Advice on which furnace design to use

Discussion in 'Furnaces and their construction' started by Lewis, Jul 16, 2019.

  1. Lewis

    Lewis Copper

    hello all im new to forging and new to the forums. ive done a lot of reading and learning on the subject and i have come to the point where i have 3 versions of furnace i can build.
    ill be using used fryer oil as the fuel as its free for me. i cant afford to buy lots of gas.
    i need the furnace to have a decent life span and after reading a lot of veterans saying the wished their first was bigger i want to build it with progression in mind.
    i want to melt cast iron, copper alloys and aluminium alloys and i want to fit an A16 crucible in it though my first will be a fair bit smaller

    what i have already:
    all the parts to make a simple gravity fed oil burner
    leaf blower
    55 gallon oil drum.

    ive costed the 3 designs i have at the moment as follows.
    thin walled cast refractory.
    internal dimensions of 350mm (14.5"ish) height and about the same for the diameter
    refractory will be 1600 degree cast face 25mm thick all round
    backing will be a simple clay sand mixture tamped in behind it for insulation
    base would be the same with a 25mm thick layer of refractory and a 40mm tall cast refractory plinth
    lid would be a cast refractory again 25mm thick with flue backed with some 1400 degree ceramic fiber
    cost for the materials for this is £125

    second design is purely refractory brick similar in size andshape to the simple one posted by oldironfarmer
    inner dimensions would be almost the same as the first on and it would cost £195

    the third is the most expensive but seems to me to have a very long life potential. it would be high grade insulating fire brick in the same design as above rated for 1530 with a 10mm thick cast refractory face all around to protect the bricks but this costs £240

    i want to cheap out and go with the first option but it would be too heavy to move far when finished and im not sure how long the unit would last with such primitive insulation. especially when getting to cast iron temps
    the loose brick design has the big advantage of being easy to disassemble for transport and replacing damaged bricks. i could also initially build it shorter while im still only doing small stuff and then buy more bricks later to build it up this would save around £30 in the short term. the third option is a fair bit more than i want to pay but if it would last a very long time id probably be willing to spend the cash.

    hopefully my descriptions are good enough for you to get an idea of what im aiming for. i was wondering if any of you have would be able to chip in your thoughts or give some advice on what you think is the best aproach

    thanks in advance for your input
     
    UserError likes this.
  2. UserError

    UserError Lead

    Hello, what did you go for in the end? Cheers.
     
  3. Jason

    Jason Gold

    Lewis what jumps out at me is use want low maintenance, decent life span and cast iron. To me that means, kaowool with a mizzou or kastolite hot face. So you'll need 2-3 55lb bags of castable refractory cement. My furnace would handle an A16 and I bought a box of 2300degree kaowool and 2 bags of mizzou. That stuff ran me about 240bucks (roughly £150)
    I built a simple kwiky burner and burn jet-fuel/used motor oil.... While I have never tried iron, I'm pretty sure it would do it if I upped the air and fuel to it. Keep in mind, Fire brick is great stuff, but it can take a long time to get it up to temperature. The goal is to not have a furnace that spends all your time and fuel heating itself and not the metal. This is called thermal mass. I think a mizzou furnace offers you what you are looking for in terms of longevity, speed and fuel economy. Even cheap fuel like your free oil still costs time and money. I have a bottomless pit of jet-fuel, but I still don't want to spend all day waiting on a melt. If you wanted to save a few pounds, you could skip out on the kaowool and back the refractory shell with sand. This is a little more difficult to build, but works well. It's really easy to line an old tank with the kaowool, make a round cylinder form, and mash the refractory cement in between the wool and the form. Once set, you remove the form and you're done. Hope this helps you.
     
  4. Lewis

    Lewis Copper

    well my decision in the end was to go for the first option with the thin walled refractory. I had some problems with my mold though and it ruptured while i was casting so i did a redesign. i reused the failed casting material as agregate in a solid wall gas cylinder. ive not had a chance to run it yet as im back studying now and so its on the other side of the country until the summer.

    on the plus side i now have 4x0.6m of 25mm kaowool without a purpose that is going to likely be used in the making of either a gas forge or maybe a glass kiln
     
  5. Lewis

    Lewis Copper

    thanks Jason i attempted that but my mold making skills wernt upto the challenge. i mentioned above how i finished it but ive yet to test it. on the plus side my redisign is considerably smaller and a bit lighter than it wouldve been otherwise so a bit more portable (though not portable enough to gome with me to uni :() im looking forward to getting it up and running properly maybe around easter though with the modifications i dont think it will like iron.
     
  6. Jason

    Jason Gold

    Don't sweat it Lewis. Many of the guys start out like you did, gain some proficiency at pouring aluminum and bronze then build another furnace with IRON in mind. People watch us on YouTube and say Oh I can do that.... But I'll tell you, until you pull a 20lb pot of liquid bronze that's just 12inches from your wedding tackle out of the furnace, you will find out real quick what you are made of.
    It still makes the hair on my neck stand up and after a safe pour, I am relieved. None of it just happens by being lucky. It's practice, dry runs and patience. I'm still not ready for iron, maybe someday.
     
  7. Lewis

    Lewis Copper

    yea the more i think about it the more im not fussed about iron. it would be nice to be able to cast usefull tool parts for vices etc but for now useful parts for me will be bronze and aluminium... well once im back with it and able to get casting
     

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