Crucible stands

Discussion in 'Foundry tools and flasks' started by Miles Lowry, Nov 21, 2020.

  1. Miles Lowry

    Miles Lowry Copper

    Someone suggested that I use something to put my crucible on in my foundry to get it out of the direct path of the flame. I've tried fire brick which turns to powder after a couple of uses. Cast iron melts and so does granite. Does anyone have a suggestion about what to use?

    I've considered wrapping something in kaowhool (sp?), does that seem viable?
     
  2. Petee716

    Petee716 Gold Banner Member

    You can use the same refractory as your furnace, assuming it's commercial refractory, or else a dense firebrick. I'm guessing the firebrick you used is the lightweight insulating type. Kaowool will deteriorate pretty rapidly.

    Pete
     
  3. Miles Lowry

    Miles Lowry Copper

    No, my refractory began it's life as a refrigerant bottle.
     
  4. metallab

    metallab Silver

    You mean a plinth ?
    You can use an abandoned worn out crucible upside down. The bottom (which is on top now) is the least worn out. This is very heat resistant.
    I did it successfully.
     
  5. Petee716

    Petee716 Gold Banner Member

    A bit of clarification. Refractory is the cement commonly used to line our small furnaces. Your steel bottle is the shell. I see from your introductory thread that your furnace is a steel container with kaowool lining and firebrick bottom. No refractory. That's all well and good, and as has probably already been mentioned the kaowool should be coated with refractory mortar (Satanite is cheap and does the job. hightemptools.com). The firebricks your using are probably the insulating type-very light and friable. That's also ok for a bottom but a bit fragile. That same brick and bare kaowool are not designed to withstand the direct impact of your burner. They may last awhile but as you've seen with the brick, they won't last. The firebrick I'm referring to is the dense type. They're very heavy for their size. You can get them at tractor supply I think. Break one or two of them in half and stack them to get your crucible above the incoming flame. They'll last pretty much forever in your furnace.

    Pete
     
  6. By am I confused. I've been using lightweight firebrick for a plinth for years, as well as lightweight for my furnace lining. Much more durable than Kaowool. I'm having a hard time understanding why a wool lining would stand up but not a brick plinth. Don't get me wrong, I'm not questioning anyone's experience, it just does not match my experience. I guess I need to pull my plinth out and see if maybe I used a piece of hard brick. I don't think so, so I don't think...
     
  7. Petee716

    Petee716 Gold Banner Member

    Well I must apologize, I was talking out of school. Let me retract and restate.
    Although I've never used a insulating firebrick or raw kaowool in my furnace, my experience with both materials would lead me to believe that neither would hold up in use with a typical small furnace burner, so I've never been inclined to use them for that purpose. Others may have good success with them in that application, but given the OP's recent experience with a damaged crucible I'm not surprised that the insulating brick turns to dust after a couple uses. I do use dense firebrick along with a refractory plinth depending on how much height is required and although I've had to replace the plinth several times I have never damaged a brick.

    Pete
     
  8. Jason

    Jason Gold

    When I rammed up my FURNACE, I cast up a couple of cool whip containers of straight mizzou. Those are my plinths. Be damn sure to place a couple of pieces of cardboard under your crucible before you light the flame. Plinths have a nasty way of attaching themselves to the bottom of crucibles. Nothing like having a useless 3lb block attached and doing nothing!

    Anyone know when we are going to write the foundryman's dictionary! We have people cooking fish in a forge made out of a refractory refrigerator!o_O:D
     
    Tobho Mott likes this.
  9. Tobho Mott

    Tobho Mott Gold Banner Member

    I looked up a pic of your furnace wondering if you had your burner aimed right at the plinth, but the tuyere angle looks ok, it enters at a tangent to the ID of the bore to swirl the flames around the crucible as it ought to, from what I can see. Maybe your burner is running particularly oxidizing? If so that is likely contributing to the early crucible and plinth failures you have posted about. Just a guess...

    Jeff
     
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  10. Jason

    Jason Gold

    Might want to say too "lean".
    People seem to understand rich/lean from cars.

    Oxidizing/reducing eludes many including me in the beginning. Again, a dictionary of commonly used terms would be helpful. Where is that damn foundry book when ya need it?:confused:
     
    Tobho Mott likes this.
  11. My burner impinges on a soft brick lining and has not failed. Of course my drip burners leaves some of the contaminants in the motor oil behind.:eek:

    Center left shows the deposits from the burner fuel. I need to break that off again. It is very light and comes off easily, but it glows red quickly and works like a hot surface ignitor. I think my plinth is a hard brick.

    IMG_2970.JPG

    The brick with the impingement is a 2,300F brick. You can see it's cracked both ways. It would not lift out in one piece but it still serves it's purpose. There is another row of brick behind it. This is after 465 firings.
    IMG_2971.JPG

    A flash really shows the cracks.
    IMG_2972.JPG

    Jason mentioned about putting cardboard on the plinth when you start. For a hot furnace wet the cardboard and throw it down then set the crucible on it before it curls and burns up. You gotta be quick!:cool:

    I use cereal box cardboard. My plinth is firmly stuck down by aluminum oxide and copper oxides. It ain't coming out anytime too soon.
     
  12. dennis

    dennis Silver

    Would 1/8 inch masonite serve instead of cardboard?
     
  13. Seems like overkill but as long as it's not thick enough to tilt the crucible if only one side burns away I can't see any issues. I would think you would still need one for each run. Masonite would be easier to place onto a hot plinth.
     
  14. dennis

    dennis Silver

    I use masonite for, uh, patterns for cloth, e.g. for mace masks. There tend to be left-over pieces...

    I can also get cardboard, though it tends to be thicker than that of a cereal box - like close to a 1/16 inch!

    Thought ocurred to me was to dust the cardboard/masonite with a good dusting of graphite. (?)
     
  15. What would the graphite do? Speed the conversion of cardboard to carbon or retard it?
     
    crazybillybob likes this.
  16. dennis

    dennis Silver

    Help it be less inclined yet to stick - I hope.

    I'm thinking graphite/plumbago is some useful stuff in Foundry. Ammen mentioned it in one of his books. Which one, I disrecall.
     
    Last edited: Dec 4, 2020
  17. Jason

    Jason Gold

    I don't think graphite would help. The carbon left behind after cardboard burns up leaves a couple of pieces of paper thickness of the ideal anti-stick stuff.
    What are you guys pouring iron using?

    After I shutdown, I stop the blower and toss cardboard onto the plinth. The crucible goes on top in one swoop. Then close it up for a nice slow cool.
    Next time I lift the crucible off, there is that few layers of carbon and no sticky stick!
     

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