Wax burnout using high internal heat

Discussion in 'Lost wax casting' started by JBC, Apr 7, 2021.

  1. JBC

    JBC Copper

    Fast and cheap are the two I'm picking!
    Amazon packages won't get here till Saturday ;).

    I tried getting ahold of the guy north of me with the kiln but he wont respond. I've looked around for others as far north as Sacramento.
    I found a nice Paragon with PID but the height inside was only 5.75". Great price but too small =limiting. but thanks for the links earlier, I will continue looking.
    I want one last microwave test before I change directions though.
     
    Last edited: Apr 14, 2021
  2. JBC

    JBC Copper

    Thanks Kelly. I have the multimeter and the K-type port/connector that have been part of my garage for a while. I'm surprised I still had the connector.

    jbc
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    It seems unlikely to me that the investment is being burned out properly in the microwave.
    So your going to need to gate into your part at the bottom and vent it out the top. This will allow the trapped air to escape.

    On a side note, I wonder what would happen if there was graphite mixed into the refractory?
    Would this let the microwave heat the investment to a higher temp???
     
  4. JBC

    JBC Copper

    The pattern is completely gone (though the walls still show the color of the wax left behind. Could that be signaling a problem?) and with more microwave heating, the walls where the pattern was, absorbed water at the same rate as the rest of the mold (Un-scientific approach but it's all I could think of).
    I wondered about that. I have vacuum assist going pulling 28-30 on the vacuum gauge which I thought would negate the need to add vents or fill from the bottom up for small molds. I'm new to this but I don't see other people doing that in these smallish molds while using vacuum assist. Don't take me wrong, I appreciate all comments, I can't see the forest for the trees sometimes.

    I haven't tried mixing graphite into the investment but it would heat up like a mutha! When painted on PLA 3D printed models (I used to do this a long time ago) it turns most of the plastic into smoke rather than liquid. And that was after 5 minutes on high. one issue was getting the graphite uniformly dense. Graphite doesn't mix well with other things, meaning it sinks usually and needs constant stirring. Areas with more graphite heat up a lot more.
    (Mixing just a little graphite with wax is a different story. That showed a lot of promise and is something I planned on going back to. Maybe today!)

    My first post in this thread had graphite painted onto the wax pattern. The small cavity got torched. I planned on playing with the power settings of my microwave but on my second attempt, I made the mold forgetting to paint the graphite on the wax pattern. The wax melted out nicely. Nothing but light blue wax coloring was left on the cavity's wall so I started heading in that direction and now get a really light blue I'm pleased with.
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    The whole point of the burn out is not only to remove the pattern, but also to calcify the investment. There are additives in the investment to add porosity when it is fully burned out.
    What were you using for investment??
     
  6. JBC

    JBC Copper

    That's a really good idea!

    There have been studies done adding graphite to cement. It made the cement (nothing I've found using investment) stronger. I think more crack-resistant also (I'm not having cracking issues).
    I can try that after my infrared thermometer gets delivered (today/tonight?) and see what the temps get to.
    That might also help the investment go through its chemical transition during temp increases.
    I'll just have to figure out:
    Time and power settings to mimic the investment burnout routine.
    Graphite by weight relative to investment and mix it in prior to adding water.​
    I do love a good rabbit hole.

    jbc
     
  7. JBC

    JBC Copper

    Agreed, we were typing at the same time.
    Calcify = new term for me thanks.

    OK. Good to know.

    Ultra-Vest® BANDUST™ investment
     
    DavidF likes this.
  8. JBC

    JBC Copper

    That's pretty handy info. I thought the investment was basically hardened during burnout. I had not considered it becoming more porous.

    I'll need to make a little igloo out of a ceramic fiber blanket to keep my microwave from melting.

    ~~....a few moments later as I was thinking on the subject.~~

    I'm starting to lose my interest in microwaving the investment.
    If I mix the investment with graphite so the thing can calcify I would still need to follow the burnout cycle a kiln would. That wouldn't have any time or energy savings.
    I was wanting to shave off a lot of time.

