Cupola furnace ?

Discussion in 'Furnaces and their construction' started by DavidF, Mar 20, 2019.

  1. PatJ

    PatJ Silver

    Coal is not coke.
    Coke is made by heating coal in the absence of oxygen, which takes energy.

    It is easy to buy a truckload of coke around Birminham, AL, and as I recall it was about $12,000.00 a few years ago.
    I am not sure how many lbs a truckload of coke is.

    By comparison, if you run an oil burner for 1 hour at 3 gal/hr, then that is 21 lbs of oil, or
    maybe about $9.00 @ $3.00/gal of diesel (waste oil is basically free).
    .
     
    Last edited: Mar 21, 2019
  2. If you use coal it has to be coked first, like making charcoal out of wood. It is always cheaper to make your own stuff.
     
  3. _Jason

    _Jason Silver

    And it's just the coolest thing ever that we're able to interact with YouTubers a world away in forums like this, too!
     
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  4. Tobho Mott

    Tobho Mott Gold Banner Member

    I found a coupl'a cupola videos on Ironsides' channel:





    I remember watching these a few years ago, probably when the second one came online, as I had just discovered backyard casting and signed up on AA a few months before then. Thanks for the reminder!

    Jeff
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Ok, so the casting weight would be approx 130 lbs, and guessing another 70 for gating and risers.... So looking for a 200# tap... Or maybe build 2 smaller copulets and try to synchronize the melting so two 100# taps could be poured at the same time??
     
  6. PatJ

    PatJ Silver

    If your 200 lb casting is a one-off affair, then perhaps consider two smaller cupolettes.
    If many/all of your castings will be in the 150-200 lb range, I would say just build one cupolette with a 200 lb tap capacity.

    I would think that running a 200 lb capacity cupolette for small castings would be very inefficient.

    You could also build two cupolettes, one large and one small, and use the same blower and perhaps air distribution header for either one, and use one for large melts and one for small melts, but not both at the same time.
    This assumes that you want to go whole-hog into the cupolette thing in an efficient way.

    I don't think a cupolette shell with refractory is that expensive.
    Perhaps 200-300 dollars each.

    I have a large furnace for iron and a small furnace for aluminum.
    I am considering building a small furnace for iron but I am not sure of the wisdom of that yet since my parts and crucibles tend to be on the larger side.

    .
     
  7. Melterskelter

    Melterskelter Gold Banner Member

    DavidF,

    I imagine you are far past basic the information contained in this article from 20 yrs ago. But it is a very "nut and bolts" approach to cupolette construction. In the modest sized cupolette outlined in the paper 900 pounds of high density refractory (he used AP Green "Super G Plus") is needed for his 100# per tap furnace.

    https://mountainscholar.org/bitstre...rer_John_Cupolette.pdf?sequence=1&isAllowed=y

    I have wanted for a long time to see a cupola/cupolette furnace in operation. I think this would be a cool project.

    Denis
     
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  8. PatJ

    PatJ Silver

    Cupolas/cupolettes are very labor intensive.
    I guess you get what you play for.

    .
     
  9. DavidF

    DavidF Administrator Staff Member Banner Member

    Actually, this is my first look into a cupola type furnace. I tend to do things on an as needed basis and prior to this hair brained idea I've been thinking about, well there was just no need.
    That's a really good article !!
     
  10. DavidF

    DavidF Administrator Staff Member Banner Member

    Damn :(
    Just missed out on this lol bit of iron..
    20190321_152937.jpg
     
  11. ESC

    ESC Silver Banner Member

    I did a 3 day session at Knight Foundry in Sutter Creek back in the 90's. I think the cupola there was about a 30" and as I remember had about a 5 man crew to run it. I didn't understand what was going on with the furnace since I was new at casting then, but ran all the machine shop equipment including the double headstock lathe. They had a 15' swing lathe to turn the wheels for the deep rock mines around Jackson, Ca. I molded a stove back and was given some broken 4 pin flasks that I repaired and used for the smallblock casting.
    https://knightfoundry.com/
     
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  12. Ironsides

    Ironsides Silver

    David, here are some facts about cupolas I used to make my cupola. It comes from a chart that gives guidelines to build a one ton per hour cupola to 29 tons per hour. I used the one ton per hour to scale it down to what I wanted. Lucky for you it gives two charts one in metric and the other in imperial sizes.

    A one ton per hour cupola needs 254 sq. inch area (18”inside dia.) The height above the tuyeres where the first charge of iron is placed is 38” The height from the tuyeres to where the cupola is full with coke and iron charges is 96”. A cupola is a continuously running furnace so it has to be kept full to get hot metal. If you place less charges in the cupola the blower has to be cut back otherwise there will be less back pressure and the height will change. Less blast means cold iron.

    Moving on, one coke charge will weigh 25 pounds and one iron charge will weigh 250 pounds. So to melt your 100 pounds of iron this cupola will melt it in 2.68 minutes. So the 254 sq. inch area can be scaled down so if you want to melt half a ton per hour you will need 127 sq. inch area. There are many facts you need to know but this will give you a starting point to work out what size you need and how much coke you will need. Before I made this post I made an 18” circle of bricks to see how much area a 25 pound coke charge would take. It was roughly 115mm high and an average sized piece of coke weighed 180 grams.

