Propane burner for a monster of a furnace

Discussion in 'Burners and their construction' started by Cooper Campbell, May 26, 2020.

  1. Hi all, I was recently gifted a furnace that had been living in the backyard of a friends shop for the past 10 years, it’s a beast of a thing, the interior volume being 18”x 22” with what appears to be #100 crucible cemented into the interior volume (the furnace is capable of axial tilt for pouring)

    My issue is getting or building a burner capable of getting this thing up to temp. I have an interior volume of approx 2000 cubic inches to heat and was hoping to run this furnace off propane. I’ve been eyeballing the devils forge burners as well as the “hybrid burners” but the math ain’t adding up. My intention is to do pours of 100-120lbs of bronze and copper (I made the mistake of being a sculptor) I have some foundry experience from undergrad but it appears that I am at the limit of said experience.

    Any and all ideas would be greatly appreciated
     

    Attached Files:

  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Couple initial thoughts:
    • If it's been sitting for 10 years I'd recommend a gradual ramp in heat the first time you light it off or that crucible and refractory may suffer from the moisture absorbed over the course of those years. If that's a weed burner I see hanging on the hose coming from that 20lb propane tank, not to worry.
    • Any idea how many pounds of refractory it has? It's going to take some real energy to bring that to temp, even without a charge of bronze.
    • Just to confirm, A100 meaning 100lbs of aluminum correct? More like ~280lb of bronze capacity. If 100-120lbs is really your usual melt size, ok but if it's the max you'll ever do, and your average melt much smaller, your furnace is much larger than you need and will cause long melt times and high fuel costs.
    • Propane would be very expensive fuel for that size furnace & melt. If you are like most artists (starving), you may want to consider a waste oil burner and/or diesel fuel or it will become the gift that keeps on taking instead of giving!
    • Can you show us a few more pictures, like with the furnace lid open looking in with some reference dimensions, and any exterior opening/locations/Tuyere on the exterior where the burner was mounted?
    • Being a tipper, I assume you'll be using a large ladle for pours?
    • As a sculptor/artist have you done metal casting before?
    Welcome aboard.

    Best,
    Kelly
     
    Last edited: May 26, 2020
  3. Peedee

    Peedee Silver

    50Kg of bronze, I'm watching!

    I can't add to what Kelly has said. Rasper has done some pretty big melts but on oil so maybe he and others can help as well.
     
  4. Tobho Mott

    Tobho Mott Silver Banner Member

    Wow, that is quite a furnace! What they said, and welcome to the forum.

    Jeff
     
  5. You are eagle eyed, yes it is a weed burner, was putting some heat into it yesterday to check the fit of the lid (not great) and dry everything out, there was indeed quite a bit of moisture trapped in the crucible.

    No clue about the weight of refractory, there appears to be 3-4” inch lining with a ceramic coating, but it has a lot of hairline fractures up and down the interior walls.

    The crucible has interior dimensions of 1o” in diameter with a depth of 16” did a little research and matched it to the dimensions of an a100 salamander (approx)
    And while this pour is planned to be 100-120 lbs I do plan on increasing the size of future pours

    I have been eyeballing a drip burner but my only hesitation is my inexperience w/ that sort of thing. The furnaces I learned on were propane w/venturi type burners, is drip the way to go?

    Pictures attached

    Was planning on tipping the whole unit to pour... is that unadvisable? The furnaces I’ve worked with before were lift out/haven’t used a tipper so my assumption/plan was to tip the whole thing towards my old with the additional guidance from a trough of some sort.


    And re: my experience
    I was fortunate enough to attend Cooper Union, took all the casting classes they had (2 to be exact) and worked pretty extensively with a gentleman named Andy Wilhelm who seems to know the subject inside and out. With him I poured about a dozen of my own works and assisted on upwards of 30 other pours. I haven’t able to get back in a foundry for a 3-4 years though, however I was able to observe some gargantuan pours at the artist Mathew Barney’s studio.

    final note, excuse the mess in the photos recently relocated from ny to or and am in the slow and painful process of cleaning out my new shop. Also excuse the slippers, it’s just that sorta day so far.
     

    Attached Files:

  6. Mathew Barney with a work partially cast in walla walla and finished in ny, absolutely mind boggling in scale and complexity
     

    Attached Files:

  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Depends on whether the lining is low mass wool or high mass castable refractory as far as thermal mass goes, but by hobby furnace standards it's a big furnace. Most furnaces will have a dense high refractory hot face and then a lower density more insulating outer layer(s). I wouldn't worry too much about hairline cracks as long as it's the furnace wall we're talking about and not the crucible.

    Sounds to me like you do need that size furnace. Most furnaces here would be 10-14" bore shading the lower end of that range. Take good care of that crucible. If you need to replace it will cost an arm & a leg.

    Opinions will vary on that but there are some good threads and practiced users here on the subject of burners. I'm not a burner guy so better you hear it from the site practitioners......but looks to me like you have the interior room to accommodate oil burner combustion.

    Tipping is ok if it will lend itself to the size investments you'll be pouring. Dunno about a trough....probably not so much enthusiasm on that. Whether it's a lift out crucible or ladle you'll still need lifting apparatus of some kind. Almost all furnaces here will be lift out.

    Just checking to make sure you had the entire task sized up. Sounds like you do. Rasper is an artist here that pours bronzes in your range. I'm sure he'll chime in with advice and description of his equipment. I think he still uses propane for his burn out kiln.

    Best,
    Kelly
     
    Last edited: May 26, 2020
  8. HT1

    HT1 Silver

    how big is the hole where the burner goes???