    If I could get the temp inside of the mold to 1350F would the lack of porosity in my mold keep details from being captured (I would think I would still get some vacuum assist). My flasks are only 4" and 6" tall max.
     
  9. DavidF

    DavidF Administrator Staff Member Banner Member

    Getting the mold to 1350 f would give you the porosity you need....
     
  10. JBC

    JBC Copper

    It just dawned on me. The temps during hold and soak are probably to get that target temp all the way inside the mold.
    If the entire mold hit 300F at the same time and then 700F at the same time, and then 1350F at the same time, how long would I really need to hold/soak it?
    When you ramp and soak, it's to minimize stress on the material right? (am I right?).
    So if everything was at the same temp the entire time, maybe stress is less so temps could be ramped up without having to hold and soak. This could be a nice time saver.

    My interest is back on.

    I called Ransom & Randolph for just that question about 30 minutes ago.


    I was thinking about just the interior. If the graphite was mixed with the wax and microwaved, just the interior of the cavity would get hot. But the rest of the mold wouldn't have calcified and could experience temp shock = fail.
     
    Last edited: Apr 15, 2021
  11. DavidF

    DavidF Administrator Staff Member Banner Member

    Yep!

    Yep, yep.

    On my 4x8 flasks, I just set the kiln to 1350 and go for it. It takes it awile to get up to that temperature. I usually do this in the evening, then go to bed. The next morning I shut off the kiln, then around noon or one I start my casting session. I'm not following the directions that's certain. But it works for me :D
     
  12. JBC

    JBC Copper

    I like how you think!

    Do you cast any patterns as small as I've shown with high detail and not lose any details that way?
    (where is my infrared thermometer????:()
     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    Yes, all the time... just finished these. 20210322_095723.jpg 20210330_105001.jpg
     
  14. JBC

    JBC Copper

    Those are nice! I'm jelly.

    Do you have any pics of the backside? I'd like to see how those little ribs turned out (and the thickness of the ribs in the pattern if you know it.)
    And were those printed with castable resin?
     
  15. Jason

    Jason Gold

    I'm sure the ribs on the back look exactly like the wax. Ultravest doesn't miss a beat.

    If you wanna run printable resin, you MUST have a kiln and a PID. We have a b9creator that prints jewelry and it took us a good 2 months to sort out the burnout schedule. But now we print, invest the print, burnout and pour lickity split! It's cool, but you aren't doing that one in a microwave.:p
     
  16. JBC

    JBC Copper

    No printable resins here. I'm learning the art of mold making, cutting and injecting. "Learning' seems more like a goal. The patterns are turning out ok but not to my liking yet.
     
  17. Jason

    Jason Gold

    Do you have a wax injector yet?
     
  18. DavidF

    DavidF Administrator Staff Member Banner Member

    Sorry, no picture of the back side. But it did come out fine. The ribs were around .025"
    These were done in lost wax. If printed with a 3d printer, it would have likely fractured the investment on the ribs during burn out.
     
  19. JBC

    JBC Copper

    No.
    I'm using a turkey baster and injecting the molds that way......while searching Craigslist and Facebook.
    I did find one locally that uses a compressor (which I have) but I think I'd rather have one with a pump so I'm not tied to one location.
     
  20. JBC

    JBC Copper

    I have no plans in using printed printable resins. They seem too fidly, and really expensive. The resins I use cover a wide range of uses for me.

    My molds have nice detail but I'm not filling some small areas of the mold .5 mm-1 mm wide. Other areas with similar widths get filled.
    I've tried forcing wax in more, and less forcibly. Most looks great but there's always one area in the center that can't fill all the way.
    So today I'm warming my molds to 90F on a heating pad (yesterday and earlier temps were about 70F).

    With my new infrared temp gun I see I had my wax at 210F = yea scalding hot!
    So I'm dropping it down to the suggested 160 on the package as we speak/type.

    Time to head to the garage and get waxy!
     

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