Wax burnout using high internal heat

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

  1. JBC

    JBC Copper

    I wanted to show you guys some pictures and ask you what you think the problem is, and how I can dial in my process.
    -Ultra-Vest® BANDUST™ investment
    -Joe's Jewelry Investment Wax Turquoise

    -Tap water (instructions call for deionized water-I'll use that when I get near the end zone).

    To get a perspective on size, the mold frame was a Solo cup and the interior cavity is approx. 45mm long = 1.75" long)

    I am using a microwave to melt out my wax after painting graphite on it (known as a susceptor).
    I have a feeling the graphite is getting too hot and wanted to show you the pictures to get your take on what you see.

    (I will post my findings for everyone once I get this dialed in. I used this when casting larger aluminum pieces and it worked well but I used crap materials (Lowes/Home Depot investment materials lol) and got lousy quality results).

    I cast the model in investment and let it cure for four hours and then put it in the microwave.
    The wax melted out in approx. six minutes and smoke started at minute eight. I turned the mold over and let the smoke/burnout cycle continue for two more minutes. I have a feeling the wax was gone but the graphite was burning the investment.
    When you guys see smoke from the burnout in your burnout kilns how long do you let it smoke? This info is valuable to me so I can calibrate your response to my process.

    After the wax burnout, I took the mold over to my compressor and blew out the ash (a lot = too much).
    The compressor was probably set to 60 PSI. First, black ash came out. So I did it again. If a little came out a lot more is better right? lol!
    So I blew out more. The third time what blew out of the hole was white (uh oh).
    I have a long, direct-blowing tube attached to the compressor so the air blast was focused (insert stupid tears).
    I had no intention to cast this mold. I wanted to see how everything looked and have never tried clearing ash from the mold before. Next time I'll try not using hurricane Katrina.
    What do you guys do when blowing out the ash? Light gusts? Small Japanese fan?

    I broke the mold open to inspect everything. I wanted to see that all of the wax was gone and to inspect for mold damage and detail captured.

    The two things that I didn't like:
    1. Cracks in the spout near the cavity. I don't mind them but should I be aiming for crack-free or does that look like a win?
    2. I expected more detail as the lost wax part had some fine details (mostly texture of the piece, not thin areas) I wanted to capture. Did I blow out the details with my 60 PSI nozzle aimed into the hole?
    I'm about to try it again and don't plan on blowing out any ash so that I can work on the microwave process rather than cleaning out the cavity since I'm not casting yet.

    IMG_4735.jpg IMG_4737.jpg

    I hope you guys can zoom in to see the details. While looking at the pictures themselves, I can see they don't show didly. But everyone likes pictures right :)?

    On the next attempt, I won't run the burnout as long and I won't be using the compressor. My gut tells me I ran the burnout too long.

    What do you look for, or what is your process when you see smoke during burnout? Smoke = burnout is done so stop before you cook the details out of the mold?
    Hopefully, you all are not just running a burnout kiln that uses an electronic PID (that's what I want to avoid$$+time. The microwave took a total of 10 minutes (plus the four-hour mold cure/dry time)).

    I'll post some new and better pictures of the 2nd test around 8pm PST (West Coast US).
    Last edited: Apr 7, 2021
  2. Jason

    Jason Gold

    Why are you using a microwave? And who says you cook details out of a mold? We preheat to 300, give it a couple of hours with a vent going, then crank the heat and pour metal. If you are having ash issues because of the shear volume of your piece, shut it off after you hit 1300. Allow to slowly return closed up in the kiln to room temp. Then rinse any remaining trash with water. Leave upside for a day and reheat. Go slow up to 300 this time, wait there for a couple of hours, then usual routine up to 1300 for pouring.

    But as far as blowing out a flask for small jewelry work? nope.

  3. Jason

    Jason Gold

    I was doing some more thinking about your issue. You should not be seeing ash and there really should be zero need for blown air or water rinses. Get that sucker up around 1400 and leave it there for 3hrs. Then slow cool it back to 1100 and pour your metal. I think you arent getting hot enough or long enough. Dont nuke your stuff, that's just asking for trouble.
  4. JBC

    JBC Copper

    Microwaves are fast.
    Is it normal to use one? Heck no. But hey. I don't have a kiln. And the BBQ I use to use for my burnouts a long time ago was tossed.

    By "burning the investment" I meant it degrades to the point where it falls apart. Microwaving graphite can turn into plasma and get incredibly hot.

    So here is test #2:
    Sadly I forgot to paint on the graphite (microwave susceptor) but I wanted to see what would happen anyway.
    The mold sat for four hours after investment.

    I lowered the power level of the microwave and set the time to 10 minutes.
    The wax melted out in seven minutes. I then flipped it so gases could escape.

    Below are the results (and another wax model I'll get ready on Friday.

