Saucer Cup & Spoon – The Lost Foam Edition

Discussion in 'Lost foam casting' started by Al2O3, Mar 22, 2020.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I needed a challenge to christen the latest iteration of my lost foam molding rig.

    https://forums.thehomefoundry.org/index.php?threads/my-new-lost-foam-casting-rig.516/#post-24052

    …….so like the title says, I chose the old saucer, cup, and spoon. As many of you probably know, it was sort of a right of passage molders.

    There were a couple reasons I selected this and before HT1 starts bustin’ my balls, let me first state:
    1. Unlike molding it in greensand, in lost foam this will require no molding skill whatsoever……and that’s the point and one of the benefits of lost foam.
    2. I didn’t want to invest much time making patterns and when I saw the Styrofoam cups and dishes at work, and measured the cups at only 1/16” thick, I thought hey, just add the spoon, handle, and voila.
    So, here are the pieces. The plates were only .030” thick, so I glued two together. I cut the diameter down with a pair of scissors on the smaller one, hotwired the handles, and then hotwired .060” foam sheet and cut the spoons with a razor knife. I formed the spoon by shaping it with my fingers.

    1 SCS Pieces.JPG

    Here they are assembled...

    2 SCS Assembled.JPG

    It took me as long to sprue them as it did to make the patterns. Here’s how I sprued them.

    3 SCS Sprued.JPG 4 SCS Sprued.JPG 5 SCS Sprued.JPG

    I think the foam plates are quite a bit denser than 1-1.3 lb/ft3 foam I have been using. When I dip coated them, the plates also have a shiny surface and even my commercial slurry didn’t willing wet them at first but improved as I re-dipped them several times. I pre-dip my patterns in a bucket of soapy (dawn) water before I dip them in slurry as an added surfactant. That may have been a mistake with these patterns because if the water got between the two foam plates, I probably won’t be able to get it out of there……we’ll see.

    It’ll be interesting to see if I can get them to fill with vacuum assist. The middle of the spoon handles and the perimeter of the largest plate seem like the greatest challenge, but at .060” I can’t discount the cups either.

    ......and the famous lost foam prayer.......This is never gonna work….:). Place your bets gentlemen.

    Best,
    Kelly
     
    Barrybooth, OMM and Tobho Mott like this.
  2. Tobho Mott

    Tobho Mott Gold Banner Member

    Cute, I thought you were the one who said he couldn't get his artsy fartsy on? :D

    I don't think it would all fill if I tried it. But you have pulled off some really thin lost foam castings that I'd thought the same thing about before this... so I bet you can get this to work too. Sure hope so, should be fun to see how it went in any case. Fingers crossed & good luck with it!

    Jeff
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Before ya-know it I'll be bare dog'n skulls and belt buckles.........but before I go Picasso all over ya, let's see if I can get this thing to cast LoL!

    Best,
    Kelly
     
  4. ESC

    ESC Silver Banner Member

    If anyone can do it it is you. I tried it about five years ago and since I don't have any artifacts from my attempt I'm guessing failure. I know I did not sprue like you did and was not pushing my temps then.
     
  5. Gippeto

    Gippeto Silver

    .060" seems awful thin, but nothing ventured nothing gained right? Good luck! :)

    Are you going to bump the pouring temperature at all?

    Al
     
  6. Al Puddle

    Al Puddle Silver

    Someone needs to say it... It'll never work!
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks ESC, fingers crossed. Probably give it a shot this weekend.
    Yes......I usually pour at 1475F but probably ~1600F.
    You missed the last sentence of Post #1!

    Best,
    Kelly
     
  8. rocco

    rocco Silver

    He can blame it on the quarantine:p.

    Anyways, I have no idea what to expect from this so pour already, the suspense is killing us.
     
  9. Zapins

    Zapins Gold

    I'm pretty sure it will cast with bronze. Just make sure it is a tall pouring sprue of at least a foot. That should provide the pressure needed to force it into the ceramic shell quickly before it cools.
     
  10. Al Puddle

    Al Puddle Silver

    I can understand more head pressure but why more heat? There seems to be less foam to absorb energy?
     
  11. DavidF

    DavidF Administrator Staff Member Banner Member

    Density of the foam is probably higher...
     
