First skull attempt

Discussion in 'Lost foam casting' started by Miles Lowry, Sep 19, 2020.

  1. Miles Lowry

    Miles Lowry Copper

    this is the result of my first copper lost foam casting of a skull. Obviously there was more than enough metal for the pour, so I'm not sure what happened to the spot that I circled I red. Also, I'm not sure why the details didn't come out that sharp. Lastly, what's with the color shift do yellow and red copper not mix? 20200919_131903.jpg 20200919_131925.jpg 20200919_132040.jpg
     
  2. Miles Lowry

    Miles Lowry Copper

    Well, after having cleaned it up a bit it turns out that the discoloration was just a film of sorts. Some can still be seen towards the back. 20200919_165113.jpg 20200919_165106.jpg
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    That would totally freak someone out if they dug it up!! Lol :)
     
  4. Jason

    Jason Gold

    If you were going after creepy AF, you nailed it!
     
  5. Al2O3

    Al2O3 Administrator Staff Member

    Well, you haven't given us a whole lot of information to go on but here are some comments and potential contributing factors:
    1. When you say copper, what was the metal source? Pure copper is a poor casting alloy with poor fluidity and highly reactive.
    2. Did you coat the lost foam pattern? Uncoated patterns can sometimes allow the pattern to vent too fast and this coupled with pour fluidity, cold pour temp, poor packing could all produce similar defects.
    3. What was the pour temp? Looks a bit cold. LF generally requires several hundred F higher pour temps than conventional sand casting.
    4. How did you pack and position the pattern in the mold? I can see a short sprue in the base of the skull but if it was buried that shallow, I doubt the mold could be very well packed. It should be buried at least 6" deep in the mold. Deeper is better.
    5. Did you vibrate the mold to pack it? A loosely packed mold can easily collapse or be displaced, especially by denser metals. If you pour sand into a 5gal bucket, even moderate vibration will cause at least an inch of settling (aka packing). If you are just wrapping it with a mallet, not so much.
    6. Did you use some kind of pouring cup to act as a buffer and maintain a continuous pour? It can be hard to hit a sprue protruding from the mold surface especially when your view is obscured by fire and smoke, and of course the infamous lost foam pause in how the mold takes metal. A tin can or short section of exhaust pipe 2-3" in diameter placed over the sprue and then buried up to the top in the mold will usually do. Keep a pair of pliers handy to remove the cup while the metal is still molten so you don't have to do so afterward to reclaim your sprue for later casting stock.
    Being copper, probably just oxides and reaction with other mold and pattern material. It's likely just surface film and can be relatively easily removed.

    Best,
    Kelly
     
  6. Miles Lowry

    Miles Lowry Copper

    I'm always going for creepy, I'm thinking about putting it on a walking stick.

    kelly,
    Thanks for the info.

    1. My source is primarily wires, all Stripped of insulation, also scrap plumbing fittings.

    2. Coat it? With what? It's the first I've heard of coating the pattern

    3. I'm not sure what temp it was, my thermometer only goes 3 digits and it didn't occur to me to take the temp

    4. It was pretty shallow but that's all the room I had

    5. I was using a small container, maybe a gallon and a half, I dropped it a few times but probably not a enough

    6. Yes I used a cup, all of the copper went down into the mold, there wasn't anything left in the cup.
     
  7. Al2O3

    Al2O3 Administrator Staff Member

    That will be pretty much pure copper. You'll have better luck with bronzes and should keep your eye out for scrap sources.
    Thinned, non setting drywall joint compound and let it dry. Just thin it with water to the consistency where it will just begin to run off a chip brush in a stream and brush it on. If you seal the container you can reuse it indefinitely and a small pail cost a couple bucks at the big box stores. It need not be applied to the foam pattern in a thick coat, just thick enough to cover the color of the foam so it is white with no color showing through when it dries. Besides controlling the rate at which vaporized foam is expelled, it will reproduce the surface quality of the foam completely and in fine detail so put additional effort into sanding and finishing your pattern. The coating will also make the mesh size of mold sand irrelevant and prevent the sand from creating glassy patches on your casting. If you demold while the casting is hot, dipping in a water bucket will blow most of the coating off the casting and the rest can be removed with compressed air.
    Well, then get it hot!
    Make more room. Do you want good castings or just the best you can get with an inadequate flask/container? If you don't have enough sand, you can reduce the extra volume in a larger flask with a brick or rock or two. Make sure they are dry.
    People use plastic 5 gal buckets for small parts successfully BUT, a large part and high melt point metal will soften them as the mold temp rises and if you spill around the pouring cup, the metal will melt through the edge of the bucket like it isn't there and spill onto the ground and potentially your feet. Scrounge up a steel 5gal bucket or pail. You can even use a piece of round duct work inside the bucket (or not if you seal the end. Dropping can actually work well for packing if you do it several times during the fill as long as the flask doesn't deform from the weight when you pick it up each time. You need a rigid pattern when you use this method because it will deform/deflect less rigid patterns. If your serious about achieving good LF castings you should attach a strong vibrating device to your flask. This will make packing effective and effortless. Here's a shot of one of my molds from a previous post where ~3 ft of height was required. Yah, that's a section of concrete casting Sonatube in there.
    22 Ready to Pour 4-on.JPG
    If there wasn't anything left in the cup you didn't melt enough metal for the job. This meant you lost the additional mold pressure/head available from the additional feed system height available and in all likelihood had an interrupted pour, which will quite often produce defects. Try again with 8-12" of total sprue/cup/mold height above your casting and fill that cup up with molten metal.

    Best,
    Kelly
     
    Last edited: Sep 21, 2020
    Tobho Mott likes this.
  8. rocco

    rocco Silver

    Miles, if you haven't already done so, go back and look at Kelly's old foam lost posts. He is our resident King of Foam!
     
    Last edited: Sep 21, 2020
  9. Miles Lowry

    Miles Lowry Copper

    It was a brass bucket if that makes any difference
     
  10. Al2O3

    Al2O3 Administrator Staff Member

    That sounds like a pretty fancy bucket for a casting flask. Seriously, cut the top out of a 5-gal steel can of anything and it will be a good casting flask. I've used particle board and mdf boxes to fit large awkward parts with success but I'd take a steel cylinder/bucket/barrel as first choice any day.

    Best,
    Kelly
     
    Last edited: Sep 21, 2020
  11. garyhlucas

    garyhlucas Silver

    Hey Kelly,
    Where did you get the commercial coating material? Can't find a supplier anywhere!
     
  12. Al2O3

    Al2O3 Administrator Staff Member

  13. Zapins

    Zapins Silver

    Lancaster foundry supply in Lancaster PA is the closest and cheapest to you in NJ
     

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