Plaster investment

Discussion in 'Home Foundry & Casting Projects' started by kadora, Jul 7, 2013.

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  1. Jul 7, 2013 #1

    kadora

    kadora

    kadora

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    Hello friends
    My question is based on ANEOMARINEs thread "lost pla casting"
    because i don not want to interrupt his thread with my beginner
    questions i have decided to start new thread.

    I read on internet that plaster form is very dangerous for metal
    casting .
    Could you casting experts explain me how should be cured
    plaster form before pouring liquid metal into it?
    Then why is prefer casting to sand ? Plaster form seems to me easier
    and cheaper way to go
    thank you.
     
  2. Jul 7, 2013 #2

    Tin Falcon

    Tin Falcon

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    No expert but have done a bit of reading.

    investment casting requires more equipment and takes more labor time therefore is more expensive. also with lost wax casting the pastern is lost as well as the investment. so there is an additional step to make a new pattern for every part.
    If you watched the video you may have notices the investment was placed in a vacuum chamber to remove air bubbles. the investment was then carefuly poured on the side of the flask away from the pattern and the pour was done on a vibrating table to prevent air bubbles on the pattern and defects in the finished part.

    I think what you are referring to as plaster being dangerous is the normal moisture content in regular plaster.

    in investment casting after the intial drying process at room temperature the investment is fired at low temp to melt out the wax. then at higher temps to cure the investment and and bring the mold to the same or near the same temp as the molten metal.

    These methods allow for fine detail and are used primarily for art and jewelry work . but can be used for hi tech items such as golf club heads and aircraft parts. and produce a near finished part.

    Investment casting is centuries old as is sand casting.

    Sand casting is a relatively simple process in comparison ram up half the mold flip sprinkle with parting powder ram up the second half cut the gates and sprues poke a few vent holes remove the pattern assemble the mold and pour. Make a pattern board with patterns and gates in place and ramming up is fast and easy.

    in green sand casting the sand can be used over and over again and there are viruly no material loses. many less steps in the process therefore less labor and less supplies to replenish.

    Tin
     
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  3. Jul 7, 2013 #3

    Tin Falcon

    Tin Falcon

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    Keep something in mind here home casting is a whole separate hobby and skill set from machining. Investment casting requires a large different set of equipment.

    typical steps are make a metal pattern -Machine tools assumed

    make a rubber mold - Need tools equipment to make mold

    make wax patterns from mold -need wax injector.

    need flasks

    need tools to mix investment

    need vacuum pump vacuum chamber and vibratory table.

    need burnout oven to remove recover wax and kiln to cure investment.

    then your are ready for the furnace.


    Granted what aone is doing removes a few steps but substitutes a 3-d printer.


    IMHO start simple and sand cast a few aluminum parts in sand this will minimize financial investment and limit the skils needing to be learned up front.
    Tin
     
  4. Jul 7, 2013 #4

    kadora

    kadora

    kadora

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    TIN thank you very much for your excellent explanation
    of the investment casting process now i am a bit closer to
    this art.
    Thank you
    Kadora
     
  5. Jul 7, 2013 #5

    aonemarine

    aonemarine

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    Tin, you explained that much better than I ever could. Think I need to hire you as the narrator on my next video.
    I dont mind questions being asked on my thread, I welcome it. That's what forums are for.
     
  6. Jul 7, 2013 #6

    RonGinger

    RonGinger

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    From all I have read, and the few casts I have made, the material used is NOT plaster, even though it looks a bit like it. Since you will be pouring molten metal into the mold, I feel better using the proper material, and not getting a nasty surprise when you find out why plaster is not used.

    I bought a small box of the Kerr Investment from one of the Jewelery suppliers. Most big cities likely have a Jewelery supply place, and Ordering it for UPS shipment was not to bad.
     
  7. Jul 7, 2013 #7

    aonemarine

    aonemarine

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    On most commercial investment powders rated for non ferris work plaster of parris makes up 30-50% of the product. The rest is a mix of silica sand and other stuff to give the investment the desired properties.
    Using straight plaster could be explosive. Id recommend buying a proper investment material when starting out, its one less thing you have to worry about.
     
  8. Jan 9, 2014 #8

    44-henry

    44-henry

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    Late response to this post, but I purchase Satin Cast investment from Rio Grande supply for my university lab. A 100 pound container is about $75.00 + shipping so not cheap, but it will last a long time as long as the castings you are making are not too large. There are cheaper investments supplied by Rio Grande as well, but I really like the Satin Cast.

    It really helps if you have a vacuum pump and bell jar to remove bubbles from the mix before and after filling your flasks. This is not absolutely necessary, but it really is nice. I also highly recommend using a vacuum for the pour if you are making small, delicate parts as it will greatly improve the quality of your parts. We have a commercial vacuum casting machine, but something similar could be built by hand fairly easily as long as you have a vacuum pump. One of the advantages of a good commercial investment, aside from surface quality, is that the parts can be invested and cast much quicker. I typically make the investment molds the day before I cast and have never had a problem. Some places do it all in the same day.
     
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