Lost Wax Casting Failure

Discussion in 'Lost wax casting' started by IvanAlmighty, Nov 15, 2019.

  1. IvanAlmighty

    IvanAlmighty Copper

    (Sorry to duplicate this from AA, some thread there mentioned things might be more active here but apologies to any regulars seeing double)

    Tried casting some small aluminum figures, in the second attempt the metal flowed even less than the first time. Previously the flask was room temperature but this time I heated it up to 1000 degrees for the poor and it came out worse than before! The investment process went over well but I'm running into issues, gonna try degassing but I'm wondering what im missing/screwing up on here

    Tobho mentioned flask temperature could be an element and I’ll be researching more on what an appropriate level should be

    First Attempt: upload_2019-11-15_10-22-25.jpeg

    upload_2019-11-15_10-23-5.jpeg



    Second Attempt:
    upload_2019-11-15_10-23-41.jpeg

    upload_2019-11-15_10-24-16.jpeg
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    What are you using for investment??
    Aluminum is actually more difficult then say brass or bronze when investment casting because of its low weight. If you are not using vacuum assist, then you should gate the part with a J sprue so it fills bottom up and vents out the top into a large riser. You will also need about 4" of head pressure over the casting....
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    On the flask temperature, You are better off pouring with the flask temp at room temps especially with a thick casting like yours. Reason being, the investment insulates the molten metal slowing the solidification of the casting. The gating and risers which are exposed to the open air cool first and will actually rob metal from the casting causing all sorts of strange shrink defects. Bury the riser/ shrink bob in the center of the mold so it is the last thing to cool.....
     
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  4. IvanAlmighty

    IvanAlmighty Copper

    This is R&R ultravest plaster based investment.

    Dang, I would’ve figured aluminum was the proper training grounds. This is without vacuum and amateurishly sprued at the top with some gating/vents and pouring straight to the bottom.. I’ll rework the gating for a flow from the bottom-up like you recommend. I’m guessing anything less than 4 inches would lack the pressure to flow? Thanks a ton for the advice, greatly appreciated!
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Lacks pressure to displace the air through the investment in a timely manner... Thats why I suggest gating into the bottom, so it fills from the bottom and pushes the air out the top, this also flushes out the mold cavity of any crap that might be in there. Be sure to bury a shrink bob in the center of the mold so it cools last, your in gate and riser vent can be small, like 3/8" and the shrink bob at least half the mass of the part you are casting....
    How are you handling burn out??
     
  6. IvanAlmighty

    IvanAlmighty Copper

    Makes a ton of sense, thanks chief.

    I’ve been using the standard burnout procedure with a kiln for a 4x6 and letting it soak at 1000F for the last interval. Although this time I let it cool after the burnout cycle and reheated it for a few hours

    upload_2019-11-15_11-40-30.jpeg
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    If you want to go "by the book" the mold should not be allowed to drop below 250'F after burn out or cracking may occur.... I tend to break some of the rules LOL
     
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  8. Zapins

    Zapins Silver

    I do lost wax bronze casting and don't have experience with aluminum casting, but I think David is right that it is harder to cast because of its low weight. To counter that you need to increase the height of the column of metal in the pouring shaft. That will increase the pressure and force it into all the crevices in your mold.

    It looks like the aluminum didn't have enough pressure to force its way into the smaller areas. If you can double or triple the height of the pouring sprue you'll probably get a better casting.
     
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  9. Jason

    Jason Gold Banner Member

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  10. DavidF

    DavidF Administrator Staff Member Banner Member

    Regarding the vacuum pump question you asked on AA... a cheapy harbor freight one will get you by for a long time. I'm working on going bigger and better....
    20191122_223300.jpg

    Posting pictures on AA sucks!!
     
    Jason likes this.
  11. Jason

    Jason Gold Banner Member

    YES IT DOES!
     
  12. IvanAlmighty

    IvanAlmighty Copper

    Hey again, back at it with an update on this!