    Becuase I would shove a forced air Propane burner sized to that hole with a matching blower and melt some Brass, to many people here just in love with oil
    propane is so much easier to work with, and considering that prices are getting closer to normal, Propane is almost as economical as oil. and all you guys with gallons and gallons of free oil need to SHUSH, that is noty normal

    V/r HT1
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Wouldn't argue that at all

    It is? Almost as cheap as free? Maybe line it up with diesel. What do you reckon your melt cost per pound to be? You do multiple melts per session right? Presuming he will be doing single pours, his will likely be a lot more due to the furnace size. The price of poker goes up with big furnaces because the amount of refractory and mas goes as the square of diameter so he likely has 4x the mass you have to heat.......and that aint free! Cost aside, he'll be consuming so LP and if he doesn't have a large stationary tank to be filled hauling those size tanks in and out wont be fun.

    Best,
    Kelly
     
  10. Peedee

    Peedee Silver

    Do we reckon that ran NG originally?
     
  11. After doing some reading and making some calls I think I’m gonna be able to come by some waste oil from my brothers chicken cart in Portland. Plus we got a surplus of diesel for our tractor so as far as cost goes I’m warming up to this whole thing. The only issue is that I don’t have a lathe yet and won’t have one till the end of the summer at least so fabrication may be an issue. Do you all have any recommendations for plans to oil burners that may suit my needs that can be built w/ out a lathe? I got a clapped out mill out here that I’ve been giving some love too so cross drilling shouldn’t be an issue. It’s just the turning I’m stuck on.

    Also thank you all for your help!!!
     
  12. Tobho Mott

    Tobho Mott Silver Banner Member

    You can most definitely build an oil burner without a lathe, I practically built mine in the plimbing aisle.

    Here's a typical pretty large drip injection type waste oil burner:

    https://www.backyardmetalcasting.com/oilburners09.html

    I believe many people have modified that design a little in certain ways for their own use. There are also atomizing nozzle based burners that others here know more about than I do.

    Jeff
     
  13. Propane is possible but not that practical for a furnace of that size: you need the largest gas cylinder you can get to avoid the liquid gas freezing to slush and causing the pressure to drop. There's a smaller furnace than your which uses A25 size crucibles and can freeze a 210Kg cylinder in an Australian summer if run continuously through the day. So for a furnace of your size you might get 2-3 crucibles before the pressure drops from cooling.

    gas.png
     
  14. rocco

    rocco Silver

    Sorry if this is a little bit of a side tangent, I'm a numbers guy and I was hoping to add a bit of context to this fuel discussion by calculating how much fuel would actually be required to melt 100lbs of bronze but I'm missing one critical piece of data and that's a reasonable estimate of furnace efficiency at bronze melting temperatures. A few years back there was a furnace efficiency thread on Alloyavenue and at aluminum melting temperatures, typical efficiency of a propane fired crucible furnace was in 10-15% range. I would expect higher temperature would translate to more heat loss and hence lower efficiency. Anyone here have an educated guess at furnace efficiency at bronze temps?
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    10% is a nice easy number to work with Rocco, and while you're at it, look up the specific heat of Al2O3 and calculate how much energy it takes to raise the temperature of 400-500lbs of it 2400F!

    Best,
    Kelly
     
  16. Petee716

    Petee716 Silver Banner Member

    It looks like we have a new member with some experience with a furnace just like Cooper's. Maybe we'll get some feedback.

    Pete
     
  17. rocco

    rocco Silver

    Running the numbers with various metals is what lead me to think about furnace efficiency. As an example, if you assume that same furnace efficiency at both aluminum and iron melting temperatures, it would take only very slightly more fuel to melt iron than it would the same weight of aluminum, which I'm sure just about everyone here would say is not realistic therefore the assumption about efficiency must not be realistic.

    Considering the specific heat of Al2O3 certainly makes one appreciate a low mass furnace, that stuff REALLY sucks up the heat!
     
  18. F25A8B46-F013-433C-B72D-F3E019E26EE4.jpeg After some reading and rummaging (I’m blessed to have a wealth of old parts and materials from the previous owner) I was able to turn up pretty much everything save some copper tubing for a fuel line. Attached is an image of what I figure.

    I didn’t add a taper to the main chamber because if the pressure is from compressed air rather than atmospheric pressure pushed through a Venturi I saw no need for the extra work, additionally I figure leaving the back end open would hurt? Again the compressed air.

    Maybe I’m wrong!

    would love to hear yalls opinions
     
  19. Tobho Mott

    Tobho Mott Silver Banner Member

    That looks like the Brute I linked above, more or less. That's actually a forced air burner, not a venturi burner. You might be better off using a different source of air unless you have an insane compressor. Mine runs off a small shop vac or a leaf blower... If you want to use compressed air, why not just go with an atomizing nozzle burner and lose the propane preheat line? I believe those need less adjustment during the course of a normal melt, but the downside to that which pushed me towards drip burners in the first place is the need for compressed air. You would still need a blower too.

    I use similar burners, one smaller (like a Hot Shot, also seen on bymc, though technically mine is a Moya burner... the difference is trivial) and one that is just a little bigger than the Brute.

    I have a YT video showing how the small one gets taken apart and put back together for maintenance/cleaning:



    And a 2-part series showing how I built the bigger one:

    https://www.youtube.com/playlist?list=PLo6k_ZP-VFj5e0A8YOiI0295sY16C8zKD

    Maybe you will find them helpful. Good luck!

    Jeff
     
  20. Petee716

    Petee716 Silver Banner Member

    Your compressor will definitely not provide enough air. A leaf blower on a router speed controller or blowoff gate will probably do the job.

    Pete
     

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