Copper Lost Foam Fail

Discussion in 'Lost foam casting' started by Mach, Oct 17, 2021.

  1. Mach

    Mach Silver

    Casting weather arrived this week so I fired up the furnace. The good news is that my furnace can hit 2000F+ on natural gas (3 inches of water) and notched another learning experience. The bad news is no decent casting. Any suggestions or feedback on what I can do better on are welcome.

    The project is a layered computer water block made from 3mm Depron foam (typically used for model airplanes). I laser cut 4 layers and glued them together with Clear Gel Tacky Glue. The goal was to cast a pure copper water block that was thermally conductive without porosity.

    [​IMG]
    I started out with a half pound heel which melted in 15 minutes mixed with graphite and charcoal cover.

    [​IMG]

    [​IMG]
    I then added the remaining 1lb of wire which took another 15 minutes to melt. I then removed the crucible from the furnace and removed the charcoal cover. I plunged 20 grams of lithium copper on a copper rod. The temperature was 2000F but cooled too fast. I put it back in the furnace and reheated it for 10 min which certainly did not help with porosity. The metal appeared to be dancing but not sure if it was turbulence. I dropped in another 20 grams of lithium copper at that point. I immediately pulled it from the furnace and poured it.

    The bad news is it wasn't hot enough for copper. The metal froze before it really got out of the sprue.
    [​IMG]
    On the top is the failed casting that froze just as it was entering the main body. The bottom is another foam in drywall mud to give an idea of how the sprue was attached. The top was coated in Suspenda Slurry. Interestingly, it does look like it cracked on the sprue top where the bleed through veins are visible. Good news it seems to work as well as the drywall mud and dries thinner and faster. I've got some aluminum tests that I'll run in another project.

    The casting failed to fill and also failed on the no porosity requirement as can be seen in the sprue cross section.
    [​IMG]

    Copper is notoriously difficult to cast without porosity. I started with copper wire and used a crushed charcoal and graphite cover with 2% lithium copper from Belmont to degas. The failure points were obviously not hot enough, possibly too much lithium and I should have tried pouring with the cover in place. I may try again in an electric furnace instead but will likely give further attempts a pass.

    The first trial with the pouring cup went well - Thanks Kelly for the idea. Although I did not get the copper out of it fast enough and it spalled slightly. It's patchable.
    [​IMG]
     
  2. You'd have more time to pour if you fill the crucible with more copper and later on pour it into an ingot mould after the casting. The extra thermal mass will help with heat loss: for not much more surface area you'll have a lot more volume of hot metal to retain heat. With 1.5 lbs of copper you'd almost have to pour within seconds of getting it out of the furnace.
     
  3. Mach

    Mach Silver

    Thanks Mark, that makes sense. I've got two more foams made up - I'll give it another go.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Will need to be much hotter, especially for 3mm......that's pretty sporty. So it's four stacked 3mm plates? Does that mean they have 3mm spacing? If so, is it vibrated sand into that mold space or other?

    On your NG pressure, are you regulating down to 3"? Seems most residential pressure is 6-7". Unless you have a lot of other demand it is usually stable enough becuase it is regulated at you supply/meter so you can just tap it directly. 6" is better than 3"H2O!

    Do you know the foam density?

    Best,
    Kelly
     
  5. Mach

    Mach Silver

    Depron 3mm is twice Foamular 150 at 40 kg/m3 - the 6mm is 33kg/m3 http://depronfoam.com/products/

    4 stacked 3 mm - total 12 mm. The are glued layer cake fashion. The interior 2 layers have a water channel cut into them. The image on the right is the glued one. They are pretty small - 2.5" x 3".

    upload_2021-10-18_10-3-46.png

    It was cast it in a gallon paint can vibrated using ceramic media. To try to control float, I used a perforated lid and cut a 2 inch hole for the 1" sprue to exit into the pouring basin.
    [​IMG]

    Its regulated - The gas company tech who replaced the regulator, due to a leak recently, said its possible to go to a 2psi regulator. So there is more capacity there.
     
  6. metallab

    metallab Silver

    Why don't you use propane ? That makes it hotter.
     
  7. Mach

    Mach Silver

    I could but I've already got the natural gas hookup. I'd may need to if I don't upgrade the regulator. I'd like to try nickel silver at some point which has a higher melting point than copper.
     
  8. metallab

    metallab Silver

    I just did a test of my Frosty T burner to melt copper and pour it into two 3mm sheets and one 5mm sheet as blanks for rolling sheet.
    The copper melted in 15 minutes, starting from a cold furnace and I overheated it to 1200 C to prevent premature freezing. It filled the 3mm thick sheet well.

    RX602238.JPG
     
  9. Mach

    Mach Silver

    Thanks that's encouraging. I'll check out the Frosty T burner design. You were pouring into foam correct? What was crucible size? Any visible porosity?
     
  10. metallab

    metallab Silver

    No, just in sand. I pushed three plastic sheets of 3 and 5mm thickness into the sand and removed the sheets. Then I poured the copper into the voids. Maybe your foam takes up energy and cools the copper further which speeds up freezing.
    The crucible was about 100-200ml (A2 size).
    A video:
    https://www.metallab.net/jwplayer/video.php?f=/forums/coppermelt-20211019.mp4

    And here what happened to the ingots after rolling, the top one being about 1 ft long. The center one has some porosity.

    When annealing between rolling, I used borax + denatured alcohol which reduces firescale considerably. I learnt this from NOBOX7.

    RX602240.JPG
     
    Last edited: Oct 19, 2021
  11. Mach

    Mach Silver

    Very cool, thank you - especially for the video. Your pour was definitely grab and go. The foam will absorb energy and maybe too dense for a clean burnout before freezing. I was reading ASM Copper and Copper Alloys where it suggests 2300-2350 F for pouring small items. That seem very high and will likely result in added porosity.

    I gave the gas company a ring about swapping in a 2 psi regulator but it'll be a few weeks. I may still have a go at propane but want to tune the natural gas first. Porosity will be the big limiting factor either way.
     
  12. mytwhyt

    mytwhyt Silver

    How did the borax work.. The roach poison is just 99% boric acid.. Most jewelers keep a pickle pot with hot water/sulfuric acid on their bench.. Strips the glaze off as soon as a hot piece of jewelry hits the solution..
     
  13. metallab

    metallab Silver

    I said 'borax' but is was actually boric acid in my case, like NOBOX7 did.
    Borax = sodium tetraborate Na2B4O7 and boric acid H3BO3.
    I have such a pickle pot as well, when I roll silver sheet. Recently I made a sterling silver photo frame of which I rolled the sheets needed myself and used the same boric acid / alcohol when annealing and pickle for cleaning. It worked awesome.
     

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