Casting copper

Discussion in 'Lost foam casting' started by garyhlucas, Sep 5, 2020.

  1. garyhlucas

    garyhlucas Silver

    So we did a test casting of a simple part I had ready for aluminum. I didn’t have anything for a cup around the riser so it just stuck out of the sand and I poured right into it.

    Melted 10 lbs of clean copper wire and poured borax on top and used a bottom pour crucible.

    Part filled completely, but I would say it was too cold and lots of poor fusion. Pouring temp was around 2100F.

    Going to try a sand casting next. Parts we want to cast are flat plaques about 5” square with a 3” tall Roman numeral 1/4” high on each.

    Suggestions welcome on how we should do this.
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  2. Petee716

    Petee716 Gold Banner Member

    I can't be certain but the size of your sprue may have lent to the way your casting turned out. It seems like the metal would never have filled the sprue and would have entered the mold in a very chaotic way.

  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I know this was lost foam but just thought I'd mention it for the avoidance of doubt.

    I agree that the sprue could be much smaller. Certainly 1/2-1/3 the size......probably just cut down the width. You're probably correct about it being a touch cold, but I think that coupled with the absence of a pouring cup can definitely make a mess of things. Those fusion lines also strongly resemble fold defects common in lost foam. Folds are caused by the pockets delaying the convergence of the molten metal front, creating trapped air/gas pockets which oxidize the metal and prevent fusion. Copper would be especially susceptible to this because it so readily oxidizes. This was probably aggravated by the absence of a pouring cup. Petee is right. This creates turbulence and chaos, not to mention a lots of black smoke and flame. My reusable pouring basin thread is below.

    With copper and higher melt point alloys you are much limited on materials for a pouring cup but I'd strongly suggest you make an expendable offset pouring cup. It could be made in a simple reusable mold with green sand, sand bound with molasses, corn starch, sodium silicate, polyester, epoxy, basically anything you'd use to make a green sand core. I actually prefer square sprues and rectangular (trapezoidal) shaped basins with a weir. You pack the mold right up to the top of the sprue, place the pouring cup on top of the sprue, then fill the mold to the top of the pouring cup.

    Start watching at about the 13 minute mark here.

    I'm using vacuum so I installed a plastic film layer but it's otherwise the same as what I describe above. You could hang four of those patterns on a single tree/sprue and casting them four at a time. I think you may be surprised at the improvement.

  4. garyhlucas

    garyhlucas Silver

    I ordered some of the moldable refractory to make a pouring cup. I can see how will make a difference for all the stuff I want to do.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Might be easier to make it out of 1/2" refractory fiber board and use the moldable stuff as glue and corner fillet. It's completely non wetting with aluminum but don't know how it holds up with copper. You can cut it with a razor knife. Make a sheet metal saddle so you can pull the cup and dump the excess molten metal after the pour. The fiber board is to fragile to grab directly with pliers. Be sure to provide good draft to the sides of the cup to make it easy to pull out the skin. I have done some minor patching but have gotten many, many pours with mine in aluminum service.

    I buy from this seller. There is both 2300F and & 2600F.

  6. metallab

    metallab Silver

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