then they looked wiped out, always hot and humid there.

 

You could to it with one person, but as with a standard oil-fired furnace, you would need to do the "smarter, not harder" approach.

You would need a pouring cart with non-metallic tires that were large enough to roll on uneven ground (like mine).
The art casting folks melt iron as much to put on a show as it is to actually make something from iron, and so they swarm around like bees at the hive, and it is a great show, but in no way efficient as far as manpower (personpower is the pc term).

But one person could do it.
I would use a ramp with a powered cart like they use for houses to lift shingles up to the roof from the ground, with a motor.
This would get your raw materials up to the top of the cupola with minimal effort.
I would load up all the scrap iron and coke in buckets the day before, and place then on the conveyor line, ready to go up the hoist/ramp.

The coke cannot be too large or too small, as I understand it.

The trick is to not do any manual lifting; let the hoist and cart do the work.
I think I saw an electric cart too, but for 100 lbs, you can easily roll that manually.

The insulating ladles are really nice too, and keep the iron hot for a long time after the tap.
Pre-heat them of course.

And place a metal shield over the top of the ladle, and let the very first part of the molten stream go off on the ground, to clear out the clay plug bits.



.

 

Here's a big surprise! (Not really lol).

 

There is a member here who has or has run a cupola in the past. Is it Ironsides? I seem to recall a quick YouTube video of an Australian gentleman with a small team running a cupola a couple years ago. And they had their technique down, too.

I bought Steve Chastain's book four years ago and I think I read it twice. He has a background in engineering and does a decent job at explaining several aspects of the furnace's operation mathematically so a simpleton like me can grasp it.

Here's a few take-aways from the book:

• A cupola is a batch melter. You may get 100lbs/hr of molten iron out of it but that won't be 100lbs in one shot; more like 4-5 15-20lb+ pours. And when the pour is ready, its ready right then and you have to be prepared for it.
• The iron picks up carbon as it drips down through coal/coke bed which makes for good carbon content later.
  
• Setting up a cupola to run is called a campaign and at the end of each campaign, you have to repair the refractory inside that has eroded away.
  
• Chastain borrowed a lot of Dave Gingery's work on centrifugal fans to build essentially a Gingery blower fan (which I believe he did with Dave's blessing) for his cupola. Steve's design calls for a 2hp blower and he explains why going bigger doesn't necessarily glean more air.
• He buys acorn coke by the ton.
• You'll need a pouring ladle.
• Cupolas sounded generally labor and resource intensive - and not necessarily something you can fire for a couple hours on a weeknight to for quick work.

At the time I was researching all this (pre-moving to the city apartment), mine was to cast an upsized Gingery lathe in iron. I calculated that'd take a fair amount of iron for a couple of the pours and running a cupola just sounded like way more hassle that it would be worth. Particularly, because at the same time I was digesting all this I was watching Justin (Indiscriminate Scavenger) on the AA forum making 90lb+ pours from a crucible furnace in a couple hours on a few gallons of recycled oil. I'm not sure what your goals are. If you need a bunch of castable iron but not necessarily all at once, a cupola may be the way to go. However, if you need a big charge of molten iron in one shot, you'll either need a really big cupola or a large oil-fired furnace.

 

Ammen has a chapter on cupolas. He says melt rate should be 10 lbs of iron per sq in of cupola area. A 12" cupola should make 1150# of iron per hour according to Ammen. I like his book because it is obvious he speaks from experience.

A 12" cupola doesn't sound like a big one...

 

If I were going to build a cupolette, I think I would make it at least 14" diameter interior, but I am still checking some things so don't quote me on that.

.

 

I guess you've been quoted.

 

After further research, a cupola in Stewart Marchall's book is made from two 55 gal drums, welded one on top the other, with an interior diameter of perhaps 15"-16", and between 3"-5" of refractory.

But actually I would build a cupolette with a lid, and so the whole affair would be much shorter, but I think I would stick with the 15"-16" interior diameter.
And take this info with a grain of salt, since my cupolette knowledge and experience is basically zero.

I have watched quite a few operate, and asked a lot of questions, but I still have a lot to learn.
Watching and doing are two very different things when melting iron I have found.

.

 

PatJ,

I am curious to know the construction details of the insulated ladles. What refractory lining do they use? How long will they hold metal before losing 25 to 50 degrees?

Denis

 

Luckygen1001 = ironsides

Post #11 is ironsides running his cupola.

.

 

The ladles are a commercial brand, and they don't appear to be very heavy.
They look a lot like thick compressed cardboard, but of course they will stand up to iron temps.
They seem to be quite insulating, and the pouring folks seem like they stand around for a long time before embarking upon multiple pours that span many minutes.

I can find out the exact brand if you need that.
They need to be preheated to drive off any moisture, and generally they are put upsidedown above the exhaust stream.

.

 

80 cents a pound seems very expensive. They sell coal down here in TN by the ton. Certainly not 80 a pound. Can't you source it from far away and freight ship yourself a half ton?