Bob is back!

Discussion in 'General foundry chat' started by Jason, Feb 24, 2020.

  1. Jason

    Jason Gold

  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Looks like he restored the vids that were there before he took them down......at least so far.

    Best,
    K
     
  3. Jason

    Jason Gold

    I missed them the first time. I still dont know why he pulled them.o_O It's good stuff.
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Oh yippie o_O
     
  5. Jason

    Jason Gold

    That EXACTLY what I dont understand. WTF am I missing?
     
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    Google soap box preacher.....
     
  7. Jason

    Jason Gold

    I don't care if he's in charge of the church of Bob! I just want clean castings that don't rip themselves apart as they cool or when I slice into them find out they are full of holes.
    I watched that long video on Bifilm. Makes perfect sense to me. Anyone that has scooped scum off a pot of molten lead can clearly see this.

    I'm curious how this relates to my bronze casting and ceramic shell. I've already figured out the experts are full of it by pouring my stuff upside down.
     
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    Probably very little as aluminum is a totally different beast than bronze, and aluminum oxides have a pretty high melting temperature over that of copper oxides.
    Now dont get me wrong. Bob does show some good examples of proper foundry practices, but these practices have been documented eons ago.
    Also keep in mind that we do things in a home based setting with the lack of controls that most of the commercial foundries have.
     
  9. dtsh

    dtsh Silver

    Wow, I'd seen some of his earlier stuff but a few of these are, well, kinda out there. I'm sure he knows a lot more about metal casting than I do, but he's a little light on the logic in some of those videos when he's not talking casting.
     
  10. Fascinating, he is a sharp dude.
     
  11. OMM

    OMM Silver

    His theory is relevant for gravity feed.

    Injection aluminum moulds have been doing this for over 20 years. But the moulds are in the millions of dollars and are for mass production. (Transmissions for an automobile.) There is a piston below the molten aluminum surface that pressurizes a heated cavity, that is rapidly cooled, with hundreds of ejector pins. A small burst of argon is shot through the void before aluminum is injected with a vacuum on the exit. These tool steel moulds have a cycle time of under four minutes (from the last Chrysler engine plant that I got a tour on). Some wall thicknesses being less than 1/8".

    Obviously this would not be applicable for one offs.
     
    Last edited: Feb 24, 2020
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thing is, the show is over well before the metal ever gets delivered to the die casting machine because the manufacturing processes of virtually all sources of casting ingot will naturally entrain biofilms. Even a theoretically pure ingot would be oxidized on it's exterior once exposed to air, and once created they are difficult to eliminate......at least per the Campbell doctrine......just say'in.

    Best,
    Kelly
     
  13. When the ingot is melted the biofilm floats to the top. Most die casting machines sit next to a drum of molten aluminum and it is automatically ladled in with each shot.
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not according to Campbell. Of course oxide layers form on the top of molten aluminum because that's what is exposed to air. Aluminum oxide (3.95g/cm3) is more dense than aluminum (2.7g/cm3) and would actually sink in molten aluminum if that's all there was to it but the bifilms are folded up hollow structures with gases clinging to the internal surfaces which can make them buoyant, but according to Campbell they often take on a near neutral buoyancy making them hard to extract from the molten metal......at least aluminum.

    If it was as simple as bifilms float and buoyancy, you would never have to do anything to purify aluminum except melt it and hold it quiescently near melt temperature and all the nasties would just conveniently float to the top......which would be great but it doesn't happen to any degree that yields quality metal.

    Argon degassing is supposed to help gases in solution diffuse into the Argon and drag the oxides up as the Argon bubbles buoyantly float to the surface but Campbell and Puhakka oh-Poo-Poo that too claiming H2 doesn't not leave the biflm fold by diffusion and the Argon is not pure enough and consequently just another source of oxygen and bifilm contamination to the melt.

    Best,
    Kelly
     
  15. DavidF

    DavidF Administrator Staff Member Banner Member

     
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  16. LOL. The beauty is this should all be easy to test with A B comparision testing. Just set identical molds. One with conventional sprue/runners and one with "BoB" sprue runners and gates.
     
  17. DavidF

    DavidF Administrator Staff Member Banner Member

    Its has long been established that proper gating has a positive impact on the quality of the casting. Nothing new there...
    For those that still want to chase the white rabbit, take a step back and compair the processes that commercial foundrys use to the processes we use in our home foundries.
    We the home foundry guys tend to use alot of recycled materials that been cut into smaller bits to fit our crucibles which is melted and remelted in direct contact with the furnace environment while doing very little to properly remove the oxides and nitride created. In short we are our own worst enemy and the best we can do is to simply follow the best practices that we can.
    There is no single gating system that will work for every casting. I'm tired of rambling... Who needs a carrot???;)
     
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  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Easy to test? -I wouldn't think so. It was discussed earlier in this thread but visible porosity and flaws are gross defects. Professional foundries have lots of metrology equipment, but the only thing that really matters is whether you are improving the mechanical properties. Increased elongation is the usual indicator that points to reduced flaw populations but cast aluminum is notoriously low elongation and it isn't easy to measure without good equipment and experimental methods. You also need a decent sample size because there will be significant part to part variation. I think David's point was in the hobby setting it's unlikely your castings would need or substantially benefit beyond what good casting fundamentals provide.

    59-Bugs-whats-up-doc.jpg

    Best,
    Kelly
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The 2020 AFS Metal Casting Congress is April 21st-23rd in Cleveland. I'll bet it's no coincidence he reactivated the content on his channel.

    Best,
    Kelly
     
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  20. Rotarysmp

    Rotarysmp Silver

    Those videos are pretty difficult to watch. When someone rants like that, and accuses everyone other themselves of being complete idiots, and that only they have the pure correct knowledge, it is not exactly edifying. Shame, as he probably has a lot of useful practical knowledge to share.

    Given he has built the greatest foundry, and "10-12 close by shut down immediately", and he is "a million times better", I wonder what he is like to work for as a boss, and work with as a vender?

    Mark
     
    Last edited: Feb 26, 2020
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