Replicate sea shell in brass: incomplete

Discussion in 'Sand Casting' started by metallab, Aug 27, 2022.

  1. metallab

    metallab Silver

    I found a shell which is a very nice sample (no not sponsored by the large oil and gas multinational) and it is only 1-2mm thick an about 3" wide.
    So I decided to cast it in bronze and made two molds from greensand. I melted the brass and poured into it. So far, so good, but both castings turned out to be only partially filled.
    I made scratches in the mold opposite the entry point but, probably it froze too quickly. I heated the metal to well over 1000 C (a copper tube melted quickly into it) to slow down the quick freezing, but to no avail. See the pictures (Note: the measuting tape are Centimeters, not Inches).

    Any ideas on this ?

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    RX603256.JPG
     
    Mantrid likes this.
  2. Billy Elmore

    Billy Elmore Silver

    You will have a really hard time filling that because it is so thin. Possibly try using smaller sprue and adding runner with long thin ingate the length of the casting...and ingate should be on thinnest section to insure hottest metal at thinnest section. If you can turn it vertically and pour it you may have a better chance.
     
  3. metallab

    metallab Silver

    Good idea. I tried, cast it vertically. It filled better, but still incomplete. Probably a too low hydrostatic pressure ? The sprue was less than an inch above the gate in the actual mold (where it is the thinnest) I made a semi circular runner around the mold but it dit not fill yet.


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    The smaller mold. I made runners along the side of the shell.


    RX603260.JPG
    Lots of metal spilled, I thought no metal at all came into any of these molds.


    RX603261.JPG
    ... but it was not as bad.
    Left: the small mold, right: the large mold, below the original shell pattern.
    The small mold (picture 1) filled the best.

    Should I make a deeper sprue ?
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Assuming the base/hinge end of the shell is thicker, I might be tempted to gate into that end, and yes, more sprue/head pressure, and heat can only help.....

    Investment better yet with heated mold.

    Best,
    Kelly
     
  5. metallab

    metallab Silver

    Al2O3: I tried this first, but then the metal freezes too quickly before entering the thinner parts.
    Investment is not an option as the shell pattern is made of ceramics and not plastic. So it cannot be sacrificed. I already heated it to well over 1100 C resulting in belching zinc fumes which required me to wear a respirator.

    Today I made runners along the side of the shell to add extra 'underground' sprues which (almost) succeeded. Almost, because there were two errors (red circles) in the casting, probably in each two flows met each other and froze too early. It was cast vertically (input is rght on the image).

    RX603262.jpg
     
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    I assume your using brass?? If so switch to silicon bronze, it will make it easier to get this to fill....
     
  7. Mantrid

    Mantrid Silver

    I agree with David bronze is the way to go it will almost ensure success. Judging how close you came with the last one
     
  8. Rasper

    Rasper Silver

    I have found that Everdur does not fill thin castings well. Given that I don't want to go to more complicated techniques (vacuum or steam) I just use leaded tin bronze for thin castings. It flows like water.

    Richard
     
  9. What if you rammed up the cope and drag then added a shim between them of a few mm?. You could then add some green sand outside the runner to preserve the seal against the metal, even a bead of Dow Corning silicone could be used to bridge the gap long enough for the metal to cool.
     
  10. DavidF

    DavidF Administrator Staff Member Banner Member

  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You would of course have to pull a mold and make a wax. Gravity fed sand casting isn't a very good process choice for very low mass thin parts, but I understand sometimes we feel we must......jam the square peg in the round hole.

    Besides gating into the most massive area of the part, when I have such challenges I've found gating in a manner that reduces the maximum distance metal must travel improves success. For the shell that would mean sprueing into the inside center or around the perimeter of the shell in a conventional horizontal mold. Granted, it will cause greater clean up and disturbance of the natural features, but it does increases casting success.

    For the latter, I resort to what I call ring gates......a massive runner around the thin object with multiple or continuous contact to the part. The example below is lost foam but it is very thin large part cast in sand.......my version of the square peg in round hole. Pretty close to what you have already done.

    http://forums.thehomefoundry.org/in...-the-lost-foam-edition.1020/page-2#post-24222

    With an investment process it could be cast more or less net shape with little to no clean up and better finish.