    There is a reason why that chart does not go below one ton an hour, a smaller furnace is much more difficult to operate. Smaller cupolas lose heat much faster than larger ones. Before I go into details of my cupola, underneath that chart was a long winded statement about what they say are only guidelines so my take is “results may vary in your neck of the woods”.

    For my cupola I aimed for a 63 sq. inch surface area. The metal to coke ratio in the chart suggests a 10:1 ratio and with all the different sized cupolas that ratio stayed the same. With my cupola I was not getting hot iron with that ratio so I ended up a 5:1 ratio to get hot iron. The height for the first charge of iron was 34”. The total height of my cupola is 60" The largest cupola in that chart can melt 29 tons per hour but the height of the first iron charge is only 45”. Also the total height with all the coke and iron charges is 240”.

    As you can see some things can be scaled down and others cannot. There is one mistake everyone makes when using a cupola for the first time and I made the same mistake after many melts ( getting over confident ) is a cupola has to be drained every 6 to 8 minutes. Once the bottom of the cupola collects molten iron it is losing heat very quickly. So what happened to me was the well froze and I had to destroy the cupola to remove the frozen iron. To solve that problem on my small cupola I would heat the ladle to way above the iron melting temperature with a propane fired burner before tapping and use a ladle that was capable of holding two taps. I would keep the burner running at maximum after the first tap and switch it of before the second tap. A two man ladle was used to pour between 85 to 95 pounds of iron.

    Going by the chart it was supposed to melt 250kgs per hour but I found that it would only melt 200 kgs (440 lbs) per hour. To make things run smoothly I found that four persons were needed to divide up the pouring and charging tasks and many other minor tasks that if forgotten could end up in a disaster. Two persons could do it but things happened so fast that it became organised chaos and many problems arose leading to faulty castings and shutting down the cupola early. Cupolas can be a unforgiving furnace to the beginner because it works in a very different way to a crucible furnace.

    If you like watching videos about cupolas, this one has a lot of information about running one.

     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    @Ironsides, did you add any type of flux to the charge? And approximately how large were the iron bits being melted in the charge?
    One article I just read said the iron should be broken up to 2" x 2" x 3/8" that would be a bit of a pain in the arse. Most of the scrap I have it 1" thick...
     
  14. Melterskelter

    Melterskelter Gold Banner Member

    A typical dump truck caries 10 to 12 yards of material A yard of coke should be around 3000 pounds based on GoogleFu----that needs confirmation. A truckload is probably on the order of 30,000pounds. Or 30 cents a pound in your area.

    Denis
     
  15. Melterskelter

    Melterskelter Gold Banner Member

    Ironsides,

    What is the source of the chart you are referring to? Asking not so much for my own use as for having that information recorded in this thread for future reference for the guy three years from now getting some hare-brained ;-) idea about setting up a cupola.

    Denis
     
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  16. Ironsides

    Ironsides Silver

    Yes I did, equal portions of limestone and soda ash. Very dirty scrap requires a lot more flux to wash away the dirt to the cupola well and then it is drained out of the slag spout. Scrap iron should never be more than 1/3 the dia. of the cupola. If you do put in pieces larger than that you will get a log jam of scrap iron which will stop anything going down the stack. Those two items are some of the many hurdles beginners face to get a cupola to run smoothly.

    I photocopied it from a book that I have forgotten the title. In those days there was no internet so the photocopier was used to copy very useful information.
     
  17. DavidF

    DavidF Administrator Staff Member Banner Member

    So I have received a couple of different plans from people and have started estimating the cost to build the cupola. looks like it will be around 2K or so using as much I have laying around that I can. I was also advised to find a someone local that runs a cupola to learn from them how to run and manage it before starting mine. The basics are pretty strait forward, but apparently there are some idiosyncrasies best gained through hands on experience.

    This is a pretty good read for those interested. https://www.scribd.com/doc/24270543/Cupola-Design-Operation-and-Control

    Ill post more as I acquire more information and progress. Interestingly enough, the gentleman I have been speaking with that runs a cupola fairly often is looking into using a crucible furnace instead of the cupola because he feels he can mange it by himself and not need a team of people (which has become apparent to myself that a cupola will be a group effort) He has also pointed me to a person who deals with the distribution of innoculants in quantities aimed towards the hobbyist, like 5 gallon bucket loads... Ill be reaching out to him shortly.....
     
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  18. DavidF

    DavidF Administrator Staff Member Banner Member

    Baby cupola. Didnt think it would be possible, but here's the picture so it happened...
    FB_IMG_1571868820734.jpg
     
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  19. Melterskelter

    Melterskelter Gold Banner Member

    If cupolas can be practically scaled down to the size pictured, then any size in between is possible! I was aware of cupolette furnaces weighing an estimated 500 or 750 pounds. But not one weighing 20 to 30 pounds like the one shown. I am very interested to know more about it. Tell us more please.

    Denis
     
  20. DavidF

    DavidF Administrator Staff Member Banner Member

    I'll see what I can find out. I'm going to an iron pour on Nov 16th. They are running a 30" bore cupola that taps 700 lbs a shot... I had no idea that there was any place local where I could participate until just moments ago..
    Participation might be just sweeping the floors, but I don't mind...
     
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