    I took a swing at a.. less than conventional vacuum chamber....
    I tried David's pipe system but I wasn't using a flanged flask that sat on top, I had a perforated steel container that I poured the investment/metal into and then placed it into the chamber, put the lid on top of the pipe, then activated the vacuum. This OF COURSE pulled the air through the main feeder and metal bubbled up as the air was pulled through the largest opening, it produced sharp edges and nearly all the detail of the model, but I'm guessing that turbulence also disturbed a lot of bifilms and created such a high amount of porosity on the surface!!

    I wanted to try the suggestions for J-sprues and taller feeders, but it's pretty limited with a 6 inch height in the kiln; I'm going to find a proper 5 inch flanged flask and new pipe to properly pull the vacuum before/during pouring and see how the results go.
    IMG_3232.JPG IMG_3236.JPG IMG_3240.JPG IMG_3227.JPG
     
  13. Jason

    Jason Gold Banner Member

    WTF is that? I'm guessing that thing is SOLID????? or you want it solid??? If that's the case, you really gotta figure out how to hollow that dude out.
    What's the rough measurements of your swiss cheese looking army tank? Pictures can be really deceiving here on the ol' interweb.

    At this point, you would be better off just getting a good vacuum pulled on a container of investment. Mount your tank in your flask and SLOOOOWLY pour the investment against the wall of the flask and let it flow around your part. Forget pulling another vacuum, it probably wont help you anyways. Post some photos of your flask and vacuum methods.
     
  14. DavidF

    DavidF Administrator Staff Member Banner Member

    Dude, its sitting in the palm of his hand. Get off the ludes..


    @IvanAlmighty. Still looks pretty cool even if it is a casualty....
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I agree. Stay after it Ivan....think you on the right track....Hah!

    Best,
    Kelly
     
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  16. IvanAlmighty

    IvanAlmighty Copper

    Hahah! More sturdy than it looks definitely but it's as pitted as cheese on the outside, the dimensions are about 3.1 inches in width, 3.26 inches in length, and 2.71 inches in height.

    I'm curious what points your experience to the investment vacuuming vs the metal vacuuming, also here's some pics of the crude setup,
    IMG_3246.JPG IMG_3244.JPG

    After pulling the flask from the kiln and pouring the metal, I put it inside the pipe, placed the lid on top and pulled the vacuum.

    I can't find a 5x5 perforated flask so I might try a 4x5 and hope the walls aren't thin enough to blowout, there's only one on ebay but the seller is out for most of January
     
  17. IvanAlmighty

    IvanAlmighty Copper

    Lol, and thanks man! Really appreciate your advice also, excited to take another crack
     
  18. IvanAlmighty

    IvanAlmighty Copper

    I just hope I’m treading towards success, it’s been bumpy but I’m digging the craft

    The only real bummer is the foul stench of burning PLA that always manages to linger, gonna try for all wax for a less pungent odor hopefully
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You could build a little evac system for your burn out oven. The pottery folks use them but they work like a gas furnace or gas hot water heater exhaust system. A small fan to draw on the oven and pum outside mixed with some dilution air to keep the xhaust temp down so you can use common materials for duct work......no more stink!

    Best,
    Kelly
     
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  20. Jason

    Jason Gold Banner Member

    Anything that's roughly 3x3 and SOLID is going to be a real challenge to avoid shrink etc. Keep in mind, the investments we have today are not designed to tolerate the ABUSE that melting out
    pla is going to do to them. Melting out wax is childs play.... IF and I know this is a big one... IF you can print with resin instead of pla, I have good burnout schedules for that. We are still happy as clams running an old b9creator with resin for jewelry work.

    If I was going down this road it would be..... Print plastic toy, Make silicone mold of toy, create wax toy in silicone mold, invest wax toy, melt out wax toy, pour metal.
    Burning out a solid block of wax like you would have here is going to stink, smoke like hell and could very well catch on fire if you try to peak inside a kiln up at temperature. As soon as the oxygen hits it, POOF! I lost some arm hair on my cat piss kiln last year. For fat stuff, try to make this a 2 step operation. First is called DEWAX. This is where you will rid 90% of the wax item. You can do this with steam, boiling water, flash fire etc.. Then the next step is called burnout. The second heating or subsequent heating of your investment will go to metal pouring temps. Anything left behind will vanish during this phase.

    Keep at it. No one promised results or said this stuff is easy. ;)
     

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