Foil Sprues

Discussion in 'Lost foam casting' started by Al2O3, Apr 8, 2018.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Here's a short video of how I make foil sprues from HVAC tape. Compared to just using a foam sprue, I've found they reduce misruns, sand wash, folds and oxide defects. They are just consumed with each pour and excepting the adhesive are close to pure aluminum. Compared to ordinary aluminum foil, these sprues are strong and allow more positively sealed connection between the in-gate and pouring cup and help keep the sand around the feed system stable during pours.

    When I first started lost foam casting, like everyone, I noticed a lot of turbulence during the initial contact of metal with the foam sprue, not to mention all the flame and black smoke from the foam igniting in open air. The more massive the foam sprue, the more violent the initial events. Many times I would get fold and oxide defects in my castings and they seemed to occur deep in the castings at locations that roughly corresponded to where the initial metal was introduced during the pour. Other members suggested the addition of a pouring cup (some say "Kush Cup") to provide a solid pouring target and reduce sand wash. Then another member suggested wrapping the sprue in foil to reduce sand wash as I was also experimenting with vacuum assisted LF and this often caused heavy ingestion of sand in and around the sprue.

    When I started using foil sprues in addition to pouring cups, my success rate immediately went to nearly 100%. I noticed several other interesting things. In general, the initial metal contact was much less violent, was less smoke and flame, the metal quickly settled into the cup, and the mold started drawing metal sooner and more uniformly compared to the gurgling and pronounced early hesitation in drawing metal that typically accompanied lost foam pours.

    The other thing I noticed was foam readily burns in air producing black smoke but when I started dumping the sand keg on my driveway to demold, I observed all of the smoke captured and retained in the sand was white. I did some LF metal propagation tests behind glass where I could observe the molten metal consume the foam as it advanced. In the mold it appears the foam is denied sufficient oxygen to burn like it does in open air and decomposes differently with a thin layer of vapor between the molten metal and foam as the metal advances. This vapor escapes as it is produced and that produces the uniform advance rate of the metal into the foam casting and promotes a more tranquil exchange of molten metal for foam reducing defects throughout the casting.

    Not all subscribe to the above but it is what I have observed and concluded.....and it has worked very well for me.

    Last edited: Apr 8, 2018
    Tobho Mott and oldironfarmer like this.
  2. Robert

    Robert Silver

    Brilliant idea. I am going to use this next time I cast. Thanks
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Time Marches on. Although I do believe the foil sprues yielded some improvement when used with a metal cup, for the most part, I've stopped using foil sprues. I was noticing a lot of turbulence in the pouring cup and references in the Bifilm theory thread and to Campbell's work suggested conical sprues and cylindrical cups were prone to aspirating and entraining air during the pour, and offset pouring basins with weirs reduced this tendancy and also to some degree floated and isolated biofilms from the sprue in the pouring well, so I have been using the reusable offset pouring basins linked below with further improvement.

    Nothing new but just came across this old thread and thought I'd update it to present thinking.

    ....and the contact pouring ladle.


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