    Very clean. I'm stoked.
    10 minutes in the microwave and this small mold would have been ready.
    Great test.
    IMG_4741.jpg IMG_4744.jpg IMG_4746.jpg IMG_4747.jpg IMG_4751.jpg IMG_4753.jpg
    Jason likes this.
  5. JBC

    JBC Copper

    The wax pattern was at 90 degrees from the sprue. It was set up like that not for casting but to see how well the wax would be removed.
    It's a small pattern/mold so maybe that wasn't a great test for that but the stuff melted out in 10 minutes without graphite painted on it = very nice.

    I should be out of town till Friday so will pour when I can and post pics then.

  6. Jason

    Jason Gold

    If you are degrading the investment, I would guess it's heating the water too fast that's trapped in the investment. You'd be better off lighting a charcoal fire in a hole in the ground and sticking your flask in there. The rest of the world still casts metal this way using investment made of clay, hay and pig shit. (I'm serious too!)

    Why not get a small kiln? You can pick them up cheap on craigslist or you can even make your own for a couple hundred bucks complete with a ramp and soak PID.
    How are you planning on accurately preheating your investment before pouring metal? Investment has limitations, abide by them or you will have issues in your next phase such as porosity, surface finish getting it to fill completely. Once the water is cooked off from the investment in the microwave, getting it to reheat the same isn't going to happen. Microwaves work by bouncing those moist water molecules off each other and thus creating heat. That water is long gone. You might need to dewax, burnout and pour metal in one swift go.

    Interesting method, but I'm pretty sure R&R wouldn't recommend it. lol.;) Hope you nail it!
  7. JBC

    JBC Copper

    It does have a sphincter factor of 10.

    When I did this years ago (2016?) trying to melt 3D-printed PLA parts out completely I had a hard time reaching PLA's melting temp at the deepest recesses of the mold. So I started looking for ways to cook it from the inside out as microwaves can.
    My biggest fear was having the mold explode if the water trapped in the mold instantly converted to steam. I started with small molds and slowly went to larger ones (using different types of investment like Countertop Quickerete = cheap bayschturd).
    My molds seemed to cook out the water pretty well from the inside due to the heat the microwave created in the interior of the mold (totally a guess but it melted the plastic out without causing the exterior of the mold from getting as hot).
    I poured that Quickrete and approx. an hour later put the mold in the microwave and melted out the plastic.
    The longer I let the mold dry, the more cracks the mold got creating more defects in the casting.
    After I thought the plastic was melted out I poured my aluminum. No explosion. I did that a few times but quit because I couldn't get all of the plastic out of the smaller/deeper areas.

    Now that I'm about to do close to the same thing, but replacing PLA with wax I'll do it with a small amount of metal and fully geared up for war with someone watching from a distance.
    Will it go well? I hope so.

    What other trouble comes to mind?
  8. JBC

    JBC Copper

    Thats my plan. Melt and pour.

    I've been looking but this small town has more cows than kilns for sale. And the one I like from another Californian had my finger hovering over the 'Buy' button a couple of times:

    But the max height of the kiln is 6." I might get an 8" leaner in there but if I nail this microwave approach as I hope, I can put larger molds in it. It's a big-ole microwave I got just for large molds....and melting crap.
  9. Jason

    Jason Gold

    Yeah, 650 is a bit steep for that thing if you are shopping the used market. My cat piss pottery kiln was 25bucks and my countertop jewelry kiln was free. (family in the business) But you really can build a custom setup perfect for your needs for not much money. If you are a little clever and with some lightweight refractory, you could cast yourself some walls, back it with kaowool, add some cheap ebay coils, a pid and you're off to the races. As we say, Time, Money and quality >>>>>>>> PICK TWO!

    California is a pretty big state, you might have to drive a bit. I don't know where you are.


    This one is NICE and better than the amazon model. https://sandiego.craigslist.org/ssd/art/d/national-city-kiln/7299732899.html

    Here's a deal in the north. https://sacramento.craigslist.org/art/d/fair-oaks-cress-electric-kiln/7299635556.html

  10. JBC

    JBC Copper

    Hey-Thanks for doing all of that work. It is appreciated.
    I'm in Visalia which is centrally located.
    The one in Fair Oaks looks like a nice fit. I don't need anything large. I'd have to find a PID to control the ramps which is the rabbit hole I'm trying to avoid. But I might contact him. Thanks!
    My mother-in-law has a kiln she used for dolls. I doubt that has a PID on it but it's free (no idea about size but suspect it's the size of a jewelers kiln)
    She's down in Mission Viejo= 4.5-8.5 hour drive depending on traffic (pitty tears).

