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Thread: Planning stages for a new furnace

  1. #21
    Senior Member machinemaker's Avatar
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    never used a drain hole, but always used SiCarbide crucibes or alumina crucibles in induction furnaces and kept track of their condition and thickness. The only metal on the floor of the furnaces was from my own fault of either over filing the pot or sloppy addition to the pot. Never had drains on industrial furnaces either.
    kent
    Kent
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  2. #22
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    You know Kent, there's a big difference in commercial melting and hobby melting. Most of the time we're using small crucibles that don't hold large pieces and remelting sprues and failed castings, stuff that extends over the crucibles and are prone to hot shorts and falling into the bottom. That's where my faults are, not catching them in time. If my furnace didn't have a drain, there would be a couple pounds in the bottom. You just have to keep the prospective here.
    Not trying to flame on you, just my side of the story.
    Bones

  3. #23
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    Great discussions!! Being a newbie to all of this, I am concerned about me being sloppy, spilling, or just doing something stupid to flood some metal to the floor. But I also want to keep in as much flame (heat) as possible.

    That got me to thinking (which is a scary thought). What about designing in a drain that was able to be capped. Thought #1 was a 1" pipe coming out the side, with bottom of pipe at floor level ... but then cap loosely with pipe cap. Feasible?

    Somehow I got to reading a paper from the UAB School of Engineering on constructing a cupola furnace. In that paper they were talking about tuyere covers, and they had 3-4 different cover designs (one a sliding gate of some kind of glass). I think I will make a hybrid of their designs and test it. If it doesn't work, I can always pull it and plug the drain hole. I am imagining an under plinth hole, but welding a sliding gate on the bottom of the outer shell. Probably 3/16" plate, sliding in a small frame that I fab up. Anyone ever try something like this? I suppose it may well freeze shut before I could react to getting it slid open.

  4. #24
    Senior Member r4z0r7o3's Avatar
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    You can only deploy creative options on a drain hole that's not there. Making a drain in already cured refractory is crazy-talk. Don't worry about the details, add a 2-in hole and figure out what to do with it later. There's a whole section in my build about making the form out of wooden dowels. Plastic works too. If they get stuck in, then you just burn 'em out when you fire the thing.
    "Things that are complex are not useful, things that are useful are simple."
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  5. #25
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    I'm getting some ideas from the drain discussion. I had one in my first furnace which was charcoal using steel crucibles. The drain saw a lot of service because the propane cans invariably burned through at some point. Since I've gone to regular crucibles only oversized slumping ingots and a degassing incident as mentioned above have gotten metal on the bottom of the furnace. It's small amounts and can be picked out when the furnace is cool. When I started burning oil in it as well as in my new furnace which also has a drain, I've experienced unwanted flame out the hole. I think I will try a mixture of clay and sand to create a plug for the hole which can be knocked out with a rod in case of a catastrophic flood of metal. Since the drain might only be needed rarely or never at all I think it's worth whatever effort would be necessary to remelt the spill and knock the plug out. I think my tuyere is high enough off the bottom to keep the burner out of harms way.

    Pete

  6. #26
    Yes its given me some ideas too, Pete. I roll my furnace around on a clothes cart, which has a sheet of plywood as a base so when I fire the furnace flames shoot out the bottom and while its stacked on firebricks, its still getting slightly scorched. I need to do something before it gets to be a problem.
    I'm going to try cactusdreams idea of the foil band aid, and if that doesn't work try a tiny plug of kaowool behind the bandaid. Hopefully in either case the bandaid will fail when I need it to fail the most.