    Best,
    Kelly
     
  12. metallab

    metallab Silver

    How do I make silicon bronze ? Alloy copper with silicon metal ?

    Al2O3: The ring sprue appears to be a good idea.
    I make the mold in the drag, in the cope I make 4 sprue holes 90 degrees apart, but angled to the top of the cope where a common gate appears where the metal is poured into. in the cope leading about 10mm outside the pattern, then after opening the rammed mold (with the pattern still in it) I carefully take a glass with the right size (about 10mm outside the rim of the shell) to carve a ring in the drag. See image below.

    RX603263.JPG
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Only downside is multiple converging metal fronts and hard to vent but if the metal is hot, might improve your result.

    Best,
    Kelly
     
  14. Rasper

    Rasper Silver

    How do I make silicon bronze ? Alloy copper with silicon metal?

    Yes. 4% silicon and 1% manganese. Manganese makes it flow better.

    Richard
     
  15. Billy Elmore

    Billy Elmore Silver

    Sometimes multiple metal fronts will meet inside a casting cavity and cause a misrun. This happens often with high ingates. On your last picture if you removed the top ingates...where the visible cold metal met the hot metal and formed a coldshut...you would probably be good. The metal filled around everything except where the first metal had already started to cool off and solidify.
     
  16. metallab

    metallab Silver

    Silicon bronze works awesome. After watching a video of forum member Luckygen1001 (@Ironsides, see below), I just made a small sample: 4% ferrosilicon 25/75 (= 1% Fe and 3% Si) and 1% manganese metal, balance Cu.
    It flowed very well and no dross crap or fumes appeared unlike with brass. The color is more orangish something in between copper and brass/bronze.
    So next attempt I'll cast in this alloy
    .
     
    Last edited: Sep 7, 2022
  17. metallab

    metallab Silver

    Here my result.
    I made it from silicon bronze which I alloyed myself, which pours easier than brass.
    Alloying was easy, I melted 500g of copper tubes in 10 minutes and then I added the FeSi and Mn wrapped in a paper napkin and then I stirred slightly with a thin steel bar.
    I made four sprues, but still it did not completely fill (a few gaps in the front of photo 2).
    But a lot has to be learned (castings are too rough).

    RX603273.JPG RX603274.JPG
     
    Jason and Mantrid like this.
  18. Jason

    Jason Gold

    OMG, when did you get back??? Good to see you!

    (yeah, that thin shell really needs to be poured in solid investment with Vacuum assist) And do it in silver!
    Fattening up the pattern with some wax on the back would give it the heft it needs to pour in ceramic shell or litter box sand....
    Nice job in the end, thin stuff sucks.
     
  19. Rasper

    Rasper Silver

    Jason,
    I have been doing welded wire sculpture for a couple of years. I have some things I need to pour in bronze. One problem I have is old age. I am 79 now. I operate single handed, and handling a #40 crucible full of bronze is pretty scary even when you are young.
    I was the administrator of Alloy Avenue during its final five years, but without the necessary privileges to repair it when it went down. I suspect Lionel died. I never heard from him even once during that time.

    Metalab:
    Jason is right, I think, about investment. I use traditional sand/plaster lost wax investment. Other people use shell. Both work and give a finer finish than greensand. Also it is much easier to make a higher (longer) pouring sprue which gives more pressure at the mold cavity. But both require a lot more work and equipment: (A burn-out kiln for instance.) I burn out a typical large investment for five days and nights at 1000F. A small one like your shell for two days.

    Richard
     
  20. metallab

    metallab Silver

    Investmest casting would indeed be better, I do have a burnout kiln and have cristabolite plaster investment, but no way to make a wax replica of the shell.
    I used to have a putty like substance which hardens when both components are brought together, but that was too old, so I had to discard it and don't know where I can order it.
     
    Last edited: Sep 10, 2022

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