    I have a small plunger-type plastic injection molding system I'm about to assemble. Once the PID comes in I'll start putting it together. The whole thing was designed by buster Beagle 3D https://www.youtube.com/watch?v=52z4E3QXSVM. It's an easy assemble without much of a 'OH CRAP!' factor
    Aside from trying to cast something nice and making some prototype parts in ABS my 'rabbit hole' list is about full.
    You did get me thinking though.....I'll start looking for a simple mod to get a PID on a 110V kiln for my next rabbit hole.......I starting to smell rabbit.
  11. rocco

    rocco Silver

  12. Jason

    Jason Gold

    Pids are easy to wire in. Many of us have them. I got my lesson last year. Buy an Auber instruments so we can easily help you with it.
  13. JBC

    JBC Copper

    Will do. Thanks for the info.
    This morn I make a new silicone mold for wax. If all goes as planned;
    Noon-wax patterns are made
    4pm -wax melt in microwave
    4:15 pour.
    Pics to follow.
  14. JBC

    JBC Copper

    So close!
    The microwave is doing a great job melting the wax out in 5 minutes but it was leaving too much in the mold for my taste, which might give me bad results when I vacuum cast the mold while pouring.
    So I ran it another 10 minutes and saw the wax fade. I placed a drop of water on the faded wax to see how porous it was. It did a pretty nice job drawing that in. Equally as well as the outside/top/bottom of the mold. I like it!

    I sprued up my poorly made wax patterns and made my first tree (It's a sad Charley Brown-looking thing).

    And poured the investment.

    Well.....that doesn't look right.

    I got my investment calc's wrong. Yea me.
    My window closed. Where does the time go?

    I'll put this paperweight on Etsy if anyone's interested @#%&*.

    Maybe I can pour something other than a vodka tonic later.

  15. JBC

    JBC Copper

    OK you Masters of the Melt, I need your input.
    I think I know what the problem is but I lack the tools and the experience to know = I don't know.

    Here is the opened mold after the pour. The details that the pattern left (nice!) and some areas that were partially filled.


    Here are the results of my two attempts. The wax pattern sitting on one of them is basically what I used for both casts, for reference. The left attempt had three patterns in the tree and the right one just two (below the wax example).
    IMG_4834.jpg IMG_4835.jpg

    I am using a new induction forge (approx. $350) and don't have a way to identify what the temp really is.
    (RotoMetal shows melting temp for my Zomak ZA12 is 810. My forge needed to be set at 920 to get it to melt).

    My mold was cast in a plastic sleeve that I removed prior to melting out the wax in the microwave.
    I placed the hot mold (I hoped for 300F but don't have a way to know) on the vacuum table (no sleeve around the perimeter which might help draw metal into the voids?).

    I then started the vacuum pump and poured the metal. The vacuum gauge showed around 25-28 which was nice and saw the metal get sucked down in. Everything looked great so far.

    Firstly, my wax trees arent great...they aren't even good. But I expected better details for what was cast. And I expected a lot more metal penetration.

    After the pour, I ordered a digital infrared thermometer so I can hit temps for both the metal and the mold.

    Do the pics scream cold mold and/or the pouring temp of the metal was too low?
  16. Jason

    Jason Gold

    What was the temp of the investment when you poured in your metal??? You need it to be around 1000. I think you were too cold.
    Infrared thermometers are not accurate. It would be okay for the mold, but not for judging the temperature of molten metal due to reflectivity.
    Get a 60buck mifco probe and a 6buck chinese type K meter for dipping into your melt until you sort out the timing and setting on your induction furnace,
    Here is a link for the probe, it's kinda hard to find on their website. https://mifco.com/shop/pyrometers/replacement-8-thermocouple-tip/
  17. dennis

    dennis Silver Banner Member

    Does this come with a Dank Tarn?

    (From "Ulalume," by Poe - "the dank tarn of Auber")
  18. JBC

    JBC Copper

    It had to have been less than 300F. I'd have to guess 200F. I lost some heat waiting for the metal to get to temp (forge temp needs to be calibrated....if it can).
    I thought maybe the metal's temperature was going to be more of a problem than the small mold being too cold since the mold was so small, but judging by your comment I was wrong.
    I appreciate your feedback.

    I have one more test in me using my microwave approach.
    I have an infrared thermometer coming tomorrow.
    I'll get my metal melted before I melt out the wax and cook out the mold so no time/temp is lost like last time (damn forge).
    I'll mold up the pattern and burn out the wax and get the temp of the mold as high as I think I can and check the inside temp reading with the infrared thermometer prior to the pour and report back, hopefully, tomorrow.

    I just found this youtube from The Frugal Berry. Aprox. $20 molten metal pyrometer
    This sings to my wallet!
  19. Jason

    Jason Gold

    I did the graphite thing already... It sucked. Remember, Time, money and quality>>>>> PICK TWO
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Carbon gouging rods are the hobbyist's source for graphite sheathed pyrometer. They cost a little over $1 each but you have to drill them. They work fine and last a very long time if you just dip them and don't leave them exposed to high temperature oxidizing environments (like a kiln). So far I've used 4 sheathes in 5 years, but still on the same thermocouple.

    The first sheath was consumed in a few hours before I realized they couldn't take prolonged exposure to high temp O2 rich environments. The next two I broke prematurely by inadvertently walking into them because they hang on my furnace cart. Still on #4. Easily good for 100+ dips in aluminum. At a penny a dip, that's good enough for me.

    Many multimeters already have a K-Type port and will read temp directly in either C of F. They usually take a mini k-type connector that costs a couple bucks.

    A contact pyrometer takes out all the guess work. I wouldn't be without one.

    Here's a thread.



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