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Thread: Help with investment casting small intricate parts

  1. #11
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    This is how I determine pouring temp.
    You have to watch the ingots melt in the crucible. When the last piece melts, start a timer.

    I posted this on another thread.
    I've learned from experience pouring different sized objects, that one temperature does not give the same finish or fill. I use 'time after the last charge melts'. Heavy thick pieces get 1 minute, longer thin pieces get 2 minutes, the most I've done was 3 minutes and that was because 2:45 seconds gave me a cold shut. No flux with clean ingots, no degas, just skim and pour.

    The cooler the metal, the better the finish and you get less shrinkage.
    Bones

  2. #12
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    I got an IR thermometer that goes to 1382 F: Do I still need a pyrometer?
    I have never used an IR thermometer for pouring metal. I hear from other people here that they have problems getting accurate reads from the shiny surface of the melts.

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

  3. #13
    Senior Member Tobho Mott's Avatar
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    I have read that too about the IR thermometers. Supposedly the hot furnace interior can also fool them, since the furnace walls may/will be hotter than the melt...

    I don't use a pyrometer either, but I will almost certainly build one eventually. Meanwhile the 'hot rod dip' test has worked out ok for me so far. You preheat a steel rod, skim a clean spot on the surface of the melt, and dip the rod into it. If it pulls out clean (or anything stuck to it knocks off easily into the dross bucket), you should be OK to pour. If not, keep cookin' it.

    It isn't as reliable or accurate as a pyrometer and does not take the thickness of the casting into account like Fishbonz's time-since-last-ingot-melted technique, but it is free (I was already using the same steel rod to poke at the melt, gently stir in flux, etc., anyhow when I learned about the dip test) and it has worked out OK for me doing lost foam and green sand casting in aluminum and bronze.

    Good luck!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

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  4. #14
    Just ordered this pyrometer: https://www.amazon.com/pyrometer-Ann...ords=pyrometer

    McMaster Carr and other pages are leading me to scary looking catalogs, but this one looks easy to get.

    Also, ordered these perf. flasks:

    3.5 diam x 6 h https://www.riogrande.com/Product/ne...-12-dia/702008
    4 diam x 10 h https://www.riogrande.com/Product/ne...r-4-dia/702012
    6 diam x 10 h https://www.riogrande.com/Product/Ne...-6-dia/702209N

    Still confused on what to do about the enclosing flask. Seems like I need to DIY something together, with an adapter that can accept 3.5 - 4" diameter perforated flasks, a flat flange on top that I can put a rubber gasket on for vacuum, and then make a top piece out of thick steel sheet with a fitting that connects to my vacuum pump?

  5. #15
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    You are still going to need a sheath for that thermocouple probe. You can't just dip it into molten metal and expect it to last any time at all. You can buy a thermocouple probe in an Inconel sheath from Mifco for around 50 dollars (http://mifco.com/shop/pyrometers/rep...rmocouple-tip/ ) or you can make your own from 5/8 inch graphite gouging rods as I showed in the tutorial.

    Richard.
    Last edited by Rasper; 04-21-2017 at 11:12 PM.
    When I die, Heaven can waitI want to go to McMaster-Carr.

  6. #16
    Moderator DavidF's Avatar
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    Quote Originally Posted by 01binary View Post
    Just ordered this pyrometer: https://www.amazon.com/pyrometer-Ann...ords=pyrometer

    McMaster Carr and other pages are leading me to scary looking catalogs, but this one looks easy to get.

    Also, ordered these perf. flasks:

    3.5 diam x 6 h https://www.riogrande.com/Product/ne...-12-dia/702008
    4 diam x 10 h https://www.riogrande.com/Product/ne...r-4-dia/702012
    6 diam x 10 h https://www.riogrande.com/Product/Ne...-6-dia/702209N

    Still confused on what to do about the enclosing flask. Seems like I need to DIY something together, with an adapter that can accept 3.5 - 4" diameter perforated flasks, a flat flange on top that I can put a rubber gasket on for vacuum, and then make a top piece out of thick steel sheet with a fitting that connects to my vacuum pump?
    I just glued a silicone gasket with red rtv to a piece of pipe and set the flasks into it. base is siliconed onto it also. Nothing fancy and works like a champ
    A calm sea does not make a skilled sailor....

  7. #17
    @FishbonzWVa: thanks for the tip on metal temp. I might have to modify it for my context since your metal may have a different cooling time than mine. I am not even sure what my final material will be at this point. What metal did you use?

    @DavidF: do you have any higher-res pictures of your vacuum assist setup? I got the perforated flasks and now also the thick steel pipe to put them into. I still need to find caps for both ends, seal the bottom with RTV permanently, then glue a high-temp gasket to the top with RTV.

    Is this the RTV you meant?
    http://www.acehardware.com/product/i...ductId=1295863
    or this?
    https://www.grainger.com/product/1FB...170422201150:s
    Perhaps any of these?
    http://www.ebay.com/sch/i.html?_odkw...alant&_sacat=0

    Thank you!
    Last edited by 01binary; 04-22-2017 at 08:21 PM.

  8. #18
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    "@FishbonzWVa: thanks for the tip on metal temp. I might have to modify it for my context since your metal may have a different cooling time than mine. I am not even sure what my final material will be at this point. What metal did you use?"

    We're talking aluminum here and pouring in sand moulds. With you pouring in heated moulds, the one minute mark should fill all of them.
    Bones

  9. #19
    Moderator DavidF's Avatar
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    I used the permatex silicone, but doubt it really matters. Went through my pics and this is all I could find..
    A calm sea does not make a skilled sailor....

  10. #20
    Thanks! I should be done building and trying out the vacuum assist rig next weekend.

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