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Thread: abby's foundry [Lost wax casting]

  1. #1
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    abby's foundry [Lost wax casting]

    Hi everybody, I know you all love pictures so here's some for your entertainment.
    This is a minature (1/12 scale) steam turbo generator body as fitted to some German locomotives early last century.
    cast in silicon bronze, it is about 2" long.
    .

    The pattern was rapid prototyped by the customer , don't know what process but the surface quality was not the best , as you can see , but he is happy and doesn't mind doing a little polishing!
    here is the pattern (left) the casting and a wax pattern.
    .

    This is the silicone rubber mould for making the wax patterns.
    It is held in a steel jacket to prevent distortion when filling under pressure from the injection machine.
    The aluminium core makes the hollow shape inside!
    .
    And finally all my research looking for a wax glue was wasted , well perhaps I have learned what doesn't work.
    I was getting good results with ordinary PVA wood glue but after a production run several castings had surface imperfections ....doh!
    .

    from the shape of the scars it is obvious that the glue is not burning away completely and the residue is carried into the casting surface.
    I am trying a longer burn-out cycle and increased ventilation to see if this can be cured.
    I can't see there being anything in PVA that won't burn , any ideas?
    but for now its back to sticky wax and soldering iron.
    The man who never made a mistake never made anything!

  2. #2
    Senior Member Jammer's Avatar
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    How difficult is it to get the core out of the wax? Do you just heat it up and pull it?

  3. #3
    Awesome looking castings Abby, I always appreciate a good look.

    Thanks,

    Murray
    5:55 is a state of mind

  4. #4
    The imperfections look too uniform to be residue, I would think they would be more "spotty" looking but I don't know the glue's placement.

    For kicks, try a pattern made with hot glue in place of wax.
    It woul be easy to glue. It don't really drip when melted but runs with a pulling action that sucks it out. I know a thin shell will burn out clean at aluminum temps and it is a'kin to what foam is made from.
    Heat them up, mold them out.

  5. #5
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    No need to heat it jammer just remove the pin on the pointy end, this releases the vacuum and twist the core, it comes out easily as it is coated in mould release. The wax is tuffman green jewelry wax and it is very tough.It can stand handling without damage.
    The flange is glued to the main body HH and the shape of the "scar" is exactly the shape the glue would take.
    I think the wax melts and vaporises but the glue stays behind as a solid, it must char at 720C but if insufficient oxygen is available - remember this is at the end of a tunnel with narrow sections - it doesn't totally burn away.The charred remains - if it was ash it would be widely dispersed as you say - are pushed by the metal to the outside face of the mould.
    Doing a second batch this week-end with longer burn-out.
    I will try the hot-melt glue suggestion if I can apply it fine enough.
    The man who never made a mistake never made anything!

  6. #6
    I was thinking more of uesing hot glue in place of wax and not as a glue for it, it may have a to highter temp to glue wax.

    Something like coating a stick or round of the hot glue with investment and then burning it out as your doing other burn outs and seeing if it leaves a residue on pouring the small test piece.

    I'm thinking (hopeing) the hot glue will melt out faster and cleaner than wax and even if it don't the heat of the melt will.

    Does wax soak into the investment ? I don't think hot glue will. it don't get as thin.
    Heat them up, mold them out.

  7. #7
    Senior Member Jammer's Avatar
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    What kind of mold release do you use? I tried candle making several years ago and had a lot of trouble getting the candle out of the mold. I used a commercial release. I had Honeybees and still have about 50 lbs of wax.
    Your things look great and I'll be reading all your posts. I would like to try some lost wax in the future.

  8. #8
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    Quote Originally Posted by Jammer
    I had Honeybees and still have about 50 lbs of wax.
    Add cocoa and sugar to taste.
    Angus MacGyver a.k.a Clifford C. Claven, Jr.

  9. #9
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    Most of the wax melts out but a substantial amount is absorbed by the investment, there will also be nooks and crannies in a mould that are difficult to drain.
    The wax is formulated to burn away leaving no ash regardless of any wax left in the mould.
    I have burned out moulds containing plastic model kit parts , bits of wood , feathers and leaves on twigs even pieces of cloth and apart from a little ash everything has burnt away so I am sure if I get the ventilation better it will work.
    This little boiler is from a plastic kit ! you can see the scars caused by ash and the filler from the plastic.
    I use a silicone spray mould release , someone else had carnauba wax in another thread , mixed with beeswax it is a good sculpture wax!
    The man who never made a mistake never made anything!

  10. #10
    The wax is formulated to burn away leaving no ash regardless of any wax left in the mould.
    Well OK that :!:
    I had forgot'n that little boiler was from a plastic kit. ops:
    (And I was so going to try a plastic car after it's first posting :!: )
    Heat them up, mold them out.

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