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Thread: Help with investment casting small intricate parts

  1. #31
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    The over 1000 F. is to burn out the bound water in the plaster. If you don't burn it out in the kiln, your molten metal will burn it out when you pour it and produce copious amounts of steam.

    It sounds like your thermocouple problems may be that one or both of your wires are touching ground.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  2. #32
    Moderator DavidF's Avatar
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    Quote Originally Posted by 01binary View Post
    You've used Ultravest. Basic sanity check here, I am spending 8 hours baking the perforated flask with ultravest in it, up to 1350F and then down to 500F for the pour - according to R&R instructions. Is this correct? I really need to go over a thousand degrees just to pour at 500? Is this what you do every time you cast (i.e. babysit a baking flask the whole day)?

    Thank you!
    I dont baby sit it, i have a digital temp controller on mine. But yes burn out is pretty critical.
    A calm sea does not make a skilled sailor....

  3. #33
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    I don't babysit my burnout kiln. I put in the investment and fire up the Reil burner to a setting that experience has shown me takes the kiln to around 1100 or 1200 F. I have a thermocouple probe inside the kiln which I check several times a day. A 20 kilo tank of propane lasts about 36 hours. (I burn out my largest investments for 4 or 5 days.)

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  4. #34
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    Persistence is needed here. It took me about a year of trial and mostly error before I could produce reliable casting results.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  5. #35
    This is the last leg of a 3.5 year project, it's so close I can feel it

    Thanks so much for everyone's help here, looks like I got it working (at least for the specific problem in the title of this thread):

    cast01.jpg

    cast02.jpg

    cast03.jpg

    positive.jpg

    DavidF was of course right, my burnout process had a lot more room for improvement. Due to my manual kiln, I had to sit by it for 8 hours, check the temp every 10 minutes, and adjust settings. I also stepped down to 500F on investment mold temp for pouring, and set a timer for 3.5 minutes after the last ingot melted to estimate metal temp. Lastly, I set the forge to the lowest possible propane pressure while still being able to melt something.

    In case anyone reading this later is interested in details...

    3D printed part > finish > silicone mold > vacuum > wax cast > vacuum > investment mold > vacuum > burnout > bake > metal cast > vacuum [ > finish > paint ]

    * I got vacuum metal casting supplies from Rio Grande (which also offers vacuum pumps) although my 7 CFM pump was bundled with Across International vacuum oven that I'm using to cast wax positives from silicone negatives.
    * Vacuum metal casting supplies included perforated flasks with flanges (3.5, 4 and 8" diam by 10.5" high), silicone gaskets, and graphite protector gaskets.
    * I got risers, ceramic filters, and metal casting tools from budgetcastingsupply.com. Ceramic filters and risers worked out great with this process.
    * The silicone molds were poured around 3D printed parts finished with high-detail Tamia modeling primer / 4 grits of sandpaper, about 5-7 iterations of spray / sand.
    * My model and sprue wax comes from Remet corp.
    * I got an iPhone app from Droxic OOD (called Timer Free) to setup multipart timers for baking the investment, which as anyone can read above, was very crucial to success.
    * The silicone I used was Dragon Skin Medium from SmoothOn, along with their release agent.
    * I also used a Best Value Vacs chamber & another vacuum pump for the silicone (separate to avoid contaminating silicone with wax).
    * I used a Presto pot modified for "candlewax melting" off ebay for melting and pouring wax into the silicone molds, while vacuuming them at 400F in the oven for 3-4 iterations of 30 minutes each.
    * My forge is the DFP Burner forge that shipped from Eastern Europe, and I needed a high pressure U.S. regulator before I could use it.
    * My kiln is from Kress mfg, manual model.

    I honestly can't imagine a better "as cast" surface. Even expensive CNC machined parts would require no less finishing than these.

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