  7. #27
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    I apologize for sounding like a troll. When I started I was an inexperience backwoods kid, want to be artist and did a lot of mistakes years ago. Mentors gave me a lot of advice over the years and somethings I have come to believe.
    A. my biggest failures in casting were when I was too cheap or too uninformed to do things right. (right now money is tight and unfunded retirement is looming, but scrounging and fixing what others can't can buy a lot of materials, also stop looking for materials from retailers and search for industrial suppliers. How many time have guys here gotten deals from boiler repair shops or industrial suppliers willing to talk someone excited about their hobby)
    B. I am willing to buy good crucibles. (The only crucible that has failed on me, I let rain build up in the bottom and I thought I could dry it out quickly in the furnace!!! real dumb!! After pouring, while red hot, I make sure they are drained and scraped out, Before using when cold I will inspect them for cracks and measure the wall thickness and when in doubt use a new one. Be safe, please. Steel or Iron crucibles in my opinion are great for lead, tin and zinc alloys, questionable for aluminum, and risky for copper alloys.
    C. Precautions when filling the Pot. When filling a cold crucible leave some space for the cold metal to expand. heat anything that you are adding or tools that will go into liquid metal in the exhaust to at least above boiling so it is dry. cold metal will condense water in the exhaust gas and you don't want steam blowing metal back at you. When preheating metal in the exhaust, do not let it melt and drip into the crucible, it is liquid and falling through O2 and hydrogen and will suck up that gas. FishbonzWVa you are absolutely RIGHT! we all do it. have scrap hanging out of the pot and it break off. That is where 90% of the metal I ever had in the bottom of a furnace came from and It was my fault. I doubt that a drain would have helped, maybe? I do pull those blobs off the bottom when it is cold and throw them back in the scrap(I'm cheap). A good whack with a hammer when hot usually will break things up small enough to fit in the pot.

    I am just an old fart, but hopefully you will not make the same mistakes and have lots of success. Planning my next furnace, it will be my smallest in years, build around either a #12 or #16 bilge. Small enough that I can handle by myself (have the burner, ceramic blanket and some 16 gauge for the shell). I am inspired to see what you guys are doing.
    kent
    Kent
    There is beauty, power and excitement in simple old technology!

  8. #28
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    Not at all Kent, you are just used to industrial sized melting. I whole heartily agree on the store bought crucibles. That was the #1 improvement for me, running neck and neck with it was controlling the atmosphere. I got caught up in the time race, how fast can you melt. My burner can melt a pot in 20 minutes but the ingot would probably float with all the gas en-trained. Now it's 27 minutes to get a good quality melt. It took 2 1/2 years for that to sink in.
    Bones

  9. #29
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    Well I guess it will be all systems go, as soon as I start building, lol.
    • Drum for outer skin - check
    • Form for inner HF wall - check
    • 2 1/2" x 24 exhaust pipe for burner - check
    • Delavan nozzle (.8) - check
    • 5/16 tube for air & oil to nozzle - check
    • 4 bags of Sparcast LC32AL (3200* castable from Spar Refractories)- check


    Some of these suppliers really make me shake my head. I finally ended up finding 3 within an hours drive.
    • Carpenter Bros (which is a pretty big supplier around these parts) kept trying to push a 3000 product, getting info on other items they carried was like pulling teeth and after a week plus I still had no clue what other refractories they had in the local WH and never got a price.
    • Another small outfit quoted $1.50 a pound for Kricon 32-70 that they stock ... that's $82.50 a 55lb bag.
    • So, I bought the Sparcast LC32AL for $48.95/bag. Smallish place that mostly handles IFB, but was very happy to do business with me.

    Granted folks like us are not big volume, but give me the info, let me make a decision and I am in & out in 5 minutes ... to me that would seam like gravy money.

    So, I still need to come up with a form for the outer side of the HF. I was going to use the 19ga that I have a round ... but that was a PITA even with my slip roll (course I was trying to manage and crank by myself). Also, what is the best way to lay out the tuyere hole before cutting it into the forms?? Also, is it advisable to encase the tuyere in the dense castable ... from the HF to the outer skin? I guess it would add some support, but would it conduct too much heat?

    Still need the ceramic wool. Have time for that as I need to do the casting and get the base designed and made up.

  10. #30
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    Check out the vid in post 309. http://www.alloyavenue.com/vb/showth...Casting/page31 He has a drain hole built through the refractory wall that can be plugged with a mixture of fireclay and sand and can be easily knocked out for direct melt or whathaveyou. Putting steel through your refractory through the wall is probably not a good idea. Id suggest encasing the tuyere in refractory from the hotface to the shell not only for strength but to protect the insulation. Same thing if you install a drain of some sort. You can use a piece of pipe with a half dozen turns of saran wrap around it then slide it out after the refractory has set up. I cut a slot in my pipe form so i was able to squeeze it a bit to help in pulling it out. In order to locate my tuyere holes i set both inner forms in place level to the top of the drum and set my tuyere pipe on top at an angle such that it entered the bore tangetially. I marked the top of the forms and then just extended the lines down each form and the shell to their respective heights. I used a hole saw first and finished the ovalish shapes with snips/grinder. When you put the insulation inside to mark it for cutting, dont forget to cut it oversized to accomodate the refractory tuyere.

    Pete

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