  12. rocco

    rocco Silver

    My best guess, thin foam has a higher surface area to volume ratio so a greater percentage of the heat ends up going into the sand then it would on a thicker walled casting.
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    In lost foam in general, you do need more heat because even though the low density foam weighs virtually nothing, it changes phase twice from solid to liquid and then to vapor, and consumes energy, and this is true no matter what the metal is when using the lost foam.

    These patterns are very high surface area to volume ratio which means more rapid heat loss to the mold occurs while filling the mold. This is aggravated by the fact the fill times are slow because the advancement of the metal is gated by the rate of ablation of the foam, not gravity and feed system geometry, so the metal has more time to lose heat and freeze before filling the mold. If you start at a higher pouring temperature the metal can travel farther before freezing and this would be true for all casting methods.

    The vacuum is more motive force but also helps with trapped air and is similar to venting 100% of the mold surface area. Aluminum is about 2.7x as dense as water so is about .1psi per inch of sprue height. A 10" sprue delivers about 1psi to the bottom of the mold. I can pull almost 1/2 ATM of vacuum with my staged vacuum motors but 2-3psi is what I will apply. Still, that is 3x the head pressure of a 10 sprue with aluminum. The vacuum also reduces the gap between the gas and liquid phase foam which spread up the rate the foam is consumed and the rate at which the metal advances.

    I don't know where surface tension starts becoming a major limiting factor for casting but I suspect things get more difficult in a hurry below .060" of an inch with aluminum because that was where all the best shell investment casters walked away in my aerospace days.

    Interesting factoid, Mercury Marine in Fon du lac, Wisconsin uses Vacuum/Pressure assisted lost foam casting where after pouring the flask under vacuum, they close a lid on the flask and pressurize to 100psi before solidification and claim significant benefits to the mechanical properties of the resulting castings.

    Best,
    Kelly
     
  14. HT1

    HT1 Gold Banner Member


    I can see that creating the similar properties as hot forging or even work hardening the cast metal ... very interesting


    V/r HT1
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Mercury was also instrumental in developing several aluminum casting alloys too but I had to refresh myself with the section from a Lost Foam book I bought from AFS. The pressure cycle is actually 10ATMs so more like 150psi but it reduced/improved micro porosity 100-fold from 1% to .01% for low copper aluminum alloys......so they also realized big improvements in elongation. Here's a picture of their automated 24-flask line.

    Mercury Marine.JPG

    Best,
    Kelly
     
    Mark Kravchenko and Tobho Mott like this.
  16. Jason

    Jason Gold

    I refuse to get talked into doing this one. One day, maybe, but just not right now.;)

    I hope it casts first go! Pretty cool piece. Looks like an ideal candidate for lost wax.
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Jason. I hope so too but at .060" wall and the higher foam density, I certainly have my doubts.....but hey, where's the fun without risk of failure?
    I think the best method would be block investment with a vacuum flask and preheated investment. If it was pressurized post-pouring even better.

    Best,
    Kelly
     
  18. Jason

    Jason Gold

    Yup. Big flask, ultravest and a vacuum pump to suck the metal home. The foam is fine and would burn out in an oven, but getting it to stay down when pouring the investment would be a pita.
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I poured them both tonight. Here’s the smaller of the two. I poured it at 1600F and 7.5”Hg vacuum. It’s sort of a mess. I thought this one was the more likely of the two to succeed. Surprised the cup rim did not fill. I would have thought the plate poured short at 6:00 O’Clock not 3:00 & 9:00 O’Clock like it did.

    6 Small SCS.JPG 7 Small SCS.JPG 8 Small SCS.JPG

    I figured I needed to do something different for the larger piece, so I up'd the temp to 1700F and staged the vacuum pumps in series which increased the vacuum to 13.5” Hg. So close. Just short on the plate edge at 6:00 O’Clock………everything else is pretty much as the pattern dictated.

    9 Large SCS.JPG 10 Large SCS.JPG 11 Large SCS.JPG 12 Large SCS.JPG

    Ya-know, I’d rather have missed by a mile than come that close. I told myself if these didn’t make it I wasn’t going to waste my time with another attempt……..but I can be a stubborn SOB when it comes to these things and I may hate losing more then I like winning. I have a new gating strategy and will make one more of larger patterns. -I’m going to get it.

    13 Both SCS.JPG

    I did take video. Will take some time to process it.

    Best,
    Kelly
     
  20. Jason

    Jason Gold

    Damn that was close..
     

Share This Page