PolyCast burn out schedule?

Discussion in 'Lost PLA casting' started by John Gaertner, Oct 3, 2021.

  1. John Gaertner

    John Gaertner Silver

    Has anyone developed a PolyCast slip-investment burn out schedule they are happy with. I have downloaded both of the PDF files offered by PolyMaker.

    Heat the kiln to 1100-1200 °C for an extended period of time (up to 40-60 min) to simultaneously sinter the ceramic shell and burn out the PolyCast™ patterns. The optimum burnout temperature and time may be determined by each foundry for the metal/part to be produced and the specific kiln or furnace used.

    Is this supposed to be a slow rise to temp or plop your slip cast part into a hot oven to burn out the inside material faster than then shell heats up? I did a YouTube search and did not find anything I felt was useful.

    Thanks, J Gaertner
  2. John Gaertner

    John Gaertner Silver

    I received a reply to my email from PolyMaker regarding the burn out of their PolyCast. Still a bit vague to me.
    Here is what they said.

    Thanks for your interest in our product. Are you referring to the attached PDF? (Their standard PDF)

    It requires a high-temperature oven to burn out PolyCast cleanly. The lowest temperature to burn off PolyCast is 650C, but the temperature is the higher the better. If you use fused silica, I think you can burn it out at around 900-1100C. The burning time depends on the size of the patterns but usually, 30mins should be enough for a 10*10*3cm hollow cube.

    Thank you.
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    Typically the burn out schedule is for the investment material not the pattern you are removing.
    With pla I have better luck with starting cold and ramping up over a couple hours. I seem to have less trouble with the shell cracking this way. Then hold 1100 for an hour..
  4. John Gaertner

    John Gaertner Silver

    Thanks for the reply. I have only used 2 different brands of slip, lost wax investment. Shellspan (I think that was the firm, in Florida?) and Barrons. I had much better luck with the Barrons products for breaking off the investment after pouring the aluminum or brass. Both recommended a quick heating of the wax for burn out. I know you are fighting the rapid expansion of the wax or PLA and the shell which is likely to crack if over stressed. Jgaertner
  5. Al2O3

    Al2O3 Administrator Staff Member

    Was doing some YT surfing and came across a video of a fella that was dipping his PLA prints in paraffin for the purpose of polishing and reducing cracking. It was just the low melt point canning stuff and a quick plunge and shake/drip. Claimed it not only polished/filled the print surface well but also reduced cracking since the Paraffin was so thin and low melting, it didn't create much initial expansion and shell stress, and allowed space for further PLA expansion. I'm not a practicing shell or Investment caster at the moment, but seemed interesting enough to try if you could stand the dimensional changes. Anyone ever try such?

  6. DavidF

    DavidF Administrator Staff Member Banner Member

    I've tried a bit of everything... Best all round for me has been to use silk pla filaments.
  7. John Gaertner

    John Gaertner Silver

    Reviewed some old pictures of my investment work from 2013! The company's investment slurry system I tried was www.Shellspen.com. They are still around.
    I am going to try Suspendslurry this time.
  8. Ferrisbeu

    Ferrisbeu Copper

    you are sadly mistaken. PLB has zero issues. But then again Im quitting this board because people are people. And I hate people. Delete me.
  9. Ferrisbeu

    Ferrisbeu Copper

    Hot furnace. Burn....30 min done. not hard . jeez
  10. John Gaertner

    John Gaertner Silver

    I was able to get my sprues 3D printed and glued on to my 3D casting patterns. I found a great way to smooth both the Polycast and Overture filament. I used a large, good quality zip lock bag. I poured 91% alcohol in and put my part in. Splashed it around in the bag for about 6 minutes. Then took the part out and hung it up to dry. I did this 3 times and the Polycast came out great. I also used Acetone on the Overture filament pattern and it smoothed out well.
  11. The burn-out scedule for Polycast is also my main consern at the moment.

    In my weiv, the only problem is the expansion of the material.. vax or print. The idea of putting cold mold into hot killn, has worked ok for me. What I think happends is, that the heat liquifies the hole surface of the model and sprues, so that when the expansion begins, it has a free way to expand.

    When using a slow burnout, I guess the idea is to soften the material before it starts to expand. I havent done this much.

    By experiencing, I have found that Polycast gets quite soft and can easily be deformed at 80 C. and that it runs like tap water at 275 C.

    At my latest cast I had two molds with all wax, and one with all Polycast. The Polycast and one of the wax had large plate surface. My guess is, that this plate surface was way more quick to recive the temp than the sprues.. The wax nold I was able to repair.. the Polycast I was not.

    My new iea is to construct a killn of about 275 C, in wich I can lower the mold upright down. So that there will be a free passage for expansion...

    What do you think.. A killn where you lower the mold through, and let the material of the model run out by gravity.

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