Interupted burnout

Discussion in 'Investment casting Block method' started by Rotarysmp, Dec 25, 2020.

  1. Rotarysmp

    Rotarysmp Silver

    Hi block casters,

    Does it damage the block if you do the low temp drying off part one day (those first 4H) , let it cool overnight and then do the higher temp burn out on a different day?

    [​IMG]

    Mark
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    It can cause the mold to crack....
     
  3. Rotarysmp

    Rotarysmp Silver

    Thanks. I was afraid you'd say that.
    Mark
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Happen to know why that's the case?

    K
     
  5. Actually, no. An interrupted dryout will result in extended time for more moisture to be released as it is cooling down. You just don't want to ramp up full speed on the second go, for the chart shown, if you get it to 370C first day I'd feel comfortable ramping at the same rate from cool over four hours up to 750C. Or if you only get the first four hours done, you need to take two hours to get to 370C.
     
  6. Jason

    Jason Gold

    I asked our resident jeweler and he says he doesn't have any issues with ultravest. I wouldn't make a habit of it, but things happen sometimes and they have to shut her down.
    He suggests start all over on the cycle.
     
  7. Rotarysmp

    Rotarysmp Silver

    I got up early and have it in the kitchen oven. I'll set up some lights, so that I can pour after dark today. Wish me luck.
    Mark
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Good luck Mark. Video if you can. Night pours are great.

    Best,
    Kelly
     
  9. DavidF

    DavidF Administrator Staff Member Banner Member

    Physics!!
    There are pretty strict rules for burning out investment. Can you break the rules and get away with it? Sometimes you can, but why tempt fate.

    After the molds are poured they should be allowed to sit for 2 hours before going to burn out. Burning out a mold that hasn't fully cured can cause the mold to crack.
    Burning out a mold that has dried too long may cause it to crack during burn out.
    Molds should not be allowed to dry out for too long before burn out as this can cause the mold to crack during burn out. If you can not make it to burn out withing 6 hours then wrap the mold in a damp paper towell, place inside a sealed plastic bag and put it in the refrigerator.

    Once burn out is started, it should not be interrupted.
    There is A point of transition during burn out where the mold has very little strength (which consequently is at about the glass transition temp of pla filament)
    Also allowing the mold to cool below 250c after burn out can cause the mold to crack.
     
    Last edited: Dec 26, 2020
  10. DavidF

    DavidF Administrator Staff Member Banner Member

    At this, you have driven out the moisture without calcifying the investment and would be left with a very weak investment which could crack upon refiring.
    Could being the operative word.
     
  11. Jason

    Jason Gold

    So did you get lucky??
     
  12. Rotarysmp

    Rotarysmp Silver

    Thanks for your advice. I read the instructions that you should let the mould sit for at least 90 minutes before starting burnout. I had to wait two days due to family commitments :) I thought I should be driving it, so it was sitting on my house furnace for those days. Seemded to get away with it.

    The burnout disintegrated the 0.75mm sheet steel flask I made, but it did its job. I noticed during the high temp portion of the burn out that a lot of sulphor was burning out.

    I should have the video done and uploaded later today.
     
  13. Rotarysmp

    Rotarysmp Silver

    Here is the summary of my last two weeks efforts...


    I appreciate your inputs.
    Mark
     
    Last edited: Dec 27, 2020
    Tobho Mott likes this.
  14. My error. I misread the post as "dryout" not "burnout". In dryout you don't have a pattern inside